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Chemokines are cytokines with chemoattractant capacities that exert their physiological functions through the binding of chemokine receptors. Thus, chemokine and receptor complexes exert important roles in regulating development and homeostasis during routine immune surveillance and inflammation. Compared to mammals, the physiology and structure of chemokine receptors in fish have not been systematically studied. Furthermore, the salmonid-specific whole genome duplication has significantly increased the number of functional paralogs of chemokine receptors. In this context, in the current study, trout exhibited 17 cxcr genes, including 12 newly identified and 5 previously identified receptors. Interestingly, gene expression of brain cxcr1 and cxcr4, kidney cxcr3 and cxcr4, and spleen cxcr3, cxcr4, and cxcr5 subtypes were altered by bacterial infection, whereas brain cxcr1, kidney cxcr1 and cxcr7, and liver cxcr2, cxcr3, and cxcr4 subtypes were changed in response to environmental changes. Based on protein structures predicted by ColabFold, the conserved amino acids in binding pockets between trout CXCR4.1 subtypes and human CXCR4 were also analyzed. Our study is valuable from a comparative point of view, providing new insights into the identification and physiology of salmonid chemokine receptors. [ABSTRACT FROM AUTHOR]

The melanocortin-4 receptor (MC4R) is essential for the modulation of energy balance and reproduction in both fish and mammals. Rainbow trout (Oncorhynchus mykiss) has been extensively studied in various fields and provides a unique opportunity to investigate divergent physiological roles of paralogues. Herein we identified four trout mc4r (mc4ra1, mc4ra2, mc4rb1, and mc4rb2) genes. Four trout Mc4rs (omMc4rs) were homologous to those of teleost and mammalian MC4Rs. Multiple sequence alignments, a phylogenetic tree, chromosomal synteny analyses, and pharmacological studies showed that trout mc4r genes may have undergone different evolutionary processes. All four trout Mc4rs bound to two peptide agonists and elevated intracellular cAMP levels dose-dependently. High basal cAMP levels were observed at two omMc4rs, which were decreased by Agouti-related peptide. Only omMc4rb2 was constitutively active in the ERK1/2 signaling pathway. Ipsen 5i, ML00253764, and MCL0020 were biased allosteric modulators of omMc4rb1 with selective activation upon ERK1/2 signaling. ML00253764 behaved as an allosteric agonist in Gs-cAMP signaling of omMc4rb2. This study will lay the foundation for future physiological studies of various mc4r paralogs and reveal the evolution of MC4R in vertebrates. [ABSTRACT FROM AUTHOR]

Oxytocin (OT) is a crucial regulator of reproductive behaviors, including parturition in mammals. Arg-vasopressin (AVP) is a nonapeptide homologous to Arg-vasotocin (AVT) in teleosts that has comparable affinity for the OT receptor. In the present study, ovoviviparous guppies (Poecilia reticulata) were used to study the effect of AVT on delivery mediated by the activation of prostaglandin (PG) biosynthesis via isotocin (IT) receptors (ITRs). One copy each of it and avt and two copies of itrs were identified in guppies. The results of the affinity assay showed that various concentrations of AVT and IT (10−6, 10−7, and 10−8 mol/L) significantly activated itr1 (P < 0.05). In vitro experiments revealed significant upregulation (P < 0.05) of cyclooxygenase 2 (cox2), which is the rate-limiting enzyme involved in PG biosynthesis, and itr1 by AVT and IT. Furthermore, dual in situ hybridization detected positive signals for itr1 and cox2 at the same site, implying that ITR1 may regulate cox2 gene expression. Measurement of prostaglandin F2a (PGF2a) concentrations showed that AVT induced PGF2a synthesis (P < 0.05) and that the effect of IT was not significant. Finally, intraperitoneal administration of PGF2a significantly induced premature parturition of guppies. This study is the first to identify and characterize AVT and ITRs in guppies. The findings suggest that AVT promotes PG biosynthesis via ITR and that PGF2a induces delivery behavior in ovoviviparous guppies. [ABSTRACT FROM AUTHOR]

Rainbow trout (Oncorhynchus mykiss) is one of the most common aquaculture fish species worldwide. Vibriosis disease outbreaks cause significant setbacks to aquaculture. The stress and immune responses are bidirectionally modulated in response to the health challenges. Therefore, an investigation into the regulatory mechanisms of the stress and immune responses in trout is invaluable for identifying potential vibriosis treatments. We investigated the transcriptional profiles of genes associated with stress and trout immune functions after Vibrio anguillarum infection. We compared the control trout (CT, 0.9% saline injection), asymptomatic trout (AT, surviving trout with minor or no symptoms after bacteria injection), and symptomatic trout (ST, moribund trout with severe symptoms after bacteria injection). Our results showed activated immunomodulatory genes in the cytokine network and downregulated glucocorticoid and mineralocorticoid receptors in both AT and ST, indicating activation of the proinflammatory cytokine cascade as a common response in AT and ST. Moreover, the AT specifically activated the complement- and TNF-associated immune defenses in response to V. anguillarum infection. However, the complement and coagulation cascades, as well as steroid hormone homeostasis in ST, were disturbed by V. anguillarum. Our studies provide new insights toward understanding regulatory mechanisms in stress and immune functions in response to diseases. [ABSTRACT FROM AUTHOR]

Low levels of stresses cause eustress while high stressful situations result in distress. Female rainbow trout (Oncorhynchus mykiss) was reared under crowded conditions to mimic the stressful environment of intensive fishery production. Trout was stocked for 300 days with initial densities of 4.6 ± 0.02 (final: 31.1 ± 0.62), 6.6 ± 0.03 (final: 40.6 ± 0.77), and 8.6 ± 0.04 (final: 49.3 ± 1.09) kg/m3 as SD1, SD2 and SD3. We assessed molecular, cellular and organismal parameters to understand the flexibility of neuro-endocrine-immune network during stress. Trout with higher initial density (SD3) displayed the slightly activated hypothalamus-pituitary-interrenal (HPI) axis with positively increased antioxidant enzyme activities and anti-inflammatory cytokine transcriptions on day 60 or 120. These results indicated that low level of stress was capable of exerting eustress by activating neuro-endocrine-immune network with beneficial adaptation. Transition from eustress to distress was induced by the increased intensity and duration of crowding stress on day 240 and 300. The prolonged activation of HPI axis resulted in suppressed growth hormone-insulin-like growth factor (GH-IGF) axis, up-regulated cytokine transcriptions and severe reactive oxygen species stress. Stress means reset of neuro-endocrine-immune network with energy expenditure and redistribution. Digestive ability of trout with distress was also inhibited on day 240 and 300, indicating a decreased total energy supplement and energy distribution for functions are not necessary for surviving such as growth and reproduction. Consequently, we observed the dyshomeostasis of energy balance and neuro-endocrine-immune network of trout during long-term crowding conditions. Image 1 • Low levels of crowding stress provided eustress with positive HPI activation. • Eustress stimulate adaptive mechanisms in endocrine and immune network. • Long-term crowded conditions cause distress with negatively prolonged HPI activation. • Distress caused maladaptive mechanisms in endocrine and immune network. [ABSTRACT FROM AUTHOR]

Melanocortin-4 receptor (MC4R) plays important roles in regulation of multiple physiological processes including energy homeostasis, reproduction, sexual function, and other functions in mammals. Recent studies suggested that teleost MC4Rs have different physiological functions and pharmacological characteristics when compared to mammalian MC4Rs. In this study, we investigated spotted sea bass (Lateolabrax maculatus) MC4R (Lm MC4R) physiology and pharmacology. Spotted sea bass mc4r consisted of a 984 bp open reading frame encoding a protein of 327 amino acids. Lm MC4R was homologous to those of several teleost MC4Rs and human MC4R (hMC4R). qRT-PCR and in situ hybridization revealed that mc4r transcripts were highly expressed in the brain, followed by pituitary and liver. Brain mc4r transcripts were down-regulated in long-term and short-term fasting challenges. Lm MC4R was a functional receptor with lower maximal binding and higher basal activity than hMC4R. THIQ was not able to displace 125I-NDP-MSH but could affect intracellular cAMP accumulation, suggesting that it was an allosteric ligand for Lm MC4R. In vitro studies with spotted sea bass brain cells indicated that mRNA levels of neuropeptide Y and Agouti-related peptide were down-regulated by α-MSH. In summary, we cloned spotted sea bass MC4R, and showed that it had different pharmacological properties compared to hMC4R, and potentially different functions. [ABSTRACT FROM AUTHOR]

The tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation (14-3-3) proteins are a group of highly conserved homologous and heterologous proteins involved in a wild range of physiological processes, including the regulation of many molecular phenomena under different environmental salinities. In this study, we identified eleven 14-3-3 genes from the spotted sea bass (Lateolabrax maculatus) genome and transcriptomic databases and verified their identities by conducting phylogenetic, syntenic and gene structure analyses. The spotted sea bass 14-3-3 genes are highly conserved based on sequence alignment, conserved domains and motifs, and tertiary structural feature. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis of 14-3-3 genes in gill of spotted sea bass under normal physiological conditions indicated that the expression level of 14-3-3 zeta was the highest among tested genes, followed by 14-3-3 theta. Furthermore, expression profiles of 14-3-3 genes in gill tissue (in vivo and in vitro) indicated that the 14-3-3 zeta and 14-3-3 theta genes were significantly induced by different environmental salinities in spotted sea bass, suggesting their potential involvement in response to salinity challenge. Our findings may lay the foundation for future functional studies on the 14-3-3 gene family in euryhaline teleosts. Unlabelled Image • A complete set of 11 tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation (14-3-3) proteins was identified in the Lateolabrax maculatus genome. • The evolutionary footprint of 14-3-3 genes was revealed via the analysis of phylogenetic tree, copy numbers, exon-intron structures and motif compositions. • The notably highly expression levels of 14-3-3 zeta and 14-3-3 theta in normal condition and significantly changes after salinity challenge suggesting their essential roles in osmotic regulation and salinity adaptation. [ABSTRACT FROM AUTHOR]

Acute change in water temperature causes heavy economic losses in the aquaculture industry. The present study investigated the metabolic and molecular effects of acute thermal stress on black rockfish (Sebastes schlegelii). Gas chromatography time-of-flight mass spectrometry (GC-TOF-MS)-based metabolomics was used to investigate the global metabolic response of black rockfish at a high water temperature (27°C), low water temperature (5°C) and normal water temperature (16°C). Metabolites involved in energy metabolism and basic amino acids were significantly increased upon acute exposure to 27°C (P < 0.05), and no change in metabolite levels occurred in the low water temperature group. However, certain fatty acid levels were elevated after cold stress (P < 0.05), and this effect was not observed in the 27°C group, suggesting that acute high and low temperature exposures caused different physiological responses. Using quantitative real-time PCR, we analyzed the expression of ubiquitin (ub), hypoxia-inducible factor (hif), lactate dehydrogenase (ldh), and acetyl-CoA carboxylase (acac). Higher expression levels of ub, hif, and ldh (P < 0.05) were observed in the high water temperature group, but no changes in these expression levels occurred in the low water temperature group. Our findings provide a potential metabolic profile for black rockfish when exposed to acute temperature stress and provide some insights into host metabolic and molecular responses to thermal stress. [ABSTRACT FROM AUTHOR]

To study the expression of four estrogen receptor genes ( erα1, erα2, erβ1, erβ2 ) of female rainbow trout ( Oncorhynchus mykiss ) during first ovarian development, trouts were sampled from different ovarian stages. Serum E 2 (estradiol) was measured by ELISA and estrogen receptors mRNA expression were examined by qRT-PCR. Our results showed a close association between increased erα1 and vitellogenin mRNA expression during ovarian maturation and increased erα2 mRNA expression in mature ovarian stages. Correlation analysis revealed that a negative relationship between serum E 2 and ovarian erβ1 (or hepatic erβ2 ), but ovarian erβ2 mRNA expression was relatively unchanged during first ovarian development. Trout were also reared in different densities as stocking density 1, 2 and 3 (SD1, 4.6–31.1 kg/m 3 ; SD2, 6.6–40.6 kg/m 3 ; SD3, 8.6–49.3 kg/m 3 ) to elucidate effects of high density on estrogen receptor expression. Histology observation showed ovarian development of trout in higher densities were retard with a relatively early stage and fewer vitellogenin accumulation. Trout in high densities showed significantly decreased serum E 2 , erα mRNA expression and increasing trends of erβ mRNA expression. A noticeable increase of ovarian erβ2 mRNA expression was seen in trout when density is approaching to 50 kg/m 3 . In conclusion, we may hypothesize that increased erβ mRNA expression triggered by high density result in decreased erα mRNA expression and vitellogenesis. As a result, ovarian development in higher densities was retard. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the hypothalamus-pituitary-gonad (HPG) axis of female rainbow trout ( Oncorhynchus mykiss ) during early ovarian development and under high rearing density. Trouts were sampled from 240 (ovarian stage II) to 540 (ovarian stage IV) days following hatching (DFH) as control group (Ctrl, 4.6–31.1 kg/m 3 ) to determine HPG axis during early ovarian development. Trouts from the same batch of fertilized eggs were reared in two higher densities during 240–540 DFH as stocking density 1 and 2 (SD1, 6.6–40.6 kg/m 3 ; SD2, 8.6–49.3 kg/m 3 ) to elucidate effects of high density on reproductive parameters. Dopamine, E 2 (estradiol), 17α,20β-P (17α,20β-dihydroxy4-pregnen-3-one) and P4 (progesterone) were evaluated by radioimmunoassay or ELISA. mRNA expression of hypothalamic gnrh-1, -2 (gonadotropin-releasing hormone-1, -2), pituitary gonadotropins ( fsh/lh , follicle-stimulating hormone/luteinizing hormone) and their cognate receptors ( fshr/lhr ) in ovaries were examined by qRT-PCR. Our findings demonstrated mRNA expression of hypothalamic sgnrh-1 , pituitary fsh and ovarian fshr increased in early ovarian development (360 DFH). Serum 17α,20β-P and pituitary lh mRNA expression first increased when trouts were in ovarian stage III (420 DFH). Ovaries were at different stages when reared in different densities. Long-term high density treatment (over 31.7 kg/m 3 ) resulted in decreased hypothalamic sgnrh-1 , pituitary fsh , ovarian fshr , serum E 2 , and increased hypothalamus gnrh-2 and serum dopamine during vitellogenin synthesis, suggesting HPG of rainbow trout might be retarded under dense rearing condition. [ABSTRACT FROM AUTHOR]

Cytochrome P450 aromatase (P450arom) is an enzyme responsible for the conversion of androgen into oestrogen. To study the role of ovarian aromatase (Cyp19a1a) in sex differentiation, the novel c DNA clone encoding ovarian aromatase (Cyp19a1a) was identified from the ovary of the black rockfish ( Sebastes schlegeli). The cloned c DNA is 1868 bp in length with 79 bp 5′U TR, 209 bp 3′UTR [excluding poly (A)] and contains 1550 bp ORF, encoding a protein of 516 amino acids. Alignment and phylogenetic analysis showed that the black rockfish ovarian aromatase (Cyp19a1a) shared 61-89% sequence identity with those of other seven fish species. The cyp19a1a transcript was found more highly abundant in ovary, but not detected in the testis, brain, liver, spleen, kidney, muscle, skin, heart, head kidney, gill, intestine and eyes by semi-quantitative reverse transcription ( RT)- PCR. The cyp19a1a gene is not equivalent in tissue-specific expression in the female and male, showed the possibility of distinct promoters and regulatory mechanisms. The expression level of cyp19a1a in ovary declined with the ovary development, but was higher than that in testis in all phases. These results indicated that cyp19a1a might be involved in gonadal development in S. schlegeli. [ABSTRACT FROM AUTHOR]

Cytochrome P450c17 ( CYP17, 17α-hydroxylase/17,20-lyase) is a critical enzyme in the production of androgens and estrogens in vertebrates. A 2102 bp full-length cDNA of P450c17-II ( CYP17A2) has been isolated from the ovary of half-smooth tongue sole, C ynoglossus semilaevis which encodes 524 amino acids. The putative P450c17- II enzyme shares higher sequence identity with those of teleosts than with P450c17- I of vertebrate. The similarity between the two types of tongue sole P450c17 was 48%.Semi-quantitative RT- PCR analysis of spatial expression showed the enzyme was specifically expressed in the ovary and the head kidney. However, temporal expression shows that P450c17- II can be found in the brain. Furthermore, temporal expression pattern of P450c17- II in ovary and brain revealed developmental stage-dependency, and ovary P450c17- II expressed remarkably throughout the whole reproductive cycle. Otherwise, the expression pattern of P450c17- II in head kidney indicated negative ovary development-dependence. In addition, combined with our data on P450c17- I, T and E2 levels, the results further endorse the critical role of P450c17- II during shift in steroidogenesis, suggesting that P450c17- I and - II may act together to this physiological process. Based on the present study, we indicate an important role for P450c17- II during ovarian development. [ABSTRACT FROM AUTHOR]

Abstract: The objectives of this study were to characterize polymorphisms within the coding region of estrogen receptor β (ERβ) gene in a population of 57 female Japanese flounder (Paralichthys olivaceus) and to analyze the association of ERβ polymorphisms with reproductive indices by polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP). Two single nucleotide polymorphisms (SNPs), SNP1 (c.577delC) and SNP2 [c.A891T (p.Gln114Leu)], were identified in the ERβ gene. A one-way ANOVA revealed that SNP1 was significantly associated with the gonadosomatic index (GSI) in female Japanese flounder (P <0.05). And SNP2 was significantly associated with the serum 17β-estradiol (E2) level and GSI (P <0.05). Individuals with genotype AB of SNP2 had significantly higher serum E2 level and GSI than those of genotype AA (P <0.05). Moreover, the hepatosomatic index (HSI), a marker for genetic effects, was significantly higher for diplotype D2 compared with the other three diplotypes (P <0.05). These results obtained in this study suggested that SNP2 could influence reproductive endocrinology of female Japanese flounder and be useful as a potential candidate genetic marker for the selection of reproductive indices in female Japanese flounder. [Copyright &y& Elsevier]

Abstract: Estrogen receptor (ERα) modifies the expression of genes involved in cell growth, proliferation and differentiation through binding to estrogen response elements (EREs) located in a number of gene promoters, so the ERα gene is considered as an important factor affecting reproductive endocrinology in Japanese flounder (Paralichthys olivaceus). In this study, twelve single nucleotide polymorphisms (SNPs) within eight CDS exons and 1 kb of 3′-UTR of the ERα gene were tested to association with four reproductive traits in a population of 119 Japanese flounder individuals with polymerase chain reaction-single stranded conformational polymorphism (PCR-SSCP). The association analysis of SNPs within Japanese flounder ERα gene with the reproductive traits was carried out using General Linear Model (GLM) estimation. Results indicated that two SNPs in the exon4 of ERα gene, P1 (A803G and C864T), were significantly associated with hepatosomatic index (HSI) (P <0.05) in female Japanese flounder. Other ten SNPs in 3′-UTR associated to serum 17β-estradiol (E2) and HSI showed that P2 (A1982T) was significantly associated with E2 (P <0.01) and P3 (A2149G, 2181TTACAAG2182 insertion or deletion, T2324G, A2359G and G2391A) was significantly associated with HSI (P <0.05) in female Japanese flounder. However, P2 (A1982T) and P4 (G2256T, T2294C, T2309G and A2333T) had significant effects on E2 (P <0.05 and P <0.01, respectively) in male Japanese flounder. In addition, there were significant associations between diplotype D1 based on fourteen SNPs and reproductive traits. The genetic effects for HSI (female) or E2 (male) of diplotype D1 were significantly higher than those of other eight diplotypes (P <0.05), respectively. Our findings implied that P1 of ERα gene affecting the reproductive traits could be a potential QTN (quantitative trait nucleotide) which would be useful genetic marker in the selection of some reproductive traits for its in Japanese flounder. [Copyright &y& Elsevier]

The solute carrier 4 (SLC4) family is a class of cell membranes transporters involved in base transport that plays crucial roles in diverse physiological processes. In our study, 15 slc4 genes were identified and annotated in spotted sea bass, including five members of Cl−/HCO3− exchangers, eight genes coding Na+-dependent HCO3− transporters, and two copies of Na+-coupled borate transporters. The gene sequence and structure, chromosomal and syntenic arrangement, phylogenetic and evolution profiles were analyzed. Results showed that the slc4 gene in teleosts obviously expanded compared with higher vertebrates, arising from teleost-specific whole genome duplication event. Most gene sites of slc4 in spotted sea bass were under strong purifying selection during evolution, while positive selection sites were only detected in slc4a1b, slc4a8, and slc4a10b. Additionally, qRT-PCR results showed that different slc4 genes exhibited distinct branchial expression patterns after alkalinity and salinity stresses, of which the strongly responsive members may play essential roles during these physiological processes. Our study provides the systemic overview of the slc4 gene family in spotted sea bass and enables a better understanding for the evolution of this family and further deciphering the biological roles in maintaining ion and acid–base homeostasis in teleosts. [ABSTRACT FROM AUTHOR]

• Black rockfish MC4R cDNA was cloned. • The mc4r expression in the brain increased with ovarian development. • Black rockfish mc4r was expressed in ovarian follicles. • MC4R could regulate the expression of several genes important for reproduction. Melanocortin-4 receptor (MC4R) is a G protein-coupled receptor with multiple functions in mammals. However, the functions of MC4R in fish have not been investigated extensively. The purpose of this study was to determine potential regulation of reproduction by the MC4R. We cloned the black rockfish MC4R and analyzed its tissue distribution and function. The results showed that black rockfish mc4r cDNA consisted of 981 nucleotides encoding a protein of 326 amino acids. The quantitative PCR data showed that mc4r mRNA was primarily expressed in the brain, gonad, stomach and intestine. In the brain, mc4r was found to be primarily located in the hypothalamus. Both α-MSH and β-MSH increased gnih expression and decreased sgnrh and cgnrh expression (P < 0.05). α-MSH and β-MSH had opposite effects on kisspeptin expression. In contrast, α-MSH and β-MSH increased the expression of cyp11, cyp19, 3β-hsd and star. In summary, our study shows that MC4R in black rockfish might regulate reproductive function and that the effects of α-MSH and β-MSH might differ. [ABSTRACT FROM AUTHOR]

• Hypoxia disturbed GH-IGF axis, causing prolonged negative influences on growth. • Hypoxia caused vitamin D and calcium dyshomeostasis. • Hypoxia resulted in muscle and bone dysfunction. • Hypoxia caused DEGs associated with apoptosis and osteoclast differentiation. Hypoxia generally refers to a dissolved oxygen (DO) level that is less than 2–3 mg/L. With ongoing global warming and environment pollution, environmental or geological studies showed hypoxia frequently occurs in global aquatic systems including ocean, river, estuaries and coasts. A preliminary study was performed to evaluate hypoxia tolerant of rainbow trout (Oncorhynchus mykiss) with parameters of mortality, behavior, endocrine and metabolite, identifying three DO levels including normoxia (Ctrl, 7.0 mg/L), non-lethal hypoxia (NH, 4.5 mg/L) and lethal hypoxia (LH, 3.0 mg/L). Furthermore, trout was treated by Ctrl, NH and LH for six hours to mimic the acute hypoxia in wild and/or farming conditions. A significantly higher mortality was observed in LH group. Trout of NH and LH showed stressful responses with unnormal swimming, increased serum cortisol and up-regulated gill hif1α transcription. Despite trout of NH and LH increased the oxygen delivery abilities by increasing the serum hemoglobin levels, the anerobic metabolism were inevitably observed with increased lactate. This study also showed a prolonged influence of NH and LH on growth after 30-days' recovery. Based on RNA-Seq data, different expression genes (DEGs) associated with stress, apoptosis, antioxidant, chaperone, growth, calcium and vitamin D metabolism were identified. Enrichment analysis showed DEGs were clustered in osteoclast differentiation, apoptosis and intracellular signaling transduction pathways. Results further showed NH and LH significantly decreased bone calcium content and disrupted the growth hormone-insulin-like growth factor (GH-IGF) axis. Our study might contribute to a better understanding of the effects of hypoxia on rainbow trout. [ABSTRACT FROM AUTHOR]

• The channel catfish MC3R cDNA encoded a functional MC3R homologous to several teleost MC3Rs. • Channel catfish MC3R could bind agonists and initiate both cAMP and ERK1/2 signaling. • Channel catfish MC3R had high constitutive activities at both cAMP and ERK1/2 pathways. • AgRP was an inverse agonist decreasing the high basal cAMP level. • MRAP2 preferentially inhibited MC3R-mediated cAMP production rather than ERK1/2 activation. The melanocortin-3 receptor (MC3R) is known to be involved in regulation of energy homeostasis, regulating feed efficiency and nutrient partitioning in mammals. Its physiological roles in non-mammalian vertebrates, especially economically important aquaculture species, are not well understood. Channel catfish (Ictalurus punctatus) is the main freshwater aquaculture species in North America. In this study, we characterized the channel catfish MC3R. The mc3r of channel catfish encoded a putative protein (ipMC3R) of 367 amino acids. We transfected HEK293T cells with ipMC3R plasmid for functional studies. Five agonists, including adrenocorticotropin, α-melanocyte stimulating hormone (α-MSH), β-MSH, [Nle4, D-Phe7]-α-MSH, and D-Trp8-γ-MSH, were used in the pharmacological studies. Our results showed that ipMC3R bound β-MSH with higher affinity and D-Trp8-γ-MSH with lower affinity compared with human MC3R. All agonists could stimulate ipMC3R and increase intracellular cAMP production with sub-nanomolar potencies. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation could also be triggered by ipMC3R. The ipMC3R exhibited constitutive activities in both cAMP and ERK1/2 pathways, and Agouti-related protein served as an inverse agonist at ipMC3R, potently inhibiting the high basal cAMP level. Moreover, we showed that melanocortin receptor accessory protein 2 (MRAP2) preferentially modulated ipMC3R in cAMP production rather than ERK1/2 activation. Our study will assist further investigation of the physiological roles of the ipMC3R, especially in energy homeostasis, in channel catfish. [ABSTRACT FROM AUTHOR]

Mitogen-activated protein kinase kinases (MKKs) are intermediate kinases of mitogen-activated protein kinases (MAPKs) signaling pathways. MKKs are activated by mitogen-activated protein kinase kinase kinase (MKKK) and then the activated MKKs trigger the activation of downstream MAPKs. MAPK signaling pathways play an important role in regulating immune functions including apoptosis and inflammation. However, studies on identification and characterization of mkk repertoire in rainbow trout (Oncorhynchus mykiss) are still limited. Trout experienced 4 rounds (4R) of whole genome duplication (WGD), thus exhibiting increased paralogs of mkk s with potentially functional diversity. In this study, we identified 17 mkk genes in trout and the following bacterial challenge (Vibrio anguillarum) studies showed functional diversity of different mkk subtypes. Vibrio anguillarum infection resulted in significantly up-regulated mkk2 subtypes in spleen and liver, and mkk4b3 in spleen, suggesting immunomodulation was regulated by activation of ERK, p38 and JNK pathways. Compared to other mkk subtypes, mkk6 s were down-regulated in symptomatic group, rather than asymptomatic group. The organisms present negative feedback on MAPK activation, thus reducing extra damage to cells. We observed down-regulated mkk6 s with up-regulated genes (dusp1 & dusp2) involved in negative feedback of MAPK activation. Based on these results, we might propose the distinct expression patterns of genes associated with MAPK pathways resulted in different phenotypes and symptoms of trout in response to bacterial challenge. • Due to 4 rounds of whole genome duplication, 17 mkk s were identified in trout. • Symptomatic and asymptomatic group exhibited distinct expression patterns of mkk s. • Up-regulated mkk s might mediate inflammation and apoptosis in trout. • Negative feedback system may be the reason to down-regulated mkk s. • Up-regulated dusp s might be involved in negative feedback of MAPK activation. [ABSTRACT FROM AUTHOR]

An energy trade-off is existed between immunological competence and growth. The axis of growth hormone releasing hormone, somatostatin, growth hormone, insulin-like growth factor (GHRH-SST-GH-IGF axis) regulates growth performances and immune competences in rainbow trout (Oncorhynchus mykiss). The salmonid-specific whole genome duplication event is known to result in duplicated copies of several key genes in GHRH-SST-GH-IGF axis. In this study, we evaluated the physiological functions of GHRH-SST-GH-IGF axis in regulating crosstalk between growth and immunity. Based on principal components analysis (PCA), we observed the overall expression profiles of GHRH-SST-GH-IGF axis were significantly altered by Vibrio anguillarum infection. Trout challenged with Vibrio anguillarum showed down-regulated igf1s subtypes and up-regulated igfbp1a1. The brain sst genes (sst1a , sst1b , sst3b and sst5) and igfpbs genes (igfbp4s and igfbp5b2) were significantly affected by V. anguillarum infection, while the igfbp 4s, igfbp 5 s , igfbp6s and igf 2 bps genes showed significant changes in peripheral immune tissues in response to V. anguillarum infection. Gene enrichment analyses showed functional and signaling pathways associated with apoptosis (such as p53, HIF-1 or FoxO signaling) were activated. We further proposed a possible model that describes the IGF and IGFBPs-regulated interaction between cell growth and programmed death. Our study provided new insights into the physiological functions and potentially regulatory mechanisms of the GHRH-SST-GH-IGF axis, indicating the pleiotropic effects of GHRH-SST-GH-IGF axis in regulating crosstalk between growth and immunity in trout. Image 1 • Novel genes produced by 4R in GHRH-SST-GH-IGF axis are identified. • Vibrio anguillarum infection alters the GHRH-SST-GH-IGF axis profile. • The sst , igfpbs and igf2bps genes lead to the GHRH-SST-GH-IGF differentiations. • A model is proposed to describe the crosstalk between cell growth and death. [ABSTRACT FROM AUTHOR]

The growth arrest and DNA-damage-inducible protein 45 gamma (Gadd45g) is known to play a major role in embryonic development and sex determination. In this study, two Gadd45g genes were isolated from half-smooth tongue sole ( Cynoglossus semilaevis ). Using chromosomal fluorescence in situ hybridization (FISH), Gadd45g1 and Gadd45g 2 were located on the W and Z chromosomes, respectively. The full-length cDNA sequences of Gadd45g1 (1270 bp) and Gadd45g2 (1181 bp) were predicted to contain a 480-bp coding sequence that could encode a protein of 159 amino acids residues. A phylogenetic tree showed that the predicted Gadd45g1 and Gadd45g2 amino acid sequences clustered closely in one branch. It is proposed that Gadd45g1 and Gadd45g2 are paralogous genes derived from the divergence of the sex chromosome. Ka/Ks ratios indicated that Gadd45g1 and Gadd45g2 may have undergone a high number of mutations and have a divergence time of only about 68,000 years, although Gadd45g homologs are highly conserved. The qRT-PCR demonstrated that Gadd45g1 and Gadd45g2 were highly expressed in ovary, and negligibly expressed in testis of male and neo-male. During development of the ovary (from 80 to 150 days), the expression levels of both genes reached high levels. Gadd45g1 was also highly expressed at 50 days, the stage just before gonad differentiation in C. semilaevis . All these findings imply functional divergence of the two Gadd45g homologs; Gadd45g1 may be necessary for sex differentiation in the early stage of gonad development, and then Gadd45g1 and Gadd45g2 maintain ovary development and the female character of half-smooth tongue sole. [ABSTRACT FROM AUTHOR]

Energy homeostasis, which refers to the physiological processes that the energy intake is exquisitely coordinated with energy expenditure, is critical for survival. Therefore, multiple and complex mechanisms have been involved in the regulation of energy homeostasis. The central melanocortin system plays an important role in modulating energy homeostasis. This system includes the orexigenic neurons, expressing neuropeptide Y/Agouti-related protein (NPY/AgRP), and the anorexigenic neurons expressing proopiomelanocortin (POMC). The downstream receptors of NPY, AgRP and post-translational products of POMC are G protein-coupled receptors (GPCRs). This review summarizes the compelling evidence demonstrating that NPY and melanocortin receptors are involved in energy homeostasis. Subsequently, the comparative studies on physiology and pharmacology of NPY and melanocortin receptors in humans, rodents and teleosts are summarized. Also, we provide a strategy demonstrating the potential application of the new ligands and/or specific variants of melanocortin system in aquaculture., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest., (© Ocean University of China 2021.)