title: Delineation of a slow-twitch-myofiber-specific transcriptional element by using in vivo somatic gene transfer.
abstract: Contractile proteins are encoded by multigene families, most of whose members are differentially expressed in fast- versus slow-twitch myofibers. This fiber-type-specific gene regulation occurs by unknown mechanisms and does not occur within cultured myocytes. We have developed a transient, whole-animal assay using somatic gene transfer to study this phenomenon and have identified a fiber-type-specific regulatory element within the promoter region of a slow myofiber-specific gene. A plasmid-borne luciferase reporter gene fused to various muscle-specific contractile gene promoters was differentially expressed when injected into slow- versus fast-twitch rat muscle: the luciferase gene was preferentially expressed in slow muscle when fused to a slow troponin I promoter, and conversely, was preferentially expressed in fast muscle when fused to a fast troponin C promoter. In contrast, the luciferase gene was equally well expressed by both muscle types when fused to a nonfiber-type-specific skeletal actin promoter. Deletion analysis of the troponin I promoter region revealed that a 157-bp enhancer conferred slow-muscle-preferential activity upon a minimal thymidine kinase promoter. Transgenic analysis confirmed the role of this enhancer in restricting gene expression to slow-twitch myofibers. Hence, somatic gene transfer may be used to rapidly define elements that direct myofiber-type-specific gene expression prior to the generation of transgenic mice.
authors.affiliation: Department of Biological Chemistry, University of Maryland School of Medicine, Baltimore 21201, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Corin
authors.forename: L K
authors.initials: LK
authors.lastname: Levitt
authors.forename: J V
authors.initials: JV
authors.lastname: O'Mahoney
authors.forename: J E
authors.initials: JE
authors.lastname: Joya
authors.forename: E C
authors.initials: EC
authors.lastname: Hardeman
authors.forename: R
authors.initials: R
authors.lastname: Wade
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D015500:Chloramphenicol O-Acetyltransferase / Q000032:analysis* / Q000096:biosynthesis; D004251:DNA Transposable Elements; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D008156:Luciferases / Q000032:analysis* / Q000096:biosynthesis; D051379:Mice; D008822:Mice, Transgenic; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology*; D009928:Organ Specificity; D010957:Plasmids; D011401:Promoter Regions, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D004251:DNA Transposable Elements; D008156:Luciferases; D015500:Chloramphenicol O-Acetyltransferase