Actin- and RhoA/Rac1 pathway-dependent functions in cell migration and transmigration. (a) Migratory and (b) transmigratory phenotypes of cells such as smooth muscle cells (SMCs), fibroblasts, or macrophages; depend on the polarization of microtubules emanating from centriole-containing MTOC (or centrosome) and the formation of actin-rich (shown in red) leading (lamellipodium) and trailing (uropod) edge. Lamellipodium is able to form, spiky, and actin-rich projections called filopodia that play a role in sensing of the environment and adhesion (together with actin rich focal adhesions and/or stress fibers) to the substratum. Mother and daughter centriole of MTOC and microtubules are shown in green. MTOC-derived microtubules deliver, via function of molecular motors, various molecules (such as actin-binding proteins) and vesicles to proper destinations within the cell. (c) Actin dynamics (such as polymerization, depolymerization, and binding to its partners) in uropod, lamellipodium, filopodia, and focal adhesion/stress fibers are regulated by interplay between small GTPase RhoA and Rac1 pathways.