Molecular cloning, sequencing, and characterizing the bovine receptor for gonadotropin releasing hormone (GnRH)

Receptors for gonadotropin releasing hormone (GnRH), located in the cell membranes of adeno-hypophysial gonadotropes, mediate the action of GnRH to stimulate the secretion of the gonadotropic hormones (LH and FSH). In the present studies, we have isolated a GnRH receptor cDNA from bovine pituitary, determined its primary structure, and studied the regulation of its gene expression. The cDNA is composed of 1326 nucleotides and encodes a protein containing 328 amino acids. The GnRH receptor of cattle, like that in humans and mice, is a seven transmembrane receptor and has structural characteristics homologous with the family of G protein-coupled receptors. It exhibits 91% identity at the amino acid level with the human and 86% identity with mouse and rat receptors. Northern blot analysis of the RNA from bovine pituitary, probed with 32P-labeled bovine GnRH receptor cDNA, revealed the presence of four different transcripts (5.0, 3.5, 2.5 and 1.5 kb) in the pituitary of which the 5.0 kb form was most abundant. Using the reverse transcriptase/PCR technique, we detected expression of GnRH receptor mRNA in the pituitary but not in any other extrapituitary tissues such as the hypothalamus, hippocampus, testis, corpus luteum, ovary (containing follicles), myoendometrium, adrenal, kidney, liver and spleen. Higher levels of GnRH receptor mRNA were found in the pituitaries of steers than in cohort bulls, suggesting regulation of GnRH receptor gene expression by testicular steroids.