Ring myosin II broadens the polarized actin cap and Arp2/3 complex domain. (A) Immunofluorescence detection of activated myosin II (P-MRLC) in MII oocytes treated for 1 h with DMSO (top row) or BDP9066 (1 µM; bottom row). F-actin was labeled with Alexa Fluor 568–phalloidin. (B) Box plot showing the width of the actin cap in control MII oocytes treated with DMSO and in MII oocytes treated with BDP9066 (1 µM). P value was calculated using two-tailed Student’s t test. The number of oocytes scored is indicated above each box. (C) Immunofluorescence detection of activated myosin II (P-MRLC) and the Arp2/3 complex (p34ARC) in MII oocytes treated for 1 h with DMSO (top row), BDP9066 (1 µM; middle row), or ML-141 (5 µM; bottom row). White arrows point to the colocalization of P-MRLC and p34ARC at the shoulders of the actin cap. (D) Box plot showing the width of the Arp2/3 cap in control MII oocytes treated with DMSO and in MII oocytes treated with BDP9066 (1 µM) or ML-141 (5 µM). P values were calculated using two-tailed Student’s t test. The number of oocytes scored is indicated above each box. Chromosomes were stained with TO-PRO-3 (magenta). Scale bars are 10 µm. In A and C, fluorescence intensity profiles are shown corresponding to the polarized cortex region delineated by the two gray arrowheads in the merged image.