Fig. 1. (A) In the stage 16 Xenopus embryo there are four major ectodermal domains: neural plate, neural crest, pre-placodal ectoderm (PPE) and epidermis. (B) The expression pattern of six1 coincides with the PPE. (C) An idealized depiction of the ectodermal fate of the 32-cell embryo showing four dorsal blastomeres (blue) that contribute significantly to the neural plate, two ventrolateral blastomeres (green) that contribute significantly to the neural crest and PPE, and two ventral blastomeres (yellow) that contribute significantly to the ventral epidermis (from Moody, 1987).