PCP components control anterior and posterior regeneration, with a Prickle homolog impacting muscle organization, in the acoel Hofstenia miamia

Whole-body regeneration requires wound response signals to control patterning programs to enable replacement of structures in their correct locations. While a number of molecular mechanisms underlying anterior-posterior regeneration have been identified, how small fragments of animals first re-establish polarity is less well understood, with non-canonical Wnt signaling recently emerging as a potential regulator. Here, we used the acoel worm Hofstenia miamia, a new research organism capable of robust whole-body regeneration, to assess functions of the components of the Planar Cell Polarity (PCP) pathway in establishing regeneration polarity. We identified homologs of Prickle (pk-1) and Diego (dgo-1) to be required for head and tail regeneration, respectively. RNA-sequencing analysis and experimental corroboration revealed that pk-1 RNAi resulted in diminished expression of early wound response genes as well as of wound-induced expression of the anterior-specific marker fz-7, specifically in tail fragments. In contrast, dgo-1 RNAi impacted wound-induced expression of the posterior-specific marker tf7l2, specifically in head fragments. Furthermore, pk-1 and dgo-1 are enriched in longitudinal muscle, with muscle fibers showing disorganized morphology at anterior-facing wound sites of tail fragments under pk-1 RNAi. These findings suggest that pk-1 and dgo-1 are needed for wound-induced expression of anterior- and posterior-specific genes, and raise the possibility that this action is mediated via the control of muscle fiber orientation. Our work expands the study of PCP genes by revealing their functions in the process of whole-body regeneration in acoels, the sister-group to all other animals with bilateral symmetry, and will enable future studies of PCP components in controlling cellular and tissue-wide regeneration polarity.