Transcriptomics analysis revealing candidate networks and genes for the body size sexual dimorphism of Chinese tongue sole (Cynoglossus semilaevis).

The Chinese tongue sole (Cynoglossus semilaevis) is a typical female heterogamete species that exhibits female-biased sexual size dimorphism, which has severely hindered the sustainable development of the species in aquaculture. In the present study, four important somatotropic and reproductive tissues including brain, pituitary, liver, and gonad from 15 females and 15 males were used for transcriptome analysis via RNA-seq. A mean of 37,533,991 high-quality clean reads was obtained from each library and 806, 1482, 818, and 14,695 differentially expressed genes in female and male were identified from the brain, pituitary, liver, and gonad, respectively (fold change ≥ 2 and q < 0.05). Enrichment analyses of GO terms and KEGG pathways showed that nucleic acid-binding transcription factor activity, G-protein-coupled receptor activity, MAPK signaling pathway, steroid biosynthesis, and neuroactive ligand-receptor interaction may be involved in the sexual growth differences. Furthermore, via weighted gene co-expression network analyses, two modules (yellowgreen and salmon4) were identified to be significantly positive-correlated with female-biased sexual size dimorphism. An illustrated network map drawn by these two modules enabled the identification of a series of hub genes, including nipped-B-like protein A (nipbla), transcriptional activator protein Pur-beta-like (purb), and BDNF/NT-3 growth factors receptor (ntrk2). Detailed functional investigation of these networks and hub genes will further improve our understanding of the underlying molecular mechanism of sexual size dimorphism in fish.