Some of the regions in the eye lack color, whereas others are red. This is because the white gene (required to develop red pigment) was inactivated by adjacent heterochromatin in some cells, but remained active in others.

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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

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#Unit 4. Cell Communication and Cell Signaling

Homologs

β-catenin in vertebrates = Armadillo in Drosophila

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#Unit 4. Cell Communication and Cell Signaling

“canonical” Wnt signaling uses a second TM protein, LRP that associates with Frizzled in a Wnt signal– dependent manner.

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#Unit 4. Cell Communication and Cell Signaling

Homologs

LRP in vertebrates = Arrow in Drosophila

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#Unit 4. Cell Communication and Cell Signaling

In the absence of Wnts,

“free” β-catenin are targeted for degradation by a cytosolic destruction complex that is held together by the tumor suppressor protein Axin.