A technique for making precise rearrangements in the mouse genome, such as removing a segment of a chromosome or inserting a gene at a particular location. Further, it enables such gene knockouts or knockins to be localized to specific tissues or developmental stages. Hence it is a valuable tool in investigations of mammalian gene function. The Cre protein is a recombinase enzyme originally isolated from the P1 bacteriophage, in which it resolves tangles in the virus's circular DNA. It catalyses site-specific recombination by cutting out DNA between two homologous sequences called loxP sites and joining the cut ends. Recombinant mice are bred so that they have one copy of the target site flanked by loxP sites, and a copy of the Cre gene linked to a cell-type-specific promoter. Only cells in which the promoter is active, for example in response to a hormonal signal, express the Cre gene and synthesize the Cre protein, which duly excises the target site, thereby causing loss of the corresponding function. Thus the knockout can be confined to those tissues receiving the activating signal, enabling more detailed resolution of a particular gene's function and the effects of abolishing it.
Subjects: Biological Sciences.