Figure 1

Activation of the Wnt pathway results in increased Pax3 expression in the early ophthalmic trigeminal placode. In situ hybridization showing Pax3 (blue) (A-J) and Fgf8 (red) (F, G). (A-D) Expression of Pax3; (A'-D') are higher magnification images of embryos in (A-D). At 3 somites, Pax3 expression is detectable in the somitic mesoderm, but no transcripts are detected in the neural folds or adjacent ectoderm (A, A', black arrow). At 6 somites, Pax3 transcripts are detectable in the neural folds (B, B'), and transcripts begin to emerge in the cranial ectoderm (black arrow). Pax3 expression becomes more abundant by 8 somites (C, C', black arrow). At 14 somites (HH11+) the Pax3 expressing placode is evident (D, D', black arrow. (E-J) CAGGS Wnt and green fluorescent protein (GFP) are co-electroporated at the midbrain level of the neural folds and targeted to the right side. GFP expression is shown in insets (E', F', G', J'). Embryos were cultured for 6 hours (E, F, G) or 12 hours (H-J). (E) Overexpression of Wnt1 at 6 somites leads to a premature appearance of the earliest Pax3 positive presumptive ophthalmic placodal cells (grey arrow). Embryos injected at the 8 (F) or 10 somite stage (G) also yield a greater number of Pax3 positive cells in the adjacent ectoderm (F, G, compare grey arrow, right, with black arrow, left). No change in isthmic Fgf8 expression (red) is observed (F, G). (H) HH10 embryo electroporated and incubated for 12 hours. The white arrowhead (H) delineates the expanded Pax3 expressing domain compared to the uninjected side (black arrow head). (I, J) Left and right lateral views, respectively, of the embryo viewed dorsally in (H). The arrowheads point to the ophthalmic branch of the trigeminal placode on the injected side (J, white arrowhead), and uninjected side (I, black arrowhead).