Regulation and expression of gonadotropin-releasing hormone in salmon embryo and gonad.

This study examines whether gonadotropin-releasing hormone (GnRH) expression in gonads differs from that in brain as to use of alternative promoters and time of expression in early development and reproductive maturation. Within ovary, testis, and embryos, the transcripts from sGnRH gene 1 or gene 2 were expressed using either a conventional or upstream start site and conventional and alternative splicing. In immature sockeye salmon gonads, sGnRH mRNA was expressed briefly during the first 2 years, but in precociously mature fish was expressed for 2 months in the second year. Also, a cDNA encoding another form of GnRH (chicken GnRH-II) was isolated from the gonads. We conclude that differential regulation of GnRH occurs in embryos, ovary and testis compared to brain in salmonids and that more than one form of GnRH is expressed in the salmonid gonad.