Fig. 1. Detection of Wnt signaling in Pax2⁺ ectoderm with TCF/Lef reporter mice. (A,B) Comparison of Pax2 expression, Wnt8a expression and TCF/Lef reporter ß-galactosidase activity at E8.0 and E8.25. Significant reporter expression is observed in presumptive otic ectoderm after the onset of Pax2 expression at E8.25 but not at E8.0 (arrowheads). Wnt8a expression is observed in rhombomere 4 at both E8.0 and E8.25. (C) A whole-mount E8.5 TCF/Lef reporter embryo stained for ß-galactosidase activity, with sections through the anterior and posterior regions of the presumptive otic placode. The lower panels show a similar embryo immunostained for Pax2 (red) and ß-galactosidase (green) protein. The bracket shows the extent of the Pax2 domain, and the arrowhead shows Pax2⁺, ß-galactosidase^- ectoderm. The arrow indicates migrating neural crest cells. (D) Sections through the otic cup and otocyst of E8.75 and E9.5 reporter embryos. The white arrowhead and black bars indicate ß-galactosidase^- regions of placodal epithelium. The black arrowhead indicates ß-galactosidase⁺ vestibuloacoustic ganglion cells migrating from the otocyst, and black arrows indicate ß-galactosidase⁺ migrating neural crest cells. n, neural tube. Scale bars: 100 µm.