Identification of a Novel Pituitary-Specific Chicken Gonadotropin-Releasing Hormone Receptor and Its Splice Variants1

Abstract

In all vertebrates, GnRH regulates gonadotropin secretion through binding to a specific receptor on the surface of pituitary gonadotropes. At least two forms of GnRH exist within a single species, and several corresponding GnRH receptors (GNRHRs) have been isolated with one form being pituitary specific. In chickens, only one type of widely expressed GNRHR has previously been identified. The objectives of this study were to isolate a chicken pituitary-specific GNRHR and to determine its expression pattern during a reproductive cycle. Using a combined strategy of PCR and rapid amplification of cDNA ends (RACE), a new GNRHR (chicken GNRHR2) and two splice variants were isolated in domestic fowl (Gallus gallus domesticus). Full-length GNRHR2 and one of its splice variant mRNAs were expressed exclusively in the pituitary, whereas mRNA of the other splice variant was expressed in most brain tissues examined. The deduced amino acid sequence of full-length chicken GNRHR2 reveals a seven transmembrane domain protein with 57%-65% homology to nonmammalian GNRHRs. Semiquantitative real-time PCR revealed that mRNA levels of full-length chicken GNRHR2 in the pituitary correlate with the reproductive status of birds, with maximum levels observed during the peak of lay and 4 wk postphotostimulation in females and males, respectively. Furthermore, GnRH stimulation of GH3 cells that were transiently transfected with cDNA that encodes chicken GNRHR2 resulted in a significant increase in inositol phosphate accumulation. In conclusion, we isolated a novel GNRHR and its splice variants in chickens, and spatial and temporal gene expression patterns suggest that this receptor plays an important role in the regulation of reproduction.

Molecular, cellular, morphological, physiological and behavioral aspects of gonadotropin-inhibitory hormone

“…It was suggested that GPR147 gene expression is down regulated in response to a surge in circulating estradiol and progesterone levels as the chicken undergoes sexual maturation to allow gonadotropin secretion (Maddineni et al, 2008a). Shimizu and Bédécarrats (2010) showed that GPR147 mRNA level fluctuates in an opposite manner to GnRH-R-III, a pituitary specific form of GnRH receptor, mRNA level in the chicken pituitary (Joseph et al, 2009, Shimizu andBédécarrats, 2006). Higher and lower levels of GPR147 and GnRH-R-III mRNA levels are observed during inactive and active reproductive stages, respectively.…”

Central and Direct Regulation of Testicular Activity by Gonadotropin-Inhibitory Hormone and Its Receptor

“…Shimizu and Bédécarrats (45) showed that GPR147 mRNA levels fluctuate in an opposite manner to GnRH-receptor-III, a pituitary specific form of GnRH receptor (GnRH-R), in the chicken (46, 47) according to reproductive stages. They demonstrated that the chicken GPR147 inhibits cAMP production, most likely by coupling to G αi .…”

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

“…A novel isoform of cGnRH-R was subsequently cloned by ourselves and others (Joseph et al . 2006, Shimizu & Bedecarrats 2006; Genbank AY895154). The white Leghorn isoform of the novel receptor was designated cGNRHR2 (Shimizu & Bedecarrats 2006), but it can be classified as a type III GnRH receptor.…”

“…The white Leghorn isoform of the novel receptor was designated cGNRHR2 (Shimizu & Bedecarrats 2006), but it can be classified as a type III GnRH receptor. Using PCR, this receptor showed expression of two pituitary-specific transcripts (1260 bp full length and 1065 bp splice variant; Shimizu & Bedecarrats 2006), in addition to another 501 bp splice variant that is expressed in different brain regions (Shimizu & Bedecarrats 2006). Inositol phosphate accumulation in response to GnRH-II stimulation was more potent at cGNRHR2 (Shimizu & Bedecarrats 2006) than the response to cGnRH-I.…”

“…Using PCR, this receptor showed expression of two pituitary-specific transcripts (1260 bp full length and 1065 bp splice variant; Shimizu & Bedecarrats 2006), in addition to another 501 bp splice variant that is expressed in different brain regions (Shimizu & Bedecarrats 2006). Inositol phosphate accumulation in response to GnRH-II stimulation was more potent at cGNRHR2 (Shimizu & Bedecarrats 2006) than the response to cGnRH-I. Pituitary cGNRHR2 mRNA expression levels correlated with reproductive status, suggesting that cGNRHR2 plays a role in the regulation of gonadotroph function (Shimizu & Bedecarrats 2006).…”