In situ hybridization shows that PlexinA1 is expressed in Xenopus laevis NC cells. (A–C) PlexinA1 is expressed in the animal hemisphere of a one-cell stage embryo (A), a blastula stage 8 embryo (B) and a gastrula stage 10.5 embryo (C). Sense controls are shown on the left. (D, E) PlexinA1 expression is detected in the area of the closing neural tube (white arrow) and in premigratory NC cells at neurula stage 16 (D) and neurula stage 23 (E). (F) At tadpole stages PlexinA1 is expressed in the migrating NC cells, the eye, the pronephros and the somites. Abbreviations: nc, neural crest; pn, premigratory NC cells; p, pronephros; s, somites.