Radiation Tolerance in Tardigrades: Current Knowledge and Potential Applications in Medicine.

Tardigrades represent a phylum of very small aquatic animals in which many species have evolved adaptations to survive under extreme environmental conditions, such as desiccation and freezing. Studies on several species have documented that tardigrades also belong to the most radiation-tolerant animals on Earth. This paper gives an overview of our current knowledge on radiation tolerance of tardigrades, with respect to dose-responses, developmental stages, and different radiation sources. The molecular mechanisms behind radiation tolerance in tardigrades are still largely unknown, but omics studies suggest that both mechanisms related to the avoidance of DNA damage and mechanisms of DNA repair are involved. The potential of tardigrades to provide knowledge of importance for medical sciences has long been recognized, but it is not until recently that more apparent evidence of such potential has appeared. Recent studies show that stress-related tardigrade genes may be transfected to human cells and provide increased tolerance to osmotic stress and ionizing radiation. With the recent sequencing of the tardigrade genome, more studies applying tardigrade omics to relevant aspects of human medicine are expected. In particular, the cancer research field has potential to learn from studies on tardigrades about molecular mechanisms evolved to maintain genome integrity.