Ontogenesis of expression of metabolic genes and microRNAs in rainbow trout alevins during the transition from the endogenous to the exogenous feeding period

Abstract

SUMMARYAs oviparous fish, rainbow trout change their nutritional strategy during ontogenesis. This change is divided into the exclusive utilization of yolk-sac reserves (endogenous feeding), the concurrent utilization of yolk reserves and exogenous feeds (mixed feeding) and the complete dependence on external feeds (exogenous feeding). The change in food source is accompanied by well-characterized morphological changes, including the development of adipose tissue as an energy storage site, and continuous muscle development to improve foraging. The aim of this study was to investigate underlying molecular mechanisms that contribute to these ontogenetic changes between the nutritional phenotypes in rainbow trout alevins. We therefore analyzed the expression of marker genes of metabolic pathways and microRNAs (miRNAs) important in the differentiation and/or maintenance of metabolic tissues. In exogenously feeding alevins, the last enzyme involved in glucose production (g6pca and g6pcb) and lipolytic gene expression (cpt1a and cpt1b) decreased, while that of gk, involved in hepatic glucose use, was induced. This pattern is consistent with a progressive switch from the utilization of stored (gluconeogenic) amino acids and lipids in endogenously feeding alevins to a utilization of exogenous feeds via the glycolytic pathway. A shift towards the utilization of external feeds is further evidenced by the increased expression of omy-miRNA-143, a homologue of the mammalian marker of adipogenesis. The expression of its predicted target gene abhd5, a factor in triglyceride hydrolysis, decreased concurrently, suggesting a potential mechanism in the onset of lipid deposition. Muscle-specific omy-miRNA-1/133 and myod1 expression decreased in exogenously feeding alevins, a molecular signature consistent with muscle hypertrophy, which may be linked to nutritional cues or increased foraging.Supplementary material available online at http://jeb.biologists.org/cgi/content/full/216/9/1597/DC1 Key words: metabolism, microRNA, nutrition. THE JOURNAL OF EXPERIMENTAL BIOLOGY 1598or the potential role of miRNA in the acquisition of the capacity to utilize external feeds. Specifically, we assessed potential changes in global intermediary metabolism between nutritional phenotypes by investigating the expression of genes of glucose metabolism (glycolysis and gluconeogenesis), lipid metabolism (lipogenesis and β-oxidation) and amino acid metabolism (amino acid catabolism). Additionally, we investigated the expression of specific miRNAs and their predicted target genes, whose function in metabolic tissues has been characterized in mammalian models (Rottiers and Näär, 2012). The miRNAs investigated in this study have either been associated with the differentiation and function of specific metabolic tissues in mammals, such as a role for miR-33 and miR-122 in proliferation and lipid metabolism in the liver (Cirera-Salinas et al., 2012;Elmén et al., 2008), a role for miRNA-143 in the differentiation of adipose tissue (Esau et al., 2004) and miR-1...

Glucose metabolism ontogenesis in rainbow trout (Oncorhynchus mykiss) in the light of the recently sequenced genome: new tools for intermediary metabolism programming

“…Thus, taking into consideration all duplicated genes encoding gluconeogenic enzymes, our results suggested maintenance of an active gluconeogenic pathway during nutritional transition and no inhibition in alevins utilizing an exogenous diet, as previously proposed by Mennigen et al (2013). There was a decrease in the mRNA levels of two genes involved in the last step of glucose release at the first meal, i.e.…”

“…The conservation of an active gluconeogenic pathway in exogenous feeding alevins as well as in juveniles (Marandel et al, 2015;Seiliez et al, 2011) fed without dietary carbohydrates thus made it possible to sustain endogenous glucose demands for the maintenance of normoglycaemia (Cowey et al, 1981;French et al, 1981;Cowey, 1979, 1983). Moreover, genes involved in the glycolytic pathway were maintained ( pfkl paralogues and pklr gene) or only weakly increased expression (gck genes) with advancing nutritional transition, confirming the observations of Mennigen et al (2013).…”

“…Care was taken to maintain the same daily time frame before samplings to avoid potential circadian effects, known to affect metabolism in rainbow trout (Bolliet et al, 2000). Fish were therefore consistently sampled at 12:00 h for each ontogenetic stage investigated in this study, as previously described (Mennigen et al, 2013). Embryos were directly snap-frozen, whereas alevins were killed by terminal anaesthetization by bathing in benzocaine prior to pooling and storage in liquid nitrogen.…”

High or low dietary carbohydrate:protein ratios during first-feeding affect glucose metabolism and intestinal microbiota in juvenile rainbow trout

“…We previously found that the transition from endogenous to exogenous feeding altered the expression of the studied miRNAs in trout alevins [(Mennigen et al, 2013) except for miRNA-107]. However, the drastic change in macro-nutrient intake at first feeding did not modify their expression level in the present study.…”

“…The trout alevins were fed from first-feeding (at mouth opening) diets with low or high carbohydrate/protein ratio and then challenged to eat a high-carbohydrate diet at the later juvenile stage. Compared with mammals, trout alevins (larvae) constitute a powerful and unique model with which to try to modify metabolism because of the very high plasticity (Pittman et al, 2013, Mennigen et al, 2013 and the direct acceptability of exogenous solid feed at this developmental stage. Indeed, drastic changes in metabolic gene expression occur in first-feeding rainbow trout, during the transition from endogenous (yolk-sac) to exogenous feeding, as illustrated for some genes involved in carbohydrate utilisation (Geurden et al, 2007) and for the expression of miRNAs that may contribute to the ontogenetic metabolic changes (Mennigen et al, 2013).…”