The Drosophila seminal fluid protein Acp26Aa stimulates release of oocytesby the ovary

Mating stimulates the rate of egg-laying by female insects, In Drosophila m elanogaster this stimulation is initially caused by seminal fluid molecules transferred from the male (Acps or accessory gland proteins; reviewed in [ 1-3]), Egg-laying is a multi-step process, It begins with oocyte release by the ovaries, followed by egg movement down the oviducts and the deposition of eggs onto the substratum, Although two Acps are known to stimulate egg- laying [4,5], they were detected by assays that do not discriminate between the steps of this process or allow examination of its earliest changes [4- 7]. To determine how egg-laying is regulated, we developed a generally appl icable assay to separate the process into quantifiable steps, allowing us t o assess the ovulation pattern and rate of egg movement. As the steps are i nterdependent yet potentially subject to independent controls, we determine d the contribution of each step and effector independent of the others. We used a statistical method [8,9] that separately considers and quantifies ea ch 'path' to a common end. We found that the prohormone-like molecule Acp26 Aa [5,10] stimulates the first step in egg-laying - release of oocytes by t he ovary. During mating, Acp26Aa begins to accumulate at the base of the ov aries, a position consistent with action on the ovarian musculature to medi ate oocyte release, Understanding how individual Acps regulate egg-laying i n fruitflies will help provide a full molecular picture of insects' prodigi ous fertility, of reproductive hormones, and of the roles of these rapidly evolving proteins [11,12].