Development of the GHRH-Cre Recombinase Mouse Model: A Tool to Further Study Regulation and Function of the GHRH neuron

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 88-108-GHRH, GH & IGF Biology & Signaling
Basic/Translational
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-107
Christopher Joseph Romero1, Elisavet Agathou*1, Valentina Corazzini2, Binyam Fitwi1, Sally Radovick3, Roberto Salvatori4 and Andrew M Wolfe*5
1Johns Hopkins University School of Medicine, Baltimore, MD, 2Johns Hopkins university, Baltimore, MD, 3Johns Hopkins Med Instit, Baltimore, MD, 4Johns Hopkins Univ Sch of Med, Baltimore, MD, 5Johns Hopkins Univ Schl of Med, Baltimore, MD
Introduction:  Hypothalamic growth hormone releasing hormone (GHRH) stimulates somatotroph cell proliferation and GH secretion. Several other factors from within and outside the GH-IGF-1 axis also play a role in somatotroph cell regulation. Some of these influences have been shown to indirectly affect GH production by targeting the GHRH neurons, yet the mechanism of this regulation is unclear. Our laboratory has developed a transgenic mouse containing Cre-recombinase downstream of the murine GHRH promoter as a means of selectively knocking out genes within the GHRH-expressing neurons. This mouse-model will allow us to study the function and mechanisms of regulation in the GHRH neuron as well as its role in hypothalamic and pituitary development. One of the future goals is to study IGF-1feedback on these neurons by mating the GHRH-Cre mice with IGF-1R floxed mice to produce a knockout of the IGF-1R specifically in the GHRH neurons.

Methods and Results: In order to construct the transgene, a 1458 bp mouse GHRH promoter fragment was cloned upstream of a 1353 bp Cre-recombinase gene obtained from the ACN cassette (a gift from Dr. Mario Capecchi) and sequenced to ensure that the genes were in the correct orientation and in-frame. The GHRH-CRE transgene was linearized for pronuclear injection by the Johns Hopkins Transgenic Core. In brief, 1-cell stage embryos were obtained from superovulated B6SJLF1 females and the DNA was injected into one pronucleus of each embryo.  Following injection, surviving embryos were surgically transferred to oviducts of psuedopregnant ICR females (25 embryos/female). Genomic DNA from a total of 117 pups was screened for the GHRH Cre transgene of which 16 were Cre positive. These mice were then mated with normal mice and pups that were Cre positive were sacrificed. RNA was obtained from cortex, hypothalamus, cerebellum, pituitary, heart, lung, liver, stomach, pancreas, spleen, kidney, fat, muscle, uterus and gonads.  GHRH-Cre was expressed in the hypothalamus, but not in the pituitary using Quantitative Real Time PCR with primers specific for targeting Cre recombinase in cDNA.

Conclusion: We describe the development of a transgenic GHRH-Cre mouse that can be used to selectively ablate genes in the GHRH neuron to further study and characterize the development and functional regulation of these cells. In addition, this model system will provide insight into the role of hypothalamic GHRH on regulation of mammalian growth.

Disclosure: SR: Ad Hoc Consultant, CVS/Caremark, Speaker, Novo Nordisk. Nothing to Disclose: CJR, EA, VC, BF, RS, AMW

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: NIH/NIDDK - Mentored Clinical Scientist Research Career Development Award K08 (1K08DK088996-01A1) awarded to CJR. Baltimore Diabetes Research Traning Center - P60-DK079637