Practice question

Planarian head formation anteriorly depends on precise Wnt inhibition; Notum secreted deacylase specifically inactivates Wnt ligands at anterior blastema, reducing beta-catenin activity allowing head specification genes FoxD, prep to dominate. Notum expressed in anterior pole muscle cells, enriched anteriorly after amputation, creating low Wnt environment suitable for head organizer establishment. RNAi of Notum leads to hyperactive Wnt anteriorly causing failure to regenerate normal head or formation of two-tailed animals. Hence Notum acts as anterior restricting factor localizing head fate to anterior end by antagonizing posteriorizing Wnt signals and preventing ectopic head formation posteriorly while permitting single anterior head.