A NONMUSCLE MYOSIN REQUIRED FOR EMBRYONIC POLARITY IN CAENORHABDITIS-ELEGANS

DAUGHTER cells with distinct fates can arise through intrinsically asy mmetrical divisions'. Before such divisions, factors crucial for deter mining cell fates become asymmetrically localized in the mother cell(2 ,3). In Caenorhabditis elegans, PAR proteins are required for the earl y asymmetrical divisions that establish embryonic polarity(4,8), and a re asymmetrically localized in early blastomeres(9,10), although the m echanism of their distribution is not known. Here we report the identi fication in C. elegans of a nonmuscle myosin II heavy chain (designate d NMY-2) by means of its interaction with the PAR-1 protein, a putativ e Ser/Thr protein kinase. Furthermore, injections of nmy-2 antisense R NA into ovaries of adult worms cause embryonic partitioning defects an d lead to mislocalization of PAR proteins. We therefore conclude that NMY-2 is required for establishing cellular polarity in C. elegans emb ryos.