Nematode sperm: amoeboid movement without actin

Nematodes produce amoeboid sperm that crawl over surfaces in a manner reminiscent of many actin-rich cells. However, these sperm contain no F-actin, and their motility is powered by a dynamic filament system composed of polymers of the 14-kDa major sperm protein (MSP). These simple cells use this unique motility apparatus exclusively for locomotion. Recent studies have capitalized on this feature to explore the key structural properties of MSP related to its role in motility and to reconstitute the motility apparatus both in vivo and in vitro. This review discusses how these investigations have laid the foundation for understanding the physical basis of amoeboid movement by identifying the mechanistic properties shared by the MSP-based machinery and the more familiar actin-based systems.