Practice question

Head regeneration in Hydra absolutely requires functional canonical Wnt signaling to maintain and rebuild hypostome organizer. Chemical inhibition of Wnt secretion using porcupine inhibitors Wnt-C59 or IWP-2, blocking Wnt ligand palmitoylation, eliminates endogenous Wnt3 gradient at oral pole. Without Wnt3, beta-catenin target genes including Cnox-3, Brachyury1, and tentacle markers fail to reactivate after decapitation, hypostome does not form, and remaining column adopts foot fate expressing pedibin. Tentacle morphogenesis also fails because hypostome organizer provides prerequisite inductive signals. Excessive budding not observed because organizer loss prevents new axis formation entirely, confirming Wnt requirement for head specification.