Fig. 7. Bone nodule formation by the calvarial osteoblast is defective in Icap-1^-/- mice. (A) Primary Icap-1^+/+ and Icap-1-deficient osteoblasts were cultured for 4 weeks in inductive medium and stained with Alizarin Red for monitoring bone nodule formation. Icap-1^-/- cultures show fewer and smaller mineralized nodules (arrows) compared with wild-type cultures (Icap-1^+/+). The result is representative of at least three independent experiments from three different animals. Scale bar: 1 mm. (B) Immortalized osteoblasts SV2.1 Icap-1^-/-, SV6.5 Icap-1^+/+ or SV2.1-Icap-1^resc were cultured in inductive medium for 3 weeks and mineralized nodules were identified by Alizarin Red staining. Icap-1^-/- osteoblasts show a significantly reduced nodule formation compared with wild-type or Icap-1^resc osteoblasts. The means and s.d. were calculated from three independent experiments (^*, P<0.05; ^**, P<0.0001).