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Fig. 6 Number and shape of cardiomyocytes are altered in smarcc1a mutants. (A, B) Immunofluorescence for Amhc (green) and mCherry (red) in wild-type (A) and smarcc1a mutant (B) hearts expressing Tg(myl7:H2A-mCherry) at 30 hpf. (C) Graphs depict the number of cardiomyocytes in the ventricle (V) and atrium (A), as well as the total number of cardiomyocytes, in wild-type and smarcc1a mutant hearts at 30 hpf. Mean and SE of each data set are shown. Asterisks indicate statistically significant differences from wild-type, using an unpaired t-test (**P < .01, ***P < .001). Number of hearts analyzed: wt, n = 14; smarcc1a, n = 10. The smarcc1a mutant heart contains slightly fewer ventricular cells than the wild-type heart at 30 hpf. (D–G) Cdh2 immmunostaining (green) outlines cardiomyocytes in wild-type (D, F) and smarcc1a mutant (E, G) hearts at 52 hpf. (F, G) Enlarged views of the ventricles shown in (D, E). Wild-type chamber emergence is accompanied by the increased surface area and elongation of cardiomyocytes along the outer curvature of the ventricle. In smarcc1a mutants, ventricular outer curvature cardiomyocytes do not enlarge or elongate normally and instead retain relatively small and round cell surfaces. (H, I) Graphs depict surface area (H) and circularity (I) of individual cardiomyocytes in the outer curvature of wild-type and smarcc1a mutant ventricles at 52 hpf. Mean and SE of each data set are shown. Asterisks indicate statistically significant differences from wild-type, using an unpaired t-test (****P < .0001). Number of hearts analyzed: wt, n = 3; smarcc1a, n = 3. Ventricular outer curvature cardiomyocytes in smarcc1a mutants are smaller (H) and rounder (I) than their wild-type equivalents at 52 hpf.