Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biochemistry

Supervisor

Dr. Bonnie Deroo

Abstract

Follicle stimulating hormone (FSH) promotes granulosa cell (GC) proliferation, differentiation, and steroidogenesis. This series of events is critical for female fertility, and culminates in the formation of mature follicles responsive to the surge of luteinizing hormone (LH) that triggers ovulation. Ephrins (Efn genes) and Eph receptors (Eph genes) are membrane-associated signaling molecules that mediate communication at sites of cell-cell contact, and have been extensively studied in the context of embryonic development. The published literature contains several reports of ovarian Eph and Efn expression, although their precise roles in the ovary are unknown. Dysregulation of Efna5 in GCs of the subfertile Esr2-/- mouse suggests a role for Eph-ephrin signaling in ovarian function. We sought to investigate Eph receptors and ephrins in the mouse ovary using gonadotropin-stimulated animal models and cultured GCs. We identified several Efn and Eph genes for which expression is enhanced in GCs of the gonadotropin-stimulated mouse. Furthermore, we determined that cultured GCs stimulated with recombinant ephrin-A5 or EphA5 exhibit reduced cell spreading or adhesion, respectively, indicating a cell-autonomous response to Eph-ephrin stimulation. In order to ascertain the importance of ephrin-A5 in female fertility, we performed a reproductive assessment of females lacking Efna5, the sole ephrin-encoding gene upregulated by FSH in GCs. Efna5-/- females are subfertile and exhibit an impaired response to LH, displaying attenuated ovulatory potential, reduced ovarian expression of Pgr, Ptgs2, and Adamts4, as well as abnormal follicle rupture. We also found an increased incidence of multi-oocyte follicles in adult, but not juvenile, Efna5-/- females, indicating follicle merging. Finally, we determined that the mouse genomic region upstream of Epha5 is transcriptionally activated by cAMP in a protein kinase A-dependent manner. Transcriptional activation of Efna5, Epha3, Epha5, Epha8, and Ephb2 is reduced in GCs of eCG-treated Esr2-/- females, which exhibit impaired cAMP production. These results suggest that cAMP is a novel transcriptional regulator for several Eph and Efn genes. Our findings establish a place for ephrins and their receptors within the current model of gonadotropin-dependent follicle growth and ovulation, and identify cAMP as a novel transcriptional regulator of Epha5 and possibly other Efn and Eph genes.


Included in

Endocrinology Commons

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