Fig. 6

Pax2a is necessary and sufficient for the enhancer activity of S4.2. (A) S4.2-EGFP expression was not detected in the MHB and distal optic stalk, whereas it is retained in the olfactory placode and otic vesicle in noi embryos. (B) S4.2-EGFP expression was lost only in the MHB, leaving GFP expression in the sensory regions intact in ace embryos. (C–G) fgf8 expression in the heads of noi embryos (C), ace embryos (D, G), and wild-type (WT) embryos (E, F) was examined by WMISH at 26 hpf. The insets in panels C–E show fgf8 expression in the otic vesicles. Black and white arrows show the presence and absence, respectively, of reporter expression in the distal optic stalks. (H, I) Misexpression of pax2a by mRNA injection caused ectopic induction of endogenous fgf8 in wild-type embryos (H) and egfp in S4.2-EGFP Tg embryos (I), as are marked with white arrowheads. (J, J′) S4.2-EGFP Tg embryos were injected with S4.2Δ2c-pax2a DNA and subjected to two-color in situ analysis at the 16-somite stage; first for pax2a (J, J′) and additionally for egfp (J′). Targeted misexpression of pax2a led to ectopic induction of egfp (purple) within the pax2a-positive domain (red, small white arrowheads) in the hindbrain. Black arrowheads indicate the MHB. Lateral views (A–E, H, I), frontal views (F, G), or dorsal views (J, J′) are shown. dd, dorsal diencephalon; dos, dorsal optic stalk; op, olfactory placode; os, optic stalk; ov, otic vesicle; pos, proximal optic stalk; t, telencephalon. Scale bars, 200 μm (A–I) or 100 μm (J, J′).