Fig. 3. Osteopenia and impaired calvarial bone mineralization in En1^-/- mice. (Aa,Ab) Micro-CT analysis of heterozygous and En1^-/- calvariae at P1 and P5, demonstrating reduced ossification in the mutants. (B) Quantitative morphometric measurements of calvariae ultrastructure obtained by micro-CT analysis, demonstrating reduced bone volume and increased trabecular separation in En1^-/- mice. (C) Histological assessment of tissue mineralization by Von Kossa staining. The parietal bone matrix of En1^+/- mice is mostly mineralized at birth, whereas that of En1 mutants is heavily perforated and undermineralized (arrows). (D) En1-null calvarial osteoblasts exhibit a poor capacity to mediate extracellular marix mineralization over the course of a 21-day differentiation period. (E) ALP activity, assessed spectrometrically between 7-21 days of culture, is 2- to 3-fold higher in wild-type osteoblasts than in En1^-/- cells. Scale bar: 0.1 mm in C.