Cell motility is a remarkable dynamic process which is crucial for many biological processes such as wound healing, fertilization and pathologic cases such as cancer metastasis. A moving cell is a self-organized mechano-chemical machine in which molecular components interact at small scales to generate forces and motion on much larger scales. The majority of animal cells crawl by actin-based motility where forward movement depends on the assembly and disassembly of a network formed by a protein named actin.
While the key molecular components involved in actin-based motility are known, we are far from understanding this remarkable self-organization process. Keratocyte cells cultured form fish scales are a well-established model system for studying cell motility due to their high speed and consistent behavior. Keratocyte cell fragments, which lack the cell body but retain the ability to crawl with a speed and persistence similar to whole cells, make an even simpler model system. To utilize this excellent model system we have developed efficient ways to generate keratocyte fragments. When following individual fragments for extended periods of time it was revealed that fragment shape and speed varied in a correlated manner over time. Together with observations of the actin network distribution in fragments, these findings led us to a quantitative model explaining how global shape and speed emerge from the underlying dynamics of the molecular actin components.