Steps during chemotaxis

During chemotaxis the intracellular distribution of each class of GTPase is controlled so that a gradient is formed within the cell. At the leading (growing) edge Cdc42 activation promotes formin and Arp2/Arp3 dependent actin assembly to promote filopodia and lamellipodia growth. This in turn stimulates Rac GTPase which further promotes branched actin network assembly behind the leading edge. Rac activation leads to Rho GTPase activation at the lagging edge of the cell which promotes stress fiber formation and myosin II activation which powers forward movement of the bulk of the cell contents. This systems is highly dynamic as the cell can rapidly change direction in response to changes in concentration and direction of chemotactic signals.