Fig. 4. Mutant Xdsh inhibits neural convergent extension in Keller sandwich explants. (A) Keller sandwiches were prepared by removing the entire dorsal marginal zone, which consists of dorsal axial mesoderm (AM, red), posterior neural ectoderm (PNE, blue), and some anterior ectoderm (yellow), from two different embryos. These two explants are cultured together with the deep cells facing, and superficial epithelia (black) surrounding the recombinate. Convergent extension of neural and mesodermal portions transforms the initially rectangular explant into a stereotyped morphology with two distinct domains of elongation and a collar region at the interface. (B) The stereotypical morphology of elongated Keller sandwiches in control explants (n=15). (C) Explants expressing Xdsh-D2 fail to elongate and no distinction can be made between mesodermal and ectodermal regions (n=11/11 display reduced elongation). (D) Explants expressing Xdd1 also fail to elongate (n=5/5 display reduced elongation). (E) Observation of GFP localization (green) demonstrates targeting of injected Xdsh-D2 to the neural ectoderm. Upper panels show explant morphology, lower panels show distribution of Xdsh-D2 GFP fluorescence (green). Note that the mesoderm does not express Xdsh-D2 (arrowheads) and has elongated; the adjacent neural tissue is expressing Xdsh-D2 (green) and has failed to elongate or narrow.
