Heads or Tails? Regulation of Wnt signaling and axial identity establishment during whole-body regeneration in the acoel worm Hofstenia miamia

Abstract

Whole-body regeneration relies on the re-establishment of body axes for correct patterning of tissue outgrowth. Wnt signaling is utilized to correctly regenerate tissues along the primary axis in many animals, including cnidarians, planarians, and acoels. However, the causal mechanisms that first launch Wnt signaling during regeneration are poorly characterized. I used the acoel worm Hofstenia miamia to identify processes that initiate Wnt signaling during posterior regeneration. In a two-part approach, I first used an unbiased assessment of RNA-seq data to determine the first genes with asymmetric induction between anterior- and posterior- facing wounds during regeneration, and assessed the role of these genes in polarity establishment. Second, I systematically assessed the requirement of all identified Wnt ligands in Hofstenia for proper regeneration and polarity establishment. Both analyses converged on a single Wnt ligand, wnt-3, that is upregulated early only in posterior-facing wounds and is required for regenerating posterior tissues. I then characterized the function of wnt-3 during regeneration. I found it was expressed in stem cells, was needed for their proliferation, and its function was stem cell dependent. Chromatin accessibility data revealed wnt-3 activation required input from the general wound response to be induced in posterior-facing wounds. Additionally, the expression of a different Wnt ligand, wnt-1, prior to amputation was required for wound-induced activation of wnt-3. This dissertation established a gene regulatory network for initiating Wnt signaling in posterior tissues in a bilaterian, and enables comparative studies of Wnt deployment during whole-body regeneration across Metazoa.