Fig. 2. Intact patterning of the LPM in Tbx5^del/del embryos, as demonstrated by expression of Tbx5 mRNA (A,B, arrows) from the wild-type or deleted alleles. LPM differentiation, as shown by Hand2 expression (dHand in figure), is intact in embryos of either genotype (C). Normal patterning of the forelimb field in Tbx5^del/del embryos is also apparent as demonstrated by expression of Hoxb8 and Pea3 mRNA in the LPM up to the posterior region of the forelimb field (arrowheads) in both wild-type and Tbx5^del/del embryos (D-F). After the initiation of limb bud outgrowth at E9.5, Pea3 expression is expressed in the forelimb mesenchyme of wild-type embryos, but is not detectable in the forelimb field of Tbx5^del/del embryos (F, asterisks). Hindlimb markers Pitx1 (G) and Tbx4 (H) are expressed normally in the hindlimb field (hl) but not in the forelimb field (asterisks) of wild-type or Tbx5^del/del embryos.