Fig. 6. Model illustrating the dynamic regulatory relationship between Snail2 and Cad6B in the developing avian embryo. (A) In the premigratory region of the chick trunk, Snail2 protein is required to downregulate Cad6B transcripts along the rostro-caudal axis of the embryo such that, more rostrally, higher levels of Snail2 protein lead to lower levels of Cad6B transcripts, promoting neural crest EMT. More caudally, the absence of Snail2 protein results in the presence of Cad6B. (B) A similar pattern of expression is also observed in the midbrain, where, as neural crest cells undergo EMT (and just prior to neural crest migration), high Snail2 protein levels foster the repression of Cad6B transcripts. (C) The repression of Cad6B transcription is mediated by the direct binding of Snail2 to E-box motifs in the Cad6B regulatory region.