Intercellular communication between sperm and oocyte is essential for successful sexual reproduction. In nematodes, for example, the major sperm protein (MSP) acts as a hormone that promotes oocyte meiotic maturation. But how do sperm, which lack the usual protein secretion machinery, release this cytoskeletal protein? Kosinski and co-workers now reveal that in C. elegans, MSP is exported from sperm through a novel vesicle-budding mechanism (see ). Their results suggest that the localized assembly of MSP filaments in spermatozoa and spermatids drives the formation of plasma membrane protrusions on the cell body, which form vesicles with inner and outer membranes between which MSP is sandwiched. These vesicles then function as MSP time-release capsules. Because proteins with MSP domains are found in fungi, plants and animals, this unconventional protein export pathway might also function in other developmental situations.
