Direct DNA injection into mouse tongue muscle for analysis of promoter function in vivo

The striated muscle of the tongue provides a readily accessible site for the introduction of DNA expression vectors. Parameters were established to use the striated muscle of the tongue as a model system for the examination of gene expression following the direct injection of DNA constructs bearing gene promoter sequences controlling the expression of reporter genes. Plasmid expression vectors were used that contained either constitutive or muscle-specific promoters directing the transcription of reporter genes. Chloramphenicol acetyltransferase (CAT), luciferase, and beta-galactosidase (lacZ) were used as the reporter genes to detect the promoter-specific expression of the injected DNA. The expression of the injected plasmids was directly correlated with the mass of injected DNA and the time of incubation following the injection. Maximal levels of reporter gene expression were observed seven days after the injection, and the expression was maintained for more than two months following injection. Simultaneous injection of two individual expression vectors bearing either CAT or luciferase reporter genes resulted in a dose-dependent level of expression for each of the plasmids. The linearity of the coexpression provided a means to normalize DNA uptake and analyze promoter efficiency. The troponin C-fast enhancer linked to its own promoter directed significantly more CAT expression than an enhancerless SV40 promoter-CAT plasmid, demonstrating that different promoter strengths could be determined in the mouse tongue muscle in vivo. This model system represents a convenient means to approach the functional analysis of muscle gene promoters in vivo.