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Sequencing of the stomach-less ballan wrasse (Labrus berggylta) genome and transcriptomic characterization of the intestine

ABSTRACT: Stomach-less fishes comprise a diverse phylogenetic group within the teleosts indicating that the organ has been lost several times during evolution. In the present project we have combined Illumina short read platform with the PacBio long read platform to sequence the ballan wrasse (Labrus bergylta) genome and its intestinal transcriptome. The genome was applied to investigate the elimination and conservation of genes related to stomach function and appetite regulation in wrasse in relation to the loss of stomach in this species. We have sequenced the transcriptome of four intestinal segments from six ballan wrasse (Labrus bergylta) for the purpose of identifying possible functional organization along the wrasse intestine. The transcriptomic reads were mapped against the newly assembled genome. The analysis revealed a transcriptional gradient showing genes involved in nutrient digestion and uptake being highly expressed in the anterior intestine and declining towards the end of the intestine. The last segment, hind-gut, had the most distinct expression between the four segments with increased expression of genes coding for proteins involved in lysosomal activity, antigen presenting and vitamin b12 uptake. Overall, our results suggests that the wrasse entire digestive system is comparable to the small intestine of mammals with regards to gene expression missing both a stomach and colon. Gene expression related to colon in humans such as MS4A12 were found in the last segment. The genome analysis also confirmed the lack of genes coding for gastric proteins such as gastric lipase, pepsin, gastrin and ghrelin. Although ghrelin is not only related to stomach, ghrelin was missing in all stomach-less fish species with the exception of cyprinid. Ghrelin is currently the only known orexigenic hormone.

ORGANISM(S): Labrus bergylta

PROVIDER: GSE93191 | GEO | 2017/06/01

SECONDARY ACCESSION(S): PRJNA360275

REPOSITORIES: GEO

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Project description:Background: The molecular basis of segment specific epithelial functions of the stomach and bowel has not been established. Regionally unique molecular properties of epithelial cells can be identified using cell-specific gene expression in each epithelial region by comparative mRNA analysis. Aim: To describe segment-specific epithelial mRNA content by comparative mRNA analysis of purified epithelial cell suspensions of stomach, small and large bowel. Results: 12% of all annotated genes show segment specific enrichment. The gastric (>3000 genes) and ileal (519 genes) mucosa show the most diverse expression profile. (a) Stomach: The gastric mucosa expresses the machinery for acid secretion, digestive enzyme release, and hormone release by gastric enteroendocrine cells. Associated with acid secretion is a specific set of K+, Cl-, and bicarbonate channels. Novel is a pathway for glucose and fatty acid sensing, iodine and glutamate uptake, and taurine synthesis. Specific sets of transcription factors control epithelial (Barx1, Runx) and enteroendocrine (FoxA2/N4) cell differentiation. (b) Small Bowel: This epithelium expresses genes coding for a unique fructose/glucose uptake and utilization mechanism. Enteroendocrine signalling to the gastric function is present. The upper portion expresses genes for iron uptake, bicarbonate secretion, and detoxification of food contents. Epithelial differentiation is transcriptionally controlled by Meis2/Pdx1 and Onecut 2. Expression of digestive enzymes, lipid/bile acid uptake and utilization increases distally. The ileal epithelium is also involved in innate and acquired immune defence, regulation of motility, and electrolyte and water re-absorption. Transcriptional regulation of enterocyte and goblet cell differentiation is mainly controlled by increasing expression of Cdx1 and 2. (c) Colon: This epithelium is mainly involved in Ca++-, K+, and water re-absorption, fatty acid uptake and sensing, and innate and acquired immune defence. Epithelial differentiation is controlled by Hox transcription factors in addition to Cdx1/2. Conclusion: This regional survey of gene expression by the GI tract epithelium reveals unique epithelial properties, raising several important questions as to the role of the proteins encoded in gut physiology.

Dataset Information

Sequencing of the stomach-less ballan wrasse (Labrus berggylta) genome and transcriptomic characterization of the intestine

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