Spontaneous ATM Gene Reversion in A-T iPSC to Produce an Isogenic Cell Line

• Spontaneous reversion of an ATM mutation was found in A-T iPSC
• Reversion was due to gene correction, based on LOH of a nearby SNP
• Gene expression changes between individuals overwhelm those from single mutations
• Loss of ATM in unstimulated cells primarily reduced the p53 pathway

SummaryA spontaneously reverted iPSC line was identified from an A-T subject with heterozygous ATM truncation mutations. The reverted iPSC line expressed ATM protein and was capable of radiation-induced phosphorylation of CHK2 and H2A.X. Genome-wide SNP analysis confirmed a match to source T cells and also to a distinct, non-reverted iPSC line from the same subject. Rearranged T cell receptor sequences predict that the iPSC culture originated as several independently reprogrammed cells that resolved into a single major clone, suggesting that gene correction likely occurred early in the reprogramming process. Gene expression analysis comparing ATM−/− iPSC lines to unrelated ATM+/− cells identifies a large number of differences, but comparing only the isogenic pair of A-T iPSC lines reveals that the primary pathway affected by loss of ATM is a diminished expression of p53-related mRNAs. Gene reversion in culture, although likely a rare event, provided a novel, reverted cell line for studying ATM function.