Fig. 1

Fgfr3-creER labels chondrocytes and their precursors in postnatal cranial base synchondrosis. a Cartoon illustration of cranial base spheno-occipital synchondrosis (SOS), inter-sphenoid synchondrosis (ISS), and anterior intra-occipital synchondrosis (AIOS) housed within the craniofacial complex. Pink: cartilage, gray: bone. b Fgfr3-creER; R26R-tdTomato lineage-tracing model combined with Col1a1(2.3 kb)-eGFP reporter. Single intraperitoneal injection of tamoxifen at P3 induces cre recombination, leading to the labeling of Fgfr3⁺ cells by tdTomato. If these cells differentiate into osteoblastic cells, they become simultaneously marked by Col1a1(2.3 kb)-eGFP. c Timeline for the lineage-tracing experiments. Tamoxifen injection (250 μg) at P3 and lineage-traced to P4, P10, P21, P42, 3 months and 8 months. Lineage-tracing of Fgfr3^CE-tdT⁺ SOS cells at P4 (d) P10 (e) P21 (f) P42 (g) and 3 months (h). The boxed region is shown in higher magnification. Blue arrowheads represent Col1a1(2.3 kb)-GFP⁺ osteoblasts derived from Fgfr3^CE-tdT⁺ chondrocytes at primary spongiosa. Red: Fgfr3^CE-tdT, green: Col1a1(2.3 kb)-GFP, yellow: Col1a1(2.3 kb)-GFP⁺Fgfr3^CE-tdT⁺, gray: DIC. PS: primary spongiosa. Scale bar: 100 µm. i Quantification of Col1a1(2.3 kb)-GFP⁺Fgfr3^CE-tdT⁺ cells at primary spongiosa at P4 (n = 5), P10 (n = 6), P21 (n = 6) and P42 (n = 5) collected from serial sections of the SOS. **P < 0.01, Mann-Whitney’s U-test. Data are presented as mean ± s.d