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The key feature for early migratory processes: Dependence of adhesion, actin bundles, force generation and transmission on filopodia.

Cell adhesion & migration (2010-02-25)
Claudia Schäfer, Simone Born, Christoph Möhl, Sebastian Houben, Norbert Kirchgessner, Rudolf Merkel, Bernd Hoffmann
ABSTRACT

Migration of cells is one of the most essential prerequisites to form higher organisms and depends on a strongly coordinated sequence of processes. Early migratory events include substrate sensing, adhesion formation, actin bundle assembly and force generation. While substrate sensing was ascribed to filopodia, all other processes were believed to depend mainly on lamellipodia of migrating cells. In this work we show for motile keratinocytes that all processes from substrate sensing to force generation strongly depend on filopodial focal complexes as well as on filopodial actin bundles. In a coordinated step by step process, filopodial focal complexes have to be tightly adhered to the substrate and to filopodial actin bundles to enlarge upon lamellipodial contact forming classical focal adhesions. Lamellipodial actin filaments attached to those focal adhesions originate from filopodia. Upon cell progression, the incorporation of filopodial actin bundles into the lamellipodium goes along with a complete change in actin cross-linker composition from filopodial fascin to lamellipodial alpha-actinin. alpha-Actinin in turn is replaced by myosin II and becomes incorporated directly behind the leading edge. Myosin II activity makes this class of actin bundles with their attached FAs the major source of force generation and transmission at the cell front. Furthermore, connection of FAs to force generating actin bundles leads to their stabilization and further enlargement. Consequently, adhesion sites formed independently of filopodia are not connected to detectable actin bundles, transmit weak forces to the substrate and disassemble within a few minutes without having been increased in size.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Monoclonal Anti-Vinculin antibody produced in mouse, clone hVIN-1, ascites fluid
Sigma-Aldrich
Anti-Myosin IIA, non muscle antibody produced in rabbit, affinity isolated antibody, buffered aqueous solution
Sigma-Aldrich
Anti-Fascin Antibody, clone 55K2, clone 55K2, Chemicon®, from mouse