gsdfb , But Not the Isoforms gsdfa1 and gsdfa2 , Is Up‐Regulated During the Male Program and Repressed by Estrogens in Siberian Sturgeon

The search for male‐biased genes that may drive sexual differentiation in sturgeon gonadal tissue has remained largely fruitless until now. This study explored the presence, expression, and sexual steroid regulation of gonadal soma‐derived factor (Gsdf) in Siberian sturgeon ( Acipenser baerii ). Three sequences compatible with the protein‐coding gene gsdf were identified in a Siberian sturgeon gonadal transcriptome database. The phylogenetic analysis shows the presence of two paralogues gsdfa and gsdfb , and two clearly identifiable gsdfa isoforms ( gsdfa1 and gsdfa2 ). gsdfa was expressed in sex‐undifferentiated gonads, brain, hypophysis, heart, interrenal, intestine, liver, stomach, embryos and larvae, while gsdfb was specific to the gonads. gsdfb showed significantly higher expression in genetically sexed males during late stage of sex differentiation. In contrast, gsdfa1 and gsdfa2 showed similar gonadal expression levels in both sexes. In terms of sensitivity to sexual steroids, only gsdfb was repressed significantly and in a dose‐dependent manner by estrogens. Taken together, these results indicate both that gsdfb is part of the male gonadal differentiation pathway in sturgeon and that its repression by estrogens is fundamental for female development.