Depolymerizing F-actin rescues spindle length but not multipolarity in Myo10 morphants. (a) Low-magnification confocal micrographs of mitotic spindles in untreated embryos (control and MO) or embryos incubated in 2.5 μM LatB (MO + LatB). In LatB-treated embryos, some spindles were improperly oriented perpendicular to the plane of the epithelium (arrows). Insets show z projection cross sections of a control spindle, oriented parallel to the plane of the epithelium, and a LatB spindle in the improper perpendicular orientation (the outermost cell cortex is indicated by a broken line in each inset). (b) High-magnification confocal micrographs of α-tubulin–stained spindles in Myo10 morphants either untreated (MO) or incubated in 2.5 μM LatB (MO + LatB). (c) Quantification of spindles in LatB experiment embryos shows that treatment with LatB does not significantly affect the number of bipolar or multipolar spindles (n = 11, 11, 17, and 15 embryos for control, LatB, MO, and MO + LatB, respectively). Error bars represent standard error of the mean. (d) Box and whisker plots of spindle length measurements in the LatB experiment; spindle length was calculated as a percentage of total cell length to allow for changes in cell size. Treatment with LatB significantly rescues the increased spindle length seen in Myo10 morphants (n = 82, 104, 86, and 59 spindles for control, LatB, MO, and MO + LatB, respectively). For significance testing, unpaired Student's t tests were performed: ****, P < 0.0001.