R26 LSL H2B mCherry was designed with a CAG promoter and loxP-flanked STOP sequence upstream of a nuclear-targeted H2B-mCherry fusion protein, all inserted into the Gt(ROSA)26Sor locus. While designed to have the floxed-STOP sequence preventing widespread expression of mCherry in the absence of Cre recombinase, low levels of mCherry expression are detectable prior to introduction of Cre recombinase. Importantly, after exposure to Cre recombinase, the mCherry expression levels in the nucleus have been shown to be significantly greater than those baseline levels (e.g., when bred to the strong germline Cre expressing Sox2-Cre mouse line [Stock No. <a href="https://www.jax.org/strain/008454">008454</a>]). As such, it is recommended that researchers include Cre-negative R26 LSL H2B mCherry controls to establish the baseline mCherry levels in their experiments.
 Mice that are homozygous for the R26 LSL H2B mCherry mutant allele are viable and fertile. These R26 LSL H2B mCherry mice may be useful in monitoring the Cre expression in living tissues, and tracing the lineage of such cells in embryos, young, and adult mice at desired time points.

R26 LSL H2B mCherry (Rosa26-CAG-LSL-H2B-mCherry) mutant mice have a loxP-flanked STOP sequence followed by an H2B-mCherry fusion protein inserted into the Gt(ROSA)26Sor locus. Cre inducible, nuclear expression of the mCherry protein allows the monitoring of Cre activity in living tissues and makes possible lineage tracing of such cells in embryos, young and adult mice at desired time points.
 While designed to have the floxed-STOP sequence preventing widespread expression of mCherry in the absence of Cre recombinase, low levels of mCherry expression are detectable prior to introduction of Cre recombinase. Importantly, after exposure to Cre recombinase, the mCherry expression levels in the nucleus have been shown to be significantly greater than those baseline levels (e.g., when bred to the strong germline Cre expressing Sox2-Cre mouse line [Stock No. <a href="https://www.jax.org/strain/008454">008454</a>]). As such, it is recommended that researchers include Cre-negative R26 LSL H2B mCherry controls to establish the baseline mCherry levels in their experiments.

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