Regulation of Hydra Regeneration by Hippo Pathway effector YAP and Biomechanical forces

Abstract

Hydra is a freshwater polyp belonging to the phylum Cnidaria. These polyps are known to exhibit tremendous regenerating potential. It is still unclear how the regenerating tissue is reorganized, how the complex interplay of signaling cascades required for generating positional information in regenerating tissue is produced and regulated. Specifically, the question of how biophysical forces govern the regeneration process by integrating early injury response with positional cues has been a subject of intense research in recent times in regenerative model organisms, including Zebrafish and Axolotl. Owing to the simple tissue organization and the well-characterized morphallactic regenerative biochemical signaling pathways, Hydra provides an ideal system for developing a model system to study biomechanical regulation. In this study, we employed the paradigm of head regeneration in Hydra to understand how tissue damage invokes changes in tissue mechanics and how the mechanical forces can affect the regenerative response. Hippo signalling is a well-known pathway for mechanotransduction in cells. In this study, we report for the first time the existence of a complete repertoire of the Hippo pathway core components in Hydra. By staining Hippo effector YAP during head regeneration, we report that mechanosensitive (YAP positive) cells migrate to the site of injury early during regeneration. We show that by disrupting the Hippo pathway by the perturbation of the interaction of YAP (a transcription co-activator) and its cognate transcription factor TEAD, we can accelerate the regeneration in Hydra. Further, scanning electron microscopy (SEM) based evaluation of the ultrastructure demonstrated an extensive fibrosis-like condition of the extracellular matrix (ECM) in regenerating tips of Hydra upon YAPTEAD disruption. We then characterized the role of ECM structure and tissue stiffness in regulating regeneration in Hydra. Towards this, using Atomic Force Microscopy (AFM) to measure the Young s modulus of Hydra body column, we