Weakened adherens junctions are sensitized to heightened actomyosin forces. (A) Labeling of F-actin at the fusion preinitiation stage (5–6ts) appears similar in controls (n = 3) and Ctnnd1^f/f; Crect^Tg/0 mutants (n = 3). MNP, medial nasal process; LNP, lateral nasal process. Scale bar, 50 μm. (B) At the initiation stage (8–11ts) in Ctnnd1^f/f; Crect^Tg/0 mutants (n = 3), rounded cells highly enriched in F-actin (yellow arrowheads) are found in the region that exhibits actin cables (open arrowheads) in controls (n = 5). Images were adjusted to gamma 2 to better visualize actin away from the fusion site. The green line represents Imaris-generated segments. Scale bar, 50 μm. (C) Optical slice of whole-mount–stained embryos (8ts) (n = 3 each). Rounded cells in Ctnnd1^f/f; Crect^Tg/0 mutants are often cCasp3⁺ (pink arrowheads) or cCasp3^- (blue arrowheads). Scale bar, 20 μm. (D) Actin labeling of control (n = 3) and Cdh1^f/f; Crect^Tg/0 mutants (n = 3) at the initiation stage (7–11ts) treated with calyculin A shows rounded cells (yellow arrowheads) in mutants. Gamma of images adjusted to 2. Green lines are Imaris-generated segments. Scale bar, 20 μm. (E) Lengths of Imaris-generated segments based on actin expression are less extensive in Ctnnd1^f/f; Crect^Tg/0 mutants and calyculin A–treated Cdh1^f/f; Crect^Tg/0 mutants than in respective controls. Each dot represents one sample. Error bars represent the SEM. Data were compared using two-tailed Mann–Whitney t tests.