Mechanisms for the establishment of polarity during whole-body regeneration

Harvard University, Cambridge MA

Investigators

Abstract

Regeneration is the process by which animals can restore fully functional tissues and organs that have been damaged or lost. To do so, an animal must know precisely which cells and tissues need to be replaced. This work will focus on the striking case of an animal that can restore an entire head including a new brain, or a tail, in the correct place every time it is challenged to regenerate, and will ask how the animal determines which tissues it must build. To ask how genes specific to head versus tail tissue are turned on in the right place, achieving polarity along the head-tail axis of the body, the project will examine (1) how the decision to make mRNA from these genes is made in the genomes of head- versus tail-regenerating wounds, and (2) how the actions of these genes’ mRNAs, once made, may be controlled specifically in head- versus tail-regenerating wounds. By studying two distinct levels of gene regulation, using state-of-the-art sequencing and genome editing technologies, the project’s unbiased approach will provide new insights into polarity establishment during regeneration. The researchers will broaden this work’s impact by helping the research community in using the three-banded panther worm (the research organism that this project focuses on), by training undergraduates and middle school students, and by engaging the public through an accessible video explaining the project. This project will use the acoel worm Hofstenia miamia, which regenerates robustly from small body fragments generated by amputation. During the regeneration of H. miamia, a key polarity-determining gene, wnt-3, is specifically expressed in the posterior-facing (tail-forming) wound site, but not the anterior-facing (head-forming) wound site. This asymmetric wnt-3 expression requires the wound response gene egr. However, egr is expressed at both head and tail wound sites, raising the question of how symmetric injury stimuli such as egr expression result in asymmetric outputs driving patterning. This project will first focus on cell signaling events launched upon injury that may activate early gene expression, measuring Erk and Wnt signaling levels at head and tail wounds and assessing whether perturbing these pathways affects polarity outcomes. Next, asymmetric gene expression, such as for wnt-3, will be investigated at the level of transcriptional regulation, using chromatin accessibility data to find transcriptional activators/repressors that influence gene expression. Finally, the hypothesis that the asymmetry of wnt-3 in head versus tail wounds results from differential post-transcriptional regulation mechanisms, for example by microRNAs, will be tested. This work will answer questions about a regeneration patterning phenomenon at three levels of regulation (cell signaling, transcriptional, and post-transcriptional), building an understanding of the mechanisms beneath the stunning feat of regeneration with correct polarity. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.