Functions of the rete ovarii in ovary development, adult homeostasis, and female reproductive longevity

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Abstract There is an urgent need to understand the factors determining female reproductive longevity. Female reproductive aging is characterized by a significant decline in reproductive function due to the sequential decrease in the number and quality of ovarian follicles that constitute the finite ovarian reserve. The rete ovarii (RO) is a conserved epithelial structure divided into 3 regions, the intraovarian rete (IOR), located within the ovary, the extraovarian rete (EOR), located in the periovarian tissue, and the connecting rete (CR), which links the EOR and IOR. The RO has been depicted for decades in anatomical context, and is a possible contributor to gynecological disease, yet its function has never been thoroughly investigated. The reproductive longevity of females is determined by three main factors: 1) the size of the initial primordial follicle pool, 2) the rate of ovulation and atresia during the fertile window, and 3) perturbations, such as changes in metabolic status or hormone levels, which affect ovarian function and follicle growth. The objective of this application is to elucidate the contribution of the RO to each of these determining factors. To allow visualization and functional investigation of the ovary in situ, I developed tissue clearing and 3D imaging methods that suggest a role for the rete in the assembly of ovarian cells into ovigorous cords and subsequent specification of medullary and cortical domains. I found that the RO remains closely associated with the ovary throughout adulthood, and preliminary ovary transplantation experiments suggest that the host EOR/CR reestablishes a connection to the IOR of the grafted ovary. Our transcriptomic data of the RO shows enrichment of secretory and metabolic pathways consistent with the finding that Dextran injected into the EOR is transported to the ovary. These data have led to the central hypothesis that the RO plays critical roles in the establishment of the ovarian reserve and in the regulation of ovarian follicle growth in response to physiological cues. This hypothesis will be tested by pursuing three specific aims: (1) (K99) Characterize the contribution of the RO to the development of the ovary and the establishment of the ovarian reserve; (2) (K99/R00) Define the functional differences between EOR and IOR in adult homeostasis and (3) (R00) Investigate the changes of the RO in response to physiological cues. Discovering a role for the rete ovarii in the establishment of the ovarian reserve and in the regulation of adult follicle growth under homeostatic or perturbed conditions will situate the RO as a new candidate in the search for determinants of female fertility and reproductive longevity. In addition, the approaches I develop will be useful in future investigations of interactions between the ovary and other extrinsic tissues. Pursuit of these aims requires training in single-cell RNA sequencing, mouse surgery and virally-mediated approaches for manipulating gene expression. I have assembled an advisory committee chaired by Dr. Capel, and we designed a training plan that will provide me with the skills required to run a productive, independent developmental and reproductive biology laboratory.