Fig. 2. Id3 is required for neural crest precursor formation. (A) Western blot of lysates prepared from control embryos or embryos injected with an epitope tagged Id3 and then further injected with control or Id3 MOs demonstrates successful Id3 depletion. (B) Western blot of lysates from injected embryos demonstrating that although Id3 MOs efficiently deplete Xenopus Id3 protein, they do not deplete the human Id3 used for rescue experiments. The size difference between Xenopus and human Id3 is primarily due to the presence of five rather than six Myc epitopes, respectively. (C,D) In situ hybridization of embryos injected with Id3 MOs shows loss of Slug (C) and Sox10 (D) expression on the injected side of the embryo (arrowheads). (E) Id3-depleted embryos show reduced or absent migratory neural crest cells on the injected side (arrow), as visualized by Twist expression. (F) Loss of Slug expression in Id3-depleted embryos can be rescued by subsequent injection of human Id3, translation of which is not blocked by the MOs. Arrowhead indicates the injected side, red staining is from lineage tracer ß-gal.