Figure 5.

 Distal limb defects in the hypomorphic mutants. Skeletal preparations of forelimbs (A–D) and hindlimbs (E–H) of newborn wild-type (A,E), n7 homozygous (B,F), IIIbn homozygous (C,G) and n7/null transheterozygous (D,H) newborn mice. Reduced Fgfr1 function appears to correlate with successive loss of anterior digits. Other defects include syndactyly, delayed ossification of distal phalanges, and occasional appearance of an extra postaxial cartilage condensation in the forelimbs (arrows in B,D). In n7/null transheterozygotes the limb defects are markedly enhanced resulting occasionally in defects in the development of the more proximal limb (H). Analysis of 5′ HoxD gene expression in the limb buds of IIIbn hypomorphic mutants by whole mount mRNA in situ hybridization (I–K). HoxD11 expression at E10.5 (I) in a IIIbn homozygote (IIIbn) and a wild-type littermate (wt), showing no obvious difference. In contrast, HoxD13 expression both at E10.5 (J) and E11 (K) was reduced in the mutants compared to their wild-type littermates.