Ovarian follicle development involves complex cellular and molecular processes that ultimately lead to either follicle atresia or ovulation. Despite extensive research, the mechanisms underlying these processes remain incompletely understood. This dissertation investigates the roles of vascularization and transcription factors in mouse ovarian functions.The Semaphorin 3E (Sema3E)-Plexin-D1 pathway has been well-studied in other tissue for its role in regulating vascularization. However, its expression and function in the ovary remain unknow. In Chapter 2, I explored the role of this pathway in the ovary during the preovulatory stage. Sema3e and Plxnd1 are regulated by transcription factor CCAAT/enhancer-binding protein α and β (C/EBPα/β) through alterations in chromatin accessibility in ovarian granulosa cells. The Semaphorin 3E-Plexin-D1 pathway is shown to regulate granulosa cell luteinization, ovarian vascularization and inflammation, thereby influencing ovulation and subsequent corpus luteum formation. C/EBPα/β are regulated by the luteinizing hormone (LH) surge in the ovary and are indispensable for ovulation and granulosa cell luteinization. Evidence suggests that follicle-stimulating hormone (FSH) may also regulate Cebpa/b in the ovary. However, the mechanism through which FSH regulate Cebpa/b and the function of these transcription factors under FSH regulation remain unknown. In Chapter 3, I determined that FSH regulates the expression of Cebpa/b primarily through extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. Bulk RNA sequencing analysis reveals that C/EBPα/β downstream of FSH regulates genes involved in steroidogenesis and angiogenesis during follicle maturation. While C/EBPα/β are essential for ovulation, their direct effects on the preovulatory stages remain unclear. In Chapter 4, I compared two genetically modified mouse models in which the expression of Cebpa/b was manipulated to different levels at different times in granulosa cells during preovulatory stages. The deletion of Cebpa/b during follicle development results in blocked ovulation, whereas deletion following the LH surge leads to reduced ovulation. Bulk RNA sequencing analysis reveals that C/EBPα/β regulate gene expression via different mechanisms. These findings highlight the complex regulatory mechanisms of C/EBPα/β on its downstream targets. This work provides new insights into the cellular and molecular regulation of ovarian follicle maturation and ovulation, offering potential targets for therapeutic intervention in reproductive disorders.