Efficient Cre-loxP–induced mitotic recombination in mouse embryonic stem cells

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Abstract
FLP/FRT-induced mitotic recombination provides a powerful method for creating genetic mosaics in Drosophila and for discerning the function of recessive genes in a heterozygous individual. Here we show that mitotic recombination can be reproducibly induced in mouse embryonic stem (ES) cells, by Cre/loxP technology, at frequencies ranging from 4.2 × 10 -5 (Snrpn) to 7.0 × 10 -3 (D7Mit178) for single allelic loxP sites, and to 5.0 × 10 -2 (D7Mit178) for multiple allelic lox sites, after transient Cre expression. Notably, much of the recombination occurs in G2 and is followed by X segregation, where the recombinant chromatids segregate away from each other during mitosis. It is X segregation that is useful for genetic mosaic analysis because it produces clones of homozygous mutant daughter cells from heterozygous mothers. Our studies confirm the predictions made from studies in Drosophila 1 that suggest that X segregation will not be limited to organisms with strong mitotic pairing, because the forces (sister-chromatid cohesion) responsible for X segregation are an elemental feature of mitosis in all eukaryotes. Our studies also show that genetic mosaic analysis in mice is feasible, at least for certain chromosomal regions.Link_to_subscribed_fulltex