Cytokinesis by Furrowing in Diatoms a

We have found that nocodazole reversibly inhibits nuclear migration and can be used to induce karyokinesis before the completion of nuclear migration, resulting in spindles that are displaced toward the hypothecal end of the cell. Surprisingly, displacement of mitotic nuclei results in complete spatial uncoupling of karyokinesis from cytokinesis. Nocodazole-induced displacement of mitotic nuclei will neither alter the position of the original furrow nor induce additional furrows. This demonstrates that in S. turris the location of the presumptive cleavage furrow is not determined by the position of the spindle but is cortically determined before mitosis. Therefore, although cell division in S. turris resembles certain mechanochemical aspects of cleavage in animal cells, our evidence suggests that the spatial regulation of the cytokinetic apparatus relies on a mechanism of cortical determination that is characteristic of plant cells.