Molecular Mechanisms regulating Primordial Follicle Formation

PROJECT SUMMARY/ABSTRACT Despite its importance to the continuation of species, the differentiation of primordial germ cells into functional oocytes is poorly understood. Primordial germ cells begin to differentiate into oocytes during embryonic development in the mouse. The oocytes develop in clusters called germline cysts, a conserved phase of oocyte development in both vertebrates

and invertebrates. Oocytes progress through prophase I of meiosis and arrest at the diplotene stage. They then undergo primordial follicle formation during which germ cell cysts break apart into single oocytes (cyst breakdown) and granulosa cells migrate around individual oocytes to form primordial follicles. During the process of cyst breakdown, a subset of cells in each cyst die

with only a third of the initial number of oocytes surviving to form primordial follicles. The mechanisms that control assembly of primordial follicles are not well understood. The long-term goal is to understand molecular and cellular mechanisms used to establish the primordial follicle pool in the mouse ovary. Published work from the applicant’s lab using ovary organ culture

suggests that signaling through the receptor tyrosine kinase, KIT, promotes the assembly of primordial follicles. In addition, preliminary data suggest that KIT can signal through the phosphoinositide 3-kinase (PI3K) pathway to promotes primordial follicle formation but that other signals besides KIT such as insulin may be important. The objective of this proposal is to

understand the role to understand the role of insulin in primordial follicle formation. The central hypothesis of the proposed research is that in addition to KIT signaling, insulin signaling promotes primordial follicle assembly through the PI3K signal transduction pathway activating molecules that promote follicle formation and repressing molecules that maintain oocytes in

cysts. The specific aims of this research are to: 1) elucidate the role of insulin signaling in primordial follicle formation; and 2) examine primordial follicle formation in a mouse model of gestational diabetes. These goals will be achieved through techniques including immunohistochemistry, confocal microscopy, ovary organ culture, and genetics. Research

proposed in the current application is significant because it will enhance current knowledge by elucidating the mechanisms important to establish the primordial follicle pool. Results obtained in this grant will help improve research efforts in ovarian biology and in treatment of conditions causing female infertility such as primary ovarian insufficiency.