Figure 3.

Clathrin-minus cells do not form a functional contractile ring like wild-type cells. Using cells expressing gfp–myosin, we examined cell division on a substrate. We showed by DAPI staining that dividing cells were binucleate (b, d, f, h, j, l, and n). Three examples of wild-type cells in cytokinesis are shown (a–e). Dividing wild-type cells concentrated gfp–myosin (a, c, and e) in a cleavage furrow that was bright in subsequent stages of cytokinesis. Shown are four examples of clathrin-minus cells that had a binucleate, elongate morphology suggestive of cell division (g–o). Clathrin-minus cells showed a cortical distribution of gfp–myosin (g, i, and k), but did not concentrate gfp–myosin between the nuclei of dividing cells. Also shown is a clathrin-minus cell that appears to be undergoing cell division by traction-mediated cytofission on a substratum (m–o). Immunofluorescence of control (p) and clathrin-minus (q) cells without the gfp–myosin cassette are shown. Myosin II, visualized with an anti-myosin II antibody, localized to the posterior cortex of both cells as they migrated to the right. (Scale bar = 10 μ.)