title: A previously functional tetracycline-regulated transactivator fails to target gene expression to the bone.
abstract: BACKGROUND
  The tetracycline-controlled transactivator system is a powerful tool to control gene expression in vitro and to generate consistent and conditional transgenic in vivo model organisms. It has been widely used to study gene function and to explore pathological mechanisms involved in human diseases. The system permits the regulation of the expression of a target gene, both temporally and quantitatively, by the application of tetracycline or its derivative, doxycycline. In addition, it offers the possibility to restrict gene expression in a spatial fashion by utilizing tissue-specific promoters to drive the transactivator.
  
  
  RESULTS
  In this study, we report our problems using a reverse tetracycline-regulated transactivator (rtTA) in a transgenic mouse model system for the bone-specific expression of the Hutchinson-Gilford progeria syndrome mutation. Even though prior studies have been successful utilizing the same rtTA, expression analysis of the transactivator revealed insufficient activity for regulating the transgene expression in our system. The absence of transactivator could not be ascribed to differences in genetic background because mice in a mixed genetic background and in congenic mouse lines showed similar results.
  
  
  CONCLUSIONS
  The purpose of this study is to report our negative experience with previously functional transactivator mice, to raise caution in the use of tet-based transgenic mouse lines and to reinforce the need for controls to ensure the stable functionality of generated tetracycline-controlled transactivators over time.
authors.affiliation: Department of Biosciences and Nutrition, Center for Biosciences, Karolinska Institutet, Karolinska University Hospital, Huddinge, Novum, SE-14183 Stockholm, Sweden. Maria.Eriksson.2@ki.se.
authors.forename: Eva
authors.initials: E
authors.lastname: Schmidt
authors.forename: Maria
authors.initials: M
authors.lastname: Eriksson