Function of MAP2D in Granulosa Cells

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DESCRIPTION (provided by applicant): Ovarian follicular maturation is a dynamic process that requires exquisite regulation. Follicles are restrained at the preantral (PA) stage until they are stimulated by follicle stimulating hormone (FSH). FSH signals by activating its receptor on the surface of granulosa cells via cAMP and its target protein kinase A (PKA). In response to FSH, granulosa cells proliferate and differentiate to a mature phenotype competent to respond to the preovulatory (PO) surge of luteinizing hormone (LH). LH then acts on these PO cells to activate PKA to promote terminal differentiation of granulosa into luteal cells, cessation of cell proliferation, and ovulation. While both FSH and LH signal to activate PKA, the pathways by which PKA directs responses are both similar and different in granulosa cells of PA versus PO follicles. For example, both FSH and LH promote histone H3 phosphorylation by a pathway that is blocked by the selective PKA inhibitor peptide myristoylated (Myr-) PKI. However, while both FSH and LH promote activation of ERK in a PKA-dependent manner (blocked by Myr- PKI), FSH does not promote activation of the upstream ERK kinase MEK in PA cells while LH promotes activation of MEK in PO cells. Additionally, there are numerous genes whose regulation by FSH in PA versus LH in PO cells is opposite, such as inhibin-alpha, aromatase, and LHR. The specificity of PKA action is thought to occur by the targeting of PKA and its substrates to specific cellular locales by virtue of its binding to A kinase anchoring proteins (AKAPs). We have shown that granulosa cells of PO follicles are distinguished from those of PA follicles by the presence of an 80 kDa AKAP that we recently identified as microtubule associated protein (MAP) 2D. We hypothesize that MAP2D functions as a signaling scaffold in PO granulosa cells to direct LH signals from PKA to a distinct set of substrates. Aim 1 will test the hypothesis that MAP2D functions as a scaffold to coordinate signal transduction pathways in PO granulosa cells; Aim 2 will test the hypothesis that MAP2D is obligatory for LH to signal to select pathways hi PO granulosa cells; Aim 3 will test the hypothesis that MAP2D is not associated microtubules and that the phosphorylation of MAP2D at specific sites regulates its association with PKA; and Aim 4 will test, the hypothesis that MAP2D is an Rl-preferential AKAP. Understanding how follicular maturation is regulated can translate into safer and more effective treatments for fertility.