Biomedical Engineering Reference
In-Depth Information
Chapter 3
Actin Network Flow and Turnover
Are Coupled in Migrating Cells
Dynamic turnover and transport of actin fi lament network are essential processes for
the generation of protrusive and traction forces during cell migration. Fragments
formed from the lamella of migrating cells such as fi sh keratocytes are uniquely simple
yet elegant motility systems suitable for the analysis of the dynamic coupling interac-
tion between actin network fl ow and turnover. Indeed, analysis of fl ow dynamics in the
lamella of crawling fragments derived from fi sh keratocytes has revealed that actin
network in the lamella of fragments portrays a fl ow pattern that closely resemble that
of intact cells. This suggests that actin network fl ow is an intrinsic property of migrating
cells, and thus, fundamental to cell migration. This chapter discusses actin network
dynamics that accompany cell migration and explores new insights into the organiza-
tion and regulation of actin network dynamics in migrating cells, based on the study of
cellular fragments.
3.1
Introduction
Cell migration is fundamental to many biological processes such as wound healing,
cancer metastasis and immune response. A majority of migrating cells have special-
ized structures for migration such as lamellipodia (a fl at and broad-shaped sheet-
like structure extending in the front of migrating cells) or fi lipodia (spike-like
structures protruding from the edge of a migrating cell in the direction of cell migra-
tion), as described details in Chap.
1
. These structures are in turn composed of the
cytoskeletal actin fi laments which undergo a dynamic turnover characterized by
polymerization and depolymerization to bring about cell movement.
Whereas polymerization occurs at the leading edge of the lamellipodia or
fi lopodia and generates protrusive forces that drive cell migration, depolymerization
occurs rather dispersedly in the interior of lamellipodia or fi lopodia where it
contributes to cell migration by replenishing the monomer used up during
polymerization (Borisy and Svitkina
2000
; Pollard and Borisy
2003
). Thus, these two
