Fig. 1. Inactivation of Fgfr1 by Tcre and Shh^cre. (A-D) ß-Gal staining of embryos at E8.5 (A) and E10.0 (B), an E10.0 forelimb bud in transverse section (C) and an E10.5 intact limb bud (D). The arrowheads in A and B delineate the rostral boundary of robust staining. Arrow in B indicates the forelimb bud. Inset in C is a magnified view of the boxed domain to illustrate that the staining is robust in the mesenchyme, while absent in the AER (arrowhead). (E-L) Gene expression analysis using whole-mount in situ hybridization probes indicated on the left. (E,F) E10.0 embryos. Arrows in E,F indicate forelimb buds. Arrowhead in F delineates the rostral boundary of Fgfr1 inactivation. (G,H) E10.5 forelimb buds. Broken line and arrowhead in H indicate Fgfr1 inactivation in posterior mesenchyme. (I,J) E10.0 forelimb buds. Expression of Spry4 in the mutant is reduced to the posterior mesenchyme and a thin line subjacent to the AER. (K,L) Oblique dorsoposterior view of E10.5 forelimb buds. Arrowhead in L indicates reduced Spry4 expression in the dorsoposterior mesenchyme. (M) RT-PCR of normal (n) and Tcre;Fgfr1 mutant (m) limb buds to illustrate that Fgfr1 is inactivated in mutant LBM at E10.0 and E10.5.