Practice question

Notum encodes alpha/beta hydrolase secreted enzyme that removes palmitoleate lipid modification essential for Wnt ligand activity, thereby acting as extracellular Wnt antagonist. In regenerating planaria, notum messenger accumulates predominantly at anterior pole and anterior-facing blastemas within six hours post-amputation in longitudinal muscle cells. Local inhibition of Wnt/beta-catenin creates permissive zone for head organizer transcription factors foxD and zic-1 to establish brain and eye primordia. Beta-catenin promotes opposite posterior fate, SHH regulates posterior wnt expression, BMP mediates dorsoventral patterning. Loss of Notum causes excessive posteriorization resulting in two tails, confirming role.