Fig. 3. Changes in gene expression patterns correspond to FEZ orientation. (A) Schematic lateral view of a stage 25 host FNP, indicating dorsal (green) and ventral (yellow) domains corresponding to sections shown in D,G,J,M,P,S. (B) Schematic view of a quail FEZ graft (dark green, dark yellow, red D, V) positioned on the dorsal surface of a stage 25 chick host FNP corresponding to sections shown in E,H,K,N,Q,T. (C) Schematic view of a FEZ graft that has been rotated 180° (red V,D) corresponding to sections shown in F,I,L,O,R,U. (D) In unoperated embryos, Shh (yellow) was restricted to ventral FNP ectoderm (V); Fgf8 was already down regulated in dorsal FNP ectoderm (D) but transcripts were still detectable in the optic recess (or). (E,F) Twenty-four hours after transplantation, Shh was detected in the ventral FEZ (red V) as well as in its endogenous, ventral domain (white V). Fgf8 was no longer detectable in the dorsal FEZ (red D). (G) Ptc1 transcripts were detected in ventral ectoderm and throughout FNP mesenchyme. (H,I) Ptc1 was ectopically induced in FNP mesenchyme beneath the ventral region of the graft. (J) Gli1 was expressed in ventral ectoderm and at low levels throughout FNP mesenchyme. (K,L) Gli1 was ectopically induced in mesenchyme beneath the ventral FEZ. (M) Msx1 was expressed in dorsal ectoderm and mesenchyme, corresponding to the site of outgrowth. (N,O) Msx1 was repressed beneath the ventral, and induced beneath the dorsal, FEZ; a small ectodermal patch of Msx1 was evident in dorsal host ectoderm but was absent in underlying mesenchyme (O, arrowhead). (P) AP2 was strongly expressed throughout the dorsal ectoderm and mesenchyme. (Q,R) AP2 transcripts were abundant beneath both the dorsal and ventral FEZ. (S) Lfng was expressed at low levels throughout the ectoderm and localized to the mesenchyme at the site of outgrowth. (T,U) The endogenous mesenchymal expression of Lfng was up regulated adjacent to the graft, as well as in the mesenchyme beneath the ventral graft, but was missing from the dorsal mesenchyme (arrowhead). Scale bars: 1 mm.

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