Fig. 5. Reduced proliferation of osteogenic cells in the frontal bone rudiment of Msx2 mutant mice. An antibody against serine 10-phosphorylated histone H3 (P-H3) was used to stain mitotic cells in sections of embryos in the area of the frontal bone rudiment at E12.5 (A-D) and E14.5 (F-I). Adjacent sections were stained for alkaline phosphatase activity. (A,C,F,H) Alkaline phosphatase stain; (B,D,G,I) P-H3 stain. P-H3-positive cells within the ALP stained area (arrowheads) were counted, and the counts normalized to the area of the ALP-stained region. (E,J) Plots of these normalized values. Error bars are standard deviations derived from three independent experiments. Note that at E12.5, P-H3 labeling indices of mutant and wild-type embryos were similar. At E14.5, a statistically significant (Student's t-test) reduction of labeling index was evident in mutant embryos. ch, cerebral hemisphere; fb, frontal bone; ep, epithelium. Scale bars: 100 µm.