A sperm cytoskeletal protein that signals oocyte meiotic maturation and ovulation

Caenorhabditis elegans oocytes, Like those of most animals, arrest during m eiotic prophase, Sperm promote the resumption of meiosis (maturation) and c ontraction of smooth muscle-like gonadal sheath cells, which are required f or ovulation, We show that the major sperm cytoskeletal protein (MSP) is a bipartite signal for oocyte maturation and sheath contraction. MSP also fun ctions in sperm Locomotion, playing a role analogous to actin, Thus, during evolution, MSP has acquired extracellular signaling and intracellular cyto skeletal functions for reproduction. Proteins with MSP-like domains are fou nd in plants, fungi, and other animals, suggesting that related signaling f unctions may exist in other phyla.