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No imprinting involved in the expression of DM-kinase mRNAs in mouse and human tissues
G Jansen1, M Bartolomei, V Kalscheuer
1Department of Cell Biology and Histology, Medical School University Nijmegen, The Netherlands.
Abstract:
To explain the restriction of early onset cases of myotonic dystrophy (DM) to maternal transmittance and the significant excess of male transmitters in the last asymptomatic generation, the involvement of parental effects on the autosomal dominant mode of inheritance has been suggested. Using FISH we confirmed that the DM-kinase gene is proximal to the ApoE gene on mouse chromosome 7, close to an imprinted segment. To study whether there is any firm molecular basis for the speculation that imprinting may be involved in DM we have analysed the expression of paternal and maternal alleles of the DM-kinase gene in human and mouse tissues. Length polymorphisms in the 3' non coding exons of human and mouse DM kinase genes, i.e. the variable [CTG]n repeat motif in humans and a newly identified Cn stretch variation in mice, served as tools to distinguish between allelic RNA products in various tissues. In human tissues, presence of transcripts from both parental alleles could be demonstrated by RT-PCR. In mouse, similar observations were made using a RNAse protection assay on fetal and adult muscle RNAs. We conclude that imprinting does not play a role in the expression of the DM kinase gene.
Insights
This study investigated imprinting in myotonic dystrophy (DM) by analyzing DM kinase gene expression in human and mouse tissues. Researchers found no evidence of imprinting, concluding it does not influence DM gene expression.
Area of Science:
- Molecular Genetics
- Genomic Imprinting
- Myotonic Dystrophy Research
Background:
- Myotonic dystrophy (DM) exhibits unusual inheritance patterns, including maternal transmission bias in early-onset cases.
- Previous hypotheses suggested genomic imprinting might explain these transmission anomalies in DM.
- The DM-kinase gene's location near a potentially imprinted region prompted investigation into its parental allelic expression.
Purpose of the Study:
- To determine if genomic imprinting affects the expression of the DM-kinase gene in humans and mice.
- To investigate the molecular basis for observed transmission patterns in myotonic dystrophy.
Main Methods:
- Fluorescence In Situ Hybridization (FISH) to confirm gene proximity on mouse chromosome 7.
- Analysis of paternal and maternal DM-kinase gene allele expression using RT-PCR in human tissues.
- RNAse protection assays on mouse fetal and adult muscle RNAs to assess allelic expression.
Main Results:
- Transcripts from both parental alleles of the DM-kinase gene were detected in human tissues.
- Similar biallelic expression patterns were observed in mouse fetal and adult muscle RNAs.
- Length polymorphisms in 3' non-coding exons (human [CTG]n repeat, mouse Cn stretch) facilitated allelic discrimination.
Conclusions:
- Genomic imprinting does not appear to play a role in the expression of the DM-kinase gene.
- The study refutes the hypothesis that imprinting contributes to the observed inheritance patterns in myotonic dystrophy.