Le mouvement sans actine et myosine : motilité amoeboide des spermatozoïdes de Caenorhabditis elegans – Elegant sperm

Moving without actin and myosin: sperm cell crawling in Caenorhabditis elegans Mammalian cell movement is powered by actin polymerization, in concert with molecular motors like myosin that confer contractility to the cell. The sperm cells of the nematode Caenorhabditis elegans contain a 'Major Sperm Protein' (MSP) cytoskeleton, which plays the role of actin in these cells, despite the fact that MSP has no sequence, structural or biochemical homology to actin. The equivalent of myosin in nematode sperm cells is unknown. The goal of this project is to identify the proteins that orchestrate MSP dynamics by a dual biochemistry (immunoprecipitation, GST pulldown)/genetics (RNAi) approach. With this information, we plan to develop a minimal set-up to reproduce sperm cell movement in vitro. This system will allow us to probe the biochemical and physical parameters of MSP assembly and MSP-based propulsion. In parallel, we will study sperm cell movement in vivo by producing a transgenic GFP-MSP worm that will allow us to visualize the MSP cytoskeleton in a moving cell. We will study the mechanisms of adhesion, lamellipodial extension and symmetry breaking, and compare our results to theoretical models concerning these subjects. By studying MSP dynamics, we hope to uncover novel mechanisms for cell polarization and cytoskeleton organization, and to reveal the governing principles of cell motility.