In addition to the hypothalamic GNRH1 of variable sequence, many vertebrate species express a second,
invariant GNRH form, GNRH-II (or GNRH2), with the primary structure gln-his-trp-ser-his-gly-trp-tyr-pro-gly.The widespread expression of
GNRH2 suggests it may have multiple functions. Molecular phylogenetic analysis shows that GNRH2 is likely the result
of a duplication before the appearance of vertebrates.
Retention and Silencing of Prepro-GnRH-II and Type II GnRH Receptor Genes in Mammals. Stewart AJ et al. The decapeptide hypothalamic-pituitary gonadotrophin-releasing hormone (GnRH)-I and the type I GnRH receptor drive the reproductive hormonal cascade in mammals by stimulating synthesis and secretion of luteinising hormone (LH) and follicle stimulating hormone (FSH). Mammals possess a second GnRH system composed of a related hormone, GnRH-II (differing from GnRH-I by three amino acid residues), and the type II GnRH receptor. In many mammalian species, one or both of the GnRH-II system genes are disrupted or deleted, rendering their products non-functional. This includes humans who possess a gene encoding GnRH-II but lack a functional type II GnRH receptor. Here we examined the genes encoding prepro-GnRH-II (GnRH2) and the type II GnRH receptor (GnRHR2) in more than 20 mammalian species, encompassing 10 orders, to determine whether they encode functional proteins. The structural organisation of both genes in most mammalian genome sequence assemblies was poorly annotated or incompletely described. Our findings show significant variation in the DNA sequence conservation and functional status of each gene, even between closely related species. Prepro-GnRH-II was functionally compromised in 12/22 species and the type II GnRH receptor gene was disrupted in 14/22 species. Retention of large sections of each gene in most mammalian genomes suggests that mammalian ancestors had a functional GnRH-II system. Gene disruptions were due to a spectrum of mutations which must have occurred independently after the evolutionary divergence of mammals from ancestral animals. The genetic information will be useful for understanding the physiological role of the GnRH-II system and establishing animal models for functional studies.
NCBI Summary:
The protein encoded by this gene is a preproprotein that is cleaved to form a secreted 10 aa peptide hormone. The secreted decapeptide regulates reproduction in females by stimulating the secretion of both luteinizing- and follicle-stimulating hormones. Three transcript variants that encode unique proproteins but the same peptide hormone have been found for this gene.
General function
Ligand, Hormone
Comment
Cellular localization
Secreted
Comment
Ovarian function
Steroid metabolism
Comment
Gonadotropin-Releasing Hormone-I or -II Interacts with IGF-I/Akt But Not Connexin 43 in Human Granulosa Cell Apoptosis. Hong IS et al. Background:We have recently demonstrated that GnRH-I or -II can induce apoptosis in immortalized human granulosa cells by activating the caspase signaling cascade. Whether GnRH-I or -II can affect other regulators such as Bcl-2 family members, IGF-I, or gap junctions and the mechanisms involved are unknown.Methods:Immortalized human granulosa cells were treated with GnRH-I, GnRH-II, IGF-I, or antide (a GnRH-I receptor antagonist), in various combinations. Cell proliferation and apoptotic changes were evaluated by cell counting, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and immunoblotting. Activated or total protein expression of IGF-I receptor, Akt, connexin 43 (Cx43), or caspase-3 with and without dominant-negative Akt (an Akt-suppressing vector), wortmannin (a phosphatidylinositol-3-kinase inhibitor), or Cx43 small interfering RNA transfection were assessed by immunoblotting. Gap junctional communication was determined by dye transfer assay.Results:GnRH-I or -II inhibited cell proliferation, induced TUNEL-positive cells, and increased caspase-3 activities but had no effects on Bcl-2 family members. IGF-I increased cell proliferation, decreased TUNEL-positive cells and caspase-3 activities, and increased Akt activities, and these effects were attenuated by GnRH-I or -II. Effects of IGF-I on caspase-3 activities were attenuated by dominant-negative Akt or wortmannin. GnRH-I or -II decreased dye transfer, increased Cx43 phosphorylation, and increased caspases-3 activities even after Cx43 knockdown.Conclusion:GnRH-I or -II induces apoptosis in human granulosa cells through a caspase-3-dependent extrinsic pathway rather than a Bcl-2 family-dependent intrinsic pathway and attenuates the antiapoptotic action of IGF-I through Akt. Cx43-induced gap junctional changes do not initiate granulosa cell apoptosis but likely result from apoptosis induced by GnRH-I or -II.
Kang SK, et al 2000 reported differential Regulation of Two Forms of Gonadotropin-Releasing
Hormone Messenger Ribonucleic Acid in Human
Granulosa-Luteal Cells.
The recent cloning of a second form of
GnRH (GnRH-II) with characteristics of chicken GnRH-II in the primate brain has
prompted a reevaluation of the role of GnRH in reproductive functions. The authors investigated the hormonal regulation of GnRH-II messenger
RNA (mRNA) and its functional role in the human granulosa-luteal cells (hGLCs),
and provided evidence for differential hormonal regulation of GnRH-II
vs. GnRH-I mRNA expression.
The expression levels of GnRH-II, GnRH-I, and GnRH receptor (GnRHR) mRNA
were investigated using semiquantitative or competitive RT-PCR. A significant
decrease in GnRH-II and GnRHR mRNA levels was observed in cells treated
with GnRH-II or GnRH-II-a. In contrast, GnRH-I-a revealed a biphasic effect (up-
and down-regulation) of GnRH-I and GnRHR mRNA, suggesting that GnRH-I and
GnRH-II may differentially regulate GnRHR and their ligands (GnRH-I and
GnRH-II). Treatment with FSH or hCG increased GnRH-II mRNA levels but
decreased GnRH-I mRNA levels, further indicating that GnRH-I and GnRH-II
mRNA levels are differentially regulated. To investigate the physiological role of
GnRH-II, hGLCs were treated with GnRH-II or GnRH-II-a in the presence or
absence of hCG, for 24 h, and progesterone secretion was measured by RIA. Both
GnRH-II and GnRH-II-a inhibited basal and hCG-stimulated progesterone
secretion, effects which were similar to the effects of GnRH-I treatment on
ovarian steroidogenesis. Next, hGLCs were treated with various concentrations of
GnRH-II, GnRH-II-a, or GnRH-I-a; and the expression levels of FSH receptor and
LH receptor were investigated using semiquantitative RT-PCR. A significant
down-regulation of FSH receptor and LH receptor was observed in cells treated
with GnRH-II, GnRH-II-a, and GnRH-I-a, demonstrating that GnRH-II and
GnRH-I may exert their antigonadotropic effect by down-regulating gonadotropin
receptors. Interestingly, GnRH-II and GnRH-II-a did not affect basal and
hCG-stimulated intracellular cAMP accumulation, suggesting that the
antigonadotropic effect of GnRH-II may be independent of modulation of cAMP
levels. Taken together, these results suggest that GnRH-II may have biological
effects similar to those of GnRH-I but is under differential hormonal regulation in
the human ovary.
Expression regulated by
Comment
Ovarian localization
Granulosa, Luteal cells, Surface epithelium
Comment
Kyung-Chul Choi, et al reported the
Expression and Antiproliferative Effect of a Second Form of
Gonadotropin-Releasing Hormone in Normal and Neoplastic Ovarian
Surface Epithelial Cells .
The authors demonstrated that in addition to the GnRH receptor (GnRH-R),
GnRH-II mRNA is expressed in normal OSE, immortalized OSE (IOSE) cells, primary cultures of ovarian tumors and
ovarian cancer cell lines. Treatments with increasing doses (10-9-10-7 M) of GnRH-I and -II resulted in a
growth-inhibition in both non-tumorigenic IOSE-29 and tumorigenic IOSE-29EC cells. These results indicate for the
first time the expression and potential anti-proliferative effect of GnRH-II, suggesting that GnRH-II, similar to GnRH-I,
may have a growth-regulatory effect in normal and neoplastic OSE cells.
Follicle stages
Preovulatory, Corpus luteum
Comment
Immunolocalization of Gonadotropin-Releasing Hormone (GnRH)-I, GnRH-II, and Type-I GnRH Receptor during Follicular Development in the Human Ovary. Choi JH et al. Context: Gonadotropin releasing hormone (GnRH) and its receptor have been detected, at the mRNA level, in different ovarian cell types, implicating an autocrine role of the GnRH system in the human ovary. However, the expression, at the protein level, of GnRH and its receptor in specific cell types during follicular development has not been documented in humans. Objective: We evaluated the immunohistochemical expression of GnRH-I (the classical form of mammalian GnRH), GnRH-II (the novel isoform) and the type-I GnRH receptor (GnRHR) that is known to bind both forms of GnRH, in ovaries of pre-menopausal women. Main Outcome Measures: Immunohistochemistry, immunofluorescence, immunoblot assay and real-time RT-PCR were performed. Results: GnRH-I, GnRH-II and GnRHR were not immunostained in the follicles from the primordial to the early antral stage. In preovulatory follicles, both forms of GnRH and their common receptor were localized predominantly to the granulosa cell layer, whereas the theca interna layer was weakly positive. In the corpus luteum, significant levels of GnRH-I, GnRH-II as well as GnRHR were observed in granulosa luteal cells, but not in theca luteal cells. Both GnRH isoforms and the type-I GnRHR were localized also to the ovarian surface epithelium (OSE) from which over 85% of ovarian cancer are thought to be derived. Conclusion: The expression of GnRH-I, GnRH-II and GnRHR protein in the human ovary is temporally and spatially specific, and further support the physiological role of an autocrine regulatory system involving GnRH-I, GnRH-II and GnRHR in follicular development and corpus luteal function.