Cell Motility |
Motile cells are ubiquitous in living organisms and play a crucial role in the fate and functions of human beings. Life begins thanks to sperm cells successfully swimming their way until they reach and fertilize an egg cell. At the opposite end, most cancers become life-threatening when they metastasize, and this occurs when previously static cells in a tumor acquire the ability to crawl (i.e., move on a solid substrate) on nearby tissues and then circulate in the bloodstream or lymphatic system. Other examples of cell (crawling) motility include nerve cells, which explore their surroundings to establish connections in the nervous system during fetal development, and white blood cells, presiding at the response of the immune system.
Understanding the mechanisms by which cells move is necessarily a multi-disciplinary endeavor, and the central role played by biochemical regulation in the way cells control their movements is undisputed. Mechanics can provide the tools to calculate the forces cells need to exert and the power they need to expend in order to move as we see them moving. At a deeper, more microscopic level, mechanics may contribute to the understanding of how small biological forces generated at the molecular scale can be marshalled to generate large-scale movement at the cellular or organismal scale.
For crawling motility, which is powered by growth of the cytoskeletal actin network at the leading edge of the advancing cell, the key question is how can order and synchronized motion emerge at the cell scale (several micrometers), from uncoordinated individual growth events taking place at the nanometer scale of the actin fibers. Our answer is that long range mechanical interactions between the cytoskeleton and the surrounding plasma membrane may provide the mechanism governing self-organization and co-operative growth.
Swimming motility is powered by the forces that the surrounding fluid exerts on a swimmer as a reaction to its shape changes. At small sizes, inertial forces are negligible: swimming micro-organisms are able to extact net propulsive forces from the viscous resistance of the surrounding medium. This apparent paradox and the subtleties of swimming at low Reynolds numbers have been the object of intense investigation in recent years.
L. CARDAMONE, A. LAIO, R. SHAHAPURE, V. TORRE, A. DESIMONE: Growing actin networks are critically self-organized systems synchronized by mechanical interactions. Proceedings of the National Academy of Sciences, 108:13978-13983, 2011 (pdf).
A. DESIMONE, F. ALOUGES, A. LEFEBVRE: Biological Fluid Dynamics. Springer Encyclopedia of Complexity and System Science, R.A. Meyers (ed.), 2009 (pdf).