Fig. 3. Dilated large vessels with reduced VSMCs in SM22-Cre;R26R;Bmpr1a^flox/flox mouse embryos. (A) Whole-mount PECAM staining of E10.5 embryos (a-f) shows a dilated aorta in the SM22-Cre;R26R;Bmpr1a^flox/flox compared with WT (d versus c, arrowheads). Panels c and d are high magnifications of the framed areas in a and b, respectively. Dilatation of large abdominal vessels with frequent interconnections are seen in the flox/flox mutants versus WT (f versus e, arrowheads). H&E-stained transverse sections show dilatation of the mutant aortae (h) compared with WT (g). Poor investment of lacZ staining (blue) SM22-expressing VSMCs around the mutant aortae in sections of whole-mount mutant embyros (j) versus WT (i). Sections h and j are at the same level as g and i, respectively. (B) SM-actin staining (brown) shows poor investment of SMCs in the dilated aortic wall of SM22-Cre;R26R;Bmpr1a^flox/flox (b) versus WT (a). TUNEL staining (arrows) revealed similar occasional apoptotic cells surrounding the dilated aorta in the flox/flox mutant (d) and WT (c). However, reduced PCNA staining (arrows) was seen in VSMCs of the dilated aorta and in the neighboring mesenchymal cells in the flox/flox (f) versus WT (e). Panels a, c and e are similar consecutive sections in the WT embryo as b, d and f in the flox/flox mutant embryo. (g) Quantification of percentage of PCNA-positive cells over total number of SMCs in the vessel walls in dorsal aortae of E10.5-11 WT and SM22-Cre;R26R;Bmpr1a^flox/flox mutants. Bars indicate mean±s.e.m. (n=4). ^*P<0.05. Panels depicting WT and mutants are of the same magnification. Scale bars: 100 µm in Ah,j; 50 µm in Bf.