Figure 2.

Stages in the formation of the neural crest.

A) At the neural plate stage the non-neural ectoderm signals to the neural plate, primarily through the actions of Bmp’s and wnt’s, to specify the neural plate border region. The notochord underlies the midline of the neural plate. B) As neurulation progresses, the neural plate infolds and the neural plate border rises up and forms the neural folds. At the ventral midline of the neural plate, the floor plate is induced to form by the notochord. The floor plate and notochord will act to pattern the ventral neural tube. C) Following apposition of the neural folds and their fusion across the midline, the neural tube is forms. The neural crest cells emigrate from the dorsal most region of the neural tube, which is derived from the neural folds. This dorsal territory will also generate the roof plate, and this structure will act to pattern the dorsal neural tube.