The RHOA-ROCK-myosin pathway mediates neurite retraction by increasing the phosphorylation of the regulatory chain of myosin (Amano et al. 1998). Non-muscle myosin II (NMM2) is an actin-based motor protein that plays a crucial role in a variety of cellular processes, including cell migration, polarity formation, and cytokinesis. NMM2 consists of two myosin heavy chains encoded by MYH9, MYH10 or MYH14 (NMHC-IIA, B and C), two copies of MYL6 essential light chain protein, and two regulatory light chains (MRLCs), MYL9 and MYLC2B. Myosin II activity is stimulated by phosphorylation of MRLC. Diphosphorylation at Thr-19 and Ser-20 increases both actin-activated Mg2+ ATPase activity and the stability of myosin II filaments; monophosphorylation at Ser-20 is less effective. Kinases responsible for the phosphorylation include myosin light chain kinase (MLCK), ROCK kinase, citron kinase, myotonic dystrophy kinase-related CDC42-binding protein kinase, and Zipper-interacting protein (ZIP) kinase. ROCK activity has been shown to regulate MRLC phosphorylation directly by mono- (Amano et al. 1996) or di- (Ueda et al. 2002) phosphorylation of MRLC.