Sexually dimorphic expression in developing and adult gonads shows an important role of gonadal soma-derived factor during sex differentiation in olive flounder (Paralichthys olivaceus)

Gonadal soma-derived factor (gsdf) is a new member of transforming growth factor beta (TGF-β) superfamily. As a teleost- and gonad-specific growth factor, gsdf has been indicated to play an important role in early germ cell development. However, little is known about its significance in germ cell development of olive flounder (Paralichthys olivaceus). In the present study, a 1338 bp gsdf gene was isolated from P. olivaceus for the first time. Bioinformatic analysis revealed that the genomic structure and synteny relationship of gsdf in teleosts were conserved. Quantitative real-time PCR (qRT-PCR) showed that gsdf expressed before sex gonadal differentiation, and the expression level increased rapidly after initiation of sex differentiation in males. In adult individuals, the expression of gsdf was higher in testis than that in ovary (P < 0.01). In situ hybridization (ISH) indicated that gsdf mRNA was detected in the somatic cells of both males and females, and also in the cytoplasm of oocytes. These results suggested that gsdf might play an important role as initial switches to promote testis differentiation and participate in early germ cell development, such as proliferation and differentiation of spermatogonia and oogonia in P. olivaceus.