YU, J-K; HOLLAND, L.Z.; HOLLAND, N.D.: Developmental expression of AmphiFoxD3, an amphioxus gene in the FoxD subfamily: insight into the evolutionary origin of vertebrate neural crest

Neural crest is unique to vertebrates. Embryologically, neural crest derives from the edges of the neural plate and adjacent non-neural ectoderm, and undergoes an epithelial/mesenchymal transition to become a migratory population of cells that gives rise to numerous differentiated cell types. The evolution of neural crest is thought responsible for many of the complex structures of the vertebrate head which are lacking in invertebrate chordates (amphioxus and tunicates). Previous work has shown that cells at the edges of the neural plate and adjacent non-neural ectoderm in amphioxus express several of the same genes (Pax3/7, Dll, Snail) as premigratory neural crest in vertebrates, leaving open the question of what genes are responsible for the ability of these cells to migrate and differentiate into numerous cell types in vertebrates but not in amphioxus. To address this question, we cloned the amphioxus homolog of FoxD3, which is a neural crest marker in vertebrates, and analyzed its expression. Surprisingly, unlike vertebrate FoxD3 genes, AmphiFoxD3 is not expressed in the edges of the neural plate. Instead, it is mainly expressed in the dorsal part of the notochord, the developing somites and the posterior part of the gut. Expression in the nerve cord is limited to cerebral vesicle. These results suggest that FoxD3 may have acquired a new role in cells at the edges of the neural plate in connection with their evolving migratory properties. We are further addressing this possibility by a comparative analysis of cis-regulation of AmphiFoxD3.