Fig. 2

FGFR3 is expressed in the outer region of juvenile NP. (a) Schemas show the strategy for generation of FGFR3-3*Flag-IRES-GFP (FGFR3-GFP) mice with the knock-in of GFP allele into the 18th exon of FGFR3 to detect FGFR3-expressing cells in-situ. IRES, internal ribosome entry site. (b) Representative coronal sections of lumbar and caudal NP (dotted circle) from FGFR3-GFP mice at the age of 4 weeks (w) display the expression of FGFR3 at the periphery of NP. Numbers indicate the percentages of FGFR3-expressing cells over total NP cells. Scale bars, 100 µm. (c) Most of FGFR3-expressing cells in both lumbar and caudal NP are located in the outer region. (d) Representative images from FGFR3-CreERT2;Rosa26-Tomato (R3;Tomato) and FGFR3-CreERT2;Rosa26-mTmG (R3;mTmG) mice treated with Tamoxifen (Tam) or oil (No Tam) once daily for 3 consecutive days (Tam × 3) at 2w display the distribution of the FGFR3-CreERT2-labeled (FGFR3⁺) cells in NP (dotted circle). Scale bars, 100 µm. (e) Different doses of Tam (Tam × 1, Tam × 3 and Tam × 5) at 2w result in different labeling efficiency of FGFR3⁺ NP cells in R3;mTmG mice. **P < 0.01, ***P < 0.001, One-way ANOVA with post hoc Tukey test. (f) Percentages of FGFR3⁺ NP cells in outer region reveal that the location preference of FGFR3⁺ NP cells in outer region despite different doses of Tam. (g) Representative Ki67 immunostaining images of NP (dotted circled) from R3;mTmG mic with Tam × 3 at 2w are shown. Boxed area in the left image (Scale bars, 100 µm) is amplified in the right (Scale bars, 20 µm). Arrowheads indicate FGFR3⁺Ki67⁺ NP cells in cell clusters enriched at the peripheral area. (h) Percentage of Ki67⁺ cells in FGFR3⁺ cells is significantly higher than that of Ki67⁺ cells in FGFR3^·− cells. ****P < 0.0001, Unpaired Student’s t test