Site- and time-specific gene targeting in the mouse

Methods. 2001 May;24(1):71-80. doi: 10.1006/meth.2001.1159.


The efficient introduction of somatic mutations in a given gene, at a given time, in a specific cell type, will facilitate studies of gene function and the generation of animal models for human diseases. We have established a conditional site-specific recombination system in mice using a new version of the Cre/lox system. The Cre recombinase has been fused to a mutated ligand binding domain of the human estrogen receptor (ER), resulting in a tamoxifen-dependent Cre recombinase, Cre-ER(T), that is activated by tamoxifen, but not by estradiol. Transgenic mice were generated expressing Cre-ER(T) under the control of a cytomegalovirus promoter. Administration of tamoxifen to these transgenic mice induced excision of a chromosomally integrated gene flanked by loxP sites in a number of tissues, whereas no excision could be detected in untreated animals. However, the efficiency of excision varied between tissues, and the highest level (approximately 40%) was obtained in the skin. To determine the efficiency of excision mediated by Cre-ER(T) in a given cell type, Cre-ER(T)-expressing mice were crossed with reporter mice in which expression of Escherichia coli beta-galactosidase can be induced through Cre-mediated recombination. The efficiency and kinetics of this recombination were analyzed at the cellular level in the epidermis of 6- to 8-week-old double transgenic mice. Site-specific excision occurred within a few days of tamoxifen treatment in essentially all epidermis cells expressing Cre-ER(T). These results indicate that cell-specific expression of Cre-ER(T) in transgenic mice can be used for efficient tamoxifen-dependent Cre-mediated recombination at loci containing loxP sites, to generate site-specific somatic mutations in a spatiotemporally controlled manner. This conditional site-specific recombination system should allow the analysis of knockout phenotypes that cannot be addressed by conventional gene targeting.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Animals
  • Antineoplastic Agents, Hormonal / pharmacology
  • Cell Nucleus / metabolism
  • Crosses, Genetic
  • Cytoplasm / metabolism
  • Epidermis / metabolism
  • Escherichia coli / enzymology
  • Gene Transfer Techniques*
  • Humans
  • Integrases / metabolism
  • Ligands
  • Mice
  • Mice, Knockout
  • Mice, Transgenic
  • Models, Genetic
  • Promoter Regions, Genetic
  • Receptors, Estrogen / genetics
  • Recombination, Genetic
  • Tamoxifen / pharmacology
  • Time Factors
  • Viral Proteins*
  • beta-Galactosidase / metabolism


  • Antineoplastic Agents, Hormonal
  • Ligands
  • Receptors, Estrogen
  • Viral Proteins
  • Tamoxifen
  • Cre recombinase
  • Integrases
  • beta-Galactosidase