Practice question

Localization of beta-catenin after cortical rotation creates nuclear gradient high dorsally, low ventrally that patterns secondary axis. Dorsally Dishevelled inhibits GSK-three destruction complex containing Axin and APC, stabilizing beta-catenin that accumulates in nuclei and activates organizer genes siamois, twin, goosecoid via TCF. Ventrally active GSK-three phosphorylates beta-catenin for ubiquitin-mediated proteasomal degradation, preventing dorsal fate ventrally. Resulting gradient instructs dorsal-ventral axis, not animal-vegetal axis which depends on VegT and Vg1, nor mesoderm specification alone requiring Nodal, nor neural induction needing BMP inhibition downstream of dorsal specification for complete axis.