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 tumo ur progression. Following the identification of eight new members, we have analysed the evolutionary history of these genes and found that they consti tute a superfamily that groups two independent families, Snail and Scratch. We propose that the duplication of an ancestral gene at the time of the me tazoan radiation (1000-500 Myr ago) gave rise to Snail and Scratch, and tha t independent duplications in protostomes and deuterostomes led to the pres ent situation. We discuss the implications of the distinct duplication even ts on the acquisition of new functions.