Involvement of glycolysis activation in flatfish sexual size dimorphism: Insights from transcriptomic analyses of Platichthys stellatus and Cynoglossus semilaevis.

The starry flounder (Platichthys stellatus), a flatfish cultured at the margins of the North Pacific, displays an obvious female-biased growth advantage, similar to many other fish species. To reveal the molecular mechanism underlying sexual size dimorphism, a comparative transcriptomic analysis of the somatotropic and reproductive axes was conducted. In total, 156, 67, 3434, and 378 differentially expressed genes (DEGs) between female and male samples were obtained in the brain, liver, gonad, and muscle tissues (q < 0.05). These DEGs were significantly enriched for various GO terms, including ion channel activity, protein binding, lipid transporter activity, and glycolytic process. The significantly enriched KEGG pathways included insulin secretion, axon guidance, and glycolysis/gluconeogenesis. In a detailed analysis of DEGs in these significantly enriched pathways, 35 genes showed higher expression levels in female muscle tissues than in male muscle tissues. A protein-protein interaction network further revealed specific interactions involving the glycolysis related-protein enolase (ENO), triosephosphate isomerase (TPI), Bisphosphoglycerate mutase (BPGM), fructose-bisphosphate aldolase (ALDO), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Interestingly, the role of glycolysis/gluconeogenesis was supported by an analysis of common DEGs between P. stellatus and Chinese tongue sole (Cynoglossus semilaevis). These results indicate that the activation of glycolysis in female muscle tissues contributes to flatfish sexual size dimorphism.