Identification and expression of GnRH2 and GnRH3 in the black sea bass (Centropristis striata), a hermaphroditic teleost

Abstract

We cloned two cDNAs for two gonadotropin-releasing hormones, GnRH2 (chicken GnRH-II) and GnRH3 (salmon GnRH), respectively, from the black sea bass (Centropristis striata). Black sea bass are protogynous hermaphroditic teleosts that change from females to males between 2 and 5 years of age. Similar to other GnRH precursors, the precursors of black sea bass GnRH2 and GnRH23 consisted of a signal peptide, decapeptide, a downstream processing site, and a GnRH-associated peptide. Our analyses failed to identify GnRH1. GnRH3 precursor transcript was more widely distributed in a variety of tissues compared with GnRH2. Further examination of GnRH expression and gonadal histology was done in black sea bass from three different size groups: small (11.4-44.1 g), medium (179.4-352.2 g) and large (393.8-607.3 g). Interestingly, GnRH3 expression occurred only in the pituitaries of males in the small and medium groups compared with expression of GnRH2. Future functional studies of the sea bass GnRHs will be valuable in elucidating the potential underlying neuroendocrine mechanisms of black sea bass reproduction and may ultimately contribute to management advances in this commercially important fish.