Date of Completion

6-21-2018

Embargo Period

6-7-2021

Keywords

Ovulation, Octopamine, Matrix Metalloproteinase, Drosophila

Major Advisor

Dr. Jianjun Sun

Associate Advisor

Dr. Karen Menuz

Associate Advisor

Dr. Joseph LoTurco

Associate Advisor

Dr. Andrew Moiseff

Associate Advisor

Dr. Randall Walikonis

Field of Study

Physiology and Neurobiology

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Ovulation, the liberation of a mature oocyte from its follicle within the ovary, is a requisite step for reproduction, however there is a lack of understanding of the genetic regulation of this process. The goal for this dissertation was to describe the process of ovulation in Drosophila to demonstrate the utility for using it as a model to study ovulation. Firstly, the enzyme required for follicular rupture in Drosophila was identified as Matrix metalloproteinase 2 (Mmp2). Mmps have been implicated in mammalian ovulation for decades, but this study demonstrated the first genetic evidence of its function. Furthermore, it was shown that after ovulation, the somatic cells that enveloped the oocyte remained in the ovary after ovulation and formed a corpus luteum-like structure, which highlighted the strong resemblance of Drosophila ovulation to mammalian ovulation at both cellular and molecular levels. The stimulus for activating Mmp2 activity was identified as octopamine (OA). Through development of an ex vivo follicle rupture assay, activation of the OA receptor Oamb (octopamine mushroom body receptor, a G-protein coupled receptor) on mature follicle cells was found to be both essential and sufficient to induce follicle rupture. Further, the signal transduction of the Oamb receptor was described as Gαq/IP3R signaling. Through use of ex vivo and in vivo calcium imaging, store-operated calcium entry was also demonstrated to be required for ovulation. Oamb has been implicated in many physiological and behavioral aspects of Drosophila, but this was the first description of its signal transduction pathway. Lastly, the coordination of the gain-of-competency for a follicle to be able to receive and respond to an ovulation stimulus was investigated. Hindsight, a zinc-finger transcription factor which was specifically expressed in stage-14 follicle cells, was identified as being required for ovulation through the regulation of Mmp2 and Oamb expression. The mammalian homolog to Hindsight, Ras-Responsive Element Binding Protein-1, was able to replace the function of Hindsight in ovulation, further demonstrating the conservation between fly and mammalian ovulation. Altogether, work from this dissertation describes ovulation in Drosophila at unprecedented resolution and provides a strong basis for using Drosophila as a model for further investigation.

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