Fig. 1. Defective convergent extension in Lp embryos before the onset of neural tube closure. (A-C) DiI injection of the node, and (D-F) electroporation of a GFP-expressing construct into midline neural plate. Dorsal views (rostral to the top) of DiI- or GFP-labelled embryos, cultured for 18 hours to the 5-7 somite stage. Wild-type embryos (A,D) exhibit striking midline extension of DiI- or GFP-labelled cells (arrows), while Lp/+ embryos (B,E) exhibit variable midline extension. Lp/Lp embryos (C,F) show very limited midline extension, after either DiI or GFP labelling. Arrowheads: DiI injection site in the node; asterisks: open neural tube in Lp/Lp embryos. (G-I) Transverse sections at axial levels shown in A through a wild-type embryo 18 hours after DiI injection into the node. Caudally, intense DiI labelling is present in the notochordal plate just rostral to the node (arrow in G) and in a few midline neural plate cells (arrowhead in G). More rostrally, at the level of the closed neural tube (H) and the open hindbrain (I), only the notochord is labelled (arrows in H and I). (J) Transverse section through electroporated wild-type embryo. Immunostaining with anti-GFP demonstrates labelling in neural plate only (arrows). np, neural plate; nt, neural tube. Scale bars: in F, 0.5 mm for A-F; in G, 0.1 mm for G-I; 0.05 mm in J.