In primary neurulation, 

cells surrounding the neural plate direct the neural plate cells to proliferate, invaginate into the body, and separate from the surface ectoderm to form an underlying hollow tube.

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#Unit 4. Cell Communication and Cell Signaling

Lipid modifications of Wnt are catalyzed by the 

O-acetyltransferase Porcupine.

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#Unit 4. Cell Communication and Cell Signaling

Principal signaling receptor is Frizzled (Fz), contains 

7 TM α helices.

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#Unit 4. Cell Communication and Cell Signaling

The palmitoleate attached to the Wnt protein binds to a specific site on the Fz extracellular domain and stabilizes the Wnt-Fz complex.

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#Unit 4. Cell Communication and Cell Signaling

Wnt signal transduction pathways classify into:

1. Canonical wnt pathway (β-catenin dependent)

2. Noncanonical wnt pathways (β-catenin independent)

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#Unit 4. Cell Communication and Cell Signaling

Noncanonical pathways can be divided into two types: 

1. The “planar cell polarity” pathway

2. The “Wnt/calcium” pathway

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#Unit 4. Cell Communication and Cell Signaling

Central player in the canonical Wnt pathway is β-catenin