Recombination between inverted loxP sites is cytotoxic for proliferating cells and provides a simple tool for conditional cell ablation.

The loxP/Cre recombination system is a widely used tool for mouse functional genomics, in particular for in vivo conditional mutagenesis. Depending on the relative orientation and position of loxP sites, Cre-mediated recombination can result in a variety of targeted genomic rearrangements. It was previously reported that loss of the loxP-carrying chromosome can occur when loxP sites are arranged in inverse orientation. By using a chromosome 2 carrying inverted loxP sites, we found that Cre-mediated recombination not only causes chromosomal loss but also triggers apoptosis. We show that targeted recombination between inverted loxP sites (TRIP) triggers cell death specifically in proliferating Cre-expressing cells, and we provide evidence that TRIP is an efficient tool to ablate proliferating cells within genetically defined cell populations. Furthermore, the procedure requires only a simple, one-step intercross but neither the use of toxins nor the additional step of prodrug injection. With the large repertoire of tissue-specific or inducible Cre-expressing transgenes available, TRIP-mediated cell ablation is valuable to investigate the function of a large variety of cell populations in the context of a whole organism, which includes mechanisms underlying organ development and tissue homeostasis.