Generic and context-dependent gene modulations duringHydrawhole body regeneration

Abstract

AbstractThe cnidarianHydrais a classical model of whole-body regeneration. Historically,Hydraapical regeneration has received more attention than its basal counterpart, most studies considering these two regenerative processes independently. We present here a transcriptome-wide comparative analysis of apical and basal regeneration after decapitation and mid-gastric bisection, augmented with a characterization of positional and cell-type expression patterns in non-regenerating animals. The profiles of 25’637Hydratranscripts are available on HydrATLAS (https://hydratlas.unige.ch), a web interface allowing a convenient access to each transcript profile. These data indicate that generic impulse-type modulations occur during the first four hours post-amputation, consistent with a similar integration of injury-related cues on both sides of the amputation plane. Initial divergences in gene regulations are observed in regenerating tips between four and eight hours post-amputation, followed by a dramatic transcriptomic reprogramming between eight and 16 hours when regulations become sustained. As expected, central components of apical patterning,Wnt3andHyBra1, are among the earliest genes up-regulated during apical regeneration. During early basal regeneration, a BMP signaling ligand (BMP5-8c) and a potential BMP inhibitor (NBL1)are up-regulated, suggesting that BMP signaling is involved in the basal organizer, as supported by higher levels of phosphorylated Smad in the basal region and by the LiCl-induced extension ofNBL1expression. By contrast, upon ectopic activation of Wnt/β-catenin signaling,NBL1is no longer expressed, basal differentiation is not maintained and basal regeneration is abolished. A tight cross-talk between Wnt/β-catenin apically and BMP signaling basally appears necessary for maintaining and regeneratingHydraanatomy.