New insights into the nutritional regulation of gluconeogenesis in carnivorous rainbow trout (Oncorhynchus mykiss): a gene duplication trail

Abstract

The rainbow trout (Oncorhynchus mykiss) is considered to be a strictly carnivorous fish species that is metabolically adapted for high catabolism of proteins and low utilization of dietary carbohydrates. This species consequently has a "glucose-intolerant" phenotype manifested by persistent hyperglycemia when fed a high-carbohydrate diet. Gluconeogenesis in adult fish is also poorly, if ever, regulated by carbohydrates, suggesting that this metabolic pathway is involved in this specific phenotype. In this study, we hypothesized that the fate of duplicated genes after the salmonid-specific 4th whole genome duplication (Ss4R) may have led to adaptive innovation and that their study might provide new elements to enhance our understanding of gluconeogenesis and poor dietary carbohydrate use in this species. Our evolutionary analysis of gluconeogenic genes revealed that pck1, pck2, fbp1a, and g6pca were retained as singletons after Ss4r, while g6pcb1, g6pcb2, and fbp1b ohnolog pairs were maintained. For all genes, duplication may have led to sub- or neofunctionalization. Expression profiles suggest that the gluconeogenesis pathway remained active in trout fed a no-carbohydrate diet. When trout were fed a high-carbohydrate diet (30%), most of the gluconeogenic genes were non- or downregulated, except for g6pbc2 ohnologs, whose RNA levels were surprisingly increased. This study demonstrates that Ss4R in trout involved adaptive innovation via gene duplication and via the outcome of the resulting ohnologs. Indeed, maintenance of ohnologous g6pcb2 pair may contribute in a significant way to the glucose-intolerant phenotype of trout and may partially explain its poor use of dietary carbohydrates.

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

“…mammalian G6pc, Fbp1, Gck and pfkl co-orthologues, respectively) displayed divergent patterns. These results confirmed that a sub-or neo-functionalization of these genes occurred after their duplication, as previously proposed by Marandel et al (2015).…”

“…In addition, mechanisms underlying the poor ability of carnivorous fish to use dietary carbohydrates as a major energy substrate remain poorly understood. A recent study emphasized that the fate of duplicated genes after Ss4R may participate in the initiation of the glucose-intolerant phenotype in juvenile trout fed a high-carbohydrate diet (Marandel et al, 2015). This new genomic point of view following the recent sequencing of the rainbow trout genome should provide new pathways to investigate impaired glucose metabolism in this species.…”

“…1) was performed using the MEGA package v6 software (Tamura et al, 2013), as previously described (Marandel et al, 2015). The phylogenetic tree, based on deduced full-length amino acid sequences, was produced using the neighbour-joining (NJ) method and confirmed by the minimum evolution method (data not shown).…”

“…The primer sequences used in real-time RT-PCR assays for gluconeogenic and gcka and gckb gene analysis were as previously described (Marandel et al, 2015). Primers newly designed to study the pfkl and pklr genes are listed in Table 2.…”

“…Investigations have been carried out since the 1990s to try to understand the mechanisms underlying the poor ability of carnivorous fish to use dietary carbohydrates (Caruso and Sheridan, 2011;Cowey et al, 1977;Enes et al, 2009;Hung and Storebakken, 1994;Kamalam et al, 2012;Krasnov et al, 2001;Mommsen and E., 1991;Moon, 2001;Planas et al, 2000;Polakof et al, 2011aPolakof et al, , 2012. Recent analysis of the newly sequenced rainbow trout genome has allowed identification of new genes that may contribute to the hyperglycaemic phenotype in trout (Marandel et al, 2015). Moreover, the study demonstrated the indisputable value of considering the complexity of the genome and the fate of duplicated genes after the salmonid-specific fourth whole-genome duplication event (Ss4R) to improve the understanding of the phenotype observed.…”