Inside and Outside the Pituitary: Comparative Analysis of Gnrhr Expression Provides Insight into the Mechanisms Underlying the Evolution of Gene Expression

Abstract

DNA cis-acting elements involved in gene regulation may actively contribute to adaptation processes because they are submitted to lower evolutionary constraints than coding DNA. In this regard, comparisons of the mechanisms underlying basal and regulated Gnrhr expression have revealed some features that promote stable and consistent Gnrhr expression in pituitary gonadotroph cells in different species. The presence of two divergent SF1 (NR5A1) response elements in all analysed mammalian Gnrhr promoters probably comprises one of the features that ensures reliable expression in the pituitary. By contrast, in other tissues, such as the hippocampus and testis, our analyses revealed dissimilar levels of Gnrhr expression among species. Indeed, Gnrhr was consistently expressed after birth in the rat but not the mouse hippocampus. Similar discrepancies were observed in foetal and adult testes. The ability of the rat promoter to drive reporter gene expression in the hippocampus and testis of transgenic mice just as it naturally directs the expression of the endogenous Gnrhr in rats strongly suggests that regulatory DNA sequences contained species-specific instructions prevailing over other controls. The major conclusion emerging from these studies is that Gnrhr promoter sequences are mainly responsible for directing transcriptional programmes and play a predominant role over the species-specific cell environment.

Signaling events associated with gonadotropin releasing hormone‐agonist‐induced hormonal castration and its reversal in canines

“…Although GnRH‐A‐induced inhibition of LH and FSH biosynthesis and release is likely responsible for several of the signaling events described in this investigation (Bertschinger et al, ; Ludwig et al, ), the effects may not be exclusively due to the disruption of gonadotropic support. GnRH and its receptor are not limited to the hypothalamus and pituitary—indeed, they are present in the breast, ovary, placenta, prostate, and in male and female gonads (Kraus et al, , ; Park et al, ; Ciaramella et al, ; Schang, ). In testes, GNRH mRNA is present in Sertoli cells while transcript of the GnRH receptor ( GNRHR) is expressed in Leydig cells (Bahk et al, ; Botte et al, ).…”