Snail precedes Slug in the genetic cascade required for the specification and migration of the Xenopus neural crest

The complex sequence of inductive events responsible for the generation of the neural crest at the border between the neural plate and the epidermis, triggers a genetic cascade involving several families of transcription factors. Two members of the Snail family, Snail and Slug, have both been implicated in this cascade. In chick and Xenopus, loss- and gain-of-function experiments have provided evidence that Slug plays a key role in neural crest development. However, in contrast to the chick, Snail rather than Slug is expressed in the premigratory neural crest in the mouse and, in Xenopus, Snail precedes Slug expression in this population. Thus, in order to study the function of Snail in neural crest development in Xenopus, we have carried out conditional gain- and loss-of-function experiments using different Snail constructs fused to a glucocorticoid receptor element. We show that Snail is able to induce the expression of Slug and all other neural crest markers tested (Zic5, FoxD3, Tw