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Somatostatin is a neuropeptide and a key regulator of the growth axis. Six Sst encoding genes (sst1 to sst6) have been identified in teleost fish genomes but little is known about their function. The present study aimed at replicating the context of the inflammatory bowel disease (IBD) and clarifying the involvement of sst3 in the intestine innate defence barrier in zebrafish larvae. We first established a CRISP/Cas9 sst3 deficient line (MT) and analysed the morphological and transcriptomic response to 0.4% dextran sulfate sodium (DSS). Alcian blue staining of larval sections 6 days post fertilization showed an increased in acidic mucins in the intestinal bulb and mid-intestine, with a much stronger response in the MT compared to wild type (WT). The transcriptomic analysis revealed that WT and MT shared enriched gene ontology (GO) terms and pathways linked to catabolism, chondrocyte development, innate immune system, xenobiotic metabolism and oxidative stress. In contrast, the WT specific response to DSS was enriched in GO terms and pathways linked to transcription and translation, various developmental processes, regulation of biosynthetic processes, apelin signalling and apoptosis while the MT specific response included terms and pathways linked to protein metabolism and catabolic processes, extracellular matrix – receptor interaction and proteasome and chondrocyte development. Overall, this study demonstrated that Sst3 deficiency impairs insulin growth factor and adipocytokine signalling exacerbating the inflammatory response to DSS.

Our understanding of the hormonal mechanisms underlying parental care mainly stems from research on species with uniparental care. Far less is known about the physiological changes underlying motherhood and fatherhood in biparental caring species. Here, using two biparental caring cichlid species (Neolamprologus caudopunctatus and Neolamprologus pulcher), we explored the relative gene-expression levels of two genes implicated in the control of parental care, galanin (gal) and prolactin (prl). We investigated whole brain gene expression levels in both, male and female caring parents, as well as in non-caring individuals of both species. Caring males had higher prl and gal mRNA levels compared to caring females in both fish species. Expression of gal was highest when young were mobile and the need for parental defense was greatest and gal was lowest during the more stationary egg tending phase in N. caudopunctatus. The onset of parenthood was associated with lower expression of prl and higher expression of gal in N. pulcher, but this pattern was not observed in N. caudopunctatus. Our study demonstrates that gal gene expression is correlated with changes in parental care in two biparental cichlid species and extends both knowledge and taxonomic coverage of the possible neurogenetic mechanisms underlying parental care. FWF: P 27461, UID/Multi/04326/2019, DL57/2016/CT3751 info:eu-repo/semantics/publishedVersion

Somatostatin (SST) plays important roles in growth and development. In teleost fishes six SST encoding genes (sst1 to sst6) have been identified although few studies have addressed their function. Here we aim to determine the function of the teleost specific sst4 in the zebrafish. A CRISPR/Cas9 sst4 zebrafish mutant with loss of function (sst4−/−) was produced which grew significantly faster and was heavier at the onset of gonadal maturation than the wild type (WT). Consistent with their faster growth, liver igf1, igf2a and igf2b expression was significantly upregulated in the sst4−/− fish compared to the WT. Histological examination of the ovaries and testis indicated that sst4−/− fish had slightly delayed testicular gametogenesis compared to the WT. Significantly lower expression of igf3, amh, insl3, hsd17b3, hsd11b2, hsd20b, cyp11b and cyp17 was consistently observed in the sst4−/− testis. In contrast, the ovaries had lower expression of igf1, igf2a and cyp19a1a but increased expression of igf2b and hsd20b. The gonadotrophin beta subunits (fshb and lhb) in the brain were downregulated indicating the brain-pituitary-gonadal axis was downregulated in the sst4−/− fish and suggesting that the steroid production is compromised in the maturing gonads. In addition, analysis of sst1 and sst3 mRNA levels in sst4−/− fish suggests a dosage compensation effect of sst1 in the brain and liver. Altogether, the results from the zebrafish sst4−/− line support the idea that sst4 is involved in the regulation of igf signalling, somatic growth and reproduction since steroidogenesis and gametogenesis at pubertal onset were compromised. This research was supported by institutional funds from Shanghai Ocean University and Portuguese national funds from FCT - Foundation for Science and Technology through project UID/Multi/04326/2019. info:eu-repo/semantics/publishedVersion

One of the goals of the aquaculture industry is to understand and control growth associated traits through selective breeding. In the present study the molecular basis of growth heterogeneity in the European sea bass (Dicentrarchus labrax) was addressed. To establish growth heterogeneity in a group of hatchery bred sea bass individuals were tagged and their specific growth rates (SGR) determined at monthly intervals. Gene expression in the brain, liver and white muscle from fish with the most divergent sustained SGR (6 individuals of the first and last quartile) was assessed using SuperSAGE (Serial Analysis Gene Expression) combined with next generation SOLiD4 sequencing. A total of approx. 11 million edited tags (26 bp), on average 2 million tags per SAGE library, that represented 47.071 unique transcripts were identified. Comparison of transcripts in fish with high and low SGR yielded 344, 698 and 601 differently expressed tags (0.01% false discovery rate and 4-fold change) in brain, liver and muscle, respectively. The tags were mapped onto the sea bass genome and approximately one third of the tags could be assigned to annotated genes. Pathway enrichment analysis revealed in liver, muscle and brain intricate gene expression changes in endocrine regulatory pathways involved in growth, metabolic and the stress axis, underlying divergent SGR in sea bass. Funding by the European Commission of the European Union through the Network of Excellence Marine Genomics Europe (contract GOCE-CT-2004-505403) and by the Portuguese Foundation for Science and Technology (FCT) info:eu-repo/semantics/publishedVersion

Galanin (Gal) is a neuropeptide with multiple functions that is widely expressed in the central and peripheral nervous systems of vertebrates. Anatomical and functional evidence suggests a possible role in regulating reproduction in fishes. To test this possibility, we have isolated and characterized two gal alternative transcripts in European sea bass (Dicentrarchus labrax) that encode two prepropeptides, respectively of 29 (gal_MT853221) and 53 (gal_MT853222) amino acids. The two gal transcripts are highly expressed in brain, pituitary and gonads, and appear to be differentially regulated in males and females. In males, gal_MT853222 in the hypothalamus and gal_MT853221 in the pituitary were downregulated with the progression of spermatogenesis (stages I-III). Both transcripts are downregulated in testicles of 1-year (precocious) and 2-year spermiating males compared to immature fish of the same age. Gal peptides and receptors are expressed throughout ovarian development in the hypothalamic-pituitary-gonadal (HPG) axis of females. In the testis, immunoreactive Gal-29 and Gal-53 peptides were detected in blood vessels and Leydig cells during the spermatogenesis stages I-III but Gal immunostaining was barely undetected in more advanced stages. In the ovary, both peptides localized in interstitial cells and blood vessels and in theca cells surrounding the maturing oocytes. The immunolocalization of galanin in Leydig and theca cells suggests a possible role in steroid production regulation. The different pattern of gal expression and Gal localization in the testis and ovary may suggest the possibility that androgens and estrogens may also regulate Gal gene transcription and translation. Altogether, this study showed evidence for the possible involvement of locally produced Gal in gametogenesis and that its production is differentially regulated in male and female gonads., This research was funded by the Portuguese national funds from FCT (Foundation of Science and Technology, I.P.) through projects UIDB/04326/2020 and PTDC/MAR-BIO/3890/2012 and by the European Union Seventh Framework Programme AQUAEXCEL (Grant Agreement 262336, TNA project 318). AG and GM were supported by Spanish MINECO (AGL2015-67477-C2-1-R) and CSIC (201640E073). R.S.T.M and P.I.S.P were supported by FCT under contracts of Norma transitória (DL 57/2016/CP1361/CT0021 and DL57/2016/CP6321/CT0015, respectively) with Universidade do Algarve. We acknowledge Zélia Velez for the help during sampling, Deborah Power for IHC advice and Victoria Alvarado and Alicia Felip for providing hypothalamus and pituitary RNA panels.

Summary Aging constitutes the key risk factor for age‐related diseases such as cancer and cardiovascular and neurodegenerative disorders. Human longevity and healthy aging are complex phenotypes influenced by both environmental and genetic factors. The fact that genetic contribution to lifespan strongly increases with greater age provides basis for research on which “protective genes” are carried by long‐lived individuals. Studies have consistently revealed FOXO (Forkhead box O) transcription factors as important determinants in aging and longevity. FOXO proteins represent a subfamily of transcription factors conserved from Caenorhabditis elegans to mammals that act as key regulators of longevity downstream of insulin and insulin‐like growth factor signaling. Invertebrate genomes have one FOXO gene, while mammals have four FOXO genes: FOXO1, FOXO3, FOXO4, and FOXO6. In mammals, this subfamily is involved in a wide range of crucial cellular processes regulating stress resistance, metabolism, cell cycle arrest, and apoptosis. Their role in longevity determination is complex and remains to be fully elucidated. Throughout this review, the mechanisms by which FOXO factors contribute to longevity will be discussed in diverse animal models, from Hydra to mammals. Moreover, compelling evidence of FOXOs as contributors for extreme longevity and health span in humans will be addressed.

In the present study the calcitonin receptor (CTR) sub-family of family B G-protein coupled receptors (GPCRs) in teleosts is evaluated and put in the context of the families overall evolution from echinodermates to vertebrates. Echinodermates, hemichordates, cephalochordates and tunicates have a single gene that encodes a receptor that bears similarity to the vertebrate calcitonin receptor (CTR) and calcitoninlike receptor (CTR/CLR). In tetrapods one gene encodes the calcitonin receptor (CALCR) and another gene the calcitonin receptor-like receptor (CALCRL). The evolution of CALCR has been under strong conservative pressure and a single copy is also found in fishes and high conservation of gene organisation and synteny exits from teleosts to human. A teleost specific CTR innovation that occurred after their divergence from holostei is the presence of several HBDs in the N-terminus. CALCRL had a different evolutionary trajectory from CALCR and although a single gene copy is present in tetrapods the sarcopterygii fish, the coelacanth, has 1 copy of CALCRL but also a fish specific form CALCRL3. The ray-finned fish, the spotted gar, has 1 copy of CALCRL and 1 of CALCRL3 but the teleost specific whole genome duplication has resulted in a CALCRL1 and CALCRL2 in addition to the fish specific CALCRL3. Strong conservation of CALCRL gene structure exists from human to fish. Promoter analysis in silico reveals that the duplicated CALCRL genes in the teleosts, zebrafish, takifugu, tetraodon and medaka, have divergent promoters and different putative co-regulated gene partners suggesting their function is different. We are grateful to Professor Adelino Canário for providing the sequence of sea bass EST clones. This study was supported by the European Regional Development Fund (ERDF) COMPETE – Operational Competitiveness Programme and Portuguese funds through FCT – Foundation for Science and Technology, under the project ‘‘PEst-C/MAR/LA0015/2013’’ and by FCT PTDC/BIA-BCM//73597/ 2010. RM (SFRH/BPD/66742/2009) and FV (SFRH/BPD/73597/ 2010) were in receipt of a post-doctoral grant from FCT, Portugal.

Paragangliomas are rare neuroendocrine tumors that arise in the sympathetic or parasympathetic nervous system. Sympathetic paragangliomas are mainly found in the adrenal medulla (designated pheochromocytomas) but may also have a thoracic, abdominal, or pelvic localization. Parasympathetic paragangliomas are generally located at the head or neck. Knowledge concerning the familial forms of paragangliomas has greatly improved in recent years. Additionally to the genes involved in the classical syndromic forms:VHLgene (von Hippel-Lindau),RETgene (Multiple Endocrine Neoplasia type 2), andNF1gene (Neurofibromatosis type 1), 10 novel genes have so far been implicated in the occurrence of paragangliomas/pheochromocytomas:SDHA, SDHB, SDHC, SDHD, SDHAF2, TMEM127, MAX, EGLN1, HIF2A,andKIF1B. It is currently accepted that about 35% of the paragangliomas cases are due to germline mutations in one of these genes. Furthermore, somatic mutations ofRET, VHL, NF1, MAX, HIF2A,andH-RAScan also be detected. The identification of the mutation responsible for the paraganglioma/pheochromocytoma phenotype in a patient may be crucial in determining the treatment and allowing specific follow-up guidelines, ultimately leading to a better prognosis. Herein, we summarize the most relevant aspects regarding the genetics and clinical aspects of the syndromic and nonsyndromic forms of pheochromocytoma/paraganglioma aiming to provide an algorithm for genetic testing.

DMRT1 is conserved from invertebrates to human and has been implicated in sex differentiation and testis function in many organisms. We report the cloning of two DMRT1 transcripts, DMRT1a and DMRT1b, encoded by a single gene in the European sea bass, Dicentrarchus labrax, a teleost fish with polygenic sex determination influenced by temperature. DMRT1a and DMRT1b are specific to the testis and are present as transcripts of 2.7 and 4.6 kb, as determined by Northern blot, although the cloned cDNAs are 1.2 and 1.9 kb. DMRT1a, encodes a protein of 306-amino acids, of similar size to what has been found in other teleosts, while the DMRT1b encodes a unique protein which differ from DMRT1a by having a 26 amino acids insertion which separates the S and Y domains. This insertion is the result of an extra exon (exon 4), present in the genomes of teleosts but not in other vertebrate genomes. Furthermore, unlike in the European sea bass, the putative product of DMRT1b in other teleost species is a truncated peptide. In European sea bass, the two transcripts are expressed at a similar level and have a similar expression profile in developing gonads. They are first detected by reverse transcription-polymerase chain reaction at 150 days post-hatch coinciding with the start of sex differentiation. After 200 days, expression increases in testis and decreases in ovary. Although it is not clear whether the two transcripts have differential roles it is suggested that both are required for testicular function.

Allatostatin type A receptors (AST-ARs) are a group of G-protein coupled receptors activated by members of the FGL-amide (AST-A) peptide family that inhibit food intake and development in arthropods. Despite their physiological importance the evolution of the AST-A system is poorly described and relatively few receptors have been isolated and functionally characterised in insects. The present study provides a comprehensive analysis of the origin and comparative evolution of the AST-A system. To determine how evolution and feeding modified the function of AST-AR the duplicate receptors in Anopheles mosquitoes, were characterised. Phylogeny and gene synteny suggested that invertebrate AST-A receptors and peptide genes shared a common evolutionary origin with KISS/GAL receptors and ligands. AST-ARs and KISSR emerged from a common gene ancestor after the divergence of GALRs in the bilaterian genome. In arthropods, the AST-A system evolved through lineage-specific events and the maintenance of two receptors in the flies and mosquitoes (Diptera) was the result of a gene duplication event. Speciation of Anophelesmosquitoes affected receptor gene organisation and characterisation of AST-AR duplicates (GPRALS1 and 2) revealed that in common with other insects, the mosquito receptors were activated by insect AST-A peptides and the iCa(2+)-signalling pathway was stimulated. GPRALS1 and 2 were expressed mainly in mosquito midgut and ovaries and transcript abundance of both receptors was modified by feeding. A blood meal strongly up-regulated expression of both GPRALS in the midgut (p < 0.05) compared to glucose fed females. Based on the results we hypothesise that the AST-A system in insects shared a common origin with the vertebrate KISS system and may also share a common function as an integrator of metabolism and reproduction. Highlights: AST-A and KISS/GAL receptors and ligands shared common ancestry prior to the protostome-deuterostome divergence. Phylogeny and gene synteny revealed that AST-AR and KISSR emerged after GALR gene divergence. AST-AR genes were present in the hemichordates but were lost from the chordates. In protostomes, AST-ARs persisted and evolved through lineage-specific events and duplicated in the arthropod radiation. Diptera acquired and maintained functionally divergent duplicate AST-AR genes. Foundation for Science and Technology, Portugal (FCT) [PTDC/BIA-BCM/114395/2009]; European Regional Development Fund (ERDF) COMPETE - Operational Competitiveness Programme; Portuguese funds through FCT Foundation for Science and Technology [PEst-C/MAR/LA0015/2013, UID/Multi/04326/2013, PEst-OE/SAU/LA0018/2013]; FCT [SFRH/BPD/89811/2012, SFRH/BPD/80447/2011, SFRH/BPD/66742/2009]; auxiliary research contract FCT Pluriannual funds [PEst-C/MAR/LA0015/2013, UID/Multi/04326/2013] info:eu-repo/semantics/publishedVersion

Pituitary adenylate cyclase-activating polypeptide (PACAP) administered to tilapia melanophores ex-vivo causes significant pigment aggregation and this is a newly identified function for this peptide in fish. The G-protein coupled receptors (GPCRs), adcyap1r1a (encoding Pac1a) and vipr2a (encoding Vpac2a), are the only receptors in melanophores with appreciable levels of expression and are significantly (p

Tine, Mbaye ... et. al.-- 10 pages, 5 figures, supplementary information https://doi.org/10.1038/ncomms6770, The European sea bass (Dicentrarchus labrax) is a temperate-zone euryhaline teleost of prime importance for aquaculture and fisheries. This species is subdivided into two naturally hybridizing lineages, one inhabiting the north-eastern Atlantic Ocean and the other the Mediterranean and Black seas. Here we provide a high-quality chromosome-scale assembly of its genome that shows a high degree of synteny with the more highly derived teleosts. We find expansions of gene families specifically associated with ion and water regulation, highlighting adaptation to variation in salinity. We further generate a genome-wide variation map through RAD-sequencing of Atlantic and Mediterranean populations. We show that variation in local recombination rates strongly influences the genomic landscape of diversity within and differentiation between lineages. Comparing predictions of alternative demographic models to the joint allele-frequency spectrum indicates that genomic islands of differentiation between sea bass lineages were generated by varying rates of introgression across the genome following a period of geographical isolation, This work was initiated during the MARINE GENOMICS EUROPE project EU-FP6 505403 and was supported by grants from the Max Planck Society (MPG for genome sequencing, assembly and annotation), LIFECYCLE EU-FP7 222719 and BMBF-01GS0805 to R.R., and the French ANR grants LABRAD-SEQ 11-PDOC-009-01 to P.-A.G. and REGULBASS 09-GENM-003 to B.G. M.T. received a fellowship from the MPG, H.K. was partly financed by LIFECYCLE EU-FP7 222719 and F.K. by the BMBF-01GS0805 grant. L.B. was supported by the grant Progetto 12/MI/2004 from the Veneto Region. R.S.T.M. and B.L. were in receipt of fellowships SFRH/BPD/66742/2009 and SFRH/BPD/89889/2012 from the Foundation for Science and Technology of Portugal

In fish, the onset of puberty, the transition from juvenile to sexually reproductive adult animals, is triggered by the activation of pituitary gonadotropin secretion and its timing is influenced by external and internal factors that include the growth/adiposity status of the animal. Kisspeptins have been implicated in the activation of puberty but peripheral signals coming from the immature gonad or associated to the metabolic/nutritional status are also thought to be involved. Therefore we hypothesize the importance of the galinergic system in the brain and testis of pre-pubertal male sea bass as a candidate to translate the signals leading to activation of testicular maturation. Here, the transcripts for four galanin receptors (GALR), named GALR1a, 1b, 2a and 2b, were isolated from European sea bass, Dicentrarchus labrax. Phylogenetic analysis confirmed the previously reported duplication of GALR1 in teleost fish, and unravelled the duplication of GALR2 in teleost fish and in some tetrapod species. Comparison with human showed that the key amino acids involved in ligand binding are present in the corresponding GALR1 and GALR2 orthologs. Transcripts for all four receptors are expressed in brain and testes of adult fish with GALR1a and GALR1b abundant in testes and hardly detected in ovaries. In order to investigate whether GALR1 dimorphic expression was dependent on steroid context we evaluated the effect of 11-ketotestosterone and 17β-estradiol treatments on the receptor expression in brain and testes of pre-pubertal males. Interestingly, steroid treatments had no effect on the expression of GALRs in the brain while in the testes, GALR1a and GALR1b were significantly up regulated by 11KT. Altogether, these results support a role for the galaninergic system, in particular the GALR1 paralog, in fish reproductive function. © 2014 Elsevier Inc., The research leading to these results was funded by European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 222719 – LIFECYCLE and by the Foundation for Science and Technology of Portugal (FCT), through projects PTDC/MAR-BIO/3890/2012 and PEst-C/MAR/LA0015/2011 and fellowships to PISP (SFRH/BPD/25247/2005) and RSTM (SFRH/BPD/66742/2009).

DAX1 is an orphan nuclear receptorwith actions in mammalian sex determination, regulation of steroidogenesis, embryonic development and neural differentiation. Conserved patterns of DAX1 gene expression frommammals to fish have been taken to suggest conserved function. In the present study, the European sea bass, Dicentrarchus labrax, DAX1 promoter was isolated and its conserved features compared to other fish and mammalian DAX1 promoters in order to derive common regulators and functional gene networks. Fish andmammalian DAX1 promoters share common sets of transcription factor frameworkswhichwere also present in the promoter region of another 127 genes. Pathway analysis clustered these into candidate gene networks associated with the fish and mammalian DAX1. The networks identified are concordantwith described functions for DAX1 in embryogenesis, regulation of transcription, endocrine development and steroid production. Novel candidate gene network partners were also identified, which implicate DAX1 in ion homeostasis and transport, lipid transport and skeletal development. Experimental evidence is provided supporting roles for DAX1 in steroid signalling and osmoregulation in fish. These results highlight the usefulness of the in silico comparative approach to analyse gene regulation for hypothesis generation. Conserved promoter architecture can be used also to predict potentially newgene functions. The approach reported can be applied to genes from model and non-model species. The authors acknowledge Heiner Kuhl and Richard Reinhardt for sequencing the sea bass DAX1 and DAX2 promoters and to Pedro Guerreiro for his help in the salinity transfer experiment. The research leading to these results was funded by European Community's Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 222719 - LIFECYCLE. RSTM and LAMD were in receipt, respectively, of fellowships SFRH/BPD/66742/2009 and PTDC/CVT/104750/2008 from the Portuguese Foundation for Science and Technology.

The Ca(2+)-Calmodulin (CaM) signaling pathway has previously been shown to be involved in the regulation of teleost fish ovarian steroidogenesis. However, a putative role of CaM in testicular steroidogenesis and potential targets has not been examined. To examine whether basal steroidogenesis is modulated by Ca(2+) and CaM levels in the testis of Mozambique tilapia (Oreochromis mossambicus) we have incubated testicular fragments in vitro under different conditions and analyzed steroid output. Calcium-free medium with or without EGTA did not affect testicular basal 11-ketotestosterone (11-KT) and testosterone (T) secretion. However, addition of 80microM the CaM inhibitor W7 significantly reduced basal 11-KT, T and androstenedione secretion. Interestingly, the decreased androgen production by 80microM of W7 was accompanied by increased 11-desoxicortisol output and by the activation of cortisol synthesis in the testis, the latter undetected in untreated tissues. However, production of 17,20alpha-dihydroxy-4-pregnen-3-one was unaltered by W7. This suggests that C17,20 desmolase, 21-hydroxylase and possibly 11beta-hydroxysteroid dehydrogenase are targets for CaM. In addition, androgen production was also found to be regulated by the level of cAMP since incubations with forskolin (FK) significantly increased 11-KT and T output. A cross-talk between the cAMP and Ca(2+)-CaM signaling pathways was detected since W7 administration also decreased FK stimulated androgen production. Altogether, these data show that both basal and cAMP stimulated androgen levels were modulated by intracellular Ca(2+)-dependent CaM and that possibly Ca(2+)-CaM determines the shift in steroidogenesis from C21 steroids to androgens.

Steroid P450 11beta-hydroxylase, encoded by the CYP11B gene, is a key mitochondrial enzyme for the production of 11-oxygenated androgens, which have been shown to be potent masculinising steroids in several fish species. In this study we have isolated a CYP11B cDNA of 1903 base pairs from the testis of European sea bass (Dicentrarchus labrax) encoding a predicted protein of 552 amino acids. The amino acid identities to other vertebrate 11beta-hydroxylase proteins ranged from 66% to 72% to other fish; 45% to amphibian and 35-39% to mammalian. Southern blot indicated that a single CYP11B gene is present. Northern blot analysis detected two transcripts in testis and head kidney, one of the same size of the isolated clone and the other of 3.9 kb. Reverse transcriptase-polymerase chain reaction showed abundant mRNA expression only in testis and head kidney, being residual in a range of other tissues. Expression of CYP11B and CYP19A (which encodes for ovarian aromatase) was detected from at least 4 days post-hatching and did not appear to be affected by rearing temperature (15 and 20 degrees C) during the first 60 days, a period in which high temperatures promote masculinisation in European sea bass. Throughout, gonadogenesis (60-300 dph), a highly dimorphic pattern of CYP11B expression was consistent with a role of this gene in testicular development.

Background The vertebrate brain plays a critical role in the regulation of sexual maturation and reproduction by integrating environmental information with developmental and endocrine status. The European eel Anguilla anguilla is an important species in which to better understand the neuroendocrine factors that control reproduction because it is an endangered species, has a complex life cycle that includes two extreme long distance migrations with both freshwater and seawater stages and because it occupies a key position within the teleost phylogeny. At present, mature eels have never been caught in the wild and little is known about most aspects of reproduction in A. anguilla. The goal of this study was to identify genes that may be involved in sexual maturation in experimentally matured eels. For this, we used microarrays to compare the gene expression profiles of sexually mature to immature males. Results Using a false discovery rate of 0.05, a total of 1,497 differentially expressed genes were identified. Of this set, 991 were expressed at higher levels in brains (forebrain and midbrain) of mature males while 506 were expressed at lower levels relative to brains of immature males. The set of up-regulated genes includes genes involved in neuroendocrine processes, cell-cell signaling, neurogenesis and development. Interestingly, while genes involved in immune system function were down-regulated in the brains of mature males, changes in the expression levels of several receptors and channels were observed suggesting that some rewiring is occurring in the brain at sexual maturity. Conclusions This study shows that the brains of eels undergo major changes at the molecular level at sexual maturity that may include re-organization at the cellular level. Here, we have defined a set of genes that help to understand the molecular mechanisms controlling reproduction in eels. Some of these genes have previously described functions while many others have roles that have yet to be characterized in a reproductive context. Since most of the genes examined here have orthologs in other vertebrates, the results of this study will contribute to the body of knowledge concerning reproduction in vertebrates as well as to an improved understanding of eel biology. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-799) contains supplementary material, which is available to authorized users.

Background DAX1 (NR0B1), a member of the nuclear receptors super family, has been shown to be involved in the genetic sex determination and in gonadal differentiation in several vertebrate species. In the aquaculture fish European sea bass, Dicentrarchus labrax, and in the generality of fish species, the mechanisms of sex determination and differentiation have not been elucidated. The present study aimed at characterizing the European DAX1 gene and its developmental expression at the mRNA level. Methods A full length European sea bass DAX1 cDNA (sbDAX1) was isolated by screening a testis cDNA library. The structure of the DAX1 gene was determined by PCR and Southern blot. Multisequence alignments and phylogenetic analysis were used to compare the translated sbDAX1 product to that of other vertebrates. sbDAX1 expression was analysed by Northern blot and relative RT-PCR in adult tissues. Developmental expression of mRNA levels was analysed in groups of larvae grown either at 15°C or 20°C (masculinising temperature) during the first 60 days, or two groups of fish selected for fast (mostly females) and slow growth. Results The sbDAX1 is expressed as a single transcript in testis and ovary encoding a predicted protein of 301 amino acids. A polyglutamine stretch of variable length in different DAX1 proteins is present in the DNA binding domain. The sbDAX1 gene is composed of two exons, separated by a single 283 bp intron with conserved splice sites in same region of the ligand binding domain as other DAX1 genes. sbDAX1 mRNA is not restricted to the brain-pituitary-gonadal axis and is also detected in the gut, heart, gills, muscle and kidney. sbDAX1 mRNA was detected as early as 4 days post hatching (dph) and expression was not affected by incubation temperature. Throughout gonadal sex differentiation (60–300 dph) no dimorphic pattern of expression was observed. Conclusion The sbDAX1 gene and putative protein coding region is highly conserved and has a wide pattern of tissue expression. Although gene expression data suggests sbDAX1 to be important for the development and differentiation of the gonads, it is apparently not sex specific.

Background Osteoglycin (OGN, a.k.a. mimecan) belongs to cluster III of the small leucine-rich proteoglycans (SLRP) of the extracellular matrix (ECM). In vertebrates OGN is a characteristic ECM protein of bone. In the present study we explore the evolution of SLRP III and OGN in teleosts that have a skeleton adapted to an aquatic environment. Results The SLRP gene family has been conserved since the separation of chondrichthyes and osteichthyes. Few gene duplicates of the SLRP III family exist even in the teleosts that experienced a specific whole genome duplication. One exception is ogn for which duplicate copies were identified in fish genomes. The ogn promoter sequence and in vitro mesenchymal stem cell (MSC) cultures suggest the duplicate ogn genes acquired divergent functions. In gilthead sea bream (Sparus aurata) ogn1 was up-regulated during osteoblast and myocyte differentiation in vitro, while ogn2 was severely down-regulated during bone-derived MSCs differentiation into adipocytes in vitro. Conclusions Overall, the phylogenetic analysis indicates that the SLRP III family in vertebrates has been under conservative evolutionary pressure. The retention of the ogn gene duplicates in teleosts was linked with the acquisition of different functions. The acquisition by OGN of functions other than that of a bone ECM protein occurred early in the vertebrate lineage. National funds through FCT – Foundation for Science and Technology (UID/ Multi/04326/2016). info:eu-repo/semantics/publishedVersion