Figure 5. Mouse cells deficient in clock genes are not sensitive to mitomycin C. Cells were plated at a low density, allowed to attach and then treated with mitomycin C (MMC); after colony formation, cells were stained with Giemsa, and percent survival was determined as described in the text. Each data point represents the average of at least three independent experiments and bars signify the standard deviation. (A) Mouse embryonic fibroblasts were derived from mice with the following genotypes: wild-type (squares), Clock^−/− (circles) and Bmal1^−/− (triangles). (B) Mouse skin fibroblasts were derived from mice with the following genotypes: wild-type (squares), Cry1^−/−Cry2^−/− (circles) and Per1^−/−Per2^−/− (triangles).