Formation of cambial ring

The cells of medullary rays, adjoining these intrafascicular cambium become meristematic and form the interfascicular cambium. Thus, a continuous ring of cambium is formed

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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.

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β-catenin Destruction Complex contains:

Tumor suppressor APC

Dvl protein

Constitutively active protein kinases GSK 3β and CK1

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Kinases CK1 and GSK3,

sequentially phosphorylate β-catenin at multiple serine and threonine residues

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E3 βTrCP ubiquitin ligase then binds to two phosphorylated residues on β catenin, leading to ubiquitinylation and degradation in proteasomes.

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In the absence of Wnt,

TCF is associated with transcriptional repressor proteins Groucho (Gro) that inhibit gene transcription in nucleus

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Formation of the Wnt/Fz/LRP complex at the cell

surface causes the adaptor protein Dishevelled, to bind to Fz and Axin to bind to LRP, resulting destabilization and inactivation of the destruction complex