β-Catenin-Dependent Control of Positional Information along the AP Body Axis in Planarians Involves a Teashirt Family Member

Wnt/β-catenin signaling regulates tissue homeostasis and regeneration in metazoans. In planarians—flatworms with high regenerative potential—Wnt ligands are thought to control tissue polarity by shaping a β-catenin activity gradient along the anterior-posterior axis, yet the downstream mechanisms are poorly understood. We performed an RNA sequencing (RNA-seq)-based screen and identified hundreds of β-catenin-dependent transcripts, of which several were expressed in muscle tissue and stem cells in a graded fashion. In particular, a teashirt (tsh) ortholog was induced in a β-catenin-dependent manner during regeneration in planarians and zebrafish, and RNAi resulted in two-headed planarians. Strikingly, intact planarians depleted of tsh induced anterior markers and slowly transformed their tail into a head, reminiscent of β-catenin RNAi phenotypes. Given that β-catenin RNAi enhanced the formation of muscle cells expressing anterior determinants in tail regions, our study suggests that this pathway controls tissue polarity through regulating the identity of differentiating cells during homeostasis and regeneration. [Display omitted] •Regeneration involves conserved β-catenin-dependent genes in planarians and fish•A β-catenin-dependent teashirt gene controls tissue polarity in planarians•β-catenin RNAi induces the differentiation of muscle cells with anterior identity Reuter et al. used transcriptome analyses to identify conserved downstream targets of Wnt/β-catenin signaling and their cellular sources in planarians. They discovered teashirt as a regulator of regeneration polarity and provide insights into β-catenin-mediated control of positional information along the planarian anterior-posterior body axis.