A Sperm Cytoskeletal Protein That Signals Oocyte Meiotic Maturation and Ovulation

TLDR

In Caenorhabditis elegans, oocytes arrest in meiotic prophase until sperm signals trigger maturation and gonadal sheath contraction, and MSP‑like proteins are conserved across plants, fungi, and animals, hinting at a broader signaling role. The study demonstrates that MSP acts as a dual signal for oocyte maturation and sheath contraction, also serving as an actin‑like cytoskeletal element in sperm motility, illustrating its evolutionary acquisition of both extracellular signaling and intracellular structural roles in reproduction.

Abstract

Caenorhabditis elegans oocytes, like those of most animals, arrest during meiotic prophase. Sperm promote the resumption of meiosis (maturation) and contraction of smooth muscle–like gonadal sheath cells, which are required for ovulation. We show that the major sperm cytoskeletal protein (MSP) is a bipartite signal for oocyte maturation and sheath contraction. MSP also functions in sperm locomotion, playing a role analogous to actin. Thus, during evolution, MSP has acquired extracellular signaling and intracellular cytoskeletal functions for reproduction. Proteins with MSP-like domains are found in plants, fungi, and other animals, suggesting that related signaling functions may exist in other phyla.