RU486-inducible recombination in the salivary glands of lactoferrin promoter-driven green fluorescent Cre transgenic mice

Abstract

When compared with the many tamoxifen-activated Cre mouse lines available for gene manipulation studies, relatively few RU486-inducible Cre mice are in use, due to leakiness issues. Here, we report the generation of an RU486-inducible triple fusion gene (GCrePR1e), consisting of green fluorescent protein, Cre, and the progesterone receptor ligand-binding domain (F642-L901). We sought to improve the GCrePR1e by selecting a truncated human lactoferrin (Lf) promoter to drive its expression, based on the promoter's low basal activity and innate sensitivity to RU486. The resulting vector displayed decreased leakiness and increased Cre induction by RU486 through transcriptional and posttranslational regulation in in vitro transfection assays. Inducible GCrePR1e expression was found in most organs of Lf-GCrePR1e transgenic mice and highly activated in the salivary gland, spleen, and lymph nodes. In the bigenic mouse generated by crossing the Lf-GCrePR1e mouse and the Cre reporter mouse (R26R-LacZ), we found that RU486-induced LacZ expression only in the mucous acini and striated ducts of the salivary gland and had very low background recombination in the untreated mice. Our results demonstrated that the Lf-CrePR1e vector was suitable for in vitro recombination in culture models, and Lf-CrePR1e transgenic mice could mediate spatially restricted and RU486-induced gene manipulation in the salivary gland.