Comparative transcriptome analysis of early sexual differentiation in the male and female gonads of common carp (Cyprinus carpio)

The growth rate of allotetraploid common carp (Cyprinus carpio) is sex dimorphic. Thus, intervention for controlling sex is crucial for farming this fish. However, few studies have investigated the spatiotemporal interaction of interaction of various genes related to sex determination/early gonadal differentiation in carp. In this study, comparative gonadal transcriptomic analyses were conducted during 4 key sex differentiaton stages for common carp of both sexes including sex determination stage, pre-gonadal, gonadal differentiation, and maturation stages. Altogether, 305.66 Gb raw reads were obtained form 48 libraries. Differentially expressed genes (DEGs) associated with sex differentiation and gonadal development were identified at each time point. Male-specific DEGs including dmrt1, amh, hmga2, sox3, dmrt2, wnt2b, and wnt9b, and female-biased DEGs including foxl2, cyp19a1a, zp3, zp4, and gper1 were identified. The trend analysis of the key genes of sex determination and gonadal differentiation indicated that 35 dph or earlier is the male sex determination period, 90–100 dph is the key window period of male sex differentiation, and 90–100 dph may be the key window period of female sex differentiation. Functional enrichment analysis showed that DEGs at the testicular undifferentiated stages were mainly enriched in androgen receptor signaling, while DEGs from the onset of testicular differentiation to maturity were enriched in male sex differentiation, spermatogenesis, and male gonadal development. In genetic females, DEGs at the undifferentiated ovarian stage are mainly enriched in insulin-like growth factor (IGF) transport, whereas DEGs from the onset of ovarian differentiation to maturation are mainly enriched in ovarian steroidogenesis and oocyte meiosis. Protein-protein interaction (PPI) analysis revealed that 8 DEGs, including Foxl2, Src, Ncor1, and Smad4, were identified as hub proteins. Additionally, plasma 17β-estradiol and 11-Ketotestosterone levels were sexually dimorphic in C. carpo. The study provide insights into the genetic network of the underlying mechanisms of early sex determination and gonadal differentiation in C. carpo for intervening all-female production in better way.