GnIH plays a negative role in regulating GtH expression in the common carp, Cyprinus carpio L

In birds and mammals, the gonadotrophin-inhibitory hormone (GnIH) effectively inhibits the expression of gonadotrophin (GtH). In teleosts, the effects of GnIH are still unclear and under much debate. The aim of this study is to evaluate the functions of GnIH/receptors of gonadotrophin-inhibitory hormone (GnIHRs) system during reproduction in the common carp, Cyprinus carpio L. We cloned the full cDNA sequences of GnIH /GnIHRs. Real-time PCR results showed that GnIH/GnIHRs were distributed extensively across the whole hypothalamus-pituitary-gonad (HPG) axis. We also examined the changes of GnIH/GnIHRs in the HPG axis during reproduction. GnIH mRNA expression was decreased to the minimum value in Apr, the spawning month, and increased immediately after the completion of reproduction. Expression pattern of GnIH during reproduction was the opposite to those of Gonadotrophin release hormone 3 (GnRH3) and luteinizing hormone (LH). Expression patterns of GnIHRs were similar to that of GnIH in the hypothalamus. In the pituitary, GnIHR2/3 peaked in March before spawning. In the ovaries, the GnIHR1 decreased to the minimum value in April, but GnIHR2/3 increased. By injection and incubation with synthesized GnIH-III peptide, we confirmed the negative influence of GnIH on mRNAs of the follicle-stimulating hormone-β and LH-β subunits in the common carp. These results show that the GnIH/GnIHRs system is involved in the negative regulation of reproduction in HPG axis of the common carp.

Molecular identification of GnIH/GnIHR signal and its reproductive function in protogynous hermaphroditic orange-spotted grouper (Epinephelus coioides)

Gonadotropin-inhibitory hormone (GnIH) and its receptor (GnIHR) play an important role in reproduction regulation in birds, mammals and some teleost species. In protogynous hermaphroditic orange-spotted grouper (Epinephelus coioides), the GnIH/GnIHR signaling pathway and its reproductive function have not been addressed yet. In this study, GnIH and GnIHR in orange-spotted grouper were characterized. gGnIH possessed three putative peptides (gGnIH-I, -II, -III), while gGnIHR showed the characteristics of G protein-coupled receptor and was clustered with GPR147. Functional assays demonstrated that three synthetic gGnIH peptides significantly decreased the forskolin-induced CRE promoter activity, but only gGnIH-I could significantly decrease SRE promoter activity in COS-7 cells transfected with gGnIHR. During the process of ovarian differentiation and development, gGnIH mRNA level in hypothalamus was low at the gonadal primordium stage with gonia, then increased significantly at the early differentiated gonad with primary growth oocytes, while decreased significantly at the developing gonads with cortical-alveolus and vitellogenic stage oocytes. During MT-induced sex reversal, gGnIH mRNA level in hypothalamus increased significantly when the fish completely reversed from female to male. However, gGnIHR mRNA level in pituitary decreased significantly in intersex and completely reversed male fish. Intraperitoneal injection (i.p.) of three gGnIH peptides significantly decreased GnRH1 mRNA levels in hypothalamus, and gGnIH-II significantly inhibited synthesis of LHβ in pituitary. In summary, we firstly identified the GnIH/GnIHR signal in protogynous orange-spotted grouper, which might be involved in the regulation of the reproductive function of sex differentiation, gonadal development and sex reversal via regulating the synthesis of both GnRH and GtH.