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Functional modifications associated with gastrointestinal tract organogenesis during metamorphosis in Atlantic halibut (Hippoglossus hippoglossus).

ABSTRACT: BACKGROUND:Flatfish metamorphosis is a hormone regulated post-embryonic developmental event that transforms a symmetric larva into an asymmetric juvenile. In altricial-gastric teleost fish, differentiation of the stomach takes place after the onset of first feeding, and during metamorphosis dramatic molecular and morphological modifications of the gastrointestinal (GI-) tract occur. Here we present the functional ontogeny of the developing GI-tract from an integrative perspective in the pleuronectiforme Atlantic halibut, and test the hypothesis that the multiple functions of the teleost stomach develop synchronously during metamorphosis. RESULTS:Onset of gastric function was determined with several approaches (anatomical, biochemical, molecular and in vivo observations). In vivo pH analysis in the GI-tract lumen combined with quantitative PCR (qPCR) of ? and ? subunits of the gastric proton pump (H+/K+-ATPase) and pepsinogen A2 indicated that gastric proteolytic capacity is established during the climax of metamorphosis. Transcript abundance of ghrelin, a putative orexigenic signalling molecule produced in the developing stomach, correlated (p < 0.05) with the emergence of gastric proteolytic activity, suggesting that the stomach's role in appetite regulation occurs simultaneously with the establishment of proteolytic function. A 3D models series of the GI-tract development indicated a functional pyloric sphincter prior to first feeding. Observations of fed larvae in vivo confirmed that stomach reservoir function was established before metamorphosis, and was thus independent of this event. Mechanical breakdown of food and transportation of chyme through the GI-tract was observed in vivo and resulted from phasic and propagating contractions established well before metamorphosis. The number of contractions in the midgut decreased at metamorphic climax synchronously with establishment of the stomach's proteolytic capacity and its increased peristaltic activity. Putative osmoregulatory competence of the GI-tract, inferred by abundance of Na+/K+-ATPase ? transcripts, was already established at the onset of exogenous feeding and was unmodified by metamorphosis. CONCLUSIONS:The functional specialization of the GI-tract was not exclusive to metamorphosis, and its osmoregulatory capacity and reservoir function were established before first feeding. Nonetheless, acid production and the proteolytic capacity of the stomach coincided with metamorphic climax, and also marked the onset of the stomach's involvement in appetite regulation via ghrelin.

SUBMITTER: Gomes AS

PROVIDER: S-EPMC3940299 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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Functional modifications associated with gastrointestinal tract organogenesis during metamorphosis in Atlantic halibut (Hippoglossus hippoglossus).

Gomes Ana S AS Kamisaka Yuko Y Harboe Torstein T Power Deborah M DM Rønnestad Ivar I

BMC developmental biology 20140219

<h4>Background</h4>Flatfish metamorphosis is a hormone regulated post-embryonic developmental event that transforms a symmetric larva into an asymmetric juvenile. In altricial-gastric teleost fish, differentiation of the stomach takes place after the onset of first feeding, and during metamorphosis dramatic molecular and morphological modifications of the gastrointestinal (GI-) tract occur. Here we present the functional ontogeny of the developing GI-tract from an integrative perspective in the ...[more]

PMID: 24552353

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Project description:BackgroundAtlantic halibut (Hippoglossus hippoglossus) is a high-value, niche market species for cold-water marine aquaculture. Production of monosex female stocks is desirable in commercial production since females grow faster and mature later than males. Understanding the sex determination mechanism and developing sex-associated markers will shorten the time for the development of monosex female production, thus decreasing the costs of farming.ResultsHalibut juveniles were masculinised with 17 α-methyldihydrotestosterone (MDHT) and grown to maturity. Progeny groups from four treated males were reared and sexed. Two of these groups (n = 26 and 70) consisted of only females, while the other two (n = 30 and 71) contained balanced sex ratios (50% and 48% females respectively). DNA from parents and offspring from the two mixed-sex families were used as a template for Restriction-site Associated DNA (RAD) sequencing. The 648 million raw reads produced 90,105 unique RAD-tags. A linkage map was constructed based on 5703 Single Nucleotide Polymorphism (SNP) markers and 7 microsatellites consisting of 24 linkage groups, which corresponds to the number of chromosome pairs in this species. A major sex determining locus was mapped to linkage group 13 in both families. Assays for 10 SNPs with significant association with phenotypic sex were tested in both population data and in 3 additional families. Using a variety of machine-learning algorithms 97% correct classification could be obtained with the 3% of errors being phenotypic males predicted to be females.ConclusionAltogether our findings support the hypothesis that the Atlantic halibut has an XX/XY sex determination system. Assays are described for sex-associated DNA markers developed from the RAD sequencing analysis to fast track progeny testing and implement monosex female halibut production for an immediate improvement in productivity. These should also help to speed up the inclusion of neomales derived from many families to maintain a larger effective population size and ensure long-term improvement through selective breeding.

Project description:BACKGROUND:The commercial production of Atlantic halibut (Hippoglossus hippoglossus L.) suffers from a major bottleneck due to the low success of producing juveniles for on-growing. Atlantic halibut females are routinely hand-stripped and incorrect timing of stripping can result in low quality eggs due to post-ovulatory aging. Post-ovulatory aging leads to compositional changes in eggs that include maternally provided proteins and RNAs. There have been few studies of the maternally provided mRNA transcripts that control early development in commercially important fish species. The present study aimed to study maternal gene expression in Atlantic halibut and its relation to egg quality parameters including blastomere symmetry and hatching success. RESULTS:A maternal EST library containing 2341 sequences was constructed by suppressive subtractive hybridisation. Thirty genes were selected for expression studies; 23 novel genes and 7 genes with documented roles in early development. The expressions of twenty-one selected genes were measured by qPCR from fertilization to the 10-somite stage. Three genes were identified as strictly maternal genes that were expressed until the start of gastrulation; askopos (kop), si:dkey-30j22.9 (Tudor family member), and Tudor 5 protein (Tdrd5). The expressions of 18 genes at the 8-cell stage were correlated with egg quality parameters. The majority of genes showed either no or very minor correlations with egg quality parameter. However, two genes correlated positively with hatching success (r> 0.50, HHC00353: r = 0.58, p < 0.01; HHC01517: r = 0.56, p < 0.01) and one gene (HHC00255) was negatively correlated with the percentage of normal blastomeres (r = -0.62, p < 0.05). CONCLUSIONS:During this study we have related maternal levels of gene expression to hatching success in fish. Poor hatching success was not correlated with a general decrease in transcript abundance but with low transcript levels of some specific genes. Thus, the molecular mechanisms leading to low Atlantic halibut egg quality cannot be entirely explained by post-ovulatory aging.

Project description:Real time RT-PCR has become an important tool for analyzing gene expression in fish. Although several housekeeping genes have been evaluated in Atlantic halibut (Hippoglossus Hippoglossus L.), appropriate reference genes for low copy mRNA transcripts at the earliest developmental stages have not been identified. No attempts have been reported to identify suitable reference genes in halibut infected with NNV or in stimulated halibut leucocytes. In this study, beta-actin1 (ACTB1), elongation factor 1 alpha (EF1A1), hypoxanthine-guanine phosphoribosyltransferase 1 (HPRT1), ribosomal protein L7 (RPL7), tubulin beta 2C (Tubb2C), and ubiquitin-conjugating enzyme (UbcE) were evaluated as reference genes for normalization of real time RT-PCR data during Atlantic halibut development, in tissue of healthy and NNV-infected fish, and in in vivo and in vitro stimulated anterior kidney leucocytes.The expression of all six genes was relatively stable from the unfertilized egg until 12 day degrees post fertilization (ddpf). However, none of the selected genes were found to be stably expressed throughout halibut development. The mRNA levels of the six genes increased from 18 ddpf, when zygotic transcription is likely to be activated, and stabilized at different time points. The Excel-based software programs BestKeeper, geNorm, and NormFinder ranked EF1A1 and UbcE as the best candidate reference genes before activation of zygotic transcription, and RPL7 and EF1A1 as the best candidates after hatching. EF1A1 and RPL7 were also listed as the best reference genes when exploring the expression levels of the six genes in various halibut organs, both in non-injected fish and in mock- and NNV-injected fish. None of the reference genes were found optimal for normalization of real time RT-PCR data from in vitro stimulated anterior kidney leucocytes.Generally, it was found that EF1A1 and RPL7 were the genes that showed least variation, with HPRT1 and UbcE as intermediate genes, and ACTB1 and Tubb2C as the least stable ones. None of the six reference genes can be recommended as reference gene candidates in ConA-PMA stimulated leucocytes. However, UbcE can be a good candidate in other experimental setups. This study emphasizes the need for reference gene evaluation, as universal reference genes have not been identified.

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Functional modifications associated with gastrointestinal tract organogenesis during metamorphosis in Atlantic halibut (Hippoglossus hippoglossus).

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Functional modifications associated with gastrointestinal tract organogenesis during metamorphosis in Atlantic halibut (Hippoglossus hippoglossus).

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