In Madin–Darby canine kidney cells, Rho small G protein regulates formation of stress fibres, focal adhesions, and peripheral bundles through reorganization of the actin cytoskeleton. There are two morphologically distinguishable types of Rho‐regulated stress fibres: parallel and stellate. Of these, effects of Rho small G protein, mDia1 regulates the formation of parallel stress fibres, whereas ROCK regulates the formation of stellate stress fibres, peripheral bundles and focal adhesions. Both mDia1 and ROCK are direct downstream targets of Rho small G protein.

The ROCK‐induced formation of stellate stress fibres is regulated mainly through the myosin light chain kinase‐dependent phosphorylation of myosin light chain and the LIM‐kinase‐dependent phosphorylation of cofilin. The ROCK‐induced formation of focal adhesions is mainly regulated through a downstream pathway of ROCK other than myosin light chain and cofilin. The ROCK‐induced formation of peripheral bundles is regulated at least through ERM proteins, but not through the myosin light chain or cofilin.

Our present and previous findings suggest the presence of multiple downstream signalling pathways from ROCK to reorganization of the actin cytoskeleton in Madin–Darby canine kidney cells.