SPATIAL-TEMPORAL PATTERNS OF GENE-EXPRESSION IN MOUSE SKELETAL-MUSCLEAFTER INJECTION OF LACZ PLASMID DNA

Gene therapy for muscular diseases requires the efficient transfection of a large proportion of myofiber cells within a given muscle. In the present experiments, patterns of beta-galactosidase expression were e xamined in mouse rectus femoris muscles at various time-points after a single injection of lacZ encoded plasmid DNA. beta-Galactosidase expr ession was detected 3 h after injection and rose to peak levels at 3-1 4 days, and then stabilized at lower levels. beta-Galactosidase staini ng was detected in an average of about 6% (up to 15%) of the total 400 0 myofiber cells, and in about 70% of those myofibers located in the d iscrete area containing the greatest proportion of transfected cells. Soon after injection of DNA encoding cytoplasmic or nuclear-targeted b eta-galactosidase, expression was noted predominantly in the myotendin ous junction areas, after which beta-galactosidase activity progressed toward the central parts of the myofibers. This preferential transgen e expression at the myotendinous junction may result from some unique, local property of the myofiber cells and/or from a restricted diffusi on or binding of the injected plasmid DNA at tendinous surfaces. A bet ter understanding of the reasons for this pattern of reporter gene exp ression in muscle may suggest procedures for increasing the number of myofiber cells transfected by direct DNA injections.