Doctor of Philosophy
Dr. Bonnie Deroo
Folliculogenesis is the ovarian process in which a follicle, consisting of an oocyte surrounded by granulosa cells (GCs), theca cells, a fluid-filled antrum, and a basal lamina separating GCs from TCs, grows and differentiates, culminating in development of a fertilizable oocyte. TCs under the influence of luteinizing hormone (LH) produce androgens. GCs under the influence of follicle stimulating (FSH) hormone proliferate, produce steroid hormones, and differentiate to become responsive to the surge of LH that initiates ovulation. The cellular processes of folliculogenesis require cell-extracellular matrix (ECM) interactions. Spondin 1 (SPON1) is an ECM protein primarily studied for its role in nervous system development as a nerve outgrowth signalling molecule, but is also known to affect cell viability, differentiation, and migration in non-neural tissues and cells. Evidence that Spondin 1 is functional within the ovary includes its discovery in bovine follicular fluid, its increased mRNA expression in response to estrogen in uterus and mammary gland, its decreased mRNA expression in GCs of mice null for estrogen receptor β, and its overexpression in ovarian cancer. Despite the possible importance of Spondin 1 in the ovary it has never been characterized in this tissue. This study was undertaken with the goal of elucidating roles of Spondin 1 in the ovary. Experiments with the human GC tumour cell line, KGN, found that Spondin 1 increases cell viability and proliferation possibly by activating the mTORC1 complex, and decreases cAMP-induced progesterone production by inhibiting cAMP-induced STAR transcription. Experiments with mouse primary GCs corroborated the effects of Spondin 1 on granulosa cell viability and again found a role for Spondin 1 in steroidogenesis, however, progesterone production was increased in these cells. Interestingly, Spondin 1 co-localized with vasculature markers in the mouse ovary and uterus, two of only a few tissues where the vascular network is dynamic, suggesting a role in angiogenesis. Finally, characterization of the reproductive phenotype of Spon1-/- females revealed that loss of Spondin 1 results in subfertility marked by smaller litter sizes, decreased ovulation capacity, and smaller ovarian weight. These findings support an important role for Spondin 1 in ovarian folliculogenesis and maintenance of optimal fertility.
O'Flynn, Caitlin, "Investigating the role of the extracellular matrix protein, Spondin 1, in ovarian folliculogenesis" (2015). Electronic Thesis and Dissertation Repository. 3169.