Tet-system for the regulation of gene expression during embryonic development

The ability to control gene expression in a temporal and spatial manner provides a new tool for the study of mammalian gene function particularly during development and oncogenesis. In this study the suitability of the tet-system for investigating embryogenesis was tested in detail. The tTA^CMV(M1) and rTA^CMV-3 (reverse Tc-controlled transactivator) transgenic mice were bred with NZL-2 bi-reporter mice containing the vector with a tTA/rTA responsive bidirectional promoter that allows simultaneous regulation of expression of two reporter genes encoding luciferase and β-galactosidase. In both cases reporter genes were found to be expressed in a wide spectrum of tissues of double transgenic embryos and adult mice. The earliest expression was detected in tTA^CMV(M1)/NZL-2 embryos at embryonic day 10.5 (E10.5) and rTA^CMV-3/NZL-2 embryos at E13.5. Doxycycline abolished β-gal expression in tTA^CMV(M1)/NZL-2 but induced it in rTA^CMV-3/NZL-2 embryos including late stages of embryogenesis. The tTA and rtTA transactivators thus revealed a partially complementary mode of action during second half of embryonic development. These experiments demonstrated that both Tet regulatory systems function during embryonic development. We conclude that the Tet systems allows regulation of gene expression during embryonic development and that 'double reporter' animals like the NZL-2 mice are useful tools for the characterization of newly generated tet transactivator lines expressing tTA (or rtTA) in embryonic as well as in adult tissues.