The increasing complexity of the Snail gene superfamily in metazoan evolution.

The Snail family of zinc-finger transcription factors is involved not only in the development of vertebrate and invertebrate embryos, but also in tumour progression. Following the identification of eight new members, we have analysed the evolutionary history of these genes and found that they constitute a superfamily that groups two independent families, Snail and Scratch. We propose that the duplication of an ancestral gene at the time of the metazoan radiation (1000-500 Myr ago) gave rise to Snail and Scratch, and that independent duplications in protostomes and deuterostomes led to the present situation. We discuss the implications of the distinct duplication events on the acquisition of new functions.