Inhibition of neural crest cell differentiation by embryo ectodermal extract

The white mutation in Mexican axolotls has long been thought to be a defect associated with the embryonic extracellular environment, but not with embryonic neural crest cells. Thus it was believed that pigment cells in white axolotls disappear from the skin during early development, not because they are intrinsically defective but because they have no choice but to move into an unfavorable environment. We present evidence to suggest that: (1) white neural crest cells are in fact intrinsically different from dark (wild-type) cells, and (2) an inhibitor is produced in white embryonic ectoderm that actively suppresses the migration, differentiation, and survival of pigment cells in this animal. How these observations fit into the existing body of literature on the white mutant and a model for how the white phenotype might develop are discussed.