Mice homozygous for this mT/mG mutation are viable and fertile. These mice possess loxP sites on either side of a membrane-targeted tdTomato (mT) cassette and express strong red fluorescence in all tissues and cell types examined. Tail or whole body epifluorescence is sufficient to identify mT/mG mice from wildtype mice. When bred to Cre recombinase expressing mice, the resulting offspring have the mT cassette deleted in the cre expressing tissue(s), allowing expression of the membrane-targeted EGFP (mG) cassette located just downstream. The donating investigator reports that the ACTB promoter allows stronger and persistent expression of the fluorescent proteins (especially in adult cells) compared to the endogenous Gt(ROSA) locus alone. This double-fluorescent system allows direct live visualization of both recombined and non-recombined cells at single cell resolution, offering an internal control for phenotypic analysis of Cre-induced mosaic mutants and providing a second marker for lineage tracing applications. In addition, the localization of fluorescent proteins to membrane structures outlines cell morphology and allows resolution of fine cellular processes. These mT/mG mice are useful as a Cre reporter strain; expressing red fluorescence prior to, and green fluorescence following, Cre-mediated recombination in widespread cell and tissue types.

In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. It should be noted that the phenotype could vary from that originally described. We will modify the strain description if necessary as published results become available.