Practice question

Anterior-posterior polarity during planarian regeneration is reset by graded Wnt/beta-catenin signaling along body axis. Posterior wounds upregulate wnt1 transcription within muscle positional control genes, leading to stabilization of beta-catenin that translocates to nucleus activating teashirt and posterior hox genes specifying tail fate. Anterior wounds instead express secreted Wnt inhibitor Notum that deacylates Wnt ligands reducing posterior activity, permitting head organizer genes prep and foxD. Hedgehog regulates wnt1 expression upstream, but core polarity determinant is Wnt/beta-catenin gradient, distinct from JAK-STAT maintaining neoblasts or Notch regulating brain patterning, governing head-tail decision.