Pck-ing up steam: widening the salmonid gluconeogenic gene duplication trail
Résumé
Rainbow trout have undergone sequential whole genome duplication (WGD) events, a teleost-specific WGD approximately 320–350 million years ago (MYA) and an additional salmonid-specific WGD approximately 80 MYA. Through the recent sequencing of the rainbow trout genome, the identification and study of duplicated genes has become available. A particular focus has been the evolution and regulation of rainbow trout gluconeogenic genes, as recent molecular and gene expression evidence points to a possible contribution of previously uncharacterized gluconeogenic gene paralogues to the rainbow trout long-studied glucose intolerant phenotype. We here identify a salmonid-specific genome duplication of ancestral mitochondrial phosphoenolpyruvate carboxykinase 2 isoenzyme, we termed pck2a and pck2b. Cytosolic phosphoenolpyruvate carboxykinase (Pck1) and, more recently mitochondrial Pck2, are considered to be the rate-limiting enzymes in de novo gluconeogenesis. Following in silico confirmation of salmonid pck2a and pck2b evolutionary history, we simultaneously profiled cytosolic pck1 and mitochondrial pck2a and pck2b expression in rainbow trout liver under several experimental conditions known to regulate hepatic gluconeogenesis. We here describe endocrine regulation of pck2a (decrease in abundance in response to glucagon infusion), and nutritional, social-status-dependent and hypoxia-dependent regulation of pck2b. This specific and differential expression of rainbow trout pck2 ohnologues is indicative of functional diversification.