Figure 1.

Proliferation of PARP mutant cells in response to experimental stress. (A) PARP heterozygous (+/−) and homozygous (−/−) primary fibroblasts were cultured at 37°C and 39°C for 14 days. At each time point the number of cells was counted from triplicate culture. (B) The ratio of number of cells at 37°C vs. 39°C indicates the magnitude of proliferation reduction of each genotype. (C) Southern blot analysis of genomic DNA extracted from the co-cultures of PARP−/− (mutant) and wild-type cells at different passages from passage 2 (P2) through 7 (P7). DNA was digested by PvuII and hybridized with a specific probe (see Materials and Methods). Control DNAs (Co.) are from wild-type (+/+), heterozygous (+/−) and homozygous (−/−) mouse tail biopsies respectively. The presence of mutant cells in cocultured mixtures is depicted by the intensity of the bands on the Southern blot.