Effects of Ionizing Radiation on Regeneration in Planarians

Planarians are flatworms that can regrow any missing tissue following injury using stem cells. Approximately ~25% of the planarian cells are pluripotent stem cells capable of producing any cell type. Planarian stem cells are therefore abundant, pluripotent and immortal. Ionizing radiation results death of planarian stem cells, which abolishes the ability of the animals to regenerate. Yet, characterization of the level of irradiation that leads to stem cell death is incomplete. Here, we exposed planarians to a range of ionizing radiation doses, up to a level that results in certain death. We used flow cytometry and injury assays to correlate the level of exposure to radiation and defects in regeneration, and found that at exposure to 1500 RAD, which eliminates >98% of the stem cells, does not impair new tissue growth and regeneration. Our study establishes objective parameters for analyzing stem cell viability in planarian following irradiation.