Fig. 3. Cell proliferation analysis during frontal bone development. (A) At E12.5, the frontal bone primordium (between the broken lines) is well defined. There is active cell proliferation in the CNC-derived frontal bone mesenchyme of the control sample. (B) In Tgfbr2^fl/fl;Wnt1-Cre mutants, similar cell proliferative activity is observed as compared with the control. (C,D) Comparable cell proliferative activity between the wild type and Tgfbr2^fl/fl;Wnt1-Cre mutant is observed within the CNC-derived frontal bone primordium at E13.5. (E) There is active CNC cell proliferation in both the calvarial (arrow) and the orbital aspect (arrowhead) of the frontal bone primordium in the wild-type sample at E14.5. (F) Significant reduction in CNC cell proliferation is clearly visible in both the calvarial aspect (arrow) and the orbit region of frontal bone mesenchyme (arrowhead) of Tgfbr2^fl/fl;Wnt1-Cre mutant. (G) Statistical analysis of cell proliferative activity between the wild type and the Tgfbr2^fl/fl;Wnt1-Cre mutant. There is a significant reduction in cell proliferation in the calvarial and orbital aspects of the frontal bone anlagen in the Tgfbr2^fl/fl;Wnt1-Cre mutant at E14.5. Scale bars: 100 µm.