Werner's syndrome (WS) is an inherited genetic disease in which individuals display the premature ageing of a selected subset of tissues. The disorder results from loss of function mutations in the wrn gene. Wrn codes for a member of the RecQ helicase family with a unique nuclease domain. There is significant evidence that the role of wrn is to assist in the repair and reinitiation of DNA replication forks that have stalled.
Loss of the wrn helicase imposes a distinct set of phenotypes at the cellular level. These include premature replicative senescence (in a subset of cell types), chromosomal instability, a distinct mutator phenotype and hypersensitivity to a limited number of DNA damaging agents. Unfortunately, the majority of these phenotypes are not suitable for the rapid assessment of loss of function of the wrn gene product. However WS cells have been reported to show abnormal sensitivity to the drug camptothecin (an inhibitor of type I topoisomerase). A rapid assay for this sensitivity would be a useful marker of loss of wrn function.
The comet (single cell gel electrophoresis) assay is a rapid, sensitive, versatile, and robust technique for the quantitiative assessment of DNA damage in eukaryotic cells. Using this assay we have found that a significantly increased level of strand breaks can be demonstrated in WS cells treated with camptothecin compared to normal controls. This paper details our findings in primary fibroblasts, telomerase immortalised cell lines and those immortalised with oncogenes from DNA tumour viruses.