MYOSIN-I LOCALIZES TO THE MIDBODY REGION DURING MAMMALIAN CYTOKINESIS

During cytokinesis, daughter cells are cleaved in two by the constrict ion of an actin-rich contractile ring which encircles the equator of t he dividing cell. Filamentous myosin II is present in the contractile ring and necessary for constriction of the furrow, as shown in several cell types [Satterwhite and Pollard, 1992: Curr. Opin. Cell Biol. 4:4 3-52]. However, no functional role nor distinctive localization has be en previously identified for non-filamentous ''unconventional'' myosin s, such as myosin I, during cytokinesis. Using antibodies to adrenal m edullary myosin I, we report that myosin I is localized in 3T3 fibrobl asts to the mid-equatorial plane during late-cytokinesis, as well as t o the polar edges as previously described in ameboid cells [Fukui et a l., 1989: Nature 341:328-331]. Confocal microscopy revealed that myosi n I is concentrated at the midbody region in a nearly continuous trans verse disk, extending from the cortical region of the furrow through t he midbody itself. These findings suggest that, in addition to the acc epted role of filamentous myosin II in constriction of the contractile ring, nonfilamentous myosin I might contribute to motile events occur ring late in cytokinesis. (C) 1994 Wiley-Liss, Inc.