Fig. 6. Expression of limb patterning genes in the limb buds of wild-type (+/+) and Tbx4-mutant embryos (-/-) at 10.5 dpc. (A,B) Tbx5 is expressed in the forelimb bud and absent in the hindlimb bud (arrowheads) of wild-type and mutant embryos. (C,D) Ptx1 is expressed in the hindlimb bud, but not the forelimb bud of both wild-type and mutant embryos. (E,F) Msx2 marks the ventral limb ectoderm in both normal and mutant hindlimb buds. Embryos are oriented for a posterior view of the hindlimb bud, with forelimbs at the bottom of the picture and the head removed for clarity. Arrowheads mark the dorsal boundary of Msx2 expression in the hindlimb. (G,H) dHand, an upstream regulator of Shh, is expressed strictly in the posterior edge of the hindlimb bud of normal embryos, but throughout the margin of the Tbx4-mutant hindlimb bud. Small arrowheads mark anterior and posterior boundaries of the hindlimb bud. (I,J) Tbx3 is expressed in the posterior edge of both forelimb and hindlimb buds (arrowheads) in both wild-type and mutant embryos. (K) Tbx2 is expressed in both anterior and posterior edges of the forelimb bud and in the posterior edge of the wild-type hindlimb bud (arrowhead). (L) In the Tbx4 mutants, Tbx2 is normally expressed in the forelimb but absent from the posterior hindlimb.

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