Fig. 7. Abnormal AER morphogenesis in T^-/- embryos. AER progenitors were stained with affinity-purified anti-DLX (a gift from Grace Panganiban) in transverse sections of paraffin-embedded wild-type (wt, A,C,E,G) and T^-/- (B,D,F,H,H') forelimb buds at ages (average somite number: so) indicated to the left of the panels. The small arrows indicate approximate extents of pre-AER or AER. Note poor and variable maturation of T^-/- AER, as illustrated by H and H' which show nearby sections from a T^-/- limb bud with a particularly mild phenotype. Some T^-/- limb buds were highly irregular in shape (* in B; see also Fig. 6Q,T,V). To evaluate distribution of Bmp4 expression, embryos hybridized in whole-mount were transversely cryo-sectioned and wild type (wt, I,K,M) was compared to T^-/- (J,L,N). Similar abnormalities in pre-AER and AER morphology were observed, with poor AER compaction during maturation (eg. M vs.N). Additionally, reduced mesodermal Bmp4 expression was evident in E9.25 T^-/- limb buds (J). d, dorsal; v, ventral.