Fig. 5. Osteoprogenitor proliferation at the interfrontal and coronal sutures of wild-type and En1^-/- embryos between E12.5-E18.5. (A) Immunohistochemical detection of BrdU-labeled cells within the interfrontal sutures (dashed outline). (B) Proliferation was numerically assessed as the fraction of labeled to non-labeled cells. A specific reduction in osteoprogenitor proliferation was observed in En1^-/- calvariae at E18.5. (C) Enhanced osteoprogenitor proliferation within the coronal suture (arrowheads) of En1 mutants at E18.5. p, parietal bone; f, frontal bone. Scale bar: 0.2 mm.