Localized depolymerization of the major sperm protein cytoskeleton correlates with the forward movement of the cell body in the amoeboid movement of nematode sperm

The major sperm protein (MSP)-based amoeboid motility of Ascaris suum sperm requires coordinated lamellipodial protrusion and cell body retraction. In these cells, protrusion and retraction are tightly coupled to the assembly and disassembly of the cytoskeleton at opposite ends of the lamellipodium. Although polymerization along the leading edge appears to drive protrusion , the behavior of sperm tethered to the substrate showed that an additional force is required to pull the cell body forward. To examine the mechanism of cell body movement, we used pH to uncouple cytoskeletal polymerization a nd depolymerization. In sperm treated with pH 6.75 buffer, protrusion of th e leading edge slowed dramatically while both cytoskeletal disassembly at t he base of the lamellipodium and cell body retraction continued. At pH 6.35 , the cytoskeleton pulled away from the leading edge and receded through th e lamellipodium as its disassembly at the cell body continued, The cytoskel eton disassembled rapidly and completely in cells treated at pH 5.5, but re formed when the cells were washed with physiological buffer. Cytoskeletal r eassembly occurred at the lamellipodial margin and caused membrane protrusi on, but the cell body did not move until the cytoskeleton was rebuilt and d epolymerization resumed. These results indicate that cell body retraction i s mediated by tension in the cytoskeleton, correlated with MSP depolymeriza tion at the base of the lamellipodium.