Cre & Reporter Mice

When a Cre-expressing mouse is crossed with a floxed mouse, the resulting offspring that are positive for both the Cre transgene and the floxed allele (with the floxed allele generally maintained in the homozygous state) express Cre recombinase in the cells where the Cre driver is active. Cre recognizes the loxP sites in the same orientation and excises the DNA sequence between them. This recombination event generates a loss-of-function allele, resulting in conditional knockout of the target gene in Cre-expressing cells. Consequently, the target gene is selectively inactivated in the relevant tissues or organs.

When conducting relevant research using Cre strains, Cre tissue expression can typically be evaluated using the following approaches: ① Query the references of the relevant strains; ② Query the Cre expression information induced by various promoters through MGI-Recombinase(Cre) Activity. If Cre is expressed in early embryos, the reproductive system, or widely throughout the body, then after breeding with flox strains, mice with systemic knockout of the flox gene may be directly obtained; ③ When the Cre used has no such reference information, the strain can be bred with Tool mice carrying a fluorescent reporter gene, and the applicability of Cre mice can be judged by observing the expression of the reporter gene in double-positive offspring. In addition, Cre strains driven by specific promoters may also have Cre activity in non-target tissues, and special attention needs to be paid to the leaky expression of Cre in the reproductive system. If there is leaky expression, it may prevent us from obtaining fl/fl;T mice, and the offspring may exhibit phenotypes related to systemic gene knockout. For example, the Prrx1 (paired related homeobox 1) promoter is expected to drive Cre expression in early limb buds and craniofacial regions, but staining results show that this Cre is also active in some oocytes in females and some interstitial cells in males. Therefore, to minimize the impact of leaky expression of Cre in the reproductive system, male Cre mice can be selected to breed with female flox mice, and mice with null bands can be excluded.