A cre-transgenic mouse strain for the ubiquitous deletion of loxP-flanked gene segments including deletion in germ cells.

F Schwenk, U Baron, K Rajewsky - Nucleic acids research, 1995 - ncbi.nlm.nih.gov
F Schwenk, U Baron, K Rajewsky
Nucleic acids research, 1995ncbi.nlm.nih.gov
The gene targeting approach to study gene function in mice has been recently refined using
the bacteriophage P1 Cre-loxP recombination system. Cre recombinase catalyses site-
specific DNA recombination between 34 bprecognition (loxP) sites (1, 2). If two loxP sites are
introduced in the same orientation into a genomic locus, expression of Cre results in the
deletion of the loxP-flanked DNA sequence. Cre-mediated recombinationcan be applied to
various types of gene manipulation in embryonic stem (ES) cells including the removal …
The gene targeting approach to study gene function in mice has been recently refined using the bacteriophage P1 Cre-loxP recombination system. Cre recombinase catalyses site-specific DNA recombination between 34 bprecognition (loxP) sites (1, 2). If two loxP sites are introduced in the same orientation into a genomic locus, expression of Cre results in the deletion of the loxP-flanked DNA sequence. Cre-mediated recombinationcan be applied to various types of gene manipulation in embryonic stem (ES) cells including the removal ofaselectable marker gene accompanied by the introduction of subtle mutations (3), gene replacement (4) and the deletion of large genomic regions to inactivate genes or geneclusters (5). However, Cre-mediated gene manipulation requires transient transfection ofthe mutant, loxP-containing ES cells witha vectorencoding Cre recombinase and an additional round of selection toscreen for ES cell clones carrying the desired deletion. This additional manipulation of the cells in culture is unpleasing since it might affect the capacity of ES cells to contribute to the generation of germ cells in chimeric mice, which is a serious problem in gene targeting technology. The Cre-loxP recombination system has also been used to manipulate genes in a cell type-specific (6-8) or inducible (9) manner. If two loxP sites are introduced into the genome such that they are flanking an essential part of a target gene without affecting its function, Cre-mediated deletion of the loxP-flanked segment will lead to the inactivation of the gene. Gene inactivation in vivo can be restricted to a particular cell type or time point by crossing mice with a loxP-flanked target gene to transgenic mouse strains expressing cre under the control of a cell type-specific or inducible promoter. Such experiments often involve the generation of two independent mouse strains, one harbouring a loxP-flanked gene, suitable for conditional inactivation, and the other with a deletion of the respective gene to study the gene's function during mouse development. However, this requires the injection of different mutant ES cell clones into blastocysts to generate two independent mouse strains, which is expensive and time consuming.
These problems of Cre-loxP mediated gene targeting can be largely overcome with the help of a cnr-transgenic mouse strain which we have generated. This strain mediates deletion of loxP-flanked genes in all tissues, including germ cells (Fig. 1). The strain was produced by injection of a DNA fragment
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