Practice question

Beta-catenin protein level translates Wnt signal strength into transcriptional fate choices. Inhibition via double-stranded RNA or small molecule tankyrase inhibition prevents nuclear accumulation and removes activation of posterior target genes. Posterior blastema deprived of Wnt output defaults to anterior genetic program expressing sfrp-1, notum, and prep forming ectopic head complete with brain and eyes. Anterior wound also forms head leading to animal with two heads, duplicated central nervous systems pointing outward. This multiple-head phenotype demonstrates binary switch where beta-catenin threshold determines identity. Stem cell maintenance, muscle overgrowth, or wound closure defects not observed as primary consequence of beta-catenin loss.