ANALYSIS OF ACTIN AND MICROFILAMENT-ASSOCIATED PROTEINS IN THE MITOTIC SPINDLE AND CLEAVAGE FURROW OF PTK2-CELLS BY IMMUNOFLUORESCENCE MICROSCOPY - CRITICAL NOTE

The distribution of actin and the microfilament-associated proteins myosin and tropomyosin was studied in mitotic PtK2 cells. Using fluorescent heavy meromyosin and two different antibodies against actin we have found no evidence for increased accumulations of actin in the mitotic spindle but have found increased levels of actin in the cleavage furrow and the contractile ring. Short, thin microfilament pieces remain detectable in the cytoplasm throughout mitosis. Purified antibodies against myosin and tropomyosin also revealed no increased levels of these proteins in the spindle region, although both proteins were found in the contractile ring and areas of the cytoplasm close to the intercellular bridge. These data are in agreement with functional and ultrastructural studies involving a role for actin and microfilament-related proteins in cytokinesis. They do not support models in which microfilament-related proteins are assumed to be a major constituent of the mitotic spindle. © 1979.