Figure 6. β1 Integrin Is Required for Myocardial Proliferation, Muscle Integrity and Ventricular Chamber Formation in the Compaction Stage.

(A) Whole-mount in situ hybridization (ISH) for Nkx2.5 in wild-type and mutant E9.5 embryos. (B) H&E staining of wild type and mutant E12.5 hearts. (C) Wild-type and mutant hearts at E14.5. Mutant ventricles are smaller than wild-type, while atria are same size (arrowheads). RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle. (D) Wild-type and mutant hearts at P1. The right panel shows H&E staining. Note that mutant ventricles were hypoplastic, while the atria were preserved (arrowheads). (E) Masson-trichrome staining in P7 wild-type and mutant hearts. Large amounts of fibrosis were detected in the mutant interventricular septum and right ventricular subendocardium. Arrow indicates His bundle (positive control). (F) Immunofluorescent staining for collagen1 (Col1, green) and DAPI (blue) in the wild-type and mutant P1 hearts. Collagen deposits were observed in mutant hearts. Arrowheads indicate valves (positive control). (G) The ratio of wall thickness in the compact layer to heart size (longest diameter) in wild-type or mutant hearts at P1 (n = 5). (H) Immunofluorescent staining for actinin (red), BrdU (green) and DAPI (blue) in the wild-type and mutant E16.5 left ventricles. BrdU⁺ cells were reduced in the mutant heart. (I) Percentage of BrdU⁺ cells in the wild-type and mutant hearts at E12.5 and E16.5. (J) Percentage of p-ERK⁺ cells in wild-type or mutant hearts at E16.5. (K) qRT-PCR of Spp1 and TnC mRNA (left panel), and Ccnd1, Ccne1, Ccng2, and Cdkn1a mRNA (right panel) in E12.5 wild-type and mutant hearts. Representative data are shown in each panel. All data are presented as means ± SEM. *, P<0.01; **, P<0.05 vs. relative control. Scale bars, 100 μm (B, E, F, H); 500 μm (A); 1 mm (C and D).