A Proximal AP-1 Site in the Gnrhr Gene Promoter Is Critical for Normal Pubertal and Reproductive Development in Female Mice

Presentation Number: OR30-5
Date of Presentation: June 23rd, 2014

Sekoni D. Noel*1, Cecilia Martin2, Titilayo Muyide2, Serap Simavli2, Joy N. Liang3, Victor M. Navarro4, Rona S. Carroll2 and Ursula B Kaiser2
1Brigham and Women's Hospital/Harvard Med School, Boston, MA, 2Brigham and Women's Hospital and Harvard Medical School, Division of Endocrinology/Diabetes, Boston, MA, 3Brigham and Women's Hospital/Harvard Medical School, Boston, MA, 4Harvard Medical School and Brigham and Women's Hospital, Boston, MA

Abstract

Pulsatile GnRH released from the hypothalamus binds to its receptors (GnRHR) on gonadotropes in the pituitary to stimulate the pulse frequency-dependent synthesis and secretion of LH and FSH.  This pulsatile GnRH release also regulates gonadotrope Gnrhr expression, with the highest receptor levels associated with faster GnRH pulse frequencies (e.g., every 30 minutes) and greater LH release, whereas slower GnRH pulse frequencies (e.g., every 2 hours) are associated with lower GnRHR levels and greater FSH release.  Our group previously identified an AP-1 element in the Gnrhr gene promoter necessary for full GnRH induction of GnRHR expression in vitro.  In the current study, we generated a knock-in (KI) mouse model with a point mutation in the AP-1 site of the Gnrhr gene promoter that eliminates AP-1 binding and blocks GnRH induction of Gnrhr transcription in vitro, with the goal of confirming the disruptive effects of this mutation on GnRHR expression and assessing the resulting physiological consequences in vivo.  Reproductive phenotypic analysis demonstrated that female homozygous KI mice displayed abnormal pubertal development, with significant delays in vaginal opening, first day of estrus, and mean age of onset of estrous cyclicity, compared to wild-type (WT) littermate controls. These mice also displayed disrupted estrous cycles, with significantly more time spent in diestrus, and produced smaller litters, compared to WT female controls.  Serum gonadotropin (LH and FSH) levels were similar for intact WT and KI females in diestrus. Strikingly, the KI mice showed no significant increase in serum LH levels after ovariectomy, in contrast to WT females.  RT-qPCR analysis further demonstrated that female KI mice had significantly lower pituitary Gnrhr, Lhb and Fshb mRNA levels than WT females after ovariectomy, suggesting that these KI mice had impaired post-gonadectomy induction of gonadotropin secretion.  Collectively, our data support an important role for the AP-1 site in the Gnrhr gene promoter in the regulation of GnRHR expression levels in vivo, and further demonstrate that properly coordinated regulation of GnRHR is critical for pubertal development and for reproductive cyclicity in female mice.

 

Nothing to Disclose: SDN, CM, TM, SS, JNL, VMN, RSC, UBK