Fig. 4. Defective formation of the osteogenic front in Icap-1^-/- calvaria. (A) Whole-mount lacZ staining of newborn calvariae of Icap-1^+/+ and Icap-1^-/- mice. Strong ß-gal activity visualizes Icap-1 expression in the sutural regions and the edges of the bony plates of the Icap-1-deficient calvaria. (B,C) Hematoxylin and Eosin-stained frontal section of the parietal region. The distance between the ossified ends of the parietal bones (arrows) is wider in Icap-1^-/- (C) compared with wild-type mice (B). (D-G) Frozen frontal sections through the sagittal suture of wild-type (D,F) and Icap-1^-/- (E,G) animals stained with Hematoxylin and Eosin (D,E) or for ß-gal activity (F,G). Note that the wild-type suture presents a typical condensed cell population corresponding to the osteogenic front (arrowheads) that is severely reduced in the Icap-1^-/- mice. lacZ staining indicates extensive expression of ICAP-1 in this region. B, bone; i.m, intersutural mesenchyme; SO, supraoccipital bone; P, parietal bone; F, frontal bone; S, sagittal suture; L, lambdoid suture; C, coronal suture; IF, interfrontal suture. Scale bars: 2 mm in A; 50 µm in B-G.