Practice question

Disheveled (Dsh) is key intracellular transducer of Wnt signaling vegetally localized in sea urchin egg cortex during oogenesis. It binds and inhibits Axin-GSK-3β-APC destruction complex responsible for phosphorylating β-catenin at N-terminus and marking it for ubiquitin-proteasome degradation. By preventing phosphorylation, Disheveled stabilizes β-catenin allowing cytoplasmic accumulation and subsequent nuclear import in vegetal blastomeres. Nuclear β-catenin partners with TCF/LEF to activate endomesodermal gene regulatory network and Pmar1. Hence Disheveled action preserves β-catenin, establishing vegetal polarity and micromere specification early in embryogenesis before zygotic transcription.