The Rich Evolutionary History of the Reactive Oxygen Species Metabolic Arsenal Shapes Its Mechanistic Plasticity at the Onset of Metazoan Regeneration.

Regeneration, the ability to restore body parts after injury, is widespread in metazoans; however, the underlying molecular and cellular mechanisms involved in this process remain largely unknown, and its evolutionary history is consequently unresolved. Recently, reactive oxygen species (ROS) have been shown in several metazoan models to be triggers of apoptosis and cell proliferation that drive regenerative success. However, it is not known whether the contribution of ROS to regeneration relies on conserved mechanisms. Here we performed a comparative genomic analysis of ROS metabolism actors across metazoans, and carried out a comparative study of the deployment and roles of ROS during regeneration in two different metazoan models: the annelid Platynereis dumerilii and the cnidarian Nematostella vectensis. We established that the vast majority of metazoans encode a core redox kit allowing for the production and detoxification of ROS, and overall regulation of ROS levels. However, the precise composition of the redox arsenal can vary significantly from species to species, suggesting that evolutionary constraints apply to ROS metabolism functions rather than precise actors. We found that while ROS are necessary for regeneration in both Platynereis and Nematostella, the two species deploy different enzymatic activities controlling ROS dynamics, and display distinct effects of ROS signaling on injury-induced apoptosis and cell proliferation. We conclude that, while ROS are a common feature of metazoan regeneration, their production and contribution to this phenomenon may depend on different molecular mechanisms highlighting the overall plasticity of the machinery.