Fig. 3. Microtubule organization is required for stable furrow progression and maintenance of RhoA localization. (A) Selected frames of Movie 1 in supplementary material showing phase-contrast images (upper panel) and ß-tubulin images (lower panel) of A6 cells expressing ß-tubulin-GFP. At initiation of furrowing when RhoA accumulated at the equatorial cortex, 16 µM nocodazole was added to the medium. Chromosomes are indicated by white arrows. A furrow (black arrows) formed and ingressed (3:20). But it quickly regressed (3:40-4:00). Then another furrow (white arrowheads) formed at a different position and ingressed (4:20-4:50). The furrow also regressed. This cell did not complete cytokinesis within 30 minutes. The elapsed time (minutes and seconds) from nocodazole treatment is indicated at the lower left corner of each panel. (B) The same cell as in A was fixed at 30 minutes of nocodazole application and stained for RhoA and DNA. RhoA localization was not restricted to the equatorial cortex but was found at several sites on the cortex (upper panel, arrowheads). Failure in cytokinesis is revealed by the formation of two nuclei (see DNA in lower panel). Bar, 10 µm.