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. Author manuscript; available in PMC: 2015 May 8.
Published in final edited form as: Curr Top Dev Biol. 2015 Jan 22;111:301–350. doi: 10.1016/bs.ctdb.2014.11.009

Figure 3.

Figure 3

During gastrulation, early, high BMP levels activate several NB-specifying genes and low BMP levels, controlled by the secretion of BMP antagonists, allow the expression of neural genes (e.g., SoxB1 transcription factors). The NB-specifying genes interact with each other to promote (black arrows) the formation of the NB zone, and they repress (red bars) the expression of neural genes. Indicated are the various interactions, described in the text, that result in the separation of the NB zone into the neural crest and the pre-placodal ectoderm (PPE). Contributing to this separation are several signaling pathways. Later, high levels of BMP promote an epidermal fate, but this pathway must be attenuated to produce neural crest and PPE. An FGF pulse is required for PPE formation. Wnt postitively regulates neural crest formation and represses PPE formation.