Fig. 2. Synchondrosis growth plate organization and chondrocyte proliferation are deranged in Kif3a-deficient cranial bases. (A-D) Parasagittal sections of a P7 control spheno-occipital synchondrosis. Notice the presence of resting (rz), proliferative (pr), pre-hypertrophic (phz) and hypertrophic (hz) growth plate zones and primary bone spongiosa (arrowheads in D). Areas in colored frames in A are shown at higher magnification in B-D. (E-G) Presence and location of proliferating chondrocytes in control P0 (E), P7 (F) and P15 (G) spheno-occipital synchondroses as revealed by histone 4C gene expression by in situ hybridization. The hybridization signal was given an artificial color for illustration purpose. Notice the presence of two well-defined proliferative zones (indicated by arrowheads) flanking a central resting zone. (H) Pthrp gene expression in a control P0 synchondrosis, which characterizes the resting and proliferative zones. (I-L) Parasagittal sections of a P7 Kif3a-deficient spheno-occipital synchondrosis showing that the growth plate zone structure is totally abnormal (J,K) and that there is a near absence of primary spongiosa (L). (M-O) Near absence of histone 4C-expressing proliferating chondrocytes in Kif3a-deficient synchondroses. (P) Pthrp gene expression in a Kif3a-deficient synchondrosis. Scale bars: 300 µm in I for A,I; 40 µm in J for B,C,J,K; 80 µm in L for D,L; and 150 µm in M for E-H and M-P. P, postnatal day; rz/pr/phz/hz, resting/proliferative/pre-hypertrophic/hypertrophic growth plate zones.