Avian neural crest cell fate decisions: a diffusible signal mediates induction of neural crest by the ectoderm

During neurulation, a region of central ectoderm becomes thickened to form the neural plate which then folds upon itself to generate the neural tube, from which all neurons and glia cells of the central nervous system arise. Neural crest cells form at the border of the neural plate, where it abuts the prospective epidermis. The neural crest is a transient population of cells that undergo an epithelial-mesenchymal transition, become highly migratory and subsequently differentiate into most of the peripheral nervous systems as well as numerous other derivatives. The origin of neural crest cells at the epidermal-neural plate border suggests that an interaction between these two tissues may be involved in neural crest formation. By experimentally juxtaposing prospective epidermis with naive neural plate, we previously showed that an inductive interaction between these tissues can generate neural crest cells. Here, we further characterize the nature of this inductive interaction by co-culturing isolated neural plate and prospective epidermis on opposing sides of polycarbonate filters with differing pore sizes. We find that neural crest cells are generated even when epidermis and neural plate are separated by filters that do not allow cell contact. These results suggest that the epidermal inducer is a diffusible, secreted molecule. We discuss the developmental potential of neural crest precursors and lineage decisions that effect their differentiation into numerous derivatives.