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Characterization and cell type distribution of a novel, major transcript of the Duchenne muscular dystrophy gene
D Rapaport1, D Lederfein, J T den Dunnen
1Department of Cell Biology, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
Previously we identified a novel 6.5 kb mRNA transcribed from the Duchenne muscular dystrophy (DMD) gene. This mRNA differs in coding content and tissue distribution from the known muscle type and brain type 14 kb DMD mRNAs which code for dystrophin. The novel transcript shares with dystrophin most of the sequence coding for the cysteine-rich and C-terminal domains. Here we used cDNA cloning to identify the divergence point between the common region and the sequence unique to the novel mRNA at the 5' end of the sequence encoding the cysteine-rich domain of dystrophin. This unique sequence containing the translation initiation site is located in a new exon in the intron between exons 62 and 63 of the dystrophin gene. Using probes containing RNA sequences specific to the novel mRNA, we investigated the expression of this mRNA in various tissues and cell types. The study reveals that this mRNA is the main DMD gene product detectable in a variety of nonmuscle tissues including brain cells. The amount of this mRNA in some tissues is comparable to the amount of dystrophin mRNA in the muscle. The expression of the 6.5 kb mRNA is down-regulated during differentiation of myogenic cells; it is present in small amounts in proliferating myoblasts but is undetected in differentiated muscle cultures depleted of mononucleated cells.
Insights
Researchers discovered a new 6.5 kb mRNA from the Duchenne muscular dystrophy (DMD) gene, primarily found in nonmuscle tissues like the brain. This novel transcript is a major DMD gene product outside of muscle cells.
Area of Science:
- Molecular Biology
- Genetics
- Neuroscience
Background:
- The Duchenne muscular dystrophy (DMD) gene produces 14 kb mRNAs encoding dystrophin, found in muscle and brain.
- A novel 6.5 kb mRNA transcribed from the DMD gene has been identified, distinct from known dystrophin mRNAs.
Purpose of the Study:
- To characterize the novel 6.5 kb DMD mRNA.
- To identify the genetic locus and expression pattern of this novel transcript.
Main Methods:
- cDNA cloning to pinpoint the divergence between common and unique sequences.
- RNA probe hybridization to analyze tissue and cell-type specific expression.
Main Results:
- The novel mRNA's unique sequence, including its translation initiation site, resides in a new exon within the intron between exons 62 and 63.
- This 6.5 kb mRNA is the predominant DMD gene product in various nonmuscle tissues, notably brain cells.
- Its expression is significantly downregulated during myogenic cell differentiation.
Conclusions:
- The 6.5 kb mRNA represents a distinct functional product of the DMD gene, predominantly expressed in nonmuscle tissues.
- This finding expands our understanding of DMD gene expression and potential roles beyond dystrophin production in muscle.