Evolution of vertebrates as viewed from the crest

Abstract

The origin of vertebrates was accompanied by the advent of a novel cell type: the neural crest. Emerging from the central nervous system, these cells migrate to diverse locations and differentiate into numerous derivatives. By coupling morphological and gene regulatory information from vertebrates and other chordates, we describe how addition of the neural-crest-specification program may have enabled cells at the neural plate border to acquire multipotency and migratory ability. Analysis of the topology of the neural crest gene regulatory network can serve as a useful template for understanding vertebrate evolution, including elaboration of neural crest derivatives.

Figure 1

Gene regulatory interactions controlling vertebrate neural crest formation and the tunicate a9.49 cell lineage. (A) Different stages in neural crest formation. Neural crest cells are defined by their origin at the neural plate border, epithelial to mesenchymal transition, migratory capacity and multipotency. (B) A neural crest gene regulatory network endows this cell population with its unique features. This GRN is comprised of different modules arranged hierarchically, which control each step of neural crest development. Notably, the neural crest specification module, marked in red, appears to be missing from the neural plate border of invertebrate chordates. (C) Regulatory circuit of a tunicate neural crest-like pigmented cell precursor. Diagrams adapted from Simoes-Costa and Bronner and based on the results of Abitua and colleagues.

Figure 2

Schematic cladogram of chordate features associated with neural crest cells or their derivatives. Labels at top indicate names of monophyletic groupings below. The timing of duplications is indicated in blue, while character changes are indicated by red lines. The order of character changes within a stem group is arbitrary. Adapted from Green and Bronner.