Fig. 4. PTK7 is expressed in cranial neural crest cells and required for their migration. (A-C) PTK7 expression pattern in Xenopus laevis detected by whole-mount in situ hybridization. (A,B) PTK7 is broadly expressed in premigratory neural crest cells at early neurula stages (black arrow). (C) At stage 26, PTK7 expression is detected in migrating cranial neural crest cells (black arrow). (D-M) Embryos injected in one blastomere at the two-cell stage with different constructs in combination with 100 pg GFP RNA as a lineage tracer. Neural crest migration was analyzed at neurula stages using the neural crest marker twist (D,F,H) or the midbrain-hindbrain marker engrailed (E,G,I). The injected side is shown on the right. (D,E) GFP-injected embryos. (F,G) Embryos co-injected with 10 ng control MO and GFP RNA. (H,I) Embryos co-injected with 10 ng PTK7 MO and GFP RNA. (J-M) Tadpole embryos analyzed by in situ hybridization with the neural crest markers twist (J,K) or AP-2 (L,M). The injected side is shown on the right. (J,L) Tadpoles injected with 10 ng control MO und 100 pg GFP RNA. (K,M) Tadpoles injected with 10 ng PTK7 MO and 100 pg GFP RNA. Inhibition of cranial neural crest migration is marked by arrows in H,K,M. (N) Graph summarizing the MO injection experiments. Left graph summarizes five independent experiments (analyzing neurula stages) and six independent experiments (analyzing tadpole stages), respectively. The right graph summarizes three independent rescue experiment. The percentage of migrating neural crest cells was determined by twist in situ hybridization. Columns are labeled with the number of injected embryos.