Practice question

Beta-catenin acts as transcriptional co-activator dictating posterior identity where high levels specify tail. Knockdown via RNA interference abolishes Wnt target activation, converting posterior wound fate to anterior, while pre-existing tails still present may begin anterior transformation. Because anterior identity requires active Wnt inhibition via Notum, loss of beta-catenin does not prevent head formation; instead tail regeneration program is selectively disrupted leading to formation of ectopic head or failure of posterior blastema patterning. Thus only tail regeneration appears affected initially, producing two-headed phenotype when knockdown complete, highlighting requirement for beta-catenin in posterior specification rather than global regeneration arrest.