Fig. 8. Increases in ß₁ integrin activity in Icap-1^-/- mouse cells. (A) Sagittal sections were stained with the 9EG7 monoclonal antibody (red) that recognizes ligand-bound ß₁ integrins. ß₁ integrins are highly expressed and strongly activated in wild-type cells (Icap-1^+/+) at the osteogenic front (arrowheads) and at the surface of the bony plates (arrows). In Icap-1^-/- tissues, the cells at the osteogenic front show a moderate staining for activated ß₁ integrin. Scale bar: 50 µm. (B) FACS analyses demonstrate a slight reduction in the surface expression of ß1 integrins (assayed by the MB1.2 monoclonal antibody) on Icap-1^-/- primary osteoblasts (red) compared with wild-type osteoblasts (blue). (C) Adhesion assays. The adhesion of Icap-1^-/- primary osteoblasts to FN and COL1 is moderately increased compared with that of Icap-1^+/+ cells. Adhesion is expressed as a percentage of the maximal adhesion and measured in duplicate in two independent experiments from two different animals (P<0.05). (D) FACS analysis demonstrates increased binding of FITC-Fn7-10 fragment to Icap-1^-/- osteoblasts (green). (E) The activation index (AI) of the ß₁ integrin is increased in Icap-1^-/- osteoblats. The maximum AI obtained is used to normalize both genotype groups and designated as 100.