Increase in DNA synthesis in Werner's syndrome cells by hybridization with normal human diploid and HeLa cells

The dominance or recessiveness of the senescent phenotype in cells from patients with Werner's syndrome (WS cells) was investigated using cell fusion. The [³H]thymidine labeling index of normal human diploid fibroblast cell X WS cell heterodikaryons was considerably lower than that of normal homodikaryons, but was significantly higher than that of WS homodikaryons. The labeling index of WS cell X HeLa cell heterodikaryons was the same as that of HeLa homodikaryons. The labeling indices of heterodikaryons obtained by fusion between various strains of premature aging cells were as low as those of parental homodikaryons. These results indicate: (1) the senescent phenotype of WS cells appears to be partially recessive to the phenotype of normal cells and completely recessive to that of HeLa cells; (2) the marked inhibition of DNA synthesis in normal nuclei in heterodikaryons with WS cells could be due to ‘senescent factor(s)’ in WS cells; and (3) no complementation phenomenon was observed among genetically different premature aging cells, probably due to ‘senescent factor(s)’.