Fig. 3.

The Tg(iSuRe-Cre) allele is ubiquitously expressed and is a reliable reporter of recombination of other reporter alleles. a Analysis of Tg(iSuRe-Cre) expression in the absence of Cre activity reveals its expression (N-PhiM+) in most cells of mouse embryos. The allele does not self-recombine in embryos (MbTomato-negative). b, c FACS analysis reveals that the Tg(iSuRe-Cre) allele does not self-recombine in blood, unlike its ROSA26 gene-targeted version (each dot in the chart represents quantification of one animal). d, e Confocal micrographs of postnatal day (P) 6 retina vessels from animals with the alleles depicted above the panels and induced with tamoxifen from P1 to P3. All endothelial cells (ECs; nuclei, ERG+) expressing MbTomato-2A-Int-Cre also recombined the reporter allele ROSA26^LSL-YFP. f Quantification of the different recombination events/reporters in retinal vessels with low and high frequencies of tamoxifen-induced CreERT2 recombination (n = 4 full retinas per group). g FACS analysis of liver ECs from tamoxifen-induced adult animals with the genotype indicated in d. All induced MbTomato+ cells also recombined the reporter allele ROSA26^LSL-YFP. The MbTomato reporter from the Tg(iSuRe-Cre) allele is easier to separate from baseline autofluorescence. h, i Six-channel confocal micrograph of P6 retina vessels from animals (n = 3) with the genotype indicated above panels and induced with tamoxifen at P3. All cells expressing the MbTomato reporter recombined the two reporter alleles (ROSA26^LSL-YFP and ROSA26^iChr2-Mosaic), resulting in expression of EYFP and one of the three possible nuclear-localized proteins (H2B-Cherry, H2B-EGFP, or HA-H2B-Cerulean). In contrast, only a small fraction of EYFP+ cells recombined and expressed this reporter in their chromatin/nuclei. Scale Bars 150 μm. Error bars indicate StDev; ***p < 0.0001; Two-tailed unpaired t-test (3c). Data in 3i indicate the mean frequencies obtained in the indicated cell groups