Fig. 2. Dissection of ectodermal enhancers at 5' upstream. (A) Schematic diagram depicting the 15 fragments assayed for enhancer activity. Number of lines exhibiting ß-gal expression among permanent transgenic lines established is indicated in parenthesis. Fragments displaying enhancer activity are indicated in red. (B) ß-Gal expression driven by #12 (a-f), by endogenous enhancers in Otx2^+/lacZ knock-in embryos (g-k) and by #4 (l). The ß-gal expression indicated by arrows represents the expression in anterior visceral endoderm (b), anterior mesendoderm (d) and cephalic mesenchyme (e,l) by the 1.8 kb promoter (Kimura et al., 1997). The expression in e is solely due to the activity of the 1.8 kb promoter (compare with Fig. 1B, part d). Compare the expression in d with the 1.8 kb promoter with that in Fig. 3B, part h with the hsp68 promoter. The #4 fragment exhibited ß-gal expression in a region of the ventral diencephalon and dorsal mesencephalon. In lateral views (a,c-e,g-j,l), anterior is leftwards; (b) cross-section in the plane shown in a; (f,k) frontal views. Arrowheads and double arrows indicate the position of the isthmus and the expression in the eyes, respectively. a, anterior; p, posterior. Scale bars: 100 µm in a-d,g,h; 400 µm in e,f,i-l.