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Fig. 7. Bmp signalling in double mutant limbs. (A) At 10.5 dpc, in control embryos,
Bmp4 is expressed in the AER, in the posterior mesenchyme and in a
faint anterior domain of the limb bud. (B) Bmp4 expression is similar
in the double-null limb bud. The anterior limit of the Bmp4
expression domain in the ectoderm corresponds to the anterior limit of the AER
(black arrow). (C,D) At 11.5, owing to the anterior truncation of both the AER
(arrow) and mesenchyme, the anterior Bmp4 expression domain is almost
completely absent in the mutant. A reduced Bmp4 expressing domain is
still present at the proximal anterior border (arrowhead). In the rest of the
limb bud, Bmp4 expression is normal. (E,F) At 13.5 dpc, Bmp4
expression is observed in the finger tip mesenchyme of control embryos (E,
arrowheads) but not in the mutants (F). By contrast, expression is observed in
the remaining AER of the double-null mutants (F) which has regressed at this
stage in control embryos. (G,H) At 13.5 dpc, Bmp2 expression is
similar in the control and the double mutants, except that no negative
anterior domain is observed. In the control (G), the arrowhead indicates a
posterior domain of the limb bud that expresses Bmp2 at a higher
level. (I,J) Bmp7 is expressed similarly to Bmp2 in control
and mutant limbs. (K,L) Gremlin expression persists slightly longer in the
interdigital webbing of the mutants. The dark proximal domain in K is an
artefact due to the thickness of the specimen at this site. (A-J) Forelimb
buds, (K,L) hindlimb buds. In all panels, anterior is towards the right.
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