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Fig. 7. Wnt responsiveness predicts differential growth of the facial
prominences. (A) In the E12.0 mouse face, growth of the frontonasal
prominence relative to the lateral nasal (l) and maxillary (mx) prominences
produces a midline furrow (dotted yellow line). (B) In chick, the
converse is seen, where the frontonasal prominence grows at a faster rate than
the maxillary and lateral nasal prominences, thus producing a pointed beak.
(C,D) Adipose-derived mouse mesenchymal cells infected with a
7xTcf-eGFP lentivirus and incubated in control medium do not express the GFP
reporter (C), but addition of purified Wnt3a protein activates GFP expression
(D). (E,F) In chick, injection of a control lenti-eGFP at St. 13
results in widespread infection by St. 34. GFP expression is scattered
throughout the upper beak; E, frontal view; F, lateral view. et, egg tooth;
np, nasal pit; e, eye. (G) In chick, injection with 7xTcf-eGFP at St.13
results in a robust, spatially restricted pattern of GFP expression in the
midline of the frontonasal prominence by St. 25. (H) At St. 29 in
chick, this same pattern of GFP expression is seen in the frontonasal midline.
(I,J) The frontonasal midline of avian embryos is a site of
continued growth that eventually results in the elongated upper beak. When Wnt
signaling is inhibited in avians by Ad-Dkk1 injection at St. 13, the growth of
the frontonasal midline is dramatically impeded (compare dotted yellow line in
I and J). The lateral nasal and maxillary prominences are unaffected. Scale
bars: 250 µm.
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