Preantral follicle population, spatial distribution, and ovarian tissue autotransplantation in mares

Author

Kendall A. Hyde, Southern Illinois University Carbondale

Date of Award

8-2022

Degree Name

Master of Science

Department

Animal Science

First Advisor

Gastal, Eduardo

Second Advisor

Amorim, Christiani

Third Advisor

Banz, William

Abstract

Folliculogenesis is a complex and dynamic process by which follicles grow and develop with the goal of releasing a fertilizable oocyte upon ovulation. At birth, most females have a large pool of follicles; however, this pool is naturally depleted over time until ovarian senescence occurs and ovulation ceases. Thus, the population of preantral follicles is an appealing target for studies focused on female fertility, with the hopes of extending female reproductive lifespan. The studies within this thesis characterize, for the first time in mares, the population and spatial distribution of preantral follicles within the ovary and provide preliminary results documenting the success of a novel ovarian tissue transplantation site. The results from these studies showed that the population of preantral follicles in the mare ovary is similar to that of other species and that these follicles cluster in the ovary, comparable to mice and women. Furthermore, effects of age were observed, with young mares showing (i) a higher preantral follicle population, (ii) increased preantral follicle density in portions and regions, (iii) increased follicular clustering, specifically in the lateral and dorsal area of the ovary, and (iv) more numbers of neighbors per follicle than old mares. Additionally, interesting effects of spatial distribution in the ovary were also observed, with morphologically abnormal follicles in the intermediary portion being closest to the ovarian geometric center and with a tendency for increased follicular clustering in the ventral region. Furthermore, preantral follicles with neighbors were more likely to be morphologically normal. Moreover, despite having increased odds of lacking neighbors, it was observed that morphologically normal activated follicles had a higher number of neighbors than normal resting follicles. Lastly, the novel subvulvar mucosa was comparable to the established intramuscular location for heterotopic ovarian tissue transplantation, producing similar findings for macroscopic graft appearance, follicular density, and percentages of developing/growing follicles. The findings from these studies provide vital advancements in scientific understanding of preantral folliculogenesis in the mare and build important foundations for continuing to study folliculogenesis and treatments for infertility using the mare as an animal model.