Fig. 6. Anteroposterior polarisation of the limb buds is affected in Msx1^-/-; Msx2^-/- double mutant embryos after 11.5 dpc. (A,B) At 11.5 dpc, in normal embryos, Fgf4 is expressed in the posterodistal part of the AER, and excluded from the anterior fourth of the AER. In the double mutants, Fgf4 expression level is normal but expression domain is shifted anteriorly (A,B, arrowheads). (C,D) At 12.5 dpc, Fgf4 is still detectable at the anterior tip (white arrow in D) of the AER in double mutant embryos. (E-H) Hoxd11 is expressed only in the region corresponding to the future digits II to V in both normal hind- (E) and forelimbs (G). In the double mutants (F,H), it is expressed along the whole distal mesenchyme regardless of whether the limb bud (generally hindlimbs) is truncated (F) or, conversely (essentially forelimbs), overgrown anteriorly (H). (I,J) In a few double mutant embryos, Shh is faintly expressed ectopically at the anterior margin of the forelimbs (J, arrow). The posterior domain is slightly shifted distally (arrowheads). (A-D,G-J) Forelimbs. (E,F) Hindlimbs. In all panels, anterior is towards the right.