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Apostichopus japonicus (A. japonicus) is known as one of the most popular varieties in aquaculture due to its rich nourishment and potential medicinal value. In recent years, with the abnormal change of marine environment and global climate, new challenges are arising continually in the culture process of A. japonicus. Intestinal flora plays an important role in host health and growth, and a lot of studies confirmed the close relationship between the composition change of intestinal flora and the growth of sea cucumbers. In this study, polypeptidin belonging to bacteriocins, was as an additive ingredient in sea cucumber feed. The growth of A. japonicus increased significantly after polypeptidin feeding, and the growth rate reached the highest with 1 % polypeptidin especially. Subsequently 16 S rRNA of gut microbiota from 1 % polypeptidin group was sequenced and analyzed for richness and diversity index, but the results showed that polypeptidin supplement did not markedly change the diversity and main composition of gut microbiota compared to the control. So the further analyze was performed by dependent t-test for paired samples, and found that the abundance of only a few of species at the class level changed significantly, including Alphaproteobacteria, Desulfotomaculia and Chlamydiae, but many species at the genus level changed significantly. Some important metabolic pathways were identified through function prediction, like TCA cycle, streptomycin biosynthesis and phenylalanine metabolism. At this basis, the analysis combined with the genuses and the metabolic pathways demonstrated that polypeptidin might regulate the richness of some bacteria, which could be involved in enzyme degradation, antibacterial substances secreting or underlying pathogenic tendency of gut microbiota ecosystem. These fine-tunings instead of main community structure change were probably more beneficial to the intestinal flora health, and finally contributed to the growth of A. japonicus. Thus, polypeptidin serves as a mild, non-stimulating feed supplement for A. japonicus, and has good prospects for application.

Sepia esculenta is a tasty and nutritious cephalopod. But the trend toward global warming is accelerating with massive emissions of greenhouse gases. An increase in seawater temperature and a decrease in pH are a great challenge for artificial breeding and culture of S. esculenta. In this study, we investigated the contingency mechanism of S. esculenta larvae under both high temperature and low pH conditions by transcriptome analysis. A total of 1235 DEGs were identified. functional enrichment analysis results suggest that high temperature and low pH conditions led to malignant proliferation in exceptional cells of S. esculenta larvae. A comprehensive analysis of the KEGG signaling pathway and protein-protein interaction network (PPI) identified sixteen key genes under both high temperature and low pH conditions. The three genes with the highest quantities of interactions or involved in more KEGG signaling pathways were identified as hub genes affecting normal physiological processes in S. esculenta. In this study, the effects of global warming and ocean acidification on the metabolism and immunity of S. esculenta larvae were preliminarily investigated to provide necessary help for S. esculenta captive breeding in the face of global climate change.

Nanoplastics (NPs, < 1 μm) have attracted widespread attention due to their potential threats to organisms, ecosystem, and public health. However, there is limited research on the effects of NPs on cephalopods. Sepia esculenta (Mollusks, Cephalopoda, Sepioidea), an economically major species of Sepiidea family in the world, is well received by consumers for its delicious quality and rich nutrition. In the present study, S. esculenta larvae were treated with polystyrene nanoplastics (PS-NPs) at 50 μg/mL for 4 h, and then physiological biomarkers (SOD, GSTs and MDA) and RNA-Seq in the whole body were performed. Research results suggested that PS-NPs exposure had induced oxidative stress of S. esculenta larvae. In addition, several key genes and signaling pathways related to oxidative stress were obtained based on DEGs, GO and KEGG enrichment analyses, as well as PPI construction analysis of transcriptome data. This study enriches the research on the effects of NPs exposure on different organisms and provides insights and references for revealing the mechanisms of oxidative stress caused at the molecular level.

Spermatogenesis is the production of spermatozoa by the testes, a process that is associated with reproduction in males. Amphioctopus fangsiao is an economically important species from the northern coast of China, and little research has been done on spermatogenesis in this species. In this study, we performed transcriptome analysis of testis and other somatic tissues. The maturing stage of testis development was selected, in which the emergence of spermatozoa was observed. A total of 15,773 differentially expressed genes were identified, including 8,922 upregulated genes and 6,851 downregulated genes. GO and KEGG enrichment analyses were performed to explore the functions of genes related to spermatogenesis, and the interactions between genes were examined by constructing protein interaction networks. Pathways and genes related to spermatogenesis were identified, including the oxytocin signaling pathway, the calcium signaling pathway, the FOXO signaling pathway, the DNAH family, and other key genes. The expression levels of 25 key genes were verified by qRT-PCR. The results for spermatogenesis-related genes will provide insights into the processes of spermatogenesis and testis development in A. fangsiao.

The emergence of triploid oysters has freed the oyster market from the problem of interruptions in the breeding season, allowing for year-round availability. However, according to recent statistics, the phenomenon of fertility in triploid oysters has been increasing yearly, perhaps eventually leading to the loss of the sterility characteristic. This has in turn affected the oyster farming industry. Therefore, we attempted to mine key genes through transcriptomics to find the causes of triploid fertility. During our surveys and sampling, we found that most of the fertile triploid Crassostrea gigas were females, with a much smaller percentage of males. Therefore, the main objective of this study was to analyze the differences between fertile and sterile triploid female C. gigas. We performed transcriptome analysis of fertile female triploid C. gigas and sterile female triploid C. gigas and identified 2361 up-regulated differentially expressed genes (DEGs) and 1541 down-regulated DEGs, respectively. Enrichment analysis of these DEGs revealed that most GO terms and KEGG pathways were associated with mitosis. We then created a protein–protein interaction (PPI) network using genes enriched in mitosis-associated KEGG pathways. Finally, we screened and validated 26 key genes by quantitative RT-PCR and all were found to be downregulated in expression in sterile female triploids. The main cause of sterility is the suppression of the expression of genes that control the process of germ cell proliferation, the failure of the mitotic cycle to proceed smoothly, and the inability to produce an oogonium. These results can be used to explore ways to reduce the fertility of triploid C. gigas and to promote the breeding of higher quality triploid oysters.

Sea cucumber Apostichopus japonicus, an important marine benthic animal, is particularly sensitive to environmental temperature stress, which affected the growth, metabolism, and reproduction even survival. In this study, we used whole genome bisulfite sequencing (WGBS) to perform a comprehensive comparative analysis of the DNA methylation profiles of A. japonicus at three temperatures: normal (20 °C), aestivation (26 °C), and lethal (32 °C). The results showed that the total methylation level was highest in group T26 and lowest in group T32. Most of the DNA methylation occurred on the C bases of the CG type, and the degree of DNA methylation on the CG-type C bases was 13.32–14.99%, reflecting a moderate level of DNA methylation. Comparison of differentially methylated regions (DMRs) in the CG sequence context, we identified 17,174 DMRs in group T26_vs_T20 and 16,216 DMRs in group T32_vs_T26. There were more hypermethylated regions than hypomethylated regions, and this difference was more obvious in group T32_vs_T26. DMRs analysis of the promoter regions and the gene body regions identified more DMR-related genes in the gene body region than in the promoter region in both comparison groups (T26_vs_T20 and T32_vs_T26). GO and KEGG analysis showed that pathways such as protein processing in the endoplasmic reticulum, ubiquitin mediated proteolysis, and endocytosis, etc., were highly enriched in the DMR-related genes in the comparison groups. Some of these pathways that were significantly enriched in the hypermethylated genes in group T26_vs_T20 but were enriched in the hypomethylated genes in group T32_vs_T26. Enrichment analysis of genes both differentially methylated and differentially expressed showed that downregulated genes in group T32_vs_T26 that were also hypomethylated in the gene body region were significantly enriched in the metabolic and the antioxidant-related glutathione metabolism pathway. Our results suggested that DNA methylation develop a lot of variation in the regulation of the response of A. japonicus to two levels of heat stress: at aestivation temperature and at lethal temperature, and there are many differences between the two. The results of this study provide important insights into the epigenetic mechanisms underlying the response of A. japonicus to the pressure of environmental temperature.

Sperm storage is an important reproductive strategy in Amphioctopus fangsiao. Sperm can be stored in the oviducal glands up to eight months before fertilization. However, studies on the underlying storage mechanisms remain limited. In this study, the morphological structures of the oviductal glands and the changes adapted for sperm storage and fertilization were investigated by Hematoxylin eosin (HE) staining, transmission electron microscopy (TEM), and Alcian blue periodic acid Schiff (AB-PAS) staining. Results revealed that the nucleo-cytoplasmic ratio of the peripheral gland cells decreased and the eosinophilic secretory granules (glycoproteins) appeared in the cytoplasm and lumen during sperm storage. The cytoplasm of the central gland appeared vacuolated and AB pH 2.5 (+) secretions (acid mucins) were dispersed in the cells. These secretions may pass through the central cavity into the oviducts and be involved in zygote packaging. The spermathecae are composed of columnar epithelial ciliated cells with secretory functions. PAS (+) glycoproteins were found in the lumen, providing a microenvironment conducive to sperm survival. Cilia in the oviducts, central cavity, and spermathecae may help with sperm delivery, storage, and release, and egg transport. This study enhances our understanding of the biological reproduction process in A. fangsiao.