Genetic Correlates of Neural Crest Evolution

Abstract

Neural crest cells are unique to vertebrates and generate most of the adult structures that distinguish them from their closest invertebrate relatives, the cephalochordates. To elucidate the molecular bases of neural crest evolution, I analyzed the expression, function, and cis-regulation of amphioxus genes with vertebrate homologs having established roles in neural crest development. By comparing these amphioxus genes with their agnathan and gnathostome homologs, I have uncovered genetic changes coincident with, and potentially causal to, the origins of neural crest. I demonstrate that three transcriptional regulators involved with neural crest development, AP-2, Id, and SoxE, were recruited to the neural plate border early in vertebrate evolution? implying that genetic cooption of high-order transcription factors was a major driving force in neural crest evolution. I also show that the function of the Snail protein in establishing the neural plate border was not significantly altered during vertebrate evolution, although vertebrate Snail genes may have evolved novel domains necessary for later functions in neural crest cells. Finally, I began characterizing the cis-regulation of vertebrate and amphioxus Slug/Snail orthologs to determine if divergent aspects of Snail gene expression (i.e., expression in neural crest cells) are reflected in structural differences in Snail cis-regulatory DNA. Using this 3-tiered approach I have begun to define the novel genetic regulatory interactions that drove the evolution of neural crest cells in the vertebrate lineage.