teashirt is required for head-versus-tail regeneration polarity in planarians.

Regeneration requires that the identities of new cells are properly specified to replace missing tissues. The Wnt signaling pathway serves a central role in specifying posterior cell fates during planarian regeneration. We identified a gene encoding a homolog of the Teashirt family of zinc-finger proteins in the planarian Schmidtea mediterranea to be a target of Wnt signaling in intact animals and at posterior-facing wounds. Inhibition of Smed-teashirt (teashirt) by RNA interference (RNAi) resulted in the regeneration of heads in place of tails, a phenotype previously observed with RNAi of the Wnt pathway genes β-catenin-1, wnt1, Dvl-1/2 or wntless. teashirt was required for β-catenin-1-dependent activation of posterior genes during regeneration. These findings identify teashirt as a transcriptional target of Wnt signaling required for Wnt-mediated specification of posterior blastemas.