Fig. 1. Osteoblast and osteoclast marker expression in postnatal Msx2 mutant mice. (A,B) Skull vaults of postnatal day 4 mice were stained with Alizarin Red S. Note the large foramen in the frontal bone (fb) of the Msx2^–/– skull (arrow) and increased parietal foramen (pf, open arrowhead). (C-F) Cross sections, indicated by lines in A and B, at the level of the defect, stained for alkaline phosphatase (ALP) activity. The rectangles in C and D demarcate areas shown at higher magnification in E and F. The osteogenic fronts of Msx2^–/– mutants (F) are smaller than their wild-type counterparts (E). (G,H) Autoradiograms of in situ hybridization with a radiolabeled (³⁵S) probe against bone sialoprotein. The autoradiographic signal has been transformed to red. (I,J) TRAP stains of osteoclasts (red color, arrowheads). There was no discernible difference in numbers of osteoclasts between mutant (J) and wild type (I). cs, coronal suture; e, eye; fb, frontal bone; fs, frontal suture; ls, lambdoid suture; of, osteogenic front; pb, parietal bone; pf, parietal foramen; sk, skin; ss, sagittal suture. Scale bars: 2 mm in B; 200 µm in D,J; 100 µm in F; 80 µm in H.