Figure 1: The cytokinetic ring in one plane of focus.

(a) Cells are oriented in micro-cavities during cytokinesis along the axis of division. (b) Electron microscopy image of an array of PDMS micro-cavities. Cavity diameter=25 μm. (c,d) The cytokinetic ring visualized in mammalian cells (c, HeLa) and fission yeast (d) by myosin (MHC–GFP in c; Rlc1-mCherry in d) and actin (Lifeact-mCherry in c; CHD–GFP in d) (c) shows superimposition of five z-planes. Scale bar, 5 μm in c; 2 μm in d. Time zero is the onset of constriction. (e,h) Ring diameter and the corresponding closure speed as a function of time. (e) N=14, (h) N=20. The velocity is computed from individual constriction curves and then averaged. In h, the grey dashed line indicates the linear constriction regime. (f,g) Relative mean (g) and total (f) intensity of myosin and actin in the cytokinetic ring of mammalian cells. The intensity is normalized for cells at a diameter of 10 μm. N=10 for myosin, N=6 for actin. (i,j) Relative mean (j) and total (i) intensity of myosin and actin in the cytokinetic ring of fission yeast cells. The intensity is normalized for cells at a diameter of 3.1 μm. The intensity measurements were made from individual snapshots of rings for the time period of 300–2,500 s. N=241 for both actin and myosin. The intensities before constriction were acquired from time-lapse movies of individual rings (N=3). (e–j) Error bars indicate s.d.