Comparative analysis of the pituitary and ovarian GnRH systems in the leopard gecko: signaling crosstalk between multiple receptor subtypes in ovarian follicles

Abstract

GnRH regulates reproductive functions through interaction with its pituitary receptor in vertebrates. The present study demonstrated that the leopard gecko possessed two and three genes for GnRH ligands and receptors, respectively, though one of the three receptor subtypes had long been thought not to exist in reptiles. Each receptor subtype showed a distinct pharmacology. All types of ligands and receptors showed different expression patterns, and were widely expressed both inside and outside the brain. This report also shows a comparison of the pituitary and ovarian GnRH systems in the leopard gecko during and after the egg-laying season. All three receptor subtypes were expressed in both the whole pituitary and ovary; however, only one receptor subtype could be detected in the anterior pituitary gland. In situ hybridization showed spatial expression patterns of ovarian receptors, and suggested co-expression of multiple receptor subtypes in granulosa cells of larger follicles. Co-transfection of receptor subtypes showed a distinct pharmacology in COS-7 cells compared with those of single transfections. These results suggest that distinct signaling mechanisms are involved in the pituitary and ovarian GnRH systems. Seasonal and developmental variations in receptor expression in the anterior pituitary gland and ovarian follicles may contribute to the seasonal breeding of this animal.

The chicken type III GnRH receptor homologue is predominantly expressed in the pituitary, and exhibits similar ligand selectivity to the type I receptor

“…Birds, like mammals, possess two GnRH receptor subtypes in contrast to fish, reptiles and amphibians in which three types of receptor are generally found (Morgan & Millar 2004, Ikemoto & Park 2007). The proximity of the two chicken receptor subtypes on chromosome 10 (∼2 Mb apart) and their high sequence similarity, suggests they may have been derived by gene duplication.…”

“…Two subtypes of GnRH receptor occur in the African clawed frog ( Xenopus laevis ; Troskie et al . 2000) whereas the leopard gecko expresses three receptor subtypes in the pituitary, with one receptor subtype predominating in the anterior pituitary (Ikemoto & Park 2007). The pituitary-specific GnRH receptor subtypes expressed in the bullfrog (Wang et al .…”

“…2001), African clawed frog (Troskie et al . 2000) and leopard gecko (Ikemoto & Park 2007) differ structurally, according to the nomenclature proposed by Miller et al . and phylogenetically (Millar et al .…”

“…2001, Moncaut et al . 2005, Ikemoto & Park 2007) suggests that a complex interplay between ligands and receptors may occur. The organisation of the avian GnRH system is distinct from those of teleosts, amphibians, reptiles or mammals (Ensemble database), having two receptor subtypes for two GnRH ligands (Morgan & Millar 2004).…”

Molecular Coevolution of Neuropeptides Gonadotropin-Releasing Hormone and Kisspeptin with their Cognate G Protein-Coupled Receptors

“…In the tetrapod lineage, most species except for rodents have two forms of GnRH ( GnRH1 and GnRH2 ). Due to insufficient genetic information investigators were unable to identify the GnRH2 gene in the anole lizard, but believe the gene exists in this species because other reptilian species such as the gecko has two forms of the GnRH gene (Ikemoto and Park, 2003, 2007). Fish have four or five GnRHRs and one or two of them are generated by teleost-specific genome duplication (Kim et al, 2011).…”