Fig. 9. Conditional postnatal Ihh deficiency causes cranial base abnormalities. (A,E) Skulls from P15 control (A) and Ihh-deficient (E) mice were subjected to micro-computed tomography (µCT) analysis; one orthogonal plane through the cranial base of each is shown here. Notice the presence of well-defined intrasphenoidal (is) and spheno-occipital (so) synchondroses in controls (A), and the ill-defined synchondroses and reduced anteroposterior length in mutants (E). (B-D,F-H) Sections from P7 and P15 control (B-D) and mutant (F-H) so synchondroses processed for collagen X gene expression (B,F) or for histological analysis (C,D,G,H). Notice that collagen X transcripts (red) are restricted to hypertrophic zones in controls (B) but are widespread throughout the mutant synchondrosis (F). Notice also the presence of a well-formed intramembranous bone collar flanking the pre-hypertrophic and hypertrophic zones in controls (C, arrowheads), which is undetectable in mutants (G, arrowhead). (D,H) Additionally, in mutants, much of the synchondrosis is replaced by endochondral bone by P15 (H). is, intrasphenoidal; so, spheno-occipital. Scale bar: 2 mm in E for A,E; 150 µm in F for B,F; 75 µm in G for C,G; and 250 µm in H for D,H.