Discrepancy between molecular structure and ligand selectivity of a testicular follicle-stimulating hormone receptor of the African catfish (Clarias gariepinus)

A putative FSH receptor (FSH-R) cDNA was cloned from African catfish testis , Alignment of the deduced amino acid sequence with other (putative) glycop rotein hormone receptors and analysis of the African catfish gene indicated that the cloned receptor belonged to the FSH receptor subfamily. Catfish F SH-R (cfFSH-R) mRNA expression was observed in testis and ovary; abundant m RNA expression was also detected in seminal vesicles. The isolated cDNA enc oded a functional receptor since its transient expression in human embryoni c kidney (HEK-T) 293 cells resulted in ligand-dependent cAMP production. Re markably, African catfish LH (cfLH; the catfish FSH-like gonadotropin has n ot been purified yet) had the highest potency in this system. From the othe r ligands tested, only human recombinant FSH (hrFSH) was active, showing a fourfold lower potency than cfLH, while hCG and human TSH (hTSH) were inact ive. Human CG las well as cfLH, hrFSH, eCG, but not hTSH) stimulated testic ular androgen secretion in vitro but seemed to be unable to bind to the cfF SH-R. However, it was known that hCG is biologically active in African catf ish (e.g., induction of ovulation). This indicated that an LH receptor is a lso expressed in African catfish testis. We conclude that we have cloned a cDNA encoding a functional FSH-R from African catfish testis. The cfFSH-R a ppears to be less discriminatory for its species-specific LH than its avian and mammalian counterparts.