Cell contact during expression of radiation mutation in Chinese hamster V79 spheroids

The influence of cell to cell contact during expression of radiation mutation at the HGPRT locus was examined using Chinese hamster V79 spheroids. Spheroids left intact for up to 6 days following 7.5 Gy (and then dissociated into single cells for selection in 6-thioguanine) showed no significant decrease in radiation-induced mutation frequency compared to cells of spheroids dissociated immediately following irradiation and passaged in monolayers during the expression interval. These results suggest that the intimate cell contact which occurs between cells in spheroids does not inhibit mutant expression. However, the cell selection process did appear to reduce mutation frequency when spheroids were left intact for 8 days of expression, or when spheroids received 10 Gy.