Practice question

Lithium chloride inhibits GSK-3 beta kinase by competing for magnesium binding, mimicking canonical Wnt signaling. GSK-3 inactivation prevents beta-catenin phosphorylation at Ser33/37/Thr41 and proteasomal degradation, leading ubiquitous beta-catenin stabilization throughout embryo. Nuclear beta-catenin activates Siamois and Twin everywhere, converting entire marginal zone into Nieuwkoop and organizer tissue expressing Goosecoid. Resulting embryo highly dorsalized forming expanded notochord, neural tissue and lacking ventral blood islands. Beta-catenin stabilization alone explains dorsalization, not direct Noggin activation, confirming Wnt-beta-catenin dorsal pathway and GSK-3 regulatory role.