GnRH analog stimulates gonadotropin II gene expression in maturing sockeyesalmon

Our previous study suggested that, in the pituitaries of pre-spawning chum salmon, salmon gonadotropin-releasing hormone (sGnRH) stimulates expression of genes for gonadotropin (GTH) II beta but not for I beta, since the leve ls of mRNAs encoding sGnRH and GTH II but not I were increased during the f inal stages of spawning migration. In the present study, a capsule of GnRH analog (GnRHa) was implanted into the dorsal muscle of maturing sockeye sal mon to clarify function of GnRH on expression of GTH subunit genes in pre-s pawning homing salmonids. The amounts of GTH subunit mRNAs in the individua l pituitaries were analyzed by a quantitative dot blot analysis using singl e-stranded sense DNA as the standard. The levels of GTH alpha and II beta m RNAs in the GnRHa-implanted fish were significantly higher than those in th e control fish in both the males and females, whereas the levels of GTH I b eta mRNA did not show any significant differences in both sexes. These resu lts indicate that GnRH elevates expression of GTH subunit genes which encod e the components of GTH II, alpha and II beta chains, in the pituitary of m aturing sockeye salmon, and then accelerates final maturation.