Fig. 3

Runx2 inactivation in Fgfr3⁺ cells disrupts cell organization of the synchondrosis. Fgfr3-Runx2^cHet and Fgfr3-Runx2^cKO mice were injected with a single dose of tamoxifen once at P3 and euthanized at P28 (a) and P56 (b). Safranin-O staining revealed organized chondrocyte layers in Fgfr3-Runx2^cHet mice. Boxed regions show higher magnification. Fgfr3-Runx2^cKO mice displayed a progressive fusion of the central portion of the SOS (a, b right magnified panels) while the ISS was widened. Black dashed lines highlight the fusion defect. Fgfr3-Runx2^cHet and Fgfr3-Runx2^cKO mice were injected with tamoxifen once at P3 and euthanized at P42 (c) and 3 months (d). Hematoxylin and eosin staining revealed organized chondrocyte layers in Fgfr3-Runx2^cHet mice, showing higher magnification in boxed regions. Fgfr3-Runx2^cKO mice displayed bone formation areas throughout the SOS’s central portion (c, d right panels). Arrows and arrowheads indicate hypertrophic-like cells in the central and hypertrophic zones of SOS, respectively (c, d left magnified panels) and areas of chondrocyte disorganization in the Fgfr3-Runx2^cKO SOS (c, d right magnified panels). C central zone, R resting zone, P proliferating zone, PH pre-hypertrophic zone, H hypertrophic zone. Scale bar = 100 µm