Investigating the role of CDC42 and RAC1 in germline cyst breakdown and primordial follicle formation

The National Institute of Child Health and Human Development (NICHD), a component of the Department of Health and Human Services National Institutes of Health, awarded $148,994 to the University of Wisconsin System (operating through its University of Wisconsin - Madison Division) on January 1, 2026, under the Child Health and Human Development Extramural Research program (CFDA 93.865, assistance type Project Grant F31HD119998).

The recipient will conduct research investigating the role of the Rho GTPases CDC42 and RAC1 in germline cyst breakdown and primordial follicle formation. The research addresses the biological mechanisms governing ovarian reserve establishment, which occurs between weeks 9 to 13 of human gestation and directly determines a woman's reproductive capacity. Aim 1 will establish whether CDC42 and RAC1 are present in the ovary during germline cyst breakdown and primordial follicle formation and interact with the protein CDH1. Aim 2 will test whether CDC42 and RAC1 are essential for proper primordial follicle formation. The long-term goal is to understand cell-cell interactions and signals directing the transition from oocyte-oocyte to oocyte-pre-granulosa cell connections.

Period of performance runs from January 1, 2026, through July 26, 2028. Place of performance is Madison, Wisconsin 53715.

Abstract

In the united states today, women are delaying having children. This is a critical issue because as a woman ages, her reproductive capability decreases as the ovarian reserve diminishes. Additionally, approximately 1% of women in the united states are diagnosed with primary ovarian insufficiency, by which the quantity and/or quality of the ovarian reserve is reduced. The ovarian reserve is formed between weeks 9 to 13 in gestation in humans and at the time of birth in mice; once IT's depleted, ovulation and conception can no longer occur. The ovarian reserve is comprised of primordial follicles, a singular oocyte surrounded by supporting pre-granulosa cells. The establishment of ovarian reserve is the result of germline cyst breakdown. During this process, connections between sister oocytes breakdown and singular oocyte primordial follicles are formed. The long- term goal of the jorgensen lab is to understand cell-cell interactions and signals that direct germline cyst breakdown and primordial follicle formation. The objective of this proposal is to determine the role RHO gtpases, CDC42 and RAC1, play in modulating cell-to-cell connections during the transition from oocyte- oocyte to oocyte-pre-granulosa cells when new primordial follicles form. Aim 1 will test the idea that CDC42 and RAC1 are present in the ovary during germline cyst breakdown and primordial follicle formation and interact with CDH1 in the ovary. IT has been suggested that CDC42, RAC1, and CDH1 are essential for proper primordial follicle formation but the connection between these three proteins has yet to be explored. Preliminary data suggest that CDC42 and CDH1 are both oocyte-specific throughout the processes of germline cyst breakdown and primordial follicle formation. Aim 2 will test the hypothesis that CDC42 and RAC1 are essential for proper primordial follicle formation. Using conditional knockout mice, I will characterize the phenotype and functionality of the ovary absent of CDC42 and/or RAC1 prior to germline cyst breakdown. Additionally, I will employ live imaging of germline cyst breakdown and primordial follicle formation in wild-type and conditional knockout animals to understand how the loss of CDC42 and/or RAC1 affects germline cyst breakdown and primordial follicle formation in real-time. In total, these studies will uncover the role of CDC42 and RAC1 in germline cyst breakdown and primordial follicle formation which will provide insight into early ovarian development and ultimately fertility.