Fig. 4. Nodal signalling is required for lateral neural marker gene expression, but not for neural fate. Embryo treatment is shown at the top of the panels and the marker analysed to the left of the panels. (A) Expression of Ci-Snail, Ci-Delta2 and Ci-ETR at the gastrula stage. All embryos are of vegetal pole view. Inserts show lateral view of Ci-Delta2 expression in b-line cells (weak in b8.19 and b8.17 and strong in b8.20 and b8.18). (B) Each embryo is shown in two orientations, a neural plate view (left) and a lateral view (right). A-line and a-line parts of the neural plate are indicated on the control embryos. Neural plate cells of SB431542-treated embryos were not always as well aligned as the embryos shown in the picture for Ci-Otx staining. Sometimes, cells in neighbouring rows intercalated with each other, which resulted in wider rows of 1-2 cells in depth.