title: Hemizygous Le-Cre transgenic mice have severe eye abnormalities on some genetic backgrounds in the absence of LoxP sites.
abstract: Eye phenotypes were investigated in Le-Cre(Tg/-); Pax6(fl/+) mice, which were expected to show tissue-specific reduction of Pax6 in surface ectoderm derivatives. To provide a better comparison with our previous studies of Pax6(+/-) eye phenotypes, hemizygous Le-Cre(Tg/-) and heterozygous Pax6(fl/+)mice were crossed onto the CBA/Ca genetic background. After the Le-Cre transgene had been backcrossed to CBA/Ca for seven generations, significant eye abnormalities occurred in some hemizygous Le-Cre(Tg/-); Pax6(+/+) controls (without a floxed Pax6(fl) allele) as well as experimental Le-Cre(Tg/-); Pax6(fl/+) mice. However, no abnormalities were seen in Le-Cre(-/-); Pax6(fl/+) or Le-Cre(-/-); Pax6(+/+) controls (without the Le-Cre transgene). The severity and frequency of the eye abnormalities in Le-Cre(Tg/-); Pax6(+/+) control mice diminished after backcrossing Le-Cre(Tg/-) mice to the original FVB/N strain for two generations, showing that the effect was reversible. This genetic background effect suggests that the eye abnormalities are a consequence of an interaction between the Le-Cre transgene and alleles of unknown modifier genes present in certain genetic backgrounds. The abnormalities were also ameliorated by introducing additional Pax6 gene copies on a CBA/Ca background, suggesting involvement of Pax6 depletion in Le-Cre(Tg/-); Pax6(+/+) mice rather than direct action of Cre recombinase on cryptic pseudo-loxP sites. One possibility is that expression of Cre recombinase from the Pax6-Le regulatory sequences in the Le-Cre transgene depletes cofactors required for endogenous Pax6 gene expression. Our observation that eye abnormalities can occur in hemizygous Le-Cre(Tg/-); Pax6(+/+) mice, in the absence of a floxed allele, demonstrates the importance of including all the relevant genetic controls in Cre-loxP experiments.
authors.affiliation: Centre for Integrative Physiology, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Natalie J
authors.initials: NJ
authors.lastname: Dorà
authors.affiliation: Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom.
authors.forename: J Martin
authors.initials: JM
authors.lastname: Collinson
authors.affiliation: Medical Research Council Human Genetics Unit, Medical Research Council Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Hill
authors.affiliation: Centre for Integrative Physiology, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: John D
authors.initials: JD
authors.lastname: West
mesh_terms: D000818:Animals; D005124:Eye Abnormalities / Q000235:genetics*; D019426:Integrases / Q000235:genetics*; D051379:Mice; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic
chemical_list: C045073:Cre recombinase; D019426:Integrases