1. Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan
2. Faculty of Integrated Arts and Sciences, University of Tokushima, 1-1 Minami-Josanjima, Tokushima 770-8502, Japan
It is now accepted that ancestral vertebrates underwent two rounds of genome duplication. Here we test the possible utility of these genome duplication events as a reference time for the evolutionary history of vertebrates, by tracing the molecular evolutionary history of the genes involved in vertebrate neural crest development. For most transcription factors that are involved in neural crest specification, more than two paralogs are involved in that process. These were likely involved in the specification of the neural crest before the genome duplications occurred in ancestral vertebrates, although FoxD3 may have acquired that role after the genome duplications. By contrast, the epithelial-mesenchymal transition of neural crest cells is controlled by genes that evolved after the genome duplications, such as cadherin6, cadherin7, cadherin11, and rhoB. This suggests that primitive neural crest cells control their delamination by using a small or distinct set of cell adhesion molecules. Alternatively, these observations suggest that delamination of the neural crest evolved after the genome duplications. In that case, the neural crest might have evolved in sequential steps; the specification of the neural crest occurred before the genome duplications, and the neural crest acquired a new cell migration property after the genome duplications.
Keywords: vertebrates, genome duplication, neural crest, evolutionary sequence