GnRH Analog Stimulates Gonadotropin II Gene Expression in Maturing Sockeye Salmon

Abstract

ABSTRACT-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) IIβ but not for Iβ, since the levels of mRNAs encoding sGnRH and GTH II but not I were increased during the final stages of spawning migration. In the present study, a capsule of GnRH analog (GnRHa) was implanted into the dorsal muscle of maturing sockeye salmon to clarify function of GnRH on expression of GTH subunit genes in pre-spawning homing salmonids. The amounts of GTH subunit mRNAs in the individual pituitaries were analyzed by a quantitative dot blot analysis using single-stranded sense DNA as the standard. The levels of GTH α and IIβ mRNAs in the GnRHa-implanted fish were significantly higher than those in the control fish in both the males and females, whereas the levels of GTH Iβ mRNA did not show any significant differences in both sexes. These results indicate that GnRH elevates expression of GTH subunit genes which encode the components of GTH II, α and IIβ chains, in the pituitary of maturing sockeye salmon, and then accelerates final maturation.

Effects of growth hormone over-expression on reproduction in the common carp Cyprinus carpio L.

“…In Sockeye Salmon, GnRH stimulated lhb expression while had no effects on fshb (Kitahashi et al, 1998). In goldfish, GnRH stimulated both fshb and lhb gene expression in vivo and in vitro (no matter pituitary fragments or dispersed cells) (Klausen et al, 2001).…”

“…However in catfish, GnRH inhibited lhb expression at 2 h, 4 h after GnRH injection and stimulated lhb expression at 8 h after GnRH injection in vivo while only inhibited lhb expression in vitro (Rebers et al, 2002). In vivo treatment of salmon with GnRH using fish from different developmental stages results in different lhb expression pattern (Dickey and Swanson, 2000;Kitahashi et al, 1998). These differing results indicate that gonadotroph responsiveness to GnRH is dependent on experiment conditions (in vivo or in vitro) and developmental stages.…”

Elevation of gene expression for salmon gonadotropin-releasing hormone in discrete brain loci of prespawning chum salmon during upstream migration

“…sGnRH facilitated electric activity of central neurosecretory cells (NSCs) (Saito et al, 2003). GnRHa increased amounts of mRNAs encoding gonadotropin (GTH) II (Kitahashi et al, 1998a) and SL (Taniyama et al, 2000;Bhandari et al, 2003) in the pituitary, and further accelerated final maturation (Fukaya et al, 1998). These lines of evidence suggest that sGnRH neurons are activated during upstream migration, and coordinately regulate migratory behavior and final gonadal maturation.…”

Physiological Mechanisms of Imprinting and Homing Migration of Pacific Salmon

“…Expression of GTH subunit genes in the pituitary gland was examined and revealed that the levels of GTHa and LHb mRNAs in GnRHa-implanted fish were higher than those in control fish, but the levels of FSHb mRNA showed no change (Kitahashi et al 1998b). Implantation of GnRHa caused a significant elevation of serum DHP levels in both sexes, but had no effect on levels Changes in serum steroid hormone levels of male and female chum salmon during homing migration from Site G to Site A (Fig.…”