Assessing F-actin distribution and role of actomyosin contractility in wild-type embryos. (A) Quantifying distribution of actin across nasal processes during fusion. A line drawn across fusing nasal processes is used to select representative actin surfaces in creating an intensity profile. (B) Graph shows spatial distribution of surface intensities (y axis) across tissue (x axis), peaking broadly at the junction and junction-adjacent LNP, in four individual samples (9–11ts). FJ, fusion junction; MNP, medial nasal process; LNP, lateral nasal process. Scale bar, 50 μm. (C) Examples from four different wild-type embryos (7–8ts) stained with SPY-650-FastAct_X show actin enrichment at fusion region similar to SiR-Actin–stained embryo (7ts). MNP, medial nasal process; LNP, lateral nasal process. Scale bar, 40 μm. (D) Actomyosin contractility is required for lip fusion. Time-lapse stills of F-actin in 10ts samples treated with DMSO or Y-27632. Treatment began 1 h prior to imaging. Multicellular actin cables (red arrowhead) form at the fusion junction in DMSO-treated samples (n = 3) but did not form in 2/3 Y-27632–treated samples. MNP, medial nasal process; LNP, lateral nasal process. Time reads as hh:mm. Scale bar, 20 μm.