DISTINCT EXPRESSION OF GNRH GENES IN THE RED SEABREAM BRAIN

This paper reports the molecular cloning of a cDNA encoding the precur sor of seabream gonadotropin-releasing hormone (prepro-sbGnRH) and the localization of salmon GnRH (sGnRH) and seabream GnRH (sbGnRH) expres sing neurons in the brain of the red seabream (Pagrus major). The clon ed prepro-sbGnRH cDNA has a 285 bps open reading frame encoding a 23 a mino acid signal peptide, a 10 amino acid sbGnRH, the cleavage site (G ly-Lys-Arg), and a 59 amino acid GnRH-associated peptide. The expressi on of sGnRH and sbGnRH peptides, and prepro-sGnRH and prepro-sbGnRH mR NA were studied using immunocytochemistry and non-radioactive in situ hybridization, respectively. We found cell bodies that reacted positiv ely with both the sGnRH cRNA probe and anti-sGnRH serum, but not with the sbGnRH cRNA probe or anti-sbGnRH serum in the ganglion of the term inal nerve. Cell bodies that reacted positively with the sbGnRH cRNA p robe, anti-sbGnRH serum, and anti-sGnRH serum, but negatively with the sGnRH cRNA probe were found in the preoptic area (POA). Immunocytoche mistry showed that a distinct bundle of axons arises in the POA which projected to the pituitary gland. These results suggest that sbGnRH is the most relevant hypophysiotropic form of GnRH.