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Distal transcript of the dystrophin gene initiated from an alternative first exon and encoding a 75-kDa protein
J P Hugnot1, H Gilgenkrantz, N Vincent
1Institut Cochin de Génétique Moléculaire, Institut National de la Santé et de la Recherche Médicale U129, Paris, France.
Abstract:
A transcript generated by the distal part of the Duchenne Muscular Dystrophy (DMD) gene was initially detected in cells where the full size 14-kilobase (kb) messenger RNA is not found at a significant level. This transcript, approximately 4.5 kb long, corresponds to the cysteine-rich and carboxyl-terminal domains of dystrophin. It begins with a novel 80- to 100-nucleotide exon containing an ATG start site for a new coding sequence of 17 nucleotides in-frame with the consecutive dystrophin cDNA sequence from exon 63. This result suggests the existence of a third promoter that would be localized about 8 kilobases upstream from exon 63 of the DMD gene. The distal transcript is widely distributed but is absent in adult skeletal and myometrial muscle. It is much more abundant in fetal tissues. With an antibody directed against the dystrophin carboxyl terminus, the protein corresponding to this transcript was detected as a 70- to 75-kDa entity on Western blots. It was found in all tissues analyzed except in skeletal muscle. It was not found in lymphoblastoid cells from a Duchenne patient with a complete deletion of the dystrophin gene. The role and subcellular localization of this protein is not known. It may explain extramuscular symptoms exhibited by some Duchenne patients.
Insights
Researchers discovered a new, shorter Duchenne Muscular Dystrophy (DMD) gene transcript. This distal transcript produces a protein found in various tissues, potentially explaining extramuscular symptoms in DMD patients.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The Duchenne Muscular Dystrophy (DMD) gene typically produces a 14-kilobase (kb) messenger RNA (mRNA).
- Previous research focused on the full-length DMD transcript and its role in muscle function.
- Extramuscular symptoms in Duchenne Muscular Dystrophy patients suggest potential roles for non-canonical gene products.
Purpose of the Study:
- To investigate a newly detected, shorter transcript originating from the distal part of the DMD gene.
- To characterize the protein product of this novel transcript and its tissue distribution.
- To explore the potential implications of this transcript and its protein in Duchenne Muscular Dystrophy pathogenesis.
Main Methods:
- Detection and characterization of the distal DMD transcript using molecular techniques.
- Analysis of transcript length and coding sequence, including identification of a novel exon and start site.
- Western blot analysis using an antibody against the dystrophin carboxyl terminus to detect the protein product.
- Tissue distribution studies of the transcript and protein.
Main Results:
- A 4.5 kb distal transcript of the DMD gene was identified, corresponding to cysteine-rich and carboxyl-terminal domains.
- This transcript initiates from a novel exon (80-100 nucleotides) with an ATG start site, suggesting a third promoter.
- The corresponding 70-75 kDa protein was detected in various tissues, notably abundant in fetal tissues but absent in adult skeletal muscle.
- The protein was absent in lymphoblastoid cells from Duchenne patients with complete dystrophin gene deletion.
Conclusions:
- A novel, distal transcript and its corresponding protein product derived from the DMD gene have been identified.
- This protein is widely distributed but not found in adult skeletal muscle, suggesting a non-muscle function.
- The discovery may offer insights into the extramuscular manifestations observed in Duchenne Muscular Dystrophy patients.