SMC hyperproliferation in elastin mutant aorta. (A, C, E, and G) Transverse aortic sections of embryos of the indicated elastin genotype and age stained for SMA and nuclei and for either pH3 (A and E) or Ki67 (C and G). Nuclei are stained with DAPI (A and E) or propidium iodide (PI; C and G). Staining for CD31 is also included in A and E. (B, D, F, and H) Proliferative index (fraction of pH3⁺ or Ki67⁺ cells) of SMCs of wild-type, Eln^(+/−), and/or Eln^(−/−) embryos at E17.5 (B and D) or E18.5 (F and H) in the total aorta and, for F and H, in each cell layer (i.e., layers 1–5; this analysis was limited to aortic sections with five smooth muscle layers). For each genotype, n = 3 embryos in B and H and n = 2 embryos in D and F, and 20 sections per embryo were analyzed. The total pH3⁺ aortic SMCs detected in B were 172 for wild type and 787 for Eln^(−/−) and in F were 71 for wild type and 133 for Eln^(+/−), whereas the total Ki67⁺ SMCs detected in D were 1,389 for wild type and 4,785 for Eln^(−/−) and in H were 1,765 for wild type and 3,357 for Eln^(+/−). Data are presented as mean ± SD. Student’s t test was used. *, P < 0.05; **, P < 0.01; ***, P < 0.001 versus wild type. Lu, aortic lumen. Bars, 10 µm.