Exosomes, secreted from secondary cells of the male accessory glands, fuse with sperm and female epithelia to modulate reproductive function. Laura Corrigan¹, Shih-Jung Fan¹, Carina Gandy¹, Aaron Leiblich¹, Rachel Patel¹, Siamak Redhai¹, John Morris¹, Freddie Hamdy², Clive Wilson¹. 1) Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom; 2) Nuffield Department of Surgical Sciences, University of Oxford, Oxford, United Kingdom.

   Reproduction involves more than just the transfer of gametes from males to females: it is also dependent upon secreted signals that are transported in the seminal fluid during mating, and influence sperm and female behaviour. The accessory glands of Drosophila males, along with the seminal vesicles and ejaculatory duct, secrete components of the seminal fluid. The accessory gland secretes specific factors that activate sperm, promote sperm storage and modulate female post-mating behaviours. Each gland contains approximately 40 specialised secondary cells, which selectively grow as flies age and mate. Here we show that these cells secrete exosomes, membrane-bound nanoparticles formed by vesicular budding inside the late endosomal multivesicular body (MVB). These intraluminal vesicles are released as exosomes when the MVB fuses with the plasma membrane. Intracellular secretory compartments of secondary cells are huge, 2-10m in diameter, allowing us to visualise intraluminal vesicle formation, exosome secretion and fusion in living and fixed tissue. We show that exosome production and secretion is regulated by mating and that exosomes are transferred to females during mating, where they fuse with sperm and specific epithelial cells of the female reproductive tract. Blocking secondary cell exosome production suppresses post-mating effects on female behaviour, suggesting that these exosomes act as vehicles to transfer important signals from males to females and providing novel in vivo evidence that exosomes have important physiological roles in reproduction. Exosomes produced by the prostate also fuse with sperm in vitro and transfer signalling tools that stimulate motility. Our data suggest that this mechanism may be conserved in higher eukaryotes, while raising the possibility that male exosomes can also reprogramme female cells.