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.