At E10.5, the expression of Bmp4 in the mutant fore and hindlimb is slightly downregulated (B) compared to wild type (A). At E11.5, this downregulation is clearer (C–D) shown in ventral views at the top and in anterior views at the bottom of the panel, as indicated. At E12.5, Bmp4 expression in the ectoderm appears patchy particularly in the hindlimbs shown in anterior and distal views (E, F). At E12.5, Msx2 expression is also downregulated in mutant limbs, confirming the reduction in BMP signaling at E12.5 (G–H).