Proteolysis Regulators In Drosophila Melanogaster Seminal Fluid

Abstract

In Drosophila melanogaster, seminal fluid proteins (Sfps) are transferred to females during mating and, together with sperm, are necessary for the many post-mating responses elicited in females. Identifying the functions of all individual Sfps is challenging, given the large number of Sfps and the possibility that many have redundant functions. One way to tackle this challenge is to focus on key regulators of pathways that involve multiple Sfps. Proteases are good candidates for these regulators. Proteases and protease inhibitors have been identified in the ejaculates of animals in taxa ranging from invertebrates to mammals, and form a major protein class among Drosophila Sfps. Other than a single protease cascade in mammals that regulates seminal clot liquefaction, no proteolytic cascades (i.e. pathways with at least two proteases acting in sequence) have been identified in seminal fluids. Though several Drosophila Sfps are proteolytically cleaved either during or after mating, little is known about the proteases involved in these cleavage events or the physiological consequences to the female of proteolytic activity in the seminal fluid. This thesis addresses the functions of Sfp proteases in Drosophila. Chapter 1 provides an overview of seminal fluid proteolysis regulators. In Chapter 2, I report that a D. melanogaster Sfp, the predicted serine protease 'seminase', coordinates two pathways in the mated female. One leads to the proper localization and long-term function of the Sfp sex peptide. The second leads to activation of the predicted astacin metalloprotease CG11864, through an apparent protease cascade. Chapter 3 presents experimental evidence that CG11864 is activated by proteolysis at a predicted pro-peptide cleavage site and that the male and female coordinate for efficient processing of CG11864's substrates. In Chapter 4, I focus on the proteolytic processing of ovulin and describe methods to quantify its processing rate that can be used in the future to identify additional proteins required for ovulin processing. Chapter 5 describes a computational method used to identify candidate Sfps, including proteolysis regulators, based on transcriptional profiles, and provides experimental validation of those predictions. Finally, Chapter 6 discusses future directions for research of the seminase/CG11864 protease cascade.