Seminal fluid plays an essential role in promoting male reproductive success and modulating female physiology and behavior. In the fruit fly, Drosophila melanogaster, Sex Peptide (SP) is the best-characterized protein mediator of these effects. It is secreted from the paired male accessory glands (AGs), which, like the mammalian prostate and seminal vesicles, generate most of the seminal fluid contents. After mating, SP binds to spermatozoa and is retained in the female sperm storage organs. It is gradually released by proteolytic cleavage and induces several long-term postmating responses, including increased ovulation, elevated feeding, and reduced receptivity to remating, primarily signaling through the SP receptor (SPR). Here, we demonstrate a previously unsuspected SPR-independent function for SP. We show that, in the AG lumen, SP and secreted proteins with membrane-binding anchors are carried on abundant, large neutral lipid-containing microcarriers, also found in other SP-expressing Drosophila species. These microcarriers are transferred to females during mating where they rapidly disassemble. Remarkably, SP is a key microcarrier assembly and disassembly factor. Its absence leads to major changes in the seminal proteome transferred to females upon mating. Males expressing nonfunctional SP mutant proteins that affect SP’s binding to and release from sperm in females also do not produce normal microcarriers, suggesting that this male-specific defect contributes to the resulting widespread abnormalities in ejaculate function. Our data therefore reveal a role for SP in formation of seminal macromolecular assemblies, which may explain the presence of SP in Drosophila species that lack the signaling functions seen in D. melanogaster.

精液在促进男性生殖成功和调节女性生理和行为方面起着至关重要的作用。在果蝇中，黑腹果蝇, 性肽 (SP) 是这些影响的最佳表征的蛋白质介质。它由成对的雄性副腺 (AGs) 分泌，AGs 与哺乳动物的前列腺和精囊一样，产生大部分精液内容物。交配后，SP 与精子结合并保留在雌性精子储存器官中。它通过蛋白水解逐渐释放并诱导几种长期的交配后反应，包括排卵增加、摄食增加和对重新交配的接受性降低，主要通过 SP 受体 (SPR) 发出信号。在这里，我们展示了一个以前没想到的 SP 独立于 SPR 的函数。我们表明，在 AG 腔中，SP 和具有膜结合锚的分泌蛋白承载在丰富的大型中性脂质微载体上，在其他表达 SP 的微载体中也发现了这种情况。果蝇属。这些微载体在交配过程中被转移到雌性体内，在那里它们会迅速分解。值得注意的是，SP 是一个关键的微载体组装和拆卸因素。它的缺失导致交配时转移给雌性的精液蛋白质组发生重大变化。表达影响 SP 与女性精子结合和释放的非功能性 SP 突变蛋白的男性也不会产生正常的微载体，这表明这种男性特异性缺陷导致了射精功能的广泛异常。因此，我们的数据揭示了 SP 在精液大分子组装体形成中的作用，这可以解释 SP 在缺乏D中所见信号功能的果蝇物种中的存在。黑腹果蝇.