Cell adhesion extended form

Fig. 6 Schematic of cell migrating on a surface (side view). Step-1 Cell lamellipodium extends due to the polymerization of actin filaments at the leading edge. Step-2 New adhesions are formed near the protruding leading edge. Step-3 Acto-myosin contractile force rips-off old adhesions from the rear.

Mesenchymal cells are spherical when in suspension and form stable protrusions only upon attachment to a surface [15]. The cells can adhere tightly to the substratum in tissue culture utilizing structures termed focal adhesions [26]. Upon extension of a lamellipod, close contacts to the substratum form, which then convert into localized adhesive clusters that can be detected using interference reflection microscopy [107, 166], These focal contacts have clusters of transmembrane proteins termed integrins that bind to extracellular matrix molecules and link intracellularly to the actin cytoskeleton to form stress fibers [251]. Adhesion to the substratum is necessary for stabilization of the lamellipod if a lamellipod extends over a nonadhesive surface, it then retracts [14],... 

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