Fig. 5. Mesenchymal gene expression in Pbx1^–/–;Pbx2^+/– (mutant) hindlimbs. (A) Expression of Alx4, Hand2 and Gli3 is relatively unperturbed in mutant hindlimbs, before and/or at Shh onset, indicating that until E10.5 the mesenchyme is patterned similar to wild type. (B) Shh expression is absent throughout mutant hindlimb development at E10.5 and E11.5. At E11.5, Shh absence (empty purple arrowhead) in mutant hindlimbs is associated with a similar and expected alteration in Fgf8 expression (empty blue arrowheads), compared with wild-type hindlimbs (normal Shh expression indicated by solid purple arrowhead and Fgf8 by blue arrowheads). (C) Although reduced, expression of Ptch1 and Gli1 is present (E10.75), suggesting minimal and transient Shh activity. Meis2 is unperturbed in mutant hindlimbs (E11.0), suggesting that proximal limbs remain relatively intact. (D) Grm is extended posterodistally in mutant hindlimbs (E10.75), indicating Shh absence in the ZPA (Scherz et al., 2004). Hand2 expression is reduced (E10.75) and Gli3 expression is diffused throughout mutant hindlimbs (E11), resembling expression patterns in mice that lack Hoxa/Hoxd (Kmita et al., 2005) and suggesting an AP patterning defect in the absence of sustained Shh activity. Proximal is leftwards; anterior is towards the top.