Role of microtubules in stimulating cytokinesis in animal cells.

The initiation of furrow formation is disrupted when microtubule elongation to the cell surface is inhibited either by promoting microtubule disassembly with hydrostatic pressure or by stabilizing the mitotic astral microtubules with taxol. The pressure studies confirmed Rappaport's earlier observation that stimulation of furrow formation is produced by a pair of asters and does not require chromosomes or a central spindle in the large dividing cells of echinoderm embryos. The taxol studies showed that furrow formation occurs between two stable asters when the asters are within 20 microns of the lateral cell surface. Furrow formation at the lateral edge of the cell does not appear to require microtubule dynamics, microtubule elongation, or contact of microtubule ends with the lateral cell surface. Microtubules may function to increase the concentrations of the active forms of diffusible stimulatory factors that interact with receptors at the inner cell surface to initiate the formation of the furrow apparatus and activate contraction.