Practice question

Immunostaining and in situ data from early Xenopus show beta-catenin protein and mRNA widely distributed throughout cortex and cytoplasm of fertilized egg and early cleavage blastomeres, not restricted initially. Uniform low levels present animally and vegetally, cortically and interiorly. After cortical rotation, dorsal determinants inhibit GSK-3 dorsally, preventing beta-catenin degradation selectively; ventral destruction complex with Axin, APC and GSK-3 phosphorylates beta-catenin targeting proteasome. Consequently initially uniform distribution refined to dorsal nuclear enrichment. This uniform precursor ensures all blastomeres competent to stabilize beta-catenin if Wnt signal received.