Gonadotrophin‐releasing hormone (GnRH), acting via its cognate GnRH receptor (GnRHR), is the primary regulator of mammalian reproductive function, and hence GnRH analogues are extensively used in the treatment of hormone‐dependent diseases, as well as for assisted reproductive techniques. In addition to its established endocrine role in gonadotrophin regulation in the pituitary, evidence is rapidly accumulating to support the expression and functional roles for two forms of GnRHR (GnRHR I and GnRHR II) in multiple and diverse extra‐pituitary mammalian tissues and cells. These findings, together with findings indicating that mutations of the GnRHR are linked to the disease hypogonadotrophic hypogonadism and that GnRHRs play a direct role in neuronal migration and reproductive cancers, have presented new therapeutic targets and intensified research into the structure, function and mechanisms of regulation of expression of GnRHR genes. The present review focuses on the current knowledge on tissue‐specific and hormonal regulation of transcription of mammalian GnRH receptor genes. Emerging insights, such as the discovery of diverse regulatory mechanisms in pituitary and extra‐pituitary cell types, nonclassical mechanisms of steroid regulation, the use of composite elements for cell‐specific expression, the increasing profile of hormones involved in regulation, the complexity of kinase pathways that target the GnRHR I gene, as well as species‐differences, are highlighted. Although further research is necessary to understand the mechanisms of regulation of expression of GnRHR I and GnRHR II genes, the GnRHR is emerging as a potential target gene for facilitating cross‐talk between neuroendocrine, immune and stress‐response systems in multiple tissues via autocrine, paracrine and endocrine signalling.

Regulation of GnRH receptor (GnRHR) expression levels in the pituitary is a crucial control point in reproduction. The promoter of the mouse GnRHR gene contains nuclear receptor half-sites (NRS) at -244/-236 and -15/-7 relative to the translation start site. Although binding of steroidogenic factor-1 (SF-1) to the -244/-236NRS is implicated in mediating basal and gonadotrope-specific expression, no function or protein-DNA interactions have previously been described for the -15/-7NRS. We report that levels of the endogenous GnRHR mRNA in alpha T3-1 cells are stimulated by forskolin and 8-bromo-cAMP. We also show that the orphan nuclear receptor Nur77 is expressed in alpha T3-1 cells, and that both SF-1 and Nur77 bind to the -15/-7NRS and -244/-236NRS in vitro. We show that the activity of the proximal (-579/+1) mouse GnRHR promoter is up-regulated by protein kinase A, via a mechanism that is modulated by SF-1, both positively and negatively, through binding to the -244/-236NRS or the -15/-7NRS, respectively. Nur77 appears to be capable of acting as a negative regulator of this response, via the -15/-7NRS. Furthermore, we show that forskolin up-regulates SF-1 mRNA levels in alpha T3-1 cells, indicating that the levels of SF-1 play a role in modulating the protein kinase A response.