Depolymerization-driven flow in nematode spermatozoa relates crawling speed to size and shape

¹ University of Connecticut Health Center
² University of Connecticut

^* To whom correspondence should be addressed. E-mail: cwolgemuth{at}uchc.edu.

Submitted on August 30, 2007
Revised on September 14, 2007
Accepted on 27 December 2007

	Abstract

Cell crawling is an inherently physical process that includes protrusion of the leading edge, adhesion to the substrate, and advance of the trailing cell body. Research into advance of the cell body has focused on actomyosin contraction, with cytoskeletal disassembly regarded as incidental, rather than causative; however, extracts from nematode spermatozoa, which use Major Sperm Protein rather than actin, provide one example where cytoskeletal disassembly apparently generates force in the absence of molecular motors. To test whether depolymerization can explain force production during nematode sperm crawling, we constructed a mathematical model that simultaneously describes the dynamics of both the cytoskeleton and the cytosol. We also performed corresponding whole cell experiments using Caenorhabditis elegans spermatozoa. Our experiments reveal that crawling speed is an increasing function of both cell size and anteroposterior elongation. The quantitative, depolymerization-driven model robustly predicts that cell speed should increase with cell size and yields a cytoskeletal depolymerization rate that is consistent with previous measurements. Notably, the model requires anisotropic elasticity, with the cell being stiffer along the direction of motion, to accurately reproduce the dependence of speed on elongation. Our simulations also predict that speed should increase with cytoskeletal anisotropy and depolymerization rate.

Key Words: C. elegans, MSP, cell crawling, cytoskeleton, mathematical model, nematode sperm