Practice question

GSK-three normally phosphorylates beta-catenin within destruction complex containing Axin and APC, marking it for degradation by beta-TrCP ubiquitin ligase and proteasome. Vegetal Dishevelled inhibits GSK-three locally, allowing beta-catenin accumulation in micromeres and macromeres vegetally. Chemical inhibition of GSK-three with lithium chloride or genetic dominant negative constructs eliminates degradation globally in all blastomeres. Consequently beta-catenin accumulates in all nuclei including animal pole cells that normally remain ectodermal. Animal blastomeres then ectopically activate endoderm genes like Endo16 and mesenchyme genes Msp130. Result is severe vegetalization with expanded gut and excess skeleton production.