UC San Diego

Essential to reproduction and fertility is proper functioning of the axis that is formed from the interaction of the hypothalamus, pituitary and gonads. In vivo studies have shown the crucial role played by the sine oculis-related homeobox gene-6 (Six6) in the proper development of the pituitary as well as fertility in general. In this research study, we investigated the role played by Six6 in the regulation of the gonadotropin- releasing hormone receptor (GnRH-R) and its subsequent effect on reproductive function in an in vitro setting. Experiments involving embryonic mice point to the crucial role played by Six6 in the regulation of GnRH-R expression as evidenced by the sharp difference in GnRH-R mRNA levels in wild type mice as compared to Six6-null mice. Further in vitro studies of Six6 have revealed its role in the repression of GnRH-R through binding at an ATTA site located in the -517 bp to -741 bp region of the GnRH-R promoter. We hypothesized that the repression by Six6 could be aided by the recruitment of co-repressor proteins of the Groucho/TLE family proteins and transient transfections using Grg1 and Grg4 were conducted to test this hypothesis. Finally, aiming to identify the exact sites at which Six6 binds on GnRH-R to exert its repressive function, electrophoretic mobility shift assays were performed using sequence elements of GnRH-R from within the -517 bp to -741 bp promoter region