Regulates myosin II activity and organization during embryo elongation. May be involved in the organization of mlc-5 into bundles (PubMed:19675126). Required maternally for cytokinesis during meiosis and mitosis in the early embryo and for the establishment of embryonic anterior-posterior polarity (PubMed:10427096). Myosin is a hexamer of 2 heavy chains and 4 light chains (two regulatory light chains and two essential light chains). Forms a filamentous structure which may co-localize with actin. Expressed in the spermathecal and uterine walls. Weak expression in gonadal sheath and intestinal muscle. Not detected in vulval, pharyngeal or body wall muscles. Expressed at the bean stage in the lateral hypodermal seam cells and then throughout embryogenesis and into larval stages. May be phosphorylated by let-502 or/and pak-1 and dephosphorylated by mel-11 to regulate its activation and myosin II-mediated contraction. Arrest at the 2-fold embryonic stage which is associated with a defect in embryo elongation and failure of seam cells to elongate to a narrow morphology. No abnormalities in body wall or pharyngeal muscles and in the number of hypodermal cells. This chain binds calcium.