Fig. 1. Labelling sites, donor origin and graft sites. (A) Schematic showing labelling and grafting experiments. Blue fill denotes sites of DiI label. In 8.5 d.p.c. embryos, the ventral layer of node is exposed as a hiatus in the endoderm and can therefore be labelled separately from the ectoderm layer immediately above it, whereas anterior primitive streak is labelled by inserting a pipette through the endoderm and thus labels all layers. The entire neural ectoderm surface, including the posterior ventral neural plate that overlies the notochord is labelled in 10.5 d.p.c. cultured tail pieces. Broken red lines outline sites dissected for grafting. The broken black line outlines plug of tissue at the node/streak border replaced by graft in host embryo. (B) Dissection of 10.5 d.p.c. tail bud: (left) lateral view of tail bud after removal of paraxial mesoderm, overlaid with position of CNH and TBM (broken red lines); (right, top) the same embryo after removal of dorsal neural tube and hindgut; (right, bottom) the same piece rotated so that the widened end of the notochord is upwards. CNH is outlined in red. (C) Inset shows a dissected clump containing eight GFP-labelled cells amongst 200 unlabelled cells from the CNH of the embryo in Fig. 2C,H,L. Main panel: posterior view of an embryo containing this clump grafted immediately posterior to the node (outlined by a broken white line) at the anterior of the primitive streak, the posterior limit of which is marked by a white arrow.