Fig. 3. Limb development phenotypes resulting from FGF receptor inactivation in limb mesenchyme with Prx1-Cre. (A) β-galactosidase staining of Prx1-Cre, R26R forelimb at E9.5. (B-D) Skeletal preparations of P0 wild-type control (WT), Fgfr1^Prx1-Cre and Fgfr1/2^Prx1-Cre mice. (E-L) Appearance (E-H) and histology (I-L) of E10 forelimb buds of WT, Fgfr1^Prx1-Cre, Fgfr2^Prx1-Cre and Fgfr1/2^Prx1-Cre embryos showing a reduced proximodistal axis in Fgfr1/2^Prx1-Cre forelimb buds. (M-P) Phosphohistone H3 (pHH3) immunohistochemistry to assess proliferation at E10 (M,N) and E10.5 (O,P). (Q-T) Caspase 3 immunohistochemistry used to assess cell death at E10 (Q,R) and E10.5 (S,T). Note that the region of reduced density of pHH3-positive cells in proximal mesenchyme of Fgfr1/2^Prx1-Cre embryos at E10 (N) corresponds to the region with increased apoptosis (R). Data are representative of at least three embryos. Scale bars: in A, I for I-L and M for M-T, 50 µm.