Establishment of cleavage furrows by the mitotic spindle

The purpose of this investigation was to determine the capacity for furrow establishment of the mitotic spindle in several kinds of dividing animal cells. To this end the cell shape was altered so that equatorial surface was brought in contact with the spindle and its normal geometrical relation with the asters changed. In flattened Tripneustes gratilla eggs, furrows formed at the tips of deeply cut notches that impinged upon the spindle area. In Echinarachnius parma eggs, furrows formed at the tips of deeply cut notches and also at the margins of perforations that straddled the spindle. The distance separating the perforations was less than the normal spindle diameter. In flattened, dividing cultured newt ( Diemictylus viridescens ) kidney cells furrows formed in equatorial surface that was pushed inward far enough to displace the metaphase chromosomes. These results appear to indicate that the mitotic spindle of animal cells can establish furrows. We speculate that the actual role played by the spindle in normal cytokinesis depends upon the relative sizes of the asters and the spindle and upon the normal distance between the spindle and the equatorial surface.