Fig. 8. A stabilized Slug mutant rescues neural crest formation in Ppa-injected embryos. (A) Embryos were injected with Slug (a-d) or Slug^1,2 (e-h), together with the lineage tracer nß-gal (red) and in situ hybridization was used to analyze neural crest precursor formation and migration. Both Slug (a) and Slug^1,2 (e) expand Slug expression at stage 15. Slug overexpression increases the number of migratory neural crest cells at stage 24 (b, injected side; c, control side) whereas Slug^1,2 injection results in a clearing of Sox10-positive cells (f, injected side; g, control side). The presence of premature, ectopic migratory neural crest cells is observed in embryos overexpressing Slug^1,2 (h, inset) but not in embryos injected with Slug (d). (B) Embryos were injected in one of two cells with Ppa (a) Slug^1,2 (b) or Ppa and Slug^1,2 (c) along with the lineage tracer nß-gal (red). Ppa prevents neural crest precursor formation (a), whereas Slug^1,2 expands this cell population (b), as assayed by Slug expression. Co-injection of Slug^1,2 with Ppa rescues neural crest precursor formation (c).