Reproductive functions of venerose, a sexually transmitted sugar in the fruit fly Drosophila melanogaster

Abstract

Seminal fluid is more than just carrier for sperm. Its complex composition, consisting of ions, peptides, proteins, lipids, and carbohydrates, actively communicates with the female reproductive system. However, the significance of non-protein substances such as present in seminal fluid remains largely underexplored. In this thesis, I utilized Drosophila melanogaster to investigate the influence of a seminal sugar on female reproduction. I found that a significant amount of phospho-galactoside named ‘venerose,’ present in the male seminal fluid, is incorporated into female ovaries and enters the haemolymph. The findings revealed that venerose acts as a signaling molecule for promoting the mating-induced germline stem cell (GSC) proliferation and enhancing sperm storage, particularly in undernourished females. Circulating venerose directly activates Dh44-PI neurons, nutrient-sensing cells in the brain. The secreted Dh44 stimulates GSC proliferation by activating its receptor in terminal filament cells and enhancing Decapentaplegic (Dpp) signaling. Additionally, the evidence indicates that undernourished females exhibit the increased Dh44 release in response to venerose. This increased Dh44 secretion delays the removal or expulsion of the ejaculate (sperm ejection), thereby increasing the sperm uptake and venerose absorption. This study establishes a framework for understanding the function of nutrient-like substances abundant in seminal fluid and provides mechanical insights into how females assess courtship feeding for sexual selection.