Fig. 3. Gene expression analysis at E3-4 in BA1 grafted with QT6-Shh cells. (A-C) Facial views of whole-mount in situ hybridized chick embryos grafted with QT6-Shh cells in BA1 territory on the right side (left on the figure). The left BA1 (right on the figure) is the control side. Fgf8 (A) and Bmp4 (C) expression is expanded, respectively, in the posterior proximal and distal BA1 ectoderm. Fgf8 is uniformly expanded (one arrow) while Bmp4 shows two extra zones of expression (two arrows). Shh (B) is also ectopically induced in two extra zones in the posterior ectoderm of BA1 (two arrows), while it continues to be normally expressed in the oral endoderm. (D) Facial view at E4 showing a duplicated right BA1 (on the left) (I,I') while BA2 (II) is normal. Orientation of oblique sections in E-I (medial to lateral) are indicated. (E-I) In situ hybridization on adjacent sections evidenced a partial colocalization of Fgf8 (G) and Bmp4 (I) transcripts in the duplicated BA1 ectoderm and a strong Shh expression (H) in the ectodermal fold separating I and I' (arrow). Grafted QT6-Shh cells are visible on this section. (F) Pitx1 is expressed in three distinct zones of BA1. Mes, mesencephalon; Rb, rhombencephalon. Scale bar: 100 µm in E-I'.