Synthetic muscle-specific promoter C5-12 (SPc5-12)

Synthetic muscle-specific promoter (also called C5-12) built by combinatorially assembling multiple copies of E-box, MEF-2, TEF-1, and SRE transcription-factor binding sites upstream of a minimal promoter, then screening clones for maximal activity. Drives high-level expression restricted to skeletal and cardiac muscle, exceeding natural muscle and viral promoters in differentiated muscle cells.

Length: 345 bp

Strength: strong

Tissue: Skeletal and cardiac muscle; inactive in undifferentiated myoblasts and nonmuscle cell lines

Expression: constitutive

Origin: Synthetic; combinatorial assembly and screening of myogenic TF binding sites

Characteristics

Contains tandem copies of E-box, MEF-2, TEF-1, and SRE binding sites assembled combinatorially and screened for transcriptional potency in muscle. In differentiated muscle fibers, drives roughly sixfold higher reporter activity than the CMV promoter, while remaining inactive in undifferentiated myoblasts and nonmuscle cell lines. At 345 bp, compact enough for inclusion in AAV vectors alongside large therapeutic transgenes.

Applications: Muscle-restricted transgene expression in AAV vectors for muscular dystrophy and neuromuscular disease gene therapy. Drives skeletal- and cardiac-selective microdystrophin-FLAG expression after systemic AAV5, AAV8, or AAV9 delivery in non-human primates, with AAV8 giving the highest muscle transgene levels; also used to drive Klf15 overexpression in skeletal and cardiac muscle in a spinal muscular atrophy mouse model.

Limitations: Restricted to skeletal and cardiac muscle rather than a single muscle type, so it does not distinguish cardiac-only from skeletal-only applications. Delivered by AAV8 to newborn mice it is not muscle-selective: GFP mRNA is about 15-fold higher in liver and 40-fold higher in heart than in skeletal muscle at postnatal day 2, tracking AAV8 genome distribution rather than promoter activity.

Sequence

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References

  1. Liu et al. (2025). Systemic delivery of AAV5, AAV8, and AAV9 packaging a C5-12-microdystrophin-FLAG expression cassette in non-human primates. Mol Ther Methods Clin Dev - Liu 2025 SPc5-12 Microdystrophin NHP
  2. Ahlskog et al. (2020). Muscle overexpression of Klf15 via an AAV8-Spc5-12 construct does not provide benefits in spinal muscular atrophy mice. Gene Ther - Ahlskog 2020 Spc5-12 SMA Klf15