Fig. 2. Altered expression of key mesenchymal patterning genes in Fgfr2^AER-KO forelimb buds. (A-V) Whole-mount RNA in situ hybridization assays for the genes indicated. (A-H) Mkp3 expression as a read-out of mesenchymal responses to AER-FGFs. Vertical white lines in C,D indicate the depth of Mkp3-positive domain with black and white arrowheads marking the anterior and posterior boundaries, respectively. Asterisk indicates the Mkp3 expression domain in the sub-AER mesenchyme that was absent in the mutant limb bud (dotted line, H). (I-N') Expression of Shh (I-L) and Gre (M-N'). The distal strip of sub-AER mesenchyme (broken white lines), which lacks Gre expression, was much smaller in mutant forelimb buds. (M',N') The strip outlined by broken white lines, indicating the Gre-negative middle section of the LBM was greatly reduced in mutant limb buds at E11.5 (N'). (O-V) Expression of genes that primarily mark the anterior (Alx4;O,P), proximal (Meis2; Q,R) and middle mesenchyme (Hoxa11; S,T) and Hoxd11 expression (U,V) at E11.5. There are two distinct domains of Hoxd11 expression, marking the proximal and distal (^*) mesenchyme. The distal domain of Hoxd11 expression, which gives rise to the autopod, was missing in the mutant limb (broken lines in V). E11.5 is equivalent to the 45 s stage. Scale bars: 200 µm. Abbreviations: an, anterior; di, distal; do, dorsal; pr, proximal; po, posterior; ve, ventral; s, somite.