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Ectoderm becomes the primary Neural Tissue The notochord, alternatively called the chordomesoderm, plays a critical role in the formation of neural tissue. How does the induction occur? The chordomesoderm tissue releases noggin and chordin - two signaling
molecules that act as inductive agents. Noggin and chordin suppress
the effects of Bone morphogenetic Protein 4 (BMP-4)
- a growth factor in dorsal ectoderm that must be inhibited for ectoderm
to become neural. Additionally follastin suppresses the BMP-7. When
the notochord releases these inductive molecules, neural ectoderm is
formed from the overlying surface ectoderm. (Hall,
21) Experimentation with Neural Induction
Initial experiments to determine the inductive properties
of the notochord were performed by C. Waddington in 1933. (Carlson,
65). Waddington grafted Hensen's node from one chick embryo to another,
producing an early embryo with two Hensen's nodes. The two nodes subsequently
form two separate notochords. Waddington found that the resulting embryo
contained a second neural tube, confirming that the notochord indeed
induces neural ectoderm formation.
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