The Rosa26-rtTA::Col1a1-tetO-H2B-mCherry double mutant mice were generated by breeding Rosa26-rtTA mice (from Stock No. 006965) with Col1a1-tetO-H2B-mCherry mice (from Stock No. 014592). The Rosa26-rtTA targeted mutation has an optimized form of reverse tetracycline controlled transactivator (rtTA-M2) downstream of the Gt(ROSA)26Sor promoter. The Col1a1-tetO-H2B-mcherry targeted mutation contains a tet-responsive element (tetO) and a histone H2B-mCherry fusion protein, targeted to the collagen, type I, alpha 1 (Col1a1) locus. Rosa26-rtTA::Col1a1-tetO-H2B-mCherry double mutant mice that are heterozygous for both targeted mutations are viable and fertile (mice homozygous for both targeted mutations were not generated by the donating investigator but are expected to be viable and fertile as well). These double mutant Rosa26-rtTA::Col1a1-tetO-H2B-mCherry mice have widespread expression of the optimized form of reverse tetracycline-controlled transactivator (rtTA-M2) protein directed to multiple tissues by the Gt(ROSA)26Sor promoter. In the absence of the tetracycline analog doxycycline (dox), expression of the dox-inducible histone H2B-mCherry fusion protein cassette from the Col1a1 locus is not detected. Following dox administration, double mutant mice express the H2B-mCherry fusion protein in embryonic stem (ES) cells, and differentiated trophoblast stem (TS) cells. These double mutant Rosa26-rtTA::Col1a1-tetO-H2B-mCherry mice may be useful for doxycycline-inducible studies which utilize the rtTA/tet-O (tet-on/TRE) system for visualizing pluripotent cells. Mice homozygous for the Col1a1-tetO-H2B-mCherry mutation may exhibit a subtle kink in the tail. The Jackson Laboratory 2024, used with permission.