The human gonadotropin-releasing hormone receptor gene (GNRHR) maps to chromosome band 4q13

Mechanisms underlying the tissue-specific and regulated activity of the Gnrhr promoter in mammals

The GnRH receptor (GnRHR) plays a central role in the development and maintenance of reproductive function in mammals. Following stimulation by GnRH originating from the hypothalamus, GnRHR triggers multiple signaling events that ultimately stimulate the synthesis and the periodic release of the gonadotropins, luteinizing-stimulating hormone (LH) and follicle-stimulating hormones (FSH) which, in turn, regulate gonadal functions including steroidogenesis and gametogenesis. The concentration of GnRHR at the cell surface is essential for the amplitude and the specificity of gonadotrope responsiveness. The number of GnRHR is submitted to strong regulatory control during pituitary development, estrous cycle, pregnancy, lactation, or after gonadectomy. These modulations take place, at least in part, at the transcriptional level. To analyze this facet of the reproductive function, the 5' regulatory sequences of the gene encoding the GnRHR have been isolated and characterized through in vitro and in vivo approaches. This review summarizes results obtained with the mouse, rat, human, and ovine promoters either by transient transfection assays or by means of transgenic mice.

Newly recognized GnRH receptors: function and relative role

Hypothalamic gonadotropin releasing hormone (GnRH I) and its pituitary receptor are responsible for the CNS regulation of reproduction. However, a second GnRH (GnRH II) is also expressed in humans and a gene that resembles the GnRH II receptor in fish has been identified in humans and monkeys. The amino-acid sequence of this newly identified, seven-transmembrane, G-protein-coupled receptor in monkeys differs from the human GnRH I receptor by having a C-terminal, cytoplasmic tail. GnRH II is approximately 400-fold more potent at GnRH II receptors than GnRH I receptors. GnRH I directly inhibits proliferation of human tumor cells, and GnRH II and its receptor might have a similar role. Limited progress has been made, however, because of difficulty translating the mRNA that encodes the human GnRH II receptor. Nevertheless, such receptors are likely to exist in humans because GnRH II is more inhibitory to tumor cell replication than GnRH I, and GnRH I and GnRH II have reciprocal effects on human decidual stromal cells in culture. The focus of this review is the identity of a possible translatable, functional GnRH II receptor in humans. The two possibilities considered are either that GnRH II receptor mRNA is expressed that encodes either 5 or 7 transmembrane domains or that a GnRH II-responsive complex is formed by the GnRH I receptor and fragments derived from the GnRH II receptor.

Gonadotropin-releasing hormone receptor: cloning, expression and transcriptional regulation

In summary, isolation of GnRH receptor cDNA, its gene, and identification of regulatory elements in the flanking region of the gene have added to our knowledge regarding the tissue-specific expression of the GnRH receptor gene, and the mechanisms that mediate and influence its transcriptional regulation. However, the interactions of the different regulatory factors (nuclear factors) and the effects of these interactions on the regulation of the GnRH receptor gene remain unclear. Due to existence of multiple promoters and transcriptional start sites in human GnRH receptor gene and the lack of a human gonadotrope cell line, the precise promoter and transcriptional start sites in human pituitary, extra-pituitary tissues and tumors have not yet been identified.

A Gonadotropin-Releasing Hormone (GnRH) Receptor Specific for GnRH II in Primates

Mammalian gonadotropin-releasing hormone (GnRH I) is a hypothalamic decapeptide that stimulates gonadotropic hormone secretion upon interaction with its membrane receptors (type I) on pituitary cells, thereby governing reproductive processes. A second releasing hormone (GnRH II) expressed in mammals was shown earlier to be expressed in nonmammals and to have its own receptor. Here we demonstrate that a second receptor (type II) gene is present in the human genome, and report the cloning and characterization of its cDNA from monkeys. The cDNA encodes a G-protein-coupled/7 transmembrane receptor having a C-terminal cytoplasmic tail; it resembles more closely the type II receptors of amphibians and fish (approximately 55% identity) than it does the type I receptor of humans (approximately 39%). The GnRH type II receptor proved to be experimentally functional with, and specific for, GnRH II. GnRH receptor type II RNA is expressed ubiquitously in human tissues. This is the first report of a GnRH type II receptor in mammals. Its identification will permit exploration of its role in regulating gonadotropin secretion, female sexual behavior, and tumor cell growth.

FISHing chromosomes in endocrinology

Fluorescencein situ hybridization (FISH) is currently recognized as a reliable, sensitive, and reproducible technique for identification of copy number and structure of chromosomes providing information on the single-cell level. The technique permits cytogenetic investigation of metaphase spreads and interphase nuclei. Several protocols have been used for preparations from fresh samples or archival material. Alphoid or telomeric DNA probes can detect specific chromosomes, and cosmid probes can localize single copies of the segment of interest. FISH is a powerful tool in understanding physiologic mechanisms, in generating high-resolution physical genetic maps, and in resolving problems of the pathogenesis of several diseases. FISH may shed light on the cytogenetic background and chromosomal alterations in the field of endocrinology, resulting in a better understanding of functional activities and various endocrine disorders.