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

This study examines whether gonadotropin-releasing hormone (GnRH) expressio n in gonads differs from that in brain as to use of alternative promoters a nd time of expression in early development and reproductive maturation. Wit hin ovary, testis, and embryos, the transcripts from sGnRH gene 1 or gene 2 were expressed using either a conventional or upstream start site and conv entional and alternative splicing. In immature sockeye salmon gonads, sGnRH mRNA was expressed briefly during the first 2 years, but in precociously m ature fish was expressed for 2 months in the second year. Also, a cDNA enco ding another form of GnRH (chicken GnRH-II) was isolated from the gonads. W e conclude that differential regulation of GnRH occurs in embryos, ovary an d testis compared to brain in salmonids and that more than one form of GnRH is expressed in the salmonid gonad. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.