Figure 6

The ophthalmic and maxillomandibular branches of the trigeminal nerve differentiate in response to activated fibroblast growth factor (FGF) signals within the neural tube. In situ hybridization detects Islet1 expression (A, C-D, E-J), green fluorescent protein (GFP) expression (B, G', J') and anti-Islet1 (K, L) expression. FGF8, Wnt1 or FGF8 and Wnt1 were electroporated at the right side of the neural tube at HH10, and embryos were cultured until HH16 (A-L). Overexpression of FGF8 results in premature differentiation of the ophthalmic and maxillomandibular branches (compare white arrow head in (D) with the black arrow head in (C)). Similarly, following electroporation of Wnt1 in the neural tube, the expression of Islet1 is more pronounced in the right trigeminal placodes (E, G, white arrowheads) compared to the untargeted side (F, white arrowhead). Overexpression of both Wnt1 and FGF8 together (H, I, J, black arrowheads) also results in similar expansion of Islet1 expression. Confocal analysis for Islet1 expression (red) within the developing placodes reveals that both the ophthalmic and maxillomandibular branches appear prematurely differentiated (L) compared to the un-targeted side (K). (C, D) High magnification images of flat mount in (A); (F, G) high magnification images of flat mount in (E); (I, J) higher magnification images of flat mount in (H).