Characterization of the gsdf gene in channel catfish (Ictalurus punctatus): molecular cloning, tissue distribution, and expression patterns in the gonad after treatment with 17β-estradiol

The gonadal soma-derived factor (gsdf) gene was previously identified in a variety of fish and was found to be closely related to sexual differentiation and gonad development. In this study, gsdf was identified in channel catfish (Ictalurus punctatus) using a series of bioinformatics methods. Additionally, artificial compound feed containing 178-estradiol (60 & mu;g/g) was used to induce the sexual reversal of male catfish, and then gsdf expression was compared among XX females, XY females, and XY males at the age of 90 and 540 days after hatching. Synteny analysis revealed that gsdf genes were relatively conserved in bony fish. Tissue distribution analysis showed that this gene was highly expressed mainly in the testis (P < 0.01). After 178-estradiol treat-ment, gsdf expression was inhibited in XY female channel catfish. Its expression differed significantly between XY females and XY males (P < 0.01) but not between XY and XX females. In situ hybridization showed that gsdf mRNA was expressed in Sertoli cells of the testis but not in the ovary of normal female channel catfish, and only a small amount was detected in the ovary of XY female channel catfish. Results of this study provide a foundation for further analysis of the molecular mechanism by which gsdf affects sex differentiation and maintenance in channel catfish.