Genome Toxicity and Impaired Stem Cell Function after Conditional Activation of CreER in the Intestine.

With the tamoxifen-inducible CreER system, genetic recombination can be temporally controlled in a cell-type-specific manner in intact animals, permitting dissection of the molecular underpinnings of mammalian physiology. Here we present a significant drawback to CreER technology for analysis of intestinal stem cells. Using the intestine-specific Villin-CreER mouse strain, we observed delayed intestinal regeneration post irradiation. Villin-CreER activation was associated with DNA damage and cryptic loxP site cleavage. Analysis of stem cell-specific CreER strains showed that the genome toxicity impairs function of crypt base columnar stem cells, resulting in loss of organoid initiating activity. Importantly, the stem cell impairment is short-lived, with return to normal by 7 days post tamoxifen treatment. Our findings demonstrate that mouse genetic experiments that utilize CreER should consider the confounding effects of enhanced stem cell sensitivity to genome toxicity resulting from CreER activation.