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The ocean is facing a multitude of abiotic stresses due to factors such as climate change and pollution. Understanding how organisms in the ocean respond to these global changes is vital to better predicting consequences. Sea cucumbers are popular echinoderms with multiple ecological, nutritional, and pharmaceutical benefits. Here, we reviewed the effects of environmental change on an ecologically important echinoderm of the ocean, aiming to understand their response better, which could facilitate healthy culture programs under environmental changes and draw attention to knowledge gaps. After screening articles from the databases, 142 studies were included on the influence of emergent contaminants and climate variation on the early developmental stages and adults of sea cucumbers. We outlined the potential mechanism underlying the physiological response of sea cucumbers to emerging contaminants and climate change. It can be concluded that the physiological response of sea cucumbers to emergent contaminants differs from their response to climate change. Sea cucumbers could accumulate pollutants in their organs but are aestivated when exposed to extreme climate change. Research showed that the physiological response of sea cucumbers to pollutants indicates that these pollutants impair critical physiological processes, particularly during the more susceptible early phases of development compared to adults, and the accumulation of these pollutants in adults is often observed. For climate change, sea cucumbers showed gradual adaptation to the slight variation. However, sea cucumbers undergo aestivation under extreme conditions. Based on this review, critical suggestions for future research are presented, and we call for more efforts focusing on the co-occurrence of different stressors to extend the knowledge regarding the effects of environmental changes on these economically and ecologically important species., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Low dissolved oxygen (LO) in seawater negatively affects aquatic animals and has received considerable attention. However, there is still much to learn about how echinoderms, which are keystone species in benthic ecosystems, respond to hypoxic stress. Here, we detected differentially expressed metabolites (DEMs) in sea cucumber (Apositchopus japonicus) between normoxic conditions (NC group) and hypoxic conditions (2 mg L -1 ) for 3 and 7 days (i.e., LO3 and LO7 groups). A total of 243, 298, and 178 DEMs were found in the NC versus LO3, NC vs. LO7, and LO3 vs. LO7 comparisons, respectively. Amino acids were the most abundant class of DEMs, and "biosynthesis of amino acids" was an enriched pathway in all three comparisons. Most of the enriched metabolite sets under hypoxic stress were related to metabolism. As the duration of the hypoxia treatment extended, the metabolism-related process maintained an upward trend, and signaling pathways maintained a downward trend. Thus, metabolism-related processes are affected in hypoxia-stressed sea cucumber, and amino acid metabolism is the most important process for adaption to hypoxic conditions, potentially function in osmotic regulation and energy regulation. Our results shed light on the adaptative strategies of sea cucumber to challenging environmental conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The sea cucumber Apostichopus japonicus has important nutritional and medicinal value. Unfortunately, we know little of the source of active chemicals in this animal, but the plentiful pigments of these animals are thought to function in intriguing ways for translation into clinical and food chemistry usage. Here, we found key cell groups with the gene activity predicted for the color morphology of sea cucumber body using single-cell RNA-seq. We refer to these cell populations as melanocytes and quinocytes, which are responsible for the synthesis of melanin and quinone pigments, respectively. We integrated analysis of pigment biochemistry with the transcript profiles to illuminate the molecular mechanisms regulating distinct pigment formation in echinoderms. In concert with the correlated pigment analysis from each color morph, this study expands our understanding of medically important pigment production, as well as the genetic mechanisms for color morphs, and provides deep datasets for exploring advancements in the fields of bioactives and nutraceuticals.

Sea cucumber is a morphologically diverse and ecologically important clade of echinoderms. The sea cucumber Apostichopus japonicus is the most economically valuable species of sea cucumber. The initial assembly of the A. japonicus genome was released in 2017. However, this genome assembly is fragmented and lacks relative position information of genes on chromosomes. In this study, we produced a high-quality chromosome-level genome of A. japonicus using Pacbio HiFi long-reads and Hi-C sequencing data. The assembled A. japonicus genome spanned 671.60 Mb with a contig N50 size of 17.20 Mb and scaffold N50 size of 29.65 Mb. A total of 99.9% of the assembly was anchored to 23 chromosomes. In total, 19,828 genes were annotated, and 97.2% of BUSCO genes were fully represented. This high-quality genome of A. japonicus will not only aid in the development of sustainable aquaculture practices, but also lay a foundation for a deeper understanding of their genetic makeup, evolutionary history, and ecological adaptation., (© 2023. The Author(s).)

Determining the amount of microplastics (MPs) in food is key to clarifying their potential toxicity to humans. Here, we collected canned, instant, and salt-dried sea cucumbers Apostichopus japonicus, the most valued sea cucumbers, from Chinese markets to determine their content of MPs. Sea cucumbers contained MPs in the range of 0-4 MP individual -1 , an average of 1.44 MP individual -1 , and 0.081 MP g -1 . Accordingly, consuming 3 g of sea cucumbers could result in an exposure risk of an average of 0.51 MPs, 0.135 MPs, and 0.078 MPs day -1 for canned, instant, and salt-dried sea cucumbers, respectively. MPs were in size range of 12-575 μm, and fibrous shape was dominant. Furthermore, among the five polymers identified, polypropylene showed the highest energy binding with two catalysts engaged in organic chemical oxidation. This study extends the knowledge regarding MPs occurrence in food and provides a theoretical basis for MPs toxicity in humans., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Exosomes are small extracellular vesicles that contain nucleic acids such as microRNAs and may participate in important biological processes. We made the initial report of exosomes from sea cucumber Apostichopus japonicus, that were classically cup-shaped and had an average size of 74.65 nm, and identified specific exosome biomarkers (HSP70, TSG101, and CD9). We explored changes in the global expression of microRNAs in exosomes from the commercially important A. japonicus under normal conditions and heat-stressed conditions for 3 and 7 d. We found that heat stress increased exosome production and modified the expression profiles of the microRNAs that they contained. Novel_mir31, novel_mir132, novel_mir26, miR-92_1, and novel_mir27 were commonly found to be differentially expressed in three comparison groups, indicating their importance in the heat stress response. The microRNA expression levels were validated by qPCR. Function analysis of the target genes of these microRNAs indicated they were involved mainly in replication and repair in the initial response of A. japonicus to heat stress exposure. Conversely, during acclimation to the high temperature conditions, the target genes of the differentially expressed microRNAs were primarily involved in metabolism adjustments. Our results will contribute to a better understanding of the regulatory roles of exosomes in sea cucumber, and provide insights into the functions of sea cucumber exosome-shuttled microRNAs against environmental stresses exacerbated by global warming., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Sea cucumbers are economical and ecologically important species, playing a crucial role in nutrient recycling in the ocean and providing valuable bioactive compounds for nutrition. Previous research has demonstrated that microplastic fibers, which are widely recognized as emerging contaminants, are transferred to the perivisceral coelomic fluid during respiration in sea cucumbers; however, their fate in sea cucumbers is still not well understood. We tracked the status of sea cucumbers (Apostichopus japonicus) with polyester microplastic fibers in their coelomic fluid in clean water. The results showed that after transferring sea cucumbers to clean water, the number of microplastic fibers transferred significantly decreased in the coelomic fluid, but at least one microplastic fiber was found up to 60 days. In addition, sea cucumbers recovered from the effect of microplastic fiber transfer, as indicated by enzyme levels and histological observations. Furthermore, single microplastic fiber transfer over a 60-day farmed period did not significantly affect the growth of sea cucumbers. However, repetitive microplastic fiber transfer (i.e., twice and thrice a week over 60 days) significantly decreased the growth rate (p < 0.05). Accordingly, increasing microplastic fibers in sea cucumber habitats pose a threat to sea cucumbers because they can disrupt development. Thus, farmers are advised to select locations for farming sea cucumbers where low microplastic fiber concentrations are expected. Environ Toxicol Chem 2023;42:205-212. © 2022 SETAC., (© 2022 SETAC.)

The 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) is the predominant congener of polybrominated diphenyl ethers, and it is also a persistent organic pollutant that with a higher detection rate in samples from environment and animals. To date, there have been few studies of the effects of BDE-47 on locomotion in sea cucumbers. In this study, we investigated the influence of different concentrations of BDE-47 (low: 0.1 μg/L; moderate: 1.0 μg/L; high: 10.0 μg/L) on locomotion of Apostichopus japonicus and evaluated changes in their muscle physiology using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry. The behavioural studies showed that the average and maximum velocity of movement decreased significantly in both the moderate and high BDE-47 groups after 1 day of exposure. In addition, levels of 55 metabolites were identified and characterized in the longitudinal muscle of A. japonicus exposed to BDE-47. The alteration of taurine and norepinephrine levels indicated that BDE-47 had drastic physiological effects on the longitudinal muscle of A. japonicus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Ltd.)

Apostichopus japonicus achieves intestinal regeneration in a short period after evisceration, and multiple genes are involved in this process. The transcriptome of A. japonicus was screened for regeneration-associated protein (Aj-Orpin), a gene that is specifically upregulated during intestinal regeneration. The expression and function of Aj-Orpin were identified and investigated in this study. The 5' and 3' RACE polymerase chain reaction (PCR) was used to clone the full-length cDNA of Aj-Orpin. The open reading frame codes for a 164 amino-acid protein with an EF-hand&#95;7 domain and overlapping signal peptides and transmembrane regions. Moreover, Aj-Orpin mRNA and protein expression during intestinal regeneration was investigated using real-time quantitative PCR and Western blot. The expression pattern of Aj-Orpin in the regenerating intestine was investigated using immunohistochemistry. The results showed that Aj-Orpin is an exocrine protein with two EF-hand-like calcium-binding domains. Expression levels were higher in the regenerating intestine than in the normal intestine, but protein expression changes lagged behind mRNA expression changes. Aj-Orpin was found to play a role in the formation of blastema and lumen. It was primarily expressed in the serosal layer and submucosa, suggesting that it might be involved in proliferation. These observations lay the foundation for understanding the role of Orpin-like in echinoderm intestinal regeneration.

When encountering adverse environmental conditions, some holothurians can eject their internal organs in a process called evisceration. As global warming intensified, eviscerated and intact sea cucumbers both experience heat stress, but how they performed was uncertain. We constructed 24 metabolomics profiles to reveal the metabolite changes of eviscerated and intact sea cucumbers under normal and high temperature conditions, respectively. Carboxylic acids and fatty acyls were the most abundant metabolic categories in evisceration and heat stress treatments, respectively. Neural transduction was involved in sea cucumber evisceration and stress response, and the commonly enriched pathway was "neuroactive ligand-receptor interaction". Lipid metabolism in eviscerated sea cucumbers differed from those of intact individuals and was more seriously affected by heat stress. Choline is a key metabolite for revealing the evisceration mechanism. Our results contribute to understanding the mechanisms of evisceration in sea cucumbers, and how sea cucumbers might respond to increasingly warming ocean conditions., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Microplastics (MPs; ≤ 5 mm) have become a potential threat to human health due to the widespread detection of MPs in foods consumed by humans. Here, we investigated the potential of MP occurrence in the main edible part of the most valuable species of sea cucumbers (Apostichopus japonicus). Laboratory experiments showed that fluorescent MPs and microfibers (MFs) could transfer into the body wall of the sea cucumber. The evidence revealed that these MPs enter the body wall via the outer surface. Although these MPs decreased after the sea cucumbers were transferred to clean water, traces of MPs (at least one MP particle) were found up to 60 d post-transfer. To validate these laboratory observations, sea cucumber samples were collected from the field. MPs were found in 86% of live and processed sea cucumber samples. The MP abundances in the field samples ranged from 0-15 MPs animal -1 and 0-2 MP g -1 . The isolated MPs were mainly MFs, constituting 81% of MPs, followed by fragments, films, and beads. Fourier transform infrared spectroscopy revealed that the polymer composition of the isolated MPs mainly included rayon, followed by polyester and chlorinated polyethylene. The findings of this study demonstrated that the body walls of farmed and processed sea cucumbers contain MPs, thus highlighting the need to control MP pollution during the farming and processing of sea cucumbers., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The sea cucumber Apostichopus japonicus is an important economic species owing to their high nutritive and medicinal value. Body color is one of the most important traits in the cultivation, which affects taste and market price of holothurian products. Pigmentation is an important stage of sea cucumber growth and development, in addition to achieving rare and beautiful coloration. In this study, UHPLC-QTOF/MS technique was performed to analyze the metabolome of white, green and purple A. japonicus body wall during the pigmentation process. A total of 2633 metabolites were identified. OPLS-DA clearly discriminated the body wall metabolites among the three color morphs. In addition, 13 annotated metabolites that could discriminate white, green and purple A. japonicus were screened out. KEGG metabolic pathway analysis revealed that "biosynthesis of unsaturated fatty acids" and "fatty acid biosynthesis" were closely related in the different color morphs. Furthermore, we performed comparative analysis of polysaccharide and saponin among white, green and purple A. japonicus. The results showed that the content of polysaccharide and saponin in purple A. japonicus was the highest, while that in white A. japonicus was the lowest. This study will provide valuable information for future studies on sea cucumber and the molecular mechanism underlying pigmentation and color polymorphism, and may contribute to support the culturing of desirable color morphs., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Microscopic plastic particles (0.1 µm-5 mm) are widespread hazardous pollutants, and microfibres (MFs) are their dominant shape in habitats. Previous field and laboratory studies have demonstrated that MFs enter the coelomic fluid of sea cucumbers from the water through the respiratory tree. However, the possible mechanism underlying the toxicity of this process is not well understood. Herein, RNA-Seq was used to examine the responses of the respiratory tree during the MF transfer process in the sea cucumber Apostichopus japonicus. Polyester synthetic MFs were used, and the number of transferred MFs was controlled to the amount reported from the field. The results showed that the MFs altered gene expression as the transfer process increased. The top genes regulated by MF transfer were mainly related to metabolic processes and signal transduction pathways, with upregulated genes following low MF transfer and downregulated genes following high MF transfer. Functional enrichment analysis revealed the pathways in which differentially expressed genes were enriched under different MF transfer scenarios. The transcriptomic findings were further supported by histological observations, which revealed injury and loss of cell components. This study contributes to understanding the effects of MFs in a valuable echinoderm species through transcriptomic and histological examinations., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Microplastics (MPs) in the form of microfibres (MFs) are of great concern because of their size and increasing abundance, which increase their potential to interact with or be ingested by aquatic organisms. Although MFs are the dominant shape of MPs ingested by sea cucumbers in habitats, their effect on sea cucumbers remains unclear. This study examined the effect of dietary exposure to MFs on the growth and physiological status of both juvenile and adult Apostichopus japonicus sea cucumbers. MFs were mixed into the diet of sea cucumbers for 60 d at environmentally relevant concentrations of 0.6 MFs g -1 , 1.2 MFs g -1 and 10 MFs g -1 . Dietary exposure to MFs, with concentrations at or above those commonly found in the habitats, did not significantly affect the growth and faecal production rate of either juvenile or adult sea cucumbers. However, a disruption in immunity indices (acid phosphatase and alkaline phosphatase activity) and oxidative stress indices (total antioxidant capacity and malondialdehyde content) was observed in juvenile and adult sea cucumbers, indicating that these indices might be useful as potential biomarkers of the exposure to MF ingestion in sea cucumbers. This study provides insights into the toxicity mechanism of MF ingestion in a commercially and ecologically important species., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

The exacerbation of global warming has driven changes in environmental factors, including water temperature and oxygen concentration. The sea cucumber Apostichopus japonicus, an economically important aquatic animal, is constantly and directly challenged by heat and hypoxia. In this study, 12 small RNA libraries were constructed for this species, and a total of 21, 26 and 22 differentially expressed (DE) miRNAs were clarified in A. japonicus under thermal (26 °C), hypoxic (2 mg/L) and the combined stresses. Comparative miRNA sequencing analysis and real-time PCR were used to identify and validate the representative miRNAs, including Aja-miR-novel-299, Aja-let-7b-3p, Aja-miR-71b-5p, Aja-miR-novel-13218 and Aja-miR-2004 in response to high temperature, and Aja-miR-92b-3p, Aja-miR-210-5p and Aja-miR-novel-26331 in response to oxygen limitation. GO and KEGG pathway analysis revealed that the potential target genes of DE-miRNAs involved in biosynthesis, metabolism, immunity, cell growth and death, translation and signaling transduction. Key DE-miRNAs with potentially targeted genes associated with heat shock and hypoxia response were also determined. These results may help explaining the role of miRNA regulation in stress resistance, as well as the potential molecular regulation mechanism of the echinoderm A. japonicus in the context of global warming., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Although the sea cucumber Apostichopus japonicus has been characterised as a deposit feeder, nutrients sourced from the water column have been recorded in the intestines of this species. However, the mechanisms whereby nutrients in the water enter the intestinal tract of A. japonicus , and whether other suspended particles can be ingested via the mouth of A. japonicus adults, remain unknown. Here, we reveal how A. japonicus ingests suspended particles through the mouth. We used synthetic particles and video recording to confirm the suspension uptake by the sea cucumber. Apostichopus japonicus continued to ingest suspended particles (if present) over time, and the particle ingestion rate was positively correlated with the concentration of suspended particles (Pearson correlation: r =0.808). Additionally, clearance rates of the suspended particles ranged from 0.3 to 0.9 l h -1 The findings of this study thus provide evidence of a previously undescribed particle uptake mechanism in a commercially important species., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)

The sea cucumber Apostichopus japonicus (Selenka)is a typical nocturnal echinoderm, which is believed to be almost completely dependent on light intensity for the regulation of endogenous rhythms. Under conditions of high light intensity, this species shows clear evidence of light avoidance behavior, seeking out shaded areas of reef in which to reside. In this study, we performed RNA-Seq analysis to examine the tentacle transcriptome of A. japonicus specimens that had been subjected to dark and light (5 min and 1 h) conditions. We specifically focused on detecting genes involved in opsin-based light perception, including opsins and members of phototransduction-related pathways. On the basis of comparisons with both vertebrate and invertebrate phototransduction pathways, we determined that components of two of the main metazoan phototransduction pathways were altered in response to illumination. Among the key phototransduction-related genes in tentacles, we identified retinol dehydrogenase, members of the dehydrogenase/reductase family, and myosin III, and also detected a pair of visual pigment-like receptors, peropsin and peropsin-like, the homologous genes of which are believed to have the same function but show opposite expression patterns in response to different light environments. In general, the up-regulation of key genes in sea cucumber exposed to illumination indicated that the tentacles can respond to differences in the light environment at the molecular level., Competing Interests: Declaration of competing interest The authors declare that there are no conflicts of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The aquatic environment can be greatly impacted by thermal and hypoxic stresses, particularly caused by intensified global warming. Hence, there is an urgency to understand the response mechanisms of marine organisms to adverse environment. Although long non-coding RNAs (lncRNAs) are involved in many biological processes, their roles in stress responses still remain unclear. Here, differentially expressed (DE) lncRNAs and mRNAs were identified as responses to environmental stresses in the economically important sea cucumber, Apostichopus japonicus, and their potential roles were explored. Based on a total of 159, 355 and 495 significantly upregulated genes and 230, 518 and 647 significantly downregulated genes identified in the thermal, hypoxic and combination thermal + hypoxic stress treatments, respectively, we constructed DE-lncRNA-mRNA coexpression networks. Among the networks, eight shared pairs were identified from the three treatments, and based on the connectivity degree, MSTRG.27265, MSTRG.19729 and MSTRG.95524 were shown to be crucial lncRNAs. Among all the significantly changed lncRNAs identified by RT-qPCR and sequencing data, binding sites were found in four other lncRNAs (MSTRG.34610, MSTRG.10941, MSTRG.81281 and MSTRG.93731) with Aja-miR-2013-3p, a key miRNA that responds to hypoxia in sea cucumbers. The hypoxia-inducible factor (HIF-1α) was also shown as the possible targeted mRNA of Aja-miR-2013-3p. As indicated by a dual-luciferase reporter assay system, "HIF-1α gene/Aja-miR-2013-3p/MSTRG.34610" network and the "HIF-1α gene/Aja-miR-2013-3p/MSTRG.10941" network may play important roles in sea cucumbers under environmental stresses. Moreover, environmental stress altered the expression of multiple lncRNAs and mRNAs, thus affecting various biological processes in A. japonicus, including immunity, energy metabolism and the cell cycle. At the molecular level, more comprehensive responses were elicited by the combined thermal/hypoxic stress treatment than by individual stresses alone in sea cucumbers. This study lays the groundwork for future research on molecular mechanisms of echinoderm responses to thermal and hypoxic stress in the context of global climate changes., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Multiple environmental stressors caused by global warming influence the regulation of proteins involved in various biological processes in aquatic organisms. As an important component of the marine ecosystem, sea cucumber is a suitable echinoderm species for researching stress responses. In this study, we have investigated the proteomic response of respiratory trees in the sea cucumber Apostichopus japonicus, challenged with environmental stresses by using the iTRAQ technique. Results showed that 262, 155 and 433 proteins were differentially regulated in response to heat, hypoxia, and heat plus hypoxia, respectively. Expression of key genes and proteins were measured by real-time PCR and western blot to validate the accuracy of the proteome files. Results showed that the interaction between these two stressors has an additive effect at the proteome level. Proteins involved in amino acid and carbohydrate metabolic processes were largely induced by heat while repressed by hypoxia. Exposure to multiple climate change stressors caused several proteins involved in lipid metabolic progress to be down-regulated and lipid catabolic processes were induced. Additionally, hypoxia and the combined stress induced proteins involved in iron homeostasis. ATP synthesis and gluconeogenesis were induced under heat and the combined stress, while ATP and glycogen synthesis were depressed under hypoxia. Proteins related with immune and defense response were largely induced and protein synthesis ability was depressed under all three stresses. Thus, sea cucumber may adopt different strategies to cope with varied environmental stress, and the situation in heat group is more similar with the combined treatment than hypoxia group. These proteomic changes in response to high-temperature and low-oxygen levels may provide insights into the defense strategies of sea cucumber in response to global climate changes. SIGNIFICANCE OF THE STUDY: The study focused on comparative quantitative proteomics on Apostichopus japonicus respiratory tree using iTRAQ in responses to multiple climate change stressors: heat, hypoxia and the combined stress. Data showed that A. japonicus can have an acute reaction in diverse biological pathways to both individual and interacting environmental stress, including substance metabolism, signal transduction, protein synthesis, immune response and energy production. Results indicated that sea cucumber adopted different strategies to cope with varied environmental stress, and the interaction between these two stressors has an additive effect at the proteome level. These results offer insight into the molecular regulation of A. japonicus to multiple environmental stress and reveal possible molecular events in sea cucumber under climate changes. The understanding of adaptive variation under global climate changes in aquatic organisms could be improved., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The sea cucumber, an important economic species, has encountered high mortality since 2013 in northern China because of seasonal environmental stress such as hypoxia, high temperature, and low salinity. MicroRNAs (miRNAs) are important in regulating gene expression in marine organisms in response to environmental change. In this study, high-throughput sequencing was used to investigate alterations in miRNA expression in the sea cucumber under different levels of dissolved oxygen (DO). Nine small RNA libraries were constructed from the sea cucumber respiratory trees. A total of 26 differentially expressed miRNAs, including 12 upregulated and 14 downregulated miRNAs, were observed in severe hypoxia (DO 2 mg/L) compared with mild hypoxia (DO 4 mg/L) and normoxic conditions (DO 8 mg/L). Twelve differentially expressed miRNAs were clustered in severe hypoxia. In addition, real-time PCR revealed that 14 randomly selected differentially expressed miRNAs showed significantly increased expressions in severe hypoxia and the expressions of nine miRNAs, including key miRNAs such as Aja-miR-1, Aja-miR-2008, and Aja-miR-184, were consistent with the sequencing results. Moreover, gene ontology and pathway analyses of putative target genes suggest that these miRNAs are important in redox, transport, transcription, and hydrolysis under hypoxia stress. Notably, novel-miR-1, novel-miR-2, and novel-miR-3 were specifically clustered and upregulated in severe hypoxia, which may provide new insights into novel "hypoxamiR" identification. These results will provide a basis for future studies of miRNA regulation and molecular adaptive mechanisms in sea cucumbers under hypoxia stress., (Copyright © 2017 Huo et al.)

Apart from sharing common ancestry with chordates, sea cucumbers exhibit a unique morphology and exceptional regenerative capacity. Here we present the complete genome sequence of an economically important sea cucumber, A. japonicus, generated using Illumina and PacBio platforms, to achieve an assembly of approximately 805 Mb (contig N50 of 190 Kb and scaffold N50 of 486 Kb), with 30,350 protein-coding genes and high continuity. We used this resource to explore key genetic mechanisms behind the unique biological characters of sea cucumbers. Phylogenetic and comparative genomic analyses revealed the presence of marker genes associated with notochord and gill slits, suggesting that these chordate features were present in ancestral echinoderms. The unique shape and weak mineralization of the sea cucumber adult body were also preliminarily explained by the contraction of biomineralization genes. Genome, transcriptome, and proteome analyses of organ regrowth after induced evisceration provided insight into the molecular underpinnings of visceral regeneration, including a specific tandem-duplicated prostatic secretory protein of 94 amino acids (PSP94)-like gene family and a significantly expanded fibrinogen-related protein (FREP) gene family. This high-quality genome resource will provide a useful framework for future research into biological processes and evolution in deuterostomes, including remarkable regenerative abilities that could have medical applications. Moreover, the multiomics data will be of prime value for commercial sea cucumber breeding programs.

Sea cucumbers are an important economic species and exhibit high yield value among aquaculture animals. Purple sea cucumbers are very rare and beautiful and have stable hereditary patterns. In this study, isobaric tags (IBT) were first used to reveal the molecular mechanism of pigmentation in the body wall of the purple sea cucumber. We analyzed the proteomes of purple sea cucumber in early pigmentation stage (Pa), mid pigmentation stage (Pb) and late pigmentation stage (Pc), resulting in the identification of 5580 proteins, including 1099 differentially expressed proteins in Pb: Pa and 339 differentially expressed proteins in Pc: Pb. GO and KEGG analyses revealed possible differentially expressed proteins, including"melanogenesis", "melanosome", "melanoma", "pigment-biosynthetic process", "Epidermis development", "Ras-signaling pathway", "Wnt-signaling pathway", "response to UV light", and "tyrosine metabolism", involved in pigment synthesis and regulation in purple sea cucumbers. The large number of differentially expressed proteins identified here should be highly useful in further elucidating the mechanisms underlying pigmentation in sea cucumbers. Furthermore, these results may also provide the base for further identification of proteins involved in resistance mechanisms against melanoma, albinism, UV damage, and other diseases in sea cucumbers., (Copyright © 2017. Published by Elsevier Inc.)

Sea cucumbers have a striking capacity to regenerate most of their viscera after evisceration, which has drawn the interest of many researchers. In this study, the isobaric tag for relative and absolute quantitation (iTRAQ) was utilized to investigate protein abundance changes during intestine regeneration in sea cucumbers. A total of 4073 proteins were identified, and 2321 proteins exhibited significantly differential expressions, with 1100 upregulated and 1221 downregulated proteins. Our results suggest that intestine regeneration constitutes a complex life activity regulated by the cooperation of various biological processes, including cytoskeletal changes, extracellular matrix (ECM) remodeling and ECM-receptor interactions, protein synthesis, signal recognition and transduction, energy production and conversion, and substance transport and metabolism. Additionally, real-time PCR showed mRNA expression of differentially expressed genes correlated positively with their protein levels. Our results provided a basis for studying the regulatory mechanisms associated with sea cucumber regeneration., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The sea cucumber, as a member of the Echinodermata, has the capacity to restore damaged organs and body parts, which has always been a key scientific issue. MicroRNAs (miRNAs), a class of short noncoding RNAs, play important roles in regulating gene expression. In the present study, we applied high-throughput sequencing to investigate alterations of miRNA expression in regenerative intestine compared to normal intestine. A total of 73 differentially expressed miRNAs were obtained, including 59 up-regulated miRNAs and 14 down-regulated miRNAs. Among these molecules, Aja-miR-1715-5p, Aja-miR-153, Aja-miR-252a, Aja-miR-153-5p, Aja-miR-252b, Aja-miR-2001, Aja-miR-64d-3p, and Aja-miR-252-5p were differentially expressed over 10-fold at 3days post-evisceration (dpe). Notably, real-time PCR revealed that Aja-miR-1715-5p was up-regulated 1390-fold at 3dpe. Moreover, putative target gene co-expression analyses, gene ontology, and pathway analyses suggest that these miRNAs play important roles in specific cellular events (cell proliferation, migration, and apoptosis), metabolic regulation, and energy redistribution. These results will provide a basis for future studies of miRNA regulation in sea cucumber regeneration., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Sea cucumbers are excellent models for studying organ regeneration due to their striking capacity to regenerate most of their viscera after evisceration. In this study, we applied NMR-based metabolomics to determine the metabolite changes that occur during the process of intestine regeneration in sea cucumbers. Partial least-squares discriminant analysis showed that there was significant differences in metabolism between regenerative intestines at 3, 7, and 14days post evisceration (dpe) and normal intestines. Changes in the concentration of 13 metabolites related to regeneration were observed and analyzed. These metabolites included leucine, isoleucine, valine, arginine, glutamate, hypotaurine, dimethylamine, N,N-dimethylglycine, betaine, taurine, inosine, homarine, and histidine. Three important genes (betaine-aldehyde dehydrogenase, betaine-homocysteine S-methyltransferase 1, and dimethylglycine dehydrogenase) were differentially expressed to regulate the levels of betaine and N,N-dimethylglycine during intestine regeneration. These results provide an important basis for studying regenerative mechanisms and developing regenerative matrixes., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Sea cucumbers, Apostichopus japonicus, experience seasonally high water temperatures during the summer months and enter aestivation to survive. Aestivation is characterized by strong metabolic rate depression which is supported by a series of strategies including reorganizing metabolic processes, suppressing cell functions, enhancing cytoprotective mechanisms, and altered gene expression. The respiratory tree tissue of the sea cucumber is an excellent material for studying aestivation, undergoing obvious atrophy during aestivation. The present study analyzed the global gene expression profile of respiratory tree tissue of A. japonicus during aestivation by constructing and screening three libraries representing key stages of aestivation: non-aestivation (NA), deep-aestivation (DA), and arousal from aestivation (AA) using RNA-seq. A total of 1240, 1184 and 303 differentially expressed genes (DEGs) were identified following the criteria of |log2 ratio|≥1 and FDR≤0.001 in comparisons of DA vs. NA, AA vs. NA and DA vs. AA. A set of respiratory tree specific DEGs was identified the first time and, in addition, common DEGs that were responsive to aestivation in both respiratory tree and intestine were identified. Functional analysis of DEGs was further performed by GO enrichment analysis and respiratory tree specific GO terms were screened out and provide interesting hints for further studies of the molecular regulation of aestivation in A. japonicus., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The sea cucumber Apostichopus japonicus Selenka survives high summer temperature by entering aestivation, characterized by hypometabolism and global gene silencing. We investigated the hypothesis that aestivation is associated with DNA methylation-dependent epigenetic mechanisms by cloning, sequencing and measuring the transcript abundances of two genes dnmt1 and mbd2/3, which comprise the DNA methylation system in A. japonicus Selenka. The deduced amino acid sequences and characteristic motifs of sea cucumber DNMT1 and MBD2/3 showed high homology to those of their mammalian counterparts. Quantitative real-time RT-PCR analysis showed that dnmt1 and mbd2/3 genes were similarly expressed in all four tissues examined (intestine, respiratory tree, muscle and body wall). Dnmt1 expression in the intestine was up-regulated during deep aestivation (P<0.05), while mbd2/3 was over-expressed in both the intestine and respiratory tree during the same period (P<0.01). No differences in expression levels were observed between other tissues. The results of this study suggest that DNA methylation may be involved in transcriptional silencing, and that the intestine is the major site for epigenetic regulation during aestivation in the sea cucumber., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Invertebrates are increasingly raised in mariculture, where it is important to monitor immune function and to minimize stresses that could suppress immunity. The activities of phagocytosis, superoxide dismutase (SOD), catalase (CAT), myeloperoxidase (MPO), and lysozyme (LSZ) were measured to evaluate the immune capacities of the sea cucumber, Apostichopus japonicus, to acute temperature changes (from 12 degrees C to 0 degrees C, 8 degrees C, 16 degrees C, 24 degrees C, and 32 degrees C for 72 h) and salinity changes (from 30 per thousand to 20 per thousand, 25 per thousand, and 35 per thousand for 72 h) in the laboratory. Phagocytosis was significantly affected by temperature increases in 3 h, and by salinity (25 per thousand and 35 per thousand) changes in 1 h. SOD activities decreased significantly in 0.5 h to 6 h samples at 24 degrees C. At 32 degrees C, SOD activities decreased significantly in 0.5 h and 1 h exposures, and obviously increased for 12 h exposure. CAT activities decreased significantly at 24 degrees C for 0.5 h exposure, and increased significantly at 32 degrees C in 3 h to 12 h exposures. Activities of MPO increased significantly at 0 degrees C in 0.5 h to 6 h exposures and at 8 degrees C for 1 h. By contrast, activities of MPO decreased significantly in 24 degrees C and 32 degrees C treatments. In elevated-temperature treatments, activities of LSZ increased significantly except at 32 degrees C for 6 h to 12 h exposures. SOD activity was significantly affected by salinity change. CAT activity decreased significantly after only 1 h exposure to salinity of 20 per thousand. Activities of MPO and LSZ showed that A. japonicus tolerates limited salinity stress. High-temperature stress had a much greater effect on the immune capacities of A. japonicus than did low-temperature and salinity stresses.

Broodstock rearing is fundamental to produce high-quality offspring for aquaculture. However, reproduction requires large amounts of energy and nutrients, and physiological activities of digestive enzymes determine the absorption of energy and nutrients. However, the interaction between reproduction and digestive physiology is still unclear in sea cucumbers. In this study, we used laboratory experiments and field investigations to assess the variations of digestive physiology and digestive function in the sea cucumber Apostichopus japonicus during reproduction. Unexpectedly, activities of both amylase and trypsin were depressed in adult sea cucumbers during reproduction under both laboratory and field conditions. As a physiological consequence, digestive efficiencies of energy and organic matter decreased significantly during reproduction. Although reproductive output of sea cucumbers varied greatly between laboratory and wild conditions, reproductive effort had no effect on the activities of numerous digestive enzymes. Together, these data indicated that reproductive status induced digestive function decline in A. japonicus. Our study provided very important information about the reproductive biology of sea cucumbers that could be applied to broodstock rearing and conservation of this commercially important species. [ABSTRACT FROM AUTHOR]

Simple Summary: The sea cucumber Apostichopus japonicus is an important aquatic invertebrate in the aquaculture industry. It has high nutritional and medicinal value and is popular with consumers, in particular in Asia. The high demand for the species has led to declines in wild populations and A. japonicus is listed as an endangered species by IUCN. Aquaculture of sea cucumber is important to safeguard the conservation of the species in the wild, and its successful reproduction in captivity is a prerequisite for industrial production. It is known that parental nutrient reserves, in particular of lipids, are directly related to the reproductive performance of sea cucumbers. In this study, we investigated the impact of a high-fat diet on the intestinal and gonadal metabolism of male and female A. japonicus. Diet lipid content significantly affected the intestinal microbiome and metabolite profile, and also interfered with gonadal metabolites. Dietary lipid supplementation enhanced the dominance of Proteobacteria in the intestines. Other microbes in the intestines responded to a high-fat diet, which may contribute to maintain intestinal homeostasis. The physiological and metabolic responses of sea cucumbers to a high-fat diet showed sex differences. Interestingly, a correlation between intestinal and gonadal tissue levels of polyunsaturated fatty acid was found. The results of this study indicate that the lipid content in diets can be differentially adjusted for male and female sea cucumbers to improve nutrition and promote reproduction. This data also contributes to a better understanding of the reproductive biology and sex differences of sea cucumbers. Parental nutrient reserves are directly related to reproductive performance in sea cucumbers. This study focused on the lipid requirements of male and female sea cucumbers Apostichopus japonicus during the reproductive stage and analyzed their physiological responses to a high-fat diet (HFD). The intestinal lipid metabolites and microbiome profile changed significantly in animals fed with the HFD, as given by an upregulation of metabolites related to lipid metabolism and an increase in the predominance of Proteobacteria in the microbiome, respectively. The metabolic responses of male and female sea cucumbers to the HFD differed, which in turn could have triggered sex-related differences in the intestinal microbiome. These results suggest that the lipid content in diets can be differentially adjusted for male and female sea cucumbers to improve nutrition and promote reproduction. This data contributes to a better understanding of the reproductive biology and sex differences of sea cucumbers. [ABSTRACT FROM AUTHOR]

Simple Summary: The sea cucumber Apostichopus japonicus is an ecologically significant echinoderm with considerable nutritional and therapeutic value. Color variation of A. japonicus is one of its most important cultivation traits, as color affects its bioactive compounds, taste, and market price. Microphthalmia-associated transcription factor (MITF) is one of the most critical genes in melanocyte development and melanin synthesis pathways. However, how MITF regulates body color and differentiation in sea cucumbers is poorly understood. Here, we analyzed the expression level and location of MITF in white, purple, and green sea cucumbers and identified the genes regulated by MITF using chromatin immunoprecipitation followed by sequencing. Our findings suggested that MITF contributed to the body color differentiation of green, purple, and white sea cucumbers A. japonicus through expression differences and regulation of downstream genes. These findings give researchers a foundation for further research into the processes that underlie the development of body color in sea cucumbers and provide light on how genes are regulated. The results will also provide support for sea cucumber breeding and a useful theoretical basis in order to contribute to the development of the sea cucumber industry. Melanin, which is a pigment produced in melanocytes, is an important contributor to sea cucumber body color. MITF is one of the most critical genes in melanocyte development and melanin synthesis pathways. However, how MITF regulates body color and differentiation in sea cucumbers is poorly understood. In this study, we analyzed the expression level and location of MITF in white, purple, and green sea cucumbers and identified the genes regulated by MITF using chromatin immunoprecipitation followed by sequencing. The mRNA and protein expression levels of MITF were all highest in purple morphs and lowest in white morphs. In situ hybridization indicated that MITF mRNA were mainly expressed in the epidermis. We also identified 984, 732, and 1191 peaks of MITF binding in green, purple, and white sea cucumbers, which were associated with 727, 557, and 887 genes, respectively. Our findings suggested that MITF contributed to the body color differentiation of green, purple, and white sea cucumbers through expression differences and regulation of downstream genes. These results provided a basis for future studies to determine the mechanisms underlying body color formation and provided insights into gene regulation in sea cucumbers. [ABSTRACT FROM AUTHOR]

Simple Summary: Many species of sea cucumber in Echinodermata may eviscerate most of or even all internal organs when encountering predators or adverse environments, and can achieve regeneration within a certain time. Although regeneration time varies, the mechanism is common. This paper reviewed the intestinal regeneration process of sea cucumbers from the perspectives of histocytology and molecular mechanism. Echinodermata has a special evolutionary position between achordate and chordate, so we hope to explore the common regeneration conserved signals between invertebrates and vertebrates by recording the intestinal regeneration of sea cucumbers. Most species of the class Holothuroidea are able to regenerate most of their internal organs following a typical evisceration process, which is a unique mechanism that allows sea cucumbers to survive in adverse environments. In this review, we compare autotomy among different type of sea cucumber and summarize the histocytological events that occur during the five stages of intestinal regeneration. Multiple cytological activities, such as apoptosis and dedifferentiation, take place during wound healing and anlage formation. Many studies have focused on the molecular regulation mechanisms that underlie regeneration, and herein we describe the techniques that have been used as well as the development-related signaling pathways and key genes that are significantly expressed during intestinal regeneration. Future analyses of the underlying mechanisms responsible for intestinal regeneration should include mapping at the single-cell level. Studies of visceral regeneration in echinoderms provide a unique perspective for understanding whole-body regeneration or appendage regeneration. [ABSTRACT FROM AUTHOR]

Seed production plays an important role in aquaculture. The sea cucumber Apostichopus japonicus is an important marine aquaculture species in many Asian countries. By 2020, the annual total seed production of A. japonicus reached 551 billion individuals in China. However, the traditional method of culturing A. japonicus larvae is cost intensive and causes environmental pollution. In this study, we developed an eco‐friendly method for rearing sea cucumber larvae. We designed a cage system to provide a suitable living environment for larvae in open‐air outdoor ponds, and then, we identified 0.2 larvae per ml as the optimal stocking density for larval rearing. We also found that substrates made of oyster and scallop shells were optimal for larval settlement. A. japonicus larvae showed good survival, growth, development and settlement when cultured using this low‐cost and non‐polluting method. Our results can be applied to support sustainable development of the sea cucumber industry. [ABSTRACT FROM AUTHOR]

Neuropeptides are endogenous active substances that are present in nervous tissues and participate in behavioral and physiological processes of the animal system. Locomotor behavior is basic to predation, escape, reproduction in animals, and neuropeptides play an important role in locomotion. In this study, the function of pedal peptide-type neuropeptide (PDP) in the process of locomotor behavior of the sea cucumber Apostichopus japonicus was evaluated. The locomotor behavior of A. japonicus was recorded by infrared camera before and after PDP administration, and muscle physiology was studied by ultra performance liquid chromatography and quadrupole time-off-light mass spectrometry (UPLC-Q-TOF-MS) to clarify the potential physiological mechanisms. The results showed that PDP enhanced the cumulative duration of moving significantly at the 7th h after injection, and reduced the mean and maximum velocity by 16.90 and 14.22% in A. japonicus. The data of muscle metabolomics suggested that some significantly changed metabolites were related to locomotor behavior of sea cucumbers. The decreases of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) might result in the increases of lysophosphatidylcholines (lysoPC) and lysophosphatidylethanolamine (lysoPE), and suggested the change of fluidity and permeability in the muscle cell membrane, which would affect the physiology and function of muscle cells, and finally alter the locomotor behavior. In addition, the increased level of arachidonic acid (ARA) might activate K+ ion channels and then affect the signaling of muscle cells, or promote the sensitivity of muscle cells to Ca2+ and then result in the contractility of longitudinal muscles in sea cucumbers. ARA was also involved in the linoleic acid metabolism which was the only pathway that disturbed significantly after PDP administration. In conclusion, PDP participated in the regulation of locomotor behavior in the sea cucumber, and the decreased PE and PC, increased lysoPC, lysoPE and ARA might be the potential physiological mechanisms that responsible for behavioral effects of PDP in A. japonicus. [ABSTRACT FROM AUTHOR]

A water flow simulation device capable of adjusting flow velocity was designed in flow velocity range of 0–30 cm/s, with which an indoor experiment was conducted to simulate the movement and adhesive behaviors of different-sized Apostichopus japonicus under different flow velocities. Observation showed that, in slow flow (~5 cm/s), A. japonicus moved more distance than in still water, and hardly moved in the riptide (~30 cm/s); and the adhesive capacity of A. japonicus was related to the flow velocity and attachment time. A. japonicus were able to attach to the bottom after any attachment time in the slow flow, after 10 s in the medium flow (~15 cm/s), and after 60 s in the riptide (~30 cm/s). In addition, larger A. japonicus were stronger with adhesive ability than smaller ones. The transcriptome data showed that the expression of transient receptor potential cation channel subfamily A, member 1 (TRPA1) in the tube feet was increased significantly in a flowing water, but those in the tentacles and tube feet were not significantly changed. Fluorescence in-situ hybridization results showed that TRPA1 was expressed around the watervascular of tentacles, tube feet, body wall, and spines. Therefore, tube feet were important for sea cucumbers to keep themselves stable in relatively swift flow with adhesion ability. [ABSTRACT FROM AUTHOR]

Physiological plasticity allows animals to adjust their physiological function to abiotic and biotic variations. It has been mostly studied in the context of response to external factors and not much is known on how animals adjust their physiology to cope with variations in internal conditions. The process of reproduction implies gonadal maturation and other internal changes, bringing various challenges to the animal such as an increased demand for energy and oxygen. Here, the capacity of the sea cucumber, Apostichopus japonicus to adjust its respiratory function and physiological mechanisms during reproduction was studied using a time-lapse videography and metabolomics approach. The results showed that reproduction caused a significant increase in oxygen consumption in A. japonicus. Interestingly, breeding sea cucumbers can accommodate the high oxygen demand by accelerating respiratory rate. However, to maintain a necessary high level of respiratory activity during reproduction, sea cucumbers need consume large amounts of adenosine triphosphate (ATP). In addition, the metabolomic data suggests that oxidative stress and hormone regulation are the physiological mechanisms linking reproduction and respiratory function. Altogether, these findings suggest that plasticity of respiratory function is an effective tactic to cope with high oxygen demand during reproduction. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the behavioural characteristics of the epithelial tissues of sea cucumber (Apostichopus japonicus) subjected to illumination. The behavioural results indicated that the tentacles, tube feet, and spines were sensitive to light with structural changes. Among the three epithelial tissues, the tentacles were the most sensitive with the shortest reaction and recovery times, whereas the tube feet and spines had longer reaction times. Quantitative real-time PCR (q-PCR) was used to analyse the changes of Pax6 expressions before and after illumination in the tentacles, tube feet and spines. Q-PCR results indicated that Pax6 expressions in the three above tissues after illumination were higher than that before illumination. We hypothesised that sea cucumber may not have independent photoreceptors, but the epithelial tissues were capable of exhibiting a behavioural response to light. This will allow us to re-examine the functions of all epithelial tissues of sea cucumbers. [ABSTRACT FROM AUTHOR]

The mass mortalities of sea cucumber Apostichpous japonicus have prevailed in northern China, mainly attributing to the emergence of extreme environmental conditions, that is hyperthermia and hyposalinity. The high‐quality sea cucumber seedlings appear to possess more robust resistance to adverse conditions. There are usually indoor‐ and outdoor‐cultured seedlings in industrial production of sea cucumbers. Although the outdoor‐cultured sea cucumbers are practically considered to be more strong and robust, the effective evaluation approach to distinguish these seedlings has been scarce. The current study compared survival and immune performances of indoor‐ and outdoor‐cultured A. japonicus under combined exogenous stressors, that is hyperthermia and hyposalinity. Results based on secondary stress induction revealed that the activities of immune enzymes and levels of catecholamines in body wall of outdoor‐cultured seedlings were prominently higher than those of indoor‐cultured seedlings recovered for 0–72 hr following sublethal stress (30°C and 25 psu of salinity). The opposite case occurred on immune enzymes in coelomic fluid of the two sources of seedlings except for myeloperoxidase. Importantly, the outdoor‐cultured seedlings, which were recovered for 72 hr after sublethal stress, exhibited a 93% of cumulative survival rate following 7 days of recovery after lethal stress (33°C and 20 psu of salinity), 27% higher than the indoor‐cultured seedlings. Collectively, the outdoor‐cultured A. japonicus seedlings showed more superior quality than the hatchery‐produced seedlings in terms of survival and immune performance. These findings provide practically useful information towards quality distinction of the indoor‐ and outdoor‐cultured sea cucumbers, which could benefit the aquaculture industry to obtain high‐quality seedlings. [ABSTRACT FROM AUTHOR]

Sea cucumbers are free of protective exoskeleton and capable of autolysis under stress conditions. The live transport of small‐size juveniles to grown‐out sites induces hypoxia and congesting stress. The transport process is essential to production of outdoor healthy seedlings. Here, we evaluated the effects of damp transport and water transport on Apostichopus japonicus, an economic species inhabiting along the Asian coast. The survival after transport and immune performance of small‐size juveniles (0.05–0.1 g of immersed weight) were monitored during distinct duration of transport (1, 3, 5, 8 and 12 hr). The results revealed that there were no significant differences between the two transport systems within 5 hr. Given the survival for recovery of 48 hr and responses of immune enzymes and catecholamines during transport, water transport was less detrimental to sea cucumbers than damp transport when the transport duration was less than 8 hr. Once the duration prolonged to 12 hr, these immune parameters changed irregularly and the survival declined drastically. Water transport with a notably higher survival for juveniles was the more appropriate manner for long‐time transport. These findings provide insights into long‐term transport of small‐size A.  japonicus juveniles and might be beneficial for production of ecologically healthy seedlings. [ABSTRACT FROM AUTHOR]

The concentrations of eight heavy metals (As, Cd, Cr, Cu, Mn, Ni, Pb and Zn) were measured in the sediment, the isolated microplastics from the sediment and the body wall of sea cucumbers from farms in China. Accordingly, the heavy metal concentrations in the sediment were below the class I upper limit of Chinese sediment quality guidelines. Among heavy metals, the median concentrations of Cd and As were higher in the body wall than in the corresponding sediment. Additionally, the median concentrations of Cd, Pb, and Zn were higher on the microplastics than in the corresponding sediment. Furthermore, there was no significant correlation among heavy metals in sediment, sea cucumber and microplastics. This study contributes to the understanding of the heavy metal accumulation in the sediment, the microplastics and the body wall of the sea cucumber. Unlabelled Image • Microplastics may serve as a vector of heavy metals in the sea cucumber farms. • Sea cucumber may have a strategy accumulating some heavy metals in the body wall. • Sea cucumber A. japonicus might be considered as a bio-monitor for Cd. [ABSTRACT FROM AUTHOR]

The sea cucumber Apostichopus japonicus (Selenka) is a valuable economic species in Southeast Asia. It has many fascinating behavioral characteristics, such as autolysis, aestivation, regeneration, and evisceration, thus it is a notable species for studies of special behaviors. Evisceration and autotomy are controlled by the neural network and involve a complicated physiological process. The occurrence of evisceration behavior in sea cucumbers is strongly related to their environment, and it negatively impacts their economic value. Evisceration behavior plays a pivotal role in the survival of A. japonicus , and when it is induced by dramatic changes in the coastal ecological environment and the aquaculture setting it can strongly affect the economic performance of this species. Although numerous studies have focused on intestinal regeneration of A. japonicus , less is known about evisceration behavior, especially its underlying molecular mechanisms. Thus, identification of genes that regulate evisceration in the sea cucumber likely will provide a scientific explanation for this significant specific behavior. In this study, Illumina sequencing (RNA-Seq) was performed on A. japonicus specimens in three states: normal (TCQ), eviscerating (TCZ), and 3 h after evisceration (TCH). In total, 129,905 unigenes were generated with an N50 length of 2651 base pairs, and 54,787 unigenes were annotated from seven functional databases (KEGG, KOG, GO, NR, NT, Interpro, and Swiss-Prot). Additionally, 190, 191, and 320 genes were identified as differentially expressed genes (DEGs) in the comparisons of TCQ vs. TCZ, TCZ vs. TCH, and TCQ vs. TCH, respectively. These DEGs mapped to 157, 113, and 190 signaling pathways in the KEGG database, respectively. KEGG analyses also revealed that potential DEGs enriched in the categories of "environmental information processing," "organismal system," "metabolism," and "cellular processes," and they were involved in evisceration behavior in A. japonicus. These DEGs are related to muscle contraction, hormone and neurotransmitter secretion, nerve and muscle damage, energy support, cellular stress, and apoptosis. In conclusion, through our comparative analysis of A. japonicus in different stages, we identified many candidate evisceration-related genes and signaling pathways that likely are involved in evisceration behavior. These results should help further elucidate the mechanisms underlying evisceration behavior in sea cucumbers. Figure above is the hierarchical clustering of DEGs in three comparison groups of evisceration behavior (TCQ-vs-TCZ, TCZ-vs-TCH and TCQ-vs-TCH) in A. japonicus. This figure reveals the overall up- and downregulation of differentially expressed genes (DEGs) that involved in the evisceration behavior of sea cucumber A. japonicus. These DEGs fell into the categories of "stimuli response", "signal transduction", "organismal system", and "metabolism", and are suggested that muscle contraction, hormone and neurotransmitter secretion, nerve and muscle damage, energy support, cellular stress and apoptotic are involved in the evisceration behavior in A. japonicus. Unlabelled Image [ABSTRACT FROM AUTHOR]

Host-intestine microbiota interactions have been widely studied in aquatic animals, but these interactions in the intestine regeneration process of the sea cucumber Apostichopus japonicus have been rarely investigated. To understand how intestine regeneration impacts the developing intestinal microbiome composition and function, we performed a case study to characterize the intestinal microbial composition and functional genes of A. japonicus during intestine regeneration stages. High-throughput 16S rRNA gene sequencing revealed significantly different intestine microbiota compositions in different regeneration stages. The phylogenetic diversity and composition of the intestinal microbiota changed significantly in the early regeneration stage and tended to recover in the end stage. During the regeneration process, the abundance of Bacteroidetes and Rhodobacterales increased significantly. A network analysis revealed that Rhodobacteraceae and Flavobacteriaceae may function as keystone taxa in the intestinal microbial community of A. japonicus during intestine regeneration. Metagenomic analyses of representative samples revealed that the microbiomes of regenerating intestines were enriched in genes facilitating cell proliferation, digestion and immunity. The increased abundance of Bacteroidetes elevated the enrichment of genes associated with carbohydrate utilization. Some functional features in the subsystem category changed in a pattern that was consistent with the changing pattern of microbiota composition during intestine regeneration. Our results revealed that seemingly regular alterations in the intestinal microbiome composition and function are associated with intestine regeneration stages. Intestinal microbiota can increase the abundance of beneficial bacterial members and upregulate related functional genes to adapt to intestine regeneration and reconstruct a stable community structure. This study provides a new insight into the mechanism of the host-microbiota interaction response to organ regeneration. [ABSTRACT FROM AUTHOR]

Melatonin is a highly conserved hormone in evolutionary history. It occurs in numerous organisms and plays a role in the endocrine and immune systems. Locomotor behavior is a basic behavior in animals and is an important indicator of circadian rhythms, which are coordinated by the nervous and endocrine systems. To date, the effect of melatonin on locomotor behavior has been studied in vertebrates, including syrian hamsters, sparrows, rats, zebrafish, goldfish, and flatworms. However, there have been few studies of the effects of melatonin on locomotor behavior in marine invertebrates. The goals of present study were to show the existence of melatonin in the sea cucumber Apostichopus japonicus and to evaluate its effect on locomotor activity. In addition, muscle tissues from control and melatonin-treated sea cucumbers were tested using ultra performance liquid chromatography and quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) to determine the changes of metabolic activity in muscle. Melatonin was present in the coelomic fluid of A. japonicus at a concentration of ∼135.0 ng/L. The total distance traveled and number steps taken over 9 h after melatonin administration decreased with increasing concentration of the melatonin dose. Mean and maximum velocity of movement and stride length and stride frequency also decreased, but their differences were not statistically significant. Overall, these results suggest that melatonin administration had a sedative effect on A. japonicus. The levels of 22 different metabolites were altered in the muscle tissues of melatonin-treated sea cucumbers. Serotonin, 9- cis retinoic acid, all-trans retinoic acid, flavin mononucleotide in muscles were downregulated after melatonin administration. Moreover, a high free fatty acid (FFA) concentration and a decrease in the adenosine 5′-triphosphate (ATP) concentration in the muscle tissues of the melatonin-treated group were detected as well. These results suggest that the sedative effect of melatonin involves some other metabolic pathways, and the reduced locomotor modulator—serotonin, inhibited fatty acid oxidation and disturbed oxidative phosphorylation are potential physiological mechanisms that result in the inhibitory effect of melatonin on locomotion in sea cucumbers. [ABSTRACT FROM AUTHOR]

Abstract Microplastic ingestion by the farmed sea cucumber is undocumented. Microplastics were isolated from the sea cucumber Apostichopus japonicus that was collected from eight farms along the Bohai Sea and the Yellow Sea in China. To examine microplastic ingestion, the intestines were isolated, digested and then subjected to the floatation test. The microplastic abundance in the sediment ranged from 20 to 1040 particles kg−1 of dry sediment, while the ingested microplastics ranged from 0 to 30 particles intestine−1. After filtering the coelomic fluid, the extracted microplastics from the coelomic fluid ranged from 0 to 19 particles animal−1. Thus, we speculated that microplastics may transfer to the coelomic fluid of sea cucumber. The ingested microplastics did not correlate with the animal body weight but was site dependent, suggesting that sea cucumber may serve as sentinel for microplastic pollution monitoring in the sediment. The microplastics were identified by Fourier transform infrared micro spectroscopy, and the polymer types were mainly cellophane, polyester, and polyethylene terephthalate. This study revealed that, microplastics widely existed in sea cucumber farms, and that sea cucumbers ingest microplastics as suitable with their mouth open. Moreover, the microplastics might transfer to the coelomic fluid of the sea cucumber. Further investigations are needed to assess the chronic effect of the microplastics on the growth and physiological status of the sea cucumber. Graphical abstract Image 1 Highlights • The farmed sea cucumber ingested microplastics with an average of 10 MP per intestine. • Microfibres were predominantly detected from the habitat of sea cucumber. • Microplastic might transfer to the coelomic fluid of sea cucumber. • A. japonicus can serve as sentinels for microplastic pollution in the sediments. The farmed sea cucumber Apostichopus japonicus ingests microplastics as suitable with their mouth open, and these microplastics might transfer to the coelomic fluid of the sea cucumber. [ABSTRACT FROM AUTHOR]

Understanding the physiological changes of oocyte in vitro maturation are important for improving in in vitro fertilization rates and embryonic development. In this study, Apostichopus japonicus gonads were dissected, and the oocytes and gonadal fluid extracted from the gonads were dried in darkness to induce oocyte maturation. The changes in the germinal vesicle breakdown percentage (GVBDP), superoxide dismutase (SOD) activity, and the concentrations of glutathione (GSH), cyclic adenosine monophosphate (cAMP), adenylyl cyclase (AC), protein kinase C (PKC), oestradiol (E2), and metabolites in gonadal fluid–oocyte complexes (GFOC) were detected during desiccation. The GVBDP peaked at 85% after 2 hr of desiccation. The SOD activity and GSH concentration in GFOC increased significantly during desiccation, reaching their maximum values at 0.5 and 2 hr of desiccation respectively (p < 0.05). The concentrations of cAMP, AC, PKC, and E2 decreased significantly during the desiccation treatment (p < 0.05) and reached relatively stable levels after 1 hr of desiccation. After 2 hr of desiccation, among the 68 metabolites detected in the GFOC, the concentrations of 52 metabolites increased and those of 16 metabolites decreased. This study not only provides an effective and simple technique for in vitro induction of A. japonicus oocyte maturation under desiccation stress, but also improves our understanding of gamete biology in this species. [ABSTRACT FROM AUTHOR]

Abstract Economically important marine organisms face severe environmental challenges, such as high temperature and low dissolved oxygen, from global climate change. Adverse environmental factors impact the survival and growth of economically important marine organisms, thereby negatively influencing the aquaculture industry. However, little is known about the responses of sea cucumbers to combined environmental co-stressors till now. In this study, ultra-performance liquid chromatography (UPLC) was utilized to obtain metabolic profiles of sea cucumbers. Changes in the concentrations of 84, 68, and 417 metabolites related to the responses of sea cucumbers to heat (26 °C), hypoxia (2 mg/L) and the combined stress, respectively, were observed and analyzed. Representative biomarkers were discussed in detail, including deltaline, fusarin C, halichondrin B and rapanone. The concentration of metabolites involved in the regulation of energy metabolism, including amino acid, carbohydrate and lipid metabolism were significantly changed, and the tricarboxylic acid (TCA)-cycle was significantly altered under heat plus hypoxia. We interpreted these changes partly as an adaptation mechanism in response to environmental stress. Based on the decreased accumulation of glutamine, we hypothesized that heat stress is the main factor that interferes with the process of glutamic acid-glutamine metabolism. The present study showed that combined environmental stressors have a more extensive impact on the metabolites of the respiratory tree in sea cucumbers than single stress. These results would facilitate further development of the sea cucumber as an echinoderm model to study mechanisms of response to adverse environments, as well as to help advance knowledge of the adaptation of marine organisms to global climate change. Highlights • UPLC was utilized to obtain metabolic profiles of sea cucumbers under heat, hypoxia and the combined stress. • Synergistic effect of environmental stressors has an additive impact on the primary metabolome in sea cucumbers. • Ten representative potential biomarkers of heat and hypoxia in sea cucumber are illustrated. • The levels of metabolites involved in the regulation of energy metabolism were significantly changed. • The tricarboxylic acid (TCA)-cycle was significantly altered under the combined stress of heat and hypoxia. [ABSTRACT FROM AUTHOR]

Abstract Pigmentation processes provide a traceable and relevant trait for understanding key issues in evolutionary biology such as adaptation, speciation and the maintenance of balanced polymorphisms. The sea cucumber Apostichopus japonicus , which has nutritive and medical properties, is considered the most valuable commercial species in many parts of Asia. Compared with the green morph, the purple morph is rare and has great appeal to consumers. However, little is currently known about the molecular mechanism of body color formation in A. japonicus , even in echinoderm. Here, we employ illumina sequencing to examine expression patterns of the gene network underlying body wall development in purple and green morphs of A. japonicus. Overall, the number of down-regulated genes in the green morph was significantly more than in the purple morph during the pigmentation stage. We observed dynamic expression patterns of a large number of pigment, regulation and growth genes from the "Melanogenesis", "Melanoma", "Wnt signaling pathway", "Notch signaling pathway", "epithelium development", "epidermal growth factor receptor binding","growth factor activity" and "growth", including contrasting expression patterns of these genes in green and purple morph. This study provides comprehensive lists of differentially expressed genes during body wall development in the green and purple morphs, revealing potential candidate genes that may be involved in regulating body color formation and polymorphism. These data will provide valuable information for future genetic studies on sea cucumbers elucidating the molecular mechanisms underlying pigmentation, and may support the culture of desirable color morphs. [ABSTRACT FROM AUTHOR]

Sea cucumbers exposed to stressful circumstances eviscerate most internal organs, and then regenerate them rapidly under favorable environments. Reversible protein phosphorylation and acetylation are major modifications regulating protein function. Herein, for the first time, we perform quantitative phospho- and acetyl proteomics analyses of intestine regeneration in a sea cucumber species Apostichopus japonicus. We identified 1,862 phosphorylation sites in 1,169 proteins, and 712 acetylation sites in 470 proteins. Of the 147 and 251 proteins differentially modified by phosphorylation and acetylation, respectively, most were related to cytoskeleton biogenesis, protein synthesis and modification, signal recognition and transduction, energy production and conversion, or substance transport and metabolism. Phosphorylation appears to play a more important role in signal recognition and transduction than acetylation, while acetylation is of greater importance in posttranslational modification, protein turnover, chaperones; energy production and conversion; amino acid and lipid transport and metabolism. These results expanded our understanding of the regulatory mechanisms of posttranslational modifications in intestine regeneration of sea cucumbers after evisceration. [ABSTRACT FROM AUTHOR]

Abstract: As an intertidal species, Apostichopus japonicus is subject to diel and seasonal temperature fluctuations. Color variation is a distinct characteristic of A. japonicus, and a new color morph, purple A. japonicus, was recently found on the coast of Rushan, Weihai City. This study was conducted to compare the performance of green, white, and purple color morphs of A. japonicus at different water temperatures to help improving aquaculture technology and management. In this study, green, white, and purple color morphs of juvenile A. japonicus (1.5 ± 0.1 g) were cultured at 10, 14, 18, 22, and 26 C for 60 d, according to the suitable temperature range for sea cucumber growth. Temperature was shown to have a significant effect on growth, energy budget, and physiology of sea cucumbers (P < 0.05). Specific growth rates, feed conversion efficiencies, and the proportion of energy allocated to growth of all three color morphs were optimal at 18 C. Activities of the enzymes related with oxidative stress, immune response, and digestion were determined. Superoxide dismutase (SOD) and trypsin activities generally reached a maximum in all three color morphs at 18 C. The purple color morph of A. japonicus was higher in growth rate, food conversion efficiency, and proportion of energy allocated to growth than green and white color morphs at 18 and 22 C, consistent with its higher trypsin and SOD activity, indicating the mutual effect of growth and physiology. At 18, 22, and 26 C, the green color morph had the highest level of lysozyme activity and purple color morph had the lowest, indicating possible infection by external pathogens of green color morph, which might be caused by high temperature. These results suggested that the optimum temperature for culture of the three color morphs was approximately 18 C, the purple had a better adaption to high temperature, and the green and white color morphs may be more susceptible to thermal stress than the purple color morph. [ABSTRACT FROM AUTHOR]