Growth of the ovarian follicle is a developmental program dependent on stage specific expression of genes that control granulosa cell proliferation and differentiation. Recent studies have identified novel cell signaling cascades as well as new components of known cascades that impact granulosa cell function. Specifically, FSH impacts the PI3-kinase, PKB/AKT cell survival pathway in several ways. FSH induces and phosphorylates the PKB-related kinase, serum and glucocorticoid induced kinase, Sgk via PKA. In contrast, FSH like IGF-1 stimulates the phosphorylation of PKB and the down-stream transcription factor Foxo1 or FKHR (forkhead homolog of rhabdomyosarcoma=forkhead). Although the functional role of FKHR in the ovary is not yet known, we hypothesize that FKHR plays a major role in regulating granulosa cell function during follicular growth. We hypothesize that FSH engages the PI3-K/PKB/FKHR pathway by activating a novel class of cAMP binding proteins that have guanine nucleotide exchange (GEF) activity (cAMP-GEFs or Epacs, Exchange proteins directly activated by cAMP) and activate small GTPases. Thus, FSH regulates two major cAMP dependent cell signaling cascades in granulosa cells to promote follicular cell proliferation and differentiation and restrict apoptosis. Cell specific expression of transcriptional co-regulatory molecules provides another novel mechanism for FSH regulated control of granulosa cell differentiation. TAFII105, a close relative of TAFII130, is a component of the TFIID transcriptional complex that is expressed in a cell- and tissue-specific manner. The disruption of TAFII105 leads to aberrant follicular growth, altered expression of FSH-regulated genes (aromatase, cyclin D2, and SF-2 (LRH-1/NR5A2), a close relative of SF-1 (NR5A1). Expression of TAFII105 is increased by FSH and the emergence of the altered phenotype appears at or near puberty. We hypothesize that in the absence of TAFII105, FSH is unable to induce critical checkpoints of apoptosis or proliferation. Wnt-4, a Frizzled receptor ligand is essential for normal ovarian organogenesis. In its absence ovaries resemble testicular structures. In addition, Wnt-4 is expressed in the adult ovary. In vivo as well as in cultured granulosa cells Wnt-4 expression is regulated by FSH, LH and cAMP. Wnt-4 has been implicated in regulating the expression of specific genes (DAX and inhibin-alpha) via its interactions with orphan members of the nuclear receptor superfamily, SF-1 (possibly SF-2). These observations indicate that there are important functional interactions between the Wnt cascade and the actions of the gonadotropins to regulate target genes important for early follicle growth. However, proof of this has not yet been demonstrated in vivo because Wnt-4 KO mice die at birth. To integrate the novel actions of FSH with new cascades that impact granulosa cell function, the following specific aims have been designed. I) Determine the hormonal regulation and function of FKHR in the rodent ovary. 2) Determine the specific mediators of FSH signaling in granulosa cells. 3) Determine the molecular, cellular and hormonal basis of the altered ovarian phenotype of the TAFII105 null mice. 4) Determine the function of Wnt-4 in the adult ovary.
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