Wnt signaling restores evolutionary loss of regenerative potential in Hydra

The regenerative potential of animals varies widely, even among closely-related species. In a comparative study of regeneration across the Hydra genus, we found that while most species exhibit robust whole-body regeneration, Hydra oligactis and other members of the Oligactis clade consistently fail to regenerate their feet. To investigate the mechanisms underlying this deficiency, we analyzed transcriptional responses during head and foot regeneration in H. oligactis. Our analysis revealed that the general injury response in H. oligactis lacks activation of Wnt signaling, a pathway essential for Hydra vulgaris foot regeneration. Notably, transient treatment with a Wnt agonist in H. oligactis triggered a foot-specific transcriptional program, successfully rescuing foot regeneration. Our transcriptional profiling also revealed dlx2 as a likely high-level regulator of foot regeneration, dependent on Wnt signaling activation. Our study establishes a comparative framework for understanding the molecular basis of regeneration and its evolutionary loss in closely-related species. The experimental design of this study included transcriptional profiling of H. oligactis head and foot regeneration, all timepoints, tissues and treatment included at least 3 biological samples each composed of tissue extracted from ~30 animals. A first batch of Illumina sequencing was comprised of 4 biological replicates of homeostatic head and foot tissue and 3 biological replicates of head and foot regenerating tissue at 0, 3, 12 and 48 hours after a transverse bisection at the midpoint of the body column. Regenerating tissue was collected by cutting 1/3 of the body column adjacent to the wound site. Homeostatic heads and feet and 0 hpa head and foot regenerating tissue were treated for 30 seconds with 0.05% DMSO, while 3, 12 and 48 hpa samples were left in 0.5% DMSO for 3 hours before washing. In addition, this first sequencing batch included at least 3 biological replicates of foot regenerating tissue treated with Alsterpaullone 5 uM for 3 hours after amputation and collected at 3, 12 and 48 hours hpa. A second RNA-sequencing batch was comprised of 2 biological replicates of homeostatic head and foot tissue and 3 biological replicates of head and foot regenerating tissue collected at 0 and 24 hpa after 0.05% DMSO treatment and foot regenerating tissue collected at 24 hpa after treatment a 3 hours treatment with 5uM Alsterpaullone. In total this dataset is comprised of 60 RNA-seq samples.