INRA, Université de Pau et Pays d'Adour, UMR 1419, Nutrition, Metabolism and Aquaculture, Saint Pée-sur-Nivelle F-64310, France.
Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
Gene. 2019 May 25;698:129-140. doi: 10.1016/j.gene.2019.02.079. Epub 2019 Mar 5.
Rainbow trout have, as salmonid fish species, undergone sequential genome duplication events in their evolutionary history. In addition to a teleost-specific whole genome duplication approximately 320-350 million years ago, rainbow trout and salmonids in general underwent an additional salmonid lineage-specific genome duplication event approximately 80 million years ago. Through the recent sequencing of salmonid genome sequences, including the rainbow trout, the identification and study of duplicated genes has become available. A particular focus of interest 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. Since the publication of the initial rainbow trout genome draft, resequencing and annotation have further improved genome coverage. Taking advantage of these recent improvements, 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. Cytosolic pck1 abundance was increased by nutritional (diets with a high protein to carbohydrate ratio compared to diets with a low carbohydrate to protein ratio) and glucoregulatory endocrine factors (glucagon and cortisol), revealing that the well-described transcriptional regulation of pck1 in mammals is present in rainbow trout. Conversely, and in contrast to mammals, 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. Specifically, pck2b transcript abundance increased in trout fed a diet with a low protein to carbohydrate ratio compared to a diet with a high protein to carbohydrate ratio, in dominant fish compared to subordinate fish as well as hypoxia. This specific and differential expression of rainbow trout pck2 ohnologues is indicative of functional diversification, and possible functional consequences are discussed in light of the recently highlighted gluconeogenic roles of mitochondrial pck2 in mammalian models.
虹鳟鱼与其他鲑鱼鱼类一样，在其进化史上经历了连续的基因组复制事件。除了大约 3.2 亿至 3.5 亿年前的硬骨鱼特异性全基因组复制之外，虹鳟鱼和一般的鲑鱼还经历了大约 8000 万年前的另外一个鲑鱼谱系特异性基因组复制事件。通过最近对鲑鱼基因组序列的测序，包括虹鳟鱼，已经可以识别和研究复制基因。一个特别关注的焦点是虹鳟鱼糖异生基因的进化和调控，因为最近的分子和基因表达证据表明，以前未被描述的糖异生基因旁系同源物可能对虹鳟鱼长期研究的葡萄糖不耐受表型有贡献。自最初的虹鳟鱼基因组草案发布以来，重测序和注释进一步提高了基因组的覆盖度。利用这些最近的改进，我们在这里鉴定了一个鲑鱼特异性的祖先线粒体磷酸烯醇丙酮酸羧激酶 2 同工酶的基因组复制，我们称之为 pck2a 和 pck2b。细胞质磷酸烯醇丙酮酸羧激酶 (Pck1) 和最近的线粒体 Pck2，被认为是从头合成糖异生的限速酶。在通过计算机确认了鲑鱼 pck2a 和 pck2b 的进化历史之后，我们同时在几种已知调节肝糖异生的实验条件下，对虹鳟鱼肝脏中的细胞质 pck1 和线粒体 pck2a 和 pck2b 的表达进行了分析。营养（与低蛋白/碳水化合物比的饮食相比，高蛋白/碳水化合物比的饮食）和糖调节内分泌因子（胰高血糖素和皮质醇）增加了细胞质 pck1 的丰度，这表明哺乳动物中 pck1 的描述良好的转录调控在虹鳟鱼中存在。相反，与哺乳动物不同的是，我们在这里描述了 pck2a 的内分泌调节（对胰高血糖素输注的反应减少），以及营养、社会地位依赖性和缺氧依赖性的 pck2b 调节。具体而言，与高蛋白/碳水化合物比的饮食相比，低蛋白/碳水化合物比的饮食会增加虹鳟鱼 pck2b 的转录物丰度，优势鱼比劣势鱼以及缺氧时也会增加。虹鳟鱼 pck2 同系物的这种特定和差异表达表明功能多样化，并且根据最近在哺乳动物模型中强调的线粒体 pck2 的糖异生作用讨论了可能的功能后果。
