Figure 3.

Impaired Apoptosis in the Fusing Lower Sternum of B^R709C/B^R709C Embryos. a,b. H&E stained mesenchymal cells in the middle of the E14.5 fusing sternum show an extensive accumulation of apoptotic cells with condensed and/or fragmented chromosomes in B⁺/B⁺ mice (a, green arrows). Very few apoptotic cells are seen in B^R709C/B^R709C mice (b). c,d. Confocal images of TUNEL assays show apoptotic cells near the midline in the fusing sternum of B⁺/B⁺ mice (c, green) which are not seen in B^R709C/B^R709C mice (d). The insets (H&E images) indicate areas shown in panels c and d. e,f. Confocal images of the sternal area stained with antibodies for activated-caspase-3 (red) and p53 (green) from E14.5 mouse embryos show a decrease in caspase-3 positive cells in B^R709C/B^R709C mice (f, red) compared to B⁺/B⁺ mice (e, red). No difference in p53 staining was seen between B⁺/B⁺ and B^R709C/B^R709C mice (e,f, green).g-i. Confocal images of E14.5 mouse embryos stained with antibodies for NMHCII-A (g, red), II-B (h, red) and II-C (i) show that both NMHCII-A and II-B, but not II-C, are expressed in the fusing sternum. DAPI (blue) stains nuclei. Scale bars: a and b, 25 μm; c-i, 50 μm.