Signaling Mechanisms and Genetic Regulation of Follicle Cell Maturation and Ovulatory Competence in Drosophila

Female fertility is essential for reproduction, and within the ovary requires the proper development of a competent preovulatory follicle and subsequent ovulation. Follicle development into ovulatory competency is intricately orchestrated through successions of temporally coordinated signaling networks within the somatic follicle cells. However, there still remains a lack of understanding of the genetic regulation of this process. The objective of this dissertation is to characterize this process of follicle maturation and ovulatory competency in Drosophila to establish its utility as a model system to study folliculogenesis and ovulation. How follicle cells develop in the final stages leading up to ovulation has been very understudied in Drosophila. This work focuses on investigating this final maturation and understanding the conserved signaling mechanisms governing it. Firstly, a role for ecdysteroid signaling operating in mature follicle cells to control ovulation was identified. Ecdysteroid signaling had been known to regulate earlier steps of oogenesis, but this study demonstrated another requirement for this signaling in ovulatory competency, reminiscent to progesterone signaling essential for mammalian ovulation. In addition, this work describes the discovery of a novel follicle cell transition occurring in these final maturation stages that is characterized by the dynamic change in expression of follicle cell factors and these findings indicate this follicle cell transition is critical for gaining ovulatory competency. Lastly, a novel role for the NR5A nuclear receptor Ftz-f1 in regulating this final follicle cell maturation process is identified. Furthermore, the mammalian homolog of Ftz-f1, steroidogenic factor 1 (SF-1), was able to replace the function of Ftz-f1 in follicle cell maturation, demonstrating the functional conservation of this process. In summary the work in this dissertation elucidates signaling mechanisms governing follicle cell maturation and ovulatory competency in Drosophila. These findings provide enhanced evidence for the conserved nature of these ovarian processes and signifies a strong foundation to utilize Drosophila as a model to study folliculogenesis and ovulation