Practice question

Anterior-posterior patterning in planarians depends on graded canonical Wnt activity where high activity enforces posterior tail fate and inhibits anterior head fate. Wnt1 and Wnt11-2 expressed at posterior pole by muscle position control genes stabilize beta-catenin activating tailless genes including fzd4, hox4, and wntP2. RNA interference against beta-catenin causes ectopic heads posteriorly, overactivation via APC knockdown causes tails anteriorly. Thus Wnt/beta-catenin promotes tail regeneration and suppresses head identity. FGF10 regulates limb bud outgrowth, Sonic hedgehog patterns limb anterior-posterior digits via ZPA, BMP controls dorsoventral axis, not posterior versus anterior choice in planarian regeneration.