title: Overexpression of SMPX in adult skeletal muscle does not change skeletal muscle fiber type or size.
abstract: Mechanical factors such as stretch are thought to be important in the regulation of muscle phenotype. Small muscle protein X-linked (SMPX) is upregulated by stretch in skeletal muscle and has been suggested to serve both as a transcription factor and a mechanosensor, possibly giving rise to changes in both fiber size and fiber type. We have used in vivo confocal imaging to study the subcellular localization of SMPX in skeletal muscle fibers of adult rats using a SMPX-EGFP fusion protein. The fusion protein was localized predominantly in repetitive double stripes flanking the Z-disc, and was excluded from all nuclei. This localization would be consistent with SMPX being a mechanoreceptor, but not with SMPX playing a role as a transcription factor. In vivo overexpression of ectopic SMPX in skeletal muscle of adult mice gave no significant changes in fiber type distribution or cross sectional area, thus a role of SMPX in regulating muscle phenotype remains unclear.
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Einar
authors.initials: E
authors.lastname: Eftestøl
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Tine Norman
authors.initials: TN
authors.lastname: Alver
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Kristian
authors.initials: K
authors.lastname: Gundersen
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway; Atlantis Medical University College, Oslo, Norway.
authors.forename: Jo C
authors.initials: JC
authors.lastname: Bruusgaard
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D032446:Myoblasts / Q000378:metabolism; D021381:Protein Transport; D017208:Rats, Wistar; D012518:Sarcomeres / Q000378:metabolism
chemical_list: D009124:Muscle Proteins; C433890:SMPX protein, human