Figure 7

Dorsal diencephalic tissue suppresses ZLI formation. (A, B) Whole embryos and (C-F) explants were analysed by double in situ hybridisation for expression of Shh (red) and Wnt3a (blue). (A) Embryo at stage HH10, corresponding to the time when explants were dissected. Note expression of Wnt3a along the dorsal midline of the diencephalon and midbrain (black arrowheads). (B) Embryo at stage HH23, correponding to the developmental stage of explants after culture for 72 hours. Note expression of Wnt3a in a dorsal triangluar domain flanking the ZLI posteriorly (black arrowhead). (C) Explants excluding dorsal diencephalic tissue express only little Wnt3a at the time of explantation (pre-cult.) and form a ZLI after 72 hours in culture (D) (post-cult.). (E) Explants including dorsal diencephalic tissue express high levels of Wnt3a at the time of dissection and after culture but fail to express Shh after culture (F).