Spexin in the half-smooth tongue sole (Cynoglossus semilaevis): molecular cloning, expression profiles, and physiological effects

Spexin (SPX), a novel neuropeptide discovered by the bioinformatics approach, has been shown to exert pleiotropic functions in mammals. However, little information regarding the physiological role of SPX is available in teleosts. As a first step, we cloned the spexin gene from a flatfish, the half-smooth tongue sole. The open reading frame (ORF) of tongue sole spexin contained 363 nucleotides encoding a 120 amino acid (aa) preprohormone with a calculated molecular mass and isoelectric point of 14.06 kDa and 5.86, respectively. The tongue sole SPX precursor contained a 27 aa signal peptide and a 14 aa mature peptide flanked by two dibasic protein cleavage sites (RR and GRR). Tissue distribution analysis showed that spexin mRNA could be detected in various tissues, notably in the brain. In addition, fasting stimulated the hypothalamic expression of spexin mRNA. Intraperitoneal injection of SPX increased gnih and gnrh3 mRNA levels in the hypothalamus; however, SPX inhibited the pituitary expression of gh, fsh beta, and gth alpha mRNAs. Overall, our results reveal the existence of a functional SPX in the tongue sole, which could represent an important factor in the neuroendocrine control of flatfish reproduction and growth, and the spexin mRNA expression is regulated by feeding status.