A C-terminally truncated form of β-catenin acts as a novel regulator of Wnt/β-catenin signaling in planarians

Β-catenin,the core element of the wnt/β-catenin pathway,is a multifunctional and evolutionarily conserved protein which performs essential roles in a variety of developmental and homeostatic processes. despite its crucial roles,the mechanisms that control its context-specific functions in time and space remain largely unknown. the wnt/β-catenin pathway has been extensively studied in planarians,flatworms with the ability to regenerate and remodel the whole body,providing a ‘whole animal’ developmental framework to approach this question. here we identify a c-terminally truncated β-catenin (β-catenin4),generated by gene duplication,that is required for planarian photoreceptor cell specification. our results indicate that the role of β-catenin4 is to modulate the activity of β-catenin1,the planarian β-catenin involved in wnt signal transduction in the nucleus,mediated by the transcription factor tcf-2. this inhibitory form of β-catenin,expressed in specific cell types,would provide a novel mechanism to modulate nuclear β-catenin signaling levels. genomic searches and in vitro analysis suggest that the existence of a c-terminally truncated form of β-catenin could be an evolutionarily conserved mechanism to achieve a fine-tuned regulation of wnt/β-catenin signaling in specific cellular contexts. © 2017 su et al.