Biology subjects

Holen, M. M.

Publications and source records attributed to Holen, M. M..

4 recordsLinked to original sources

bioRxiv2022

The gastric mucosa of Atlantic salmon (Salmo salar) is abundant in highly active chitinases

The Atlantic salmon (Salmo salar) genome contains 10 chitinase encoding genes, but little is known about the function of these chitinases. We show that the protein products of three genes, the family 18 glycoside hydrolase (GH18) chitinases Chia.3, Chia.4, and Chia.7 are secreted in the stomach mucosa and are amongst the most abundant proteins in this matrix. Chia.3 and Chia.4, sharing 95% sequence identity, were not possible to separate by standard chromatographic methods and were thus purified as a chitinase pair. Biochemical analysis revealed chitinolytic activity towards {beta}-chitin for up to 24 hours at pH 2-6. Further in vitro analysis showed that this chitinase pair efficiently degraded various chitin-containing substrates to chitobiose (GlcNAc2) suggesting that Atlantic salmon has the potential to utilize novel chitin-containing feed sources.

biochemistry↗

bioRxiv2022

The effect of dietary chitin on Atlantic salmon (Salmo salar) chitinase activity, gene expression, and microbial composition

BackgroundChitin is a common component in the natural diet of many fish, and a range of chitinases with the potential to down chitin have been identified. Yet whether chitin is metabolized in fish is still unclear. Here we used a combination of chitinase activity assay, transcriptomics, and 16S rRNA bacterial analysis to assess the effect of chitin supplementation on Atlantic salmon gene expression and microbial community. ResultsAtlantic salmon express multiple genes associated with chitin metabolism, and we show that the expression and activity of Atlantic salmon chitinases are not affected by the addition of dietary chitin. We do, however, demonstrate an association between gut microbial composition, chitinase activity in the gut, and host chitinase expression. ConclusionThe findings presented here support the idea that chitin metabolism genes are linked to the maintenance of a chitin-based barrier in the teleost gut. These results contribute to a greater understanding of chitin metabolism in fish.

genetics↗

bioRxiv2022

Gene family expansion and functional diversification of chitinase and chitin synthase genes in Atlantic salmon (Salmo salar)

BackgroundChitin is one of the most abundant polysaccharides in nature, forming important structures in insects, crustaceans, and fungal cell walls. Vertebrates on the other hand are generally considered "non-chitinous" organisms, despite having highly conserved chitin metabolism associated genes. Recent work has revealed that the largest group of vertebrates, the teleosts, have the potential to both synthesize and degrade endogenous chitin. Yet little is still known about the genes and proteins responsible for these dynamic processes. Here we used comparative genomics, transcriptomics, and chromatin accessibility data to characterize the repertoire, evolution, and regulation of genes involved in chitin-metabolism in teleosts, with a particular focus on Atlantic salmon. ResultsReconstruction of gene family phylogenies provide evidence for an expansion of teleost and salmonid chitinase and chitin synthase genes after multiple whole-genome duplications. Analyses of multi-tissue gene expression data demonstrated a strong bias of gastrointestinal tract expression for chitin metabolism genes, but with different spatial and temporal tissue specificities. Finally, we integrated transcriptomes from a developmental time series of the gastrointestinal tract with chromatin accessibility data to identify putative transcription factors responsible for regulating chitin-metabolism gene expression (CDX1 and CDX2) as well as tissue-specific divergence in the regulation of gene duplicates (FOXJ2). These transcription factors are also potential regulators of multiple glycosyltransferases being co-expressed with the chitin remodeling genes. ConclusionThe findings presented here add support to the hypothesis that chitin metabolism genes in teleosts play a role in developing and maintaining a chitin-based barrier in the teleost gut and provide a basis for further investigations into the molecular basis of this barrier.

genetics↗

bioRxiv2020

Comparative regulomics reveals pervasive selection on gene dosage following whole genome duplication

Whole genome duplication (WGD) events have played a major role in eukaryotic genome evolution, but the consequence of these extreme events in adaptive genome evolution is still not well understood. To address this knowledge gap we used a comparative phylogenetic model and transcriptomic data from seven species to infer selection on gene expression in duplicated genes (ohnologs) following the salmonid WGD 80-100 million years ago. We find rare cases of tissue-specific expression evolution but pervasive expression evolution affecting many tissues, reflecting strong selection on maintenance of genome stability following genome doubling. Although ohnolog expression levels have evolved mostly asymmetrically, by diverting one ohnolog copy down a path towards pseudogenization, strong evolutionary constraints have frequently also favoured symmetric shifts in gene dosage of both copies, likely to achieve gene dose reduction while avoiding accumulation of toxic mutations. Mechanistically, ohnolog regulatory divergence is dictated by the number of bound transcription factors in promoters, with transposable elements being one source of novel binding sites driving tissue-specific gains in expression. Our results imply pervasive adaptive expression evolution following WGD to overcome the immediate challenges posed by genome doubling and to exploit the long-term genetic opportunities for novel phenotype evolution.

evolutionary biology↗