  The present article is an invited contribution to the Encyclopedia of
Complexity and System Science, Robert A. Meyers Ed., Springer New York (2009).
It is a review of the biophysical mechanisms that underly cell motility. It
mainly focuses on the eukaryotic cytoskeleton and cell-motility mechanisms.
Bacterial motility as well as the composition of the prokaryotic cytoskeleton
is only briefly mentioned. The article is organized as follows. In Section III,
I first present an overview of the diversity of cellular motility mechanisms,
which might at first glance be categorized into two different types of
behaviors, namely "swimming" and "crawling". Intracellular transport, mitosis -
or cell division - as well as other extensions of cell motility that rely on
the same essential machinery are briefly sketched. In Section IV, I introduce
the molecular machinery that underlies cell motility - the cytoskeleton - as
well as its interactions with the external environment of the cell and its main
regulatory pathways. Sections IV D to IV F are more detailed in their
biochemical presentations; readers primarily interested in the theoretical
modeling of cell motility might want to skip these sections in a first reading.
I then describe the motility mechanisms that rely essentially on
polymerization-depolymerization dynamics of cytoskeleton filaments in Section
V, and the ones that rely essentially on the activity of motor proteins in
Section VI. Finally, Section VII is devoted to the description of the
integrated approaches that have been developed recently to try to understand
the cooperative phenomena that underly self-organization of the cell
cytoskeleton as a whole.
