(292) The Spatiotemporal Localization of E-cadherin Throughout the Process of Germline Cyst Breakdown and Primordial Follicle Formation 

The Spatiotemporal Localization of E-cadherin Throughout the Process of Germline Cyst Breakdown and Primordial Follicle Formation 

Cora Thompson1, Jonathan Lim 1, Joan S. Jorgensen1 

1. Department of Comparative Biosciences, University of Wisconsin – Madison, United States 


Abstract Text: The female reproductive lifespan is determined during fetal development by the quantity and quality of primordial follicles formed. Primordial follicles form through germline cyst breakdown. Germline cysts arise when oocytes divide mitotically but do not complete cytokinesis and thus are interconnected. These connections are broken when pre-granulosa cells invade resulting in the surviving oocyte(s) surrounded by pre-granulosa cells forming a primordial follicle. Epithelial cadherin (E-cadherin; CDH1) is a key structural transmembrane protein involved in homotypic and heterotypic cell-to-cell connections. Within both the developing and mature ovary, E-cadherin shows oocyte-specific expression. In the ovary, E-cadherin has been shown to be present in germline cysts particularly at the junctions between oocytes. Notably, eliminating E-cadherin from differentiating oocytes results in the formation of fewer primordial follicles. It is not known how the distribution of E-cadherin influences oocyte survival and proper primordial follicle formation. Thus, we hypothesize that unequal distribution of E-cadherin is essential to maintain connections between oocytes within germline cysts and this unequal distribution will resolve when the oocyte is surrounded by somatic pre-granulosa cells at the culmination of primordial follicle formation. We will test this hypothesis by evaluating E-cadherin expression in 2D and 3D analyses. Results from 2D ovary section data show that 80.81% of oocytes show asymmetric E-cadherin distribution as measured by immunofluorescence intensity in post-natal day 0 (P0) and P2 ovaries. There was no significant difference between oocytes measured at P0 compared to P2 (p=0.17). E-cadherin is an essential part of cell-to-cell adhesion and higher E-cadherin expression may facilitate stronger cell-to-cell connections. It is known that oocytes in the germline cyst must show regionality and facilitate connections with neighboring oocytes to promote the directional transfer of essential RNA, proteins, and organelles. Thus, we propose that E-cadherin directionality may help to facilitate proper germline cyst breakdown by promoting collaborations with additional mediators within the oocyte to prepare an environment that encourages a single oocyte to be surrounded by, and connected to pre-granulosa cells that will establish healthy primordial follicles. Our studies will examine E-cadherin distribution in oocytes in germline cysts compared to oocytes in primordial follicles. In addition, we will investigate whether other cytoskeletal elements direct E-cadherin regionality and stability at the cell membrane. Finally, we are also investigating whether Rho GTPases CDC42 and RAC1 impact E-cadherin stability as has been shown in other models. This study will elucidate the critical role of E-cadherin and supporting factors in proper germline cyst breakdown and primordial follicle formation providing valuable insight into determinants of a healthy ovarian reserve and female fertility. This work is supported by the NIH R01 HD075079 grant (JSJ).