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. Author manuscript; available in PMC: 2009 Jun 1.
Published in final edited form as: Dev Biol. 2008 Mar 20;318(1):52–64. doi: 10.1016/j.ydbio.2008.02.061

Figure 11. Model for the two phases of SHH signaling required for intestinal gdnf expression and normal ENS development.

Figure 11

Diagrams illustrate the relationship between ENS development, endodermal expression of SHH and the expression of gdnf in the intestinal mesenchyme. At 24hpf prior to migration of ENS NCC from the vagal region there is no expression of shh in the endoderm or expression of gdnf in the intestinal mesenchyme. Around 30hpf shh begins to be expressed in the anterior region of the intestinal endoderm. This expression coincides with the expression of gdnf in the adjacent intestinal mesenchyme and the beginning of the migration of the ENS NCC from the vagal region to the anterior end of the intestine. We refer to this as phase I or the pre-enteric phase of ENS development. By 48hpf shh is expressed along the whole length of the intestine and gdnf is now expressed in the adjacent mesenchyme along the whole length of the intestine. In this phase II of ENS development, the enteric phase, ENS NCC migrate along the whole length of the intestine reaching the distal end by 60hpf.