Our overall goal is to determine how typical animal cells, including the cells in our bodies, crawl over their substrate. Crawling movement of individual cells is central to diverse processes in medicine and basic biology including embryogenesis, the immune response, wound healing and cancer metastasis. Although it has been studied for more than 100 years the mechanism of cell movement is unknown. Animal cells contain large numbers of thin filaments made of the protein actin, which are known to be essential for cell movement. The aim of this proposal is to find out how actin filaments promote cell movement at a molecular level. We need to know how actin filaments become arranged into specific arrays which allow and direct cell movement, and then how these filament arrays generate the force for cell movement. First we will study how actin filaments are arranged in living, moving cells, and how their arrangement changes with time. We will use mammalian tissue culture cells, which are easy to microinject and study by microscopy. We will make fluorescent marks on actin filaments, and then follow how the marked filament distribution evolves with time. This will tell us where and how fast actin filaments are moving in the cytoplasm, and how rapidly they turn over. Such basic mechanical information is needed to determine how cells position their actin filaments, and use them to move. We will then make extracts from cells, and try to recapitulate filament movement and turnover in a biochemical preparation. This will allow to probe the molecular mechanisms for organizing and moving the actin filaments. We will make antibodies to proteins which we think are important to movement, in particular actin motor proteins, and inject these back into living cells to see how filament organization and cell movement is affected.