Abstract Background Conditional gene activation is an efficient strategy for studying gene function in genetically modified animals. Among the presently available gene switches, the tetracycline-regulated system has attracted considerable interest because of its unique potential for reversible and adjustable gene regulation. Results To investigate whether the ubiquitously expressed <it>Gt(ROSA)26Sor </it>locus enables uniform DOX-controlled gene expression, we inserted the improved tetracycline-regulated transcription activator iM2 together with an iM2 dependent GFP gene into the <it>Gt(ROSA)26Sor </it>locus, using gene targeting to generate ROSA26-iM2-GFP (R26t1Δ) mice. Despite the presence of ROSA26 promoter driven iM2, R26t1Δ mice showed very sparse DOX-activated expression of different iM2-responsive reporter genes in the brain, mosaic expression in peripheral tissues and more prominent expression in erythroid, myeloid and lymphoid lineages, in hematopoietic stem and progenitor cells and in olfactory neurons. Conclusions The finding that gene regulation by the DOX-activated transcriptional factor iM2 in the <it>Gt(ROSA)26Sor </it>locus has its limitations is of importance for future experimental strategies involving transgene activation from the endogenous ROSA26 promoter. Furthermore, our ROSA26-iM2 knock-in mouse model (R26t1Δ) represents a useful tool for implementing gene function <it>in vivo </it>especially under circumstances requiring the side-by-side comparison of gene manipulated and wild type cells. Since the ROSA26-iM2 mouse allows mosaic gene activation in peripheral tissues and haematopoietic cells, this model will be very useful for uncovering previously unknown or unsuspected phenotypes.</p

Abassi, Yasmin

Bockamp, Ernesto

Cabezas-Wallscheid, Nina

Diken, Mustapha

Eshkind, Leonid

Heck, Rosario

Kim, Jinhyun

Lakaye, Bernard

Sprengel, Rolf

Wortge, Simone

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Tetracycline-controlled transgene activation using the ROSA26-iM2-GFP knock-in mouse strain permits GFP monitoring of DOX-regulated transgene-expression