Fig. 4: Examination of the actomyosin-based cortical tension during cytokinesis with OptoMYPT.

a Schematic illustration of cytokinesis in animal cells. Solid and dashed arrows indicate ring tension and cortical tension, respectively. Orange, green, and gray objects indicate actomyosin, microtubules, and chromosomes, respectively. Blue light is focused on the poles on both sides. b Representative images of SspB-mScarlet-I (upper) or SspB-mScarlet-I-MYPT169 (middle and lower) in MDCK cells during cytokinesis. The blue circular regions were locally illuminated with blue light every 3.11 s. Middle panels represent the cytokinesis of a cell under dark conditions. Scale bar, 10 μm. c Inset images of polar blebbing (the green and magenta boxed regions in panel b, representing the early and late phases, respectively). Yellow and blue arrowheads indicate small and large new blebs per stack, respectively. Scale bar, 3 μm. d, e Quantification of the total number of blebs during cytokinesis, shown as a box plot (d), and of the number of new blebs emerged within 15.54 s, shown as a line graph (e), in which thin and bold lines indicate individual and averaged data, respectively. n = 5, 10, and 13 cells for Control-pole, OptoMYPT-dark, and OptoMYPT-pole, respectively. **p = 0.002 (two-tailed Student’s t test). f, g Quantification of the furrow ingression rate after ingression onset. Averaged relative diameters are plotted as a function of time with the SD (f). The ingression rate was estimated by calculating the slope of the ingression rate from 1.0 to 0.6 in panel f, and shown as a box plot (g). n = 7, 10, and 13 cells for Control-pole, OptoMYPT-dark, and OptoMYPT-pole, respectively. *p = 0.017 (two-tailed Student’s t test).