Cloning and Spatiotemporal Expression of the Follicle-Stimulating Hormone (beta) Subunit Complementary DNA in the African Catfish (Clarias gariepinus)

The gene and cDNA encoding a putative follicle-stimulating hormone (beta) subunit (cfFSH(beta)) from African catfish (Clarias gariepinus) were cloned. Similar to other FSH(beta) genes, the cfFSH(beta) gene consisted of three exons interrupted by two introns. The cfFSH(beta) cDNA coded for a mature protein of 115 amino acids. The 12 cysteines that are required for the typical tertiary folding of glycoprotein hormone (beta) subunits were positionally conserved in cfFSH(beta). The cfFSH(beta) mRNA expression was exclusively detected in the pituitary and was detectable before pubertal development was initiated. The cfFSH(beta) transcript levels increased in particular during early stages of puberty and reached constantly high levels after the first appearance of spermatids in the testis. The cfFSH(beta) mRNA-positive cells were localized in the proximal pars distalis. Castration of mature males caused elevated cfFSH(beta) mRNA levels that were decreased by steroid replacement. Previous work indicated that the African catfish is an interesting model to study the regulation of gonadal functions because cfLH is able to activate both the catfish luteinizing hormone receptor (cfLH-R) and follicle-stimulating hormone receptor (cfFSH-R). Because cfFSH purification has failed so far, ongoing studies are directed toward the production of recombinant cfFSH. After all, the developmental and hormonal regulation of cfFSH(beta) transcript levels opens the possibility for physiologically relevant actions of the putative cfFSH, next to the presumptive bifunctionally acting cfLH.