Actions of Seminal Proteins in Mated Drosophila Females

SUMMARY From insects to mammals, seminal fluid proteins (Sfps) significantly affect the reproductive physiology of mated females, the storage and release of sperm inside females, and (in mice) even the phenotype of progeny. Males abnormal for specific Sfps are sterile or subfertile, including in humans. Some Sfps bind tightly to sperm; others are free in seminal plasma. Yet despite their importance in reproduction, little is known about exactly how Sfps act to influence the female or the behavior of sperm in females. Importantly, many Sfps evolve rapidly, consistent with roles in molecular/evolutionary sexual conflicts. Understanding functional constraints on the evolution of Sfps and the proteins with which they interact in females will guide future investigations into Sfp actions in human fertility. We will combine molecular genetic and functional approaches to investigate: (1) how Sfps interact with female molecules to elicit reproductive responses and (2) how Sfps associate with sperm to mediate their effects, as well as how both types of function have evolved. We will investigate these questions using Drosophila, a premier genetic model system for dissecting Sfp function, with extensive resources for evolutionary comparisons. Importantly, Drosophila Sfps have many molecular and phenomenological parallels to those of mammals. Aim 1 focuses on ovulin, which stimulates ovulation by inducing neuronal octopaminergic signaling. This signaling regulates muscle contraction in the female reproductive tract, relaxing the oviducts and increasing ovulation rate. Using genetic screens and signatures of protein-protein coevolution, we have identified strong candidates for the female’s receptor for ovulin (OvR). We will test these for ovulin binding and then determine OvR localization, to pinpoint the site of ovulin action. We will then examine how well different species’ ovulins mediate ovulin action and OvR binding, to elucidate the evolution of their function. In Aim 2 we will focus on seminal proteins that bind to sperm, which we have identified by their coevolution or by proteomic methods. Our recent data show that Sfps prime sperm for binding to the critical Sfp called Sex Peptide. We will ask which seminal proteins function within this priming pathway and which act independently of that pathway. We will also investigate whether female secretions are also involved in priming. Finally, we will determine the extent to which the functions of a subset of sperm-bound Sfps are conserved across related Drosophila species. Elucidating how Sfps interact with and affect the female at the molecular level, as well as how these interactions evolve, is important for understanding and diagnosing Sfp-based infertilities, in considering strategies for assisted reproductive technologies that would benefit from inclusion of critical Sfps, and for developing new ways to control dipteran insects that transmit serious diseases like dengue, Zika, and malaria.