title: Cardiac transgenesis with the tetracycline transactivator changes myocardial function and gene expression.
abstract: The cardiac-specific tetracycline-regulated gene expression system (tet-system) is a powerful tool using double-transgenic mice. The cardiac alpha-myosin heavy chain promoter (alphaMHC) drives lifetime expression of a tetracycline-inhibited transcription activator (tTA). Crossing alphaMHC-tTA mice with mice containing a tTA-responsive promoter linked to a target gene yields double-transgenic mice having tetracycline-repressed expression of the target gene in the heart. Using the tet-system, some studies use nontransgenic mice for the control group, whereas others use single-transgenic alphaMHC-tTA mice. However, previous studies found that high-level expression of a modified activator protein caused cardiomyopathy. Therefore, we tested whether cardiac expression of tTA was associated with altered function of alphaMHC-tTA mice compared with wild-type (WT) littermates. We monitored in vivo and in vitro function and gene expression profiles for myocardium from WT and alphaMHC-tTA mice. Compared with WT littermates, alphaMHC-tTA mice had a greater heart-to-body weight ratio (approximately 10%), ventricular dilation, and decreased ejection fraction, suggesting mild cardiomyopathy. In vitro, submaximal contractions were greater compared with WT and were associated with greater myofilament Ca2+ sensitivity. Gene expression profiling revealed that the expression of 153 genes was significantly changed by >20% when comparing alphaMHC-tTA with WT myocardium. These findings demonstrate that introduction of the alphaMHC-tTA construct causes significant effects on myocardial gene expression and major functional abnormalities in vivo and in vitro. For studies using the tet-system, these results suggest caution in the use of controls, since alphaMHC-tTA myocardium differs appreciably from WT. Furthermore, the results raise the possibility that the phenotype conferred by a target gene may be influenced by the modified genetic background of alphaMHC-tTA myocardium.
authors.affiliation: Department of Radiology, University of California, San Francisco, USA.
authors.forename: Diana T
authors.initials: DT
authors.lastname: McCloskey
authors.forename: Lynne
authors.initials: L
authors.lastname: Turnbull
authors.forename: Philip M
authors.initials: PM
authors.lastname: Swigart
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Zambon
authors.forename: Sally
authors.initials: S
authors.lastname: Turcato
authors.forename: Shuji
authors.initials: S
authors.lastname: Joho
authors.forename: William
authors.initials: W
authors.lastname: Grossman
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Conklin
authors.forename: Paul C
authors.initials: PC
authors.lastname: Simpson
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Baker
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D001835:Body Weight; D002118:Calcium / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004318:Doxycycline / Q000494:pharmacology; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects*; D005838:Genotype; D006321:Heart / Q000187:drug effects* / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D009206:Myocardium / Q000378:metabolism*; D009929:Organ Size; D010641:Phenotype; D013752:Tetracycline / Q000494:pharmacology*; D015534:Trans-Activators / Q000378:metabolism*; D024723:Ventricular Myosins / Q000235:genetics / Q000378:metabolism
chemical_list: D015534:Trans-Activators; D024723:Ventricular Myosins; D013752:Tetracycline; D004318:Doxycycline; D002118:Calcium