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Overexpression of SMPX in adult skeletal muscle does not change skeletal muscle fiber type or size.

Eftestøl E, Alver TN, Gundersen K, Bruusgaard JC - PLoS ONE (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.

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.

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Related in: MedlinePlus

SMPX-EGFP was localized in bands flanking the z-disc.A) In situ confocal image of EGFP or SMPX-EGFP expression from an isolated EDL rat muscle in Ringer-solution. Scale bar is 10 microns. B) In vitro confocal image of EGFP or SMPX-EGFP stained with Alexa Fluor 680 Phalloidin (red) to visualize actin filaments. Scale bar is 10 microns (inset 1 micron).
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pone-0099232-g003: SMPX-EGFP was localized in bands flanking the z-disc.A) In situ confocal image of EGFP or SMPX-EGFP expression from an isolated EDL rat muscle in Ringer-solution. Scale bar is 10 microns. B) In vitro confocal image of EGFP or SMPX-EGFP stained with Alexa Fluor 680 Phalloidin (red) to visualize actin filaments. Scale bar is 10 microns (inset 1 micron).

Mentions: Muscles from adult rats transfected with the SMPX-EGFP fusion protein were excised and immediately placed under the microscope for imaging. We found that the protein was forming thin lines appearing as doublets, the pattern being distinctly different from the broad, more diffuse lines seen with EGFP alone (Figure 3A).


Overexpression of SMPX in adult skeletal muscle does not change skeletal muscle fiber type or size.

Eftestøl E, Alver TN, Gundersen K, Bruusgaard JC - PLoS ONE (2014)

SMPX-EGFP was localized in bands flanking the z-disc.A) In situ confocal image of EGFP or SMPX-EGFP expression from an isolated EDL rat muscle in Ringer-solution. Scale bar is 10 microns. B) In vitro confocal image of EGFP or SMPX-EGFP stained with Alexa Fluor 680 Phalloidin (red) to visualize actin filaments. Scale bar is 10 microns (inset 1 micron).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4060999&req=5

pone-0099232-g003: SMPX-EGFP was localized in bands flanking the z-disc.A) In situ confocal image of EGFP or SMPX-EGFP expression from an isolated EDL rat muscle in Ringer-solution. Scale bar is 10 microns. B) In vitro confocal image of EGFP or SMPX-EGFP stained with Alexa Fluor 680 Phalloidin (red) to visualize actin filaments. Scale bar is 10 microns (inset 1 micron).
Mentions: Muscles from adult rats transfected with the SMPX-EGFP fusion protein were excised and immediately placed under the microscope for imaging. We found that the protein was forming thin lines appearing as doublets, the pattern being distinctly different from the broad, more diffuse lines seen with EGFP alone (Figure 3A).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.

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.

Show MeSH
Related in: MedlinePlus