Human cytomegalovirus IE1 promoter/enhancer drives variable gene expression in all fiber types in transgenic mouse skeletal muscle.
BACKGROUND
Versatile transgenic manipulation of skeletal muscle requires knowledge of the expression profiles of diverse promoter/enhancer elements in the transcriptionally specialized fiber types of which muscle is composed. "Universal" viral promoters/enhancers, e.g., cytomegalovirus IE1 (CMV IE1), are of interest as reagents that may drive broad expression. However, a previous study noted a marked heterogeneity of CMV IE1-driven transgene expression among muscle fibers, raising the possibility of fiber-type-restricted expression. The purpose of the present study was to characterize CMV IE1-driven expression in terms of fiber type.


RESULTS
We produced two lines of transgenic mice carrying the CMV IE1/ beta-galactosidase construct CMVLacZ, and analyzed transgene expression and fiber type by histochemical analysis of hindlimb muscle sections. In both lines CMVLacZ was expressed in all four major fiber types: type I (slow) and types IIA, IIB and IIX (fast). There was no unique pattern of fiber-type-preferential expression; fiber-type quantitative differences were observed but details varied between muscle regions and between lines. Both lines showed similar fiber-type-independent regional differences in overall expression levels, and a high level of within-fiber-type variability of expression, even among nearby fibers. The soleus muscle showed strong expression and comparatively little within-fiber-type or between-fiber-type variability.


CONCLUSIONS
The CMV IE1 promoter/enhancer is not fiber-type-restricted and can be useful for driving germ-line transgene expression in all four fiber types. However, not all fibers express the gene at high levels due in part to regional differences in overall expression levels, and to a high level of within-fiber-type variability. Given the multinucleate syncitial nature of muscle fibers, it is not likely that this variability is due to variegating heterochromatinization. The soleus muscle would make a suitable subject for near-uniform experimental gene expression driven by CMV IE1 elements.
Hallauer
P L
PL
Montreal Neurological Institute and Biology Department McGill University 3801 University Street Montreal Quebec Canada H3A 2B4. cxph@musica.mcgill.ca
Hastings
K E
KE
D000818:Animals; D003587:Cytomegalovirus / Q000235:genetics*; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005786:Gene Expression Regulation / Q000235:genetics*; D006614:Hindlimb; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics*; D051379:Mice; D008822:Mice, Transgenic; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D014764:Viral Proteins; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics
C088645:IE1 protein, cytomegalovirus; D017874:Immediate-Early Proteins; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D001616:beta-Galactosidase