A body of information relevant to the rodent documents a complete (ovarian) intrafollicular insulin-like growth factor (IGF)-I system, replete with a ligand (IGF-I), a receptor (type I), IGF binding proteins (IGFBPs 4&5) and IGFBP-4 and 5-directed endopeptidases. According to current views, shaped in large measure by numerous in vitro observations, the primary and presumably obligatory autocrine role of bioavailable intrafollicular IGF-I is the amplification of FSH action in granulose cells. It is this FSH-amplifying property of IGF-I which underlies the hypothesis that intrafollicular IGF-I constitutes an obligatory determinant of antral (FSH-dependent) follicular development. Rigorous validation of this so-called """"""""amplification"""""""" hypothesis requires demonstration of the in vivo indispensability of intrafollicular IGF-I. Although female null mutants for the igf-1 gene were reported to display reproductive dysfunction, these preliminary observations remain inconclusive given the high (<90%) neonatal mortality rate and the small (<6) number of the mice studied. Moreover, the employment of systemic (as opposed to ovary-specific) gene targeting technology precluded the determination of the relative role of circulating as opposed to intraovarian (locally-generated) IGF-I in the maintenance of ovarian function. To provide unequivocal evidence for or against the """"""""amplification"""""""" hypothesis, they propose a series of complementary in vivo approaches designed to effect ovary (granulose cell)-selective """"""""knockout"""""""" of IGF-I. In all cases, use will be made of the promoter of mouse alpha-inhibin, chosen for its proven in vivo ability to strongly drive transgene expression in an ovary-selective fashion. Specifically, they propose to generate and characterize mice engineered to overexpress rat IGFBP-1 and thus to sequester/deplete bioavailable intrafollicular IGF-I. Mice bearing Cre/loxP-driven granulose cell-selective igf-1 gene deletion; and mice bearing Tamoxifen-inducible, Cre/loxP-driven granulose cell-selective igf-1 gene deletion. Preliminary data include generation and validation of alpha-inhibin/IGFBP-1 and alpha-inhibin/Cre transgenics, successful """"""""floxing"""""""" of the ifg-1 gene, and the generation of viable and fertile ifg-1-""""""""floxed"""""""" mutants. Insight derived from this investigation may result in the confirmation or rejection of IGF-I as an obligatory intraovarian amplifier; and development of novel widely-applicable transgenic reagents designed to effect ovary-selective deletion of a gene of interest.

Agency
National Institute of Health (NIH)
Institute
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Type
Research Project (R01)
Project #
5R01HD039432-05
Application #
6833262
Study Section
Reproductive Biology Study Section (REB)
Program Officer
Taymans, Susan
Project Start
2000-07-01
Project End
2005-06-30
Budget Start
2004-07-01
Budget End
2005-06-30
Support Year
5
Fiscal Year
2004
Total Cost
$270,000
Indirect Cost
Name
University of Utah
Department
Obstetrics & Gynecology
Type
Schools of Medicine
DUNS #
009095365
City
Salt Lake City
State
UT
Country
United States
Zip Code
84112
Gao, Shaorong; Han, Zhiming; Kihara, Maki et al. (2005) Protease inhibitor MG132 in cloning: no end to the nightmare. Trends Biotechnol 23:66-8
Gao, Shaorong; Chung, Young Gie; Parseghian, Missag H et al. (2004) Rapid H1 linker histone transitions following fertilization or somatic cell nuclear transfer: evidence for a uniform developmental program in mice. Dev Biol 266:62-75
Palter, S F; Tavares, A B; Hourvitz, A et al. (2001) Are estrogens of import to primate/human ovarian folliculogenesis? Endocr Rev 22:389-424