Fig. 6. Fgf signalling can locally induce sox3 expression and is required for cells to contribute to caudal CNS. (A-L) Views of late gastrula stage wild-type embryos in which donor (d) cells (brown) overexpressing the genes/constructs indicated top right or left side of panels were transplanted at late blastula stage. In C and D, the host (h) embryos are overexpressing the RNAs indicated in the bottom left-hand corner. Genes analysed are indicated in the bottom right-hand corner. Orientation varies depending on the location of the donor cells: (A) laterodorsal, (B) lateral, (C,D) animal, (E,F) dorsal, (G,H) lateral and (I-L) ventral views. In E-L, in situ stained (purple) embryos were photographed before (E,G,I,K) and after (F,H,J,L) staining to reveal donor cells (brown). The domains where sox3 expression was suppressed (E-J) or foxi1 expression was ectopically induced (K,L) are outlined. (M,N) Lateral views of the head (M) and tail (N) of 1-day-old embryos in which XFD-expressing donor cells (d1, green) were mixed and co-transplanted with wild-type donor cells (d2, red) to the same positions in dorsal (M) or ventral (N) vegetal ectoderm at around 50% epiboly stage. In the dorsal transplant, wild-type cells localise to the hindbrain (hb), whereas XFD cells are distributed in the midbrain (mb) and on the surface of the 1-day-old embryo, possibly in the epidermis (epi) (M). In the ventral transplant, wild-type cells localise to tail spinal cord (sp) and somite muscle (mus), whereas XFD-expressing cells are excluded from the spinal cord and localise predominantly to the fin and epidermis (N).