title: Tamoxifen-Induced Cre-loxP Recombination Is Prolonged in Pancreatic Islets of Adult Mice.
abstract: Tamoxifen (Tm)-inducible Cre recombinases are widely used to perform gene inactivation and lineage tracing studies in mice. Although the efficiency of inducible Cre-loxP recombination can be easily evaluated with reporter strains, the precise length of time that Tm induces nuclear translocation of CreER(Tm) and subsequent recombination of a target allele is not well defined, and difficult to assess. To better understand the timeline of Tm activity in vivo, we developed a bioassay in which pancreatic islets with a Tm-inducible reporter (from Pdx1(PB)-CreER(Tm);R26R(lacZ) mice) were transplanted beneath the renal capsule of adult mice previously treated with three doses of 1 mg Tm, 8 mg Tm, or corn oil vehicle. Surprisingly, recombination in islet grafts, as assessed by expression of the β-galactosidase (β-gal) reporter, was observed days or weeks after Tm treatment, in a dose-dependent manner. Substantial recombination occurred in islet grafts long after administration of 3×8 mg Tm: in grafts transplanted 48 hours after the last Tm injection, 77.9±0.4% of β-cells were β-gal+; in β-cells placed after 1 week, 46.2±5.0% were β-gal+; after 2 weeks, 26.3±7.0% were β-gal+; and after 4 weeks, 1.9±0.9% were β-gal+. Islet grafts from mice given 3×1 mg Tm showed lower, but notable, recombination 48 hours (4.9±1.7%) and 1 week (4.5±1.9%) after Tm administration. These results show that Tm doses commonly used to induce Cre-loxP recombination may continue to label significant numbers of cells for weeks after Tm treatment, possibly confounding the interpretation of time-sensitive studies using Tm-dependent models. Therefore, investigators developing experimental approaches using Tm-inducible systems should consider both maximal recombination efficiency and the length of time that Tm-induced Cre-loxP recombination occurs.
authors.affiliation: Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America.
authors.forename: Rachel B
authors.initials: RB
authors.lastname: Reinert
authors.forename: Jeannelle
authors.initials: J
authors.lastname: Kantz
authors.forename: Amanda Ackermann
authors.initials: AA
authors.lastname: Misfeldt
authors.forename: Greg
authors.initials: G
authors.lastname: Poffenberger
authors.forename: Maureen
authors.initials: M
authors.lastname: Gannon
authors.forename: Marcela
authors.initials: M
authors.lastname: Brissova
authors.forename: Alvin C
authors.initials: AC
authors.lastname: Powers
mesh_terms: D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D017930:Genes, Reporter; D019426:Integrases / Q000235:genetics / Q000378:metabolism*; D007515:Islets of Langerhans / Q000187:drug effects*; D016381:Islets of Langerhans Transplantation; D051379:Mice; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic / Q000187:drug effects*; D013629:Tamoxifen / Q000494:pharmacology*; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D018931:Antineoplastic Agents, Hormonal; D011993:Recombinant Fusion Proteins; D013629:Tamoxifen; C045073:Cre recombinase; D019426:Integrases; D001616:beta-Galactosidase