Fig. 2. Transplantation of the FEZ creates an ectopic Fgf8/Shh boundary. (A) A region of stage 20 FNP ectoderm measuring 0.5-0.8 mm by 1.0-1.2 mm in width (indicated by the red striped box) was transplanted onto the dorsal FNP (D) of a stage 25 chick embryo and pinned into place. (B) Lateral schematic view of the FEZ donor site (broken red lines indicate cut sites). FEZ grafts encompassed the Fgf8 (green) ventral Shh (yellow) junction (indicated by a red arrow). (C) Lateral schematic view of the FEZ graft site in a stage 25 host FNP. The quail-derived FEZ graft is indicated by a darker green (dorsal) and a darker yellow (ventral) domain, and by red letters. Twelve hours after transplantation, (D) Shh expression persisted in the ventral FNP ectoderm (V) of stage-matched, unoperated embryos. (E) Ectopic Fgf8 and Shh in the dorsal FNP of chimeric embryos confirmed that the FEZ (red D, V) was appropriately positioned in the host FNP. (F) Higher magnification of the boxed region in E showed that only QCPN-positive quail ectoderm was transplanted. ps, palatal shelf; pe, pharyngeal endoderm; rp, Rathke's pouch; di, diencephalon; or, optic recess; t, telencephalon.