Practice question

Beta-catenin stability is controlled by destruction complex containing Axin, APC, and GSK-three kinase that phosphorylates conserved serine residues marking beta-catenin for proteasomal degradation via beta-TrCP. Wnt pathway activation recruits Dishevelled to plasma membrane via Frizzled receptor, where Dishevelled inhibits GSK-three kinase activity through protein interactions, preventing phosphorylation. Inhibition allows beta-catenin accumulation and nuclear translocation to activate TCF targets like siamois and Pmar1. In sea urchin, maternal Dishevelled localized vegetally performs this inhibition constitutively, protecting beta-catenin without exogenous Wnt ligand, establishing vegetal gradient required for endomesoderm and micromere identity establishment after cleavage.