Investigating Radiation Bystander Effects in the Single-Celled Organism S. pombe

N. Chelidze; L.C. DeVeaux; and D.P. Wells (Idaho State University)

It has been shown in recent studies that when cells are traversed by radiation, a larger portion of cells than the number irradiated display a biological effect. This effect, where unirradiated cells show a response to damage to neighboring irradiated cells is called a bystander effect, and has been seen in many mammalian cell culture systems. We have shown a bystander effect in the simple unicellular organism S. pombe. However, the nature of the signal produced by the irradiated cells has not yet been determined. To further characterize the signal, we investigated the effect of medium from irradiated cells on DNA. Conversion of supercoiled plasmid DNA to relaxed form is a direct measure of damage to the intact molecule. We incubated medium from S. pombe cultures, either irradiated or not, with supercoiled pBR322 DNA, and measured conversion to the relaxed form by agarose gel electrophoresis. The incubations were performed for varying lengths of time and at two different temperatures. There was a significant effect of radiation on damage to the DNA; however, this difference was not dependent on the presence of cells in the irradiated medium, but appeared to be an effect of radiation with the medium itself. We are currently investigating this irradiated medium-based DNA damaging effect using radical scavengers. We are further investigating the presence of a radiation-dependent cellular DNA damaging effect, using the same relaxation assay, with the addition of the DNA glycosylases Fpg and Nth. These enzymes will relax supercoiled molecules that contain bases that are chemically changed and, therefore, detect other damage that has occurred. This work was supported by the U.S. Department of Defense under Cooperative Agreement FA8650-04-2-6541.

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