Figure 5

Overexpression of Wnt1 leads to ectopic activation of Fgf8 within rhombomere 1 and a hyperdifferentiated trigeminal. Fgf8 expression (blue) detected by in situ hybridization (A-H) and anti-neurofilament (brown) (C-J). Overexpression of Wnt1 at the right-hand side of the neural tube at HH10 results in an expansion of isthmic Fgf8 expression, as analyzed at HH16 (A, B, D, F). (A) Dorsal view (anterior is to the top) of the anterior hindbrain showing expansion of Fgf8 expression in the right neural tube (black arrow). (B) Embryo as in (A) viewed laterally from the right-hand side. Embryos (C-J) are flat mount preparations, anterior is left (C, E, G, I) and right (D, F, H, J). (C) Bisected head at HH16 showing the normal development of the ophthalmic (C, G, white arrows) and maxillomandibular (C, white arrow head) lobes. (D, H) Elevated Wnt signals and expansion of isthmic Fgf8 expression promotes differentiation of both the ophthalmic (black arrows) and maxillomandibular (black arrowhead) branches. When the isthmic organizer (IsO) region is removed (J) and replaced with foil, the trigeminal ganglion appears smaller than the unoperated side (I). (E, F) High magnification images of isthmic domain (C, D). (G, H) High magnification images of ophthalmic lobe in (C, D). The asterisk in (D) delineates the rhombomere 1/2 boundary. The eye (e) is marked for reference in (C, D).