Fig. 1. Enhancer of Otx2 expression in forebrain and midbrain at 5' upstream. (A) The location of the #13 fragment that exhibited the enhancer activity in forebrain midbrain. EP/AN indicates the position of the EP and AN enhancer at –92.5 to –90 kb. (B) ß-Gal expression driven by #13 (a-f,m,q) and by endogenous enhancers in Otx2^+/acZ knock-in embryos (g-j,l,p), at the stages indicated. Endogenous Otx2 mRNA expression is presented in k,n,o. (a,k-m) frontal views; (b-j) lateral views (anterior is towards the left); (n-q) frontal sections at the telencephalic level. Arrows and arrowheads indicate expression by the 1.8 kb promoter and the position of the isthmus, respectively. Double arrowheads in c indicate the absence of the ß-gal expression in the most anterior neural plate, which may correspond to future telencephalon. Scale bars: 100 µm in a,b,g; 400 µm in c-f,h-q.