title: Toxicity of ligand-dependent Cre recombinases and generation of a conditional Cre deleter mouse allowing mosaic recombination in peripheral tissues.
abstract: Ligand-activated Cre recombinases are widely used for studying gene function in vitro and in conditional mouse models. To compare ligand-dependent Cre recombinases, different Cre estrogen receptor fusions were introduced into the ROSA26 locus of embryonic stem (ES) cells and assayed for genotoxicity and recombination efficiency. Of the tested recombinases, the CreERT2 variant showed no toxicity and was highly responsive to ligand induction. To constitutively express CreERT2 in mice and also to clarify whether the CreERT2 system displays background activity, we generated a knock-in mouse line harboring the CreERT2 coding region under the control of the ROSA26 locus. Analysis of this ROSA26-CreERT2 deleter mouse with different reporter strains revealed ubiquitous recombination in the embryo and partial recombination in peripheral and hematopoietic tissues but no effective CreERT2 expression in the brain. Furthermore, using flow cytometry, we found low-level background recombination in noninduced bitransgenic ROSA26-CreERT2/EGFP reporter mice. To determine whether background activity poses a general problem for conducting conditional in vivo experiments with the ROSA26-CreERT2 deleter, we used a sensitive conditional skin cancer model. In this assay, cancer induction was completely restricted to induced bitransgenic CreERT2/K-Ras(V12) mice, whereas noninduced control animals did not show any sign of cancer, indicating the usefulness of the ROSA-CreERT2 system for regulating conditional gene expression in vivo. The ROSA26-CreERT2 deleter strain will be a convenient experimental tool for studying gene function under circumstances requiring partial induction of recombination in peripheral tissues and will be useful for uncovering previously unknown or unsuspected phenotypes.
authors: Institute of Toxicology/Mouse Genetics, Johannes Gutenberg-Universität Mainz, Mainz, Germany.
authors: Dorothe
authors: D
authors: Hameyer
authors: Ate
authors: A
authors: Loonstra
authors: Leonid
authors: L
authors: Eshkind
authors: Steffen
authors: S
authors: Schmitt
authors: Cecilia
authors: C
authors: Antunes
authors: Annemiek
authors: A
authors: Groen
authors: Eric
authors: E
authors: Bindels
authors: Jos
authors: J
authors: Jonkers
authors: Paul
authors: P
authors: Krimpenfort
authors: Ralph
authors: R
authors: Meuwissen
authors: Loes
authors: L
authors: Rijswijk
authors: Axel
authors: A
authors: Bex
authors: Anton
authors: A
authors: Berns
authors: Ernesto
authors: E
authors: Bockamp
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004195:Disease Models, Animal; D005434:Flow Cytometry; D017353:Gene Deletion; D017930:Genes, Reporter; D023281:Genomics / Q000379:methods; D019426:Integrases / Q000378:metabolism*; D008024:Ligands; D051379:Mice; D008822:Mice, Transgenic; D008957:Models, Genetic; D009030:Mosaicism; D011995:Recombination, Genetic
chemical_list: D008024:Ligands; D004247:DNA; C045073:Cre recombinase; D019426:Integrases