Floxing

In genetics, floxing refers to the sandwiching of a DNA sequence (which is then said to be floxed) between two lox P sites. The terms are constructed upon the phrase "flanking/flanked by LoxP". Recombination between LoxP sites is catalysed by Cre recombinase. Floxing a gene allows it to be deleted (knocked out), translocated or inverted in a process called Cre-Lox recombination. The floxing of genes is essential in the development of scientific model systems as it allows spatial and temporal alteration of gene expression.

Floxed genes can also be used to produce tissue-specific knockouts. For example, using the Cre recombinase with the alpha-myosin heavy chain promoter causes the floxed gene to be inactivated in the heart alone. Further, these knockouts can be inducible. In several mouse studies, tamoxifen is used to induce the Cre recombinase; in this case Cre is fused to a portion of the mouse estrogen receptor (ER), which is naturally localized to the cytoplasm via its interactions with chaperone proteins such as heat shock protein 70 and 90 (Hsp70 and Hsp90). Tamoxifen binds to ER and disrupts its interactions with the chaperones. Disruption of chaperone interactions allows the Cre-ER fusion protein to enter the nucleus and perform recombination on the floxed gene.

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