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Mani S Mahadevan

Publications and source records attributed to Mani S Mahadevan.

6 recordsLinked to original sources
PubMed2006

Reversible model of RNA toxicity and cardiac conduction defects in myotonic dystrophy.

Myotonic dystrophy (DM1), the most common muscular dystrophy in adults, is caused by an expanded (CTG)n tract in the 3' UTR of the gene encoding myotonic dystrophy protein kinase (DMPK), which results in nuclear entrapment of the 'toxic' mutant RNA and interacting RNA-binding proteins (such as MBNL1) in ribonuclear inclusions. It is unclear if therapy aimed at eliminating the toxin would be beneficial. To address this, we generated transgenic mice expressing the DMPK 3' UTR as part of an inducible RNA transcript encoding green fluorescent protein (GFP). We were surprised to find that mice overexpressing a normal DMPK 3' UTR mRNA reproduced cardinal features of myotonic dystrophy, including myotonia, cardiac conduction abnormalities, histopathology and RNA splicing defects in the absence of detectable nuclear inclusions. However, we observed increased levels of CUG-binding protein (CUG-BP1) in skeletal muscle, as seen in individuals with DM1. Notably, these effects were reversible in both mature skeletal and cardiac muscles by silencing transgene expression. These results represent the first in vivo proof of principle for a therapeutic strategy for treatment of myotonic dystrophy by ablating or silencing expression of the toxic RNA molecules.

3' Untranslated Regions↗
PubMed2005

Woodchuck post-transcriptional element induces nuclear export of myotonic dystrophy 3' untranslated region transcripts.

The woodchuck post-transcriptional regulatory element (WPRE) can naturally accumulate hepatitis transcripts in the cytoplasm, and has been recently exploited as an enhancer of transgene expression. The retention of mutant myotonic dystrophy protein kinase (DMPK) transcripts in the nucleus of myotonic dystrophy (DM) cells has an important pathogenic role in the disease, resulting in pleiotropic effects including delayed myoblast differentiation. In this study, we report the first use of WPRE as a tool to enhance nuclear export of an aberrantly retained messenger RNA. Stable cell lines expressing the normal and mutant DMPK 3' UTR (3' untranslated region) complementary DNA, with or without WPRE, were produced. It is noteworthy that WPRE stimulated extensive transport of mutant transcripts to the cytoplasm. This was associated with repair of the defective cellular MyoD levels and a subsequent increase in myoblast differentiation. These results provide the basis for a cellular model that can be exploited in DM and in the study of RNA transport mechanisms.

3' Untranslated Regions↗
PubMed2004

Myogenic defects in myotonic dystrophy.

Myogenesis is the developmental program that generates and regenerates skeletal muscle. This process is impaired in patients afflicted with myotonic dystrophy type 1 (DM1). Muscle development is disrupted in infants born with congenital DM1, and recent evidence suggests that defective regeneration may contribute to muscle weakness and wasting in affected adults. DM1 represents the first example of a human disease that is caused, at least in part, by pathogenic mRNA. Cell culture models have been used to demonstrate that mutant DM1 mRNA takes on a gain-of-function and inhibits myoblast differentiation. Although the molecular mechanism(s) by which this mutant mRNA disrupts myogenesis is not fully understood, recent findings suggest that anomalous RNA-protein interactions have downstream consequences that compromise key myogenic factors. In this review, we revisit morphological studies that revealed the nature of myogenic abnormalities seen in patients, describe cell culture systems that have been used to investigate this phenotype and discuss recent discoveries that for the first time have identified myogenic events that are disrupted in DM1.

Animals↗
PubMed2002

Mutant DMPK 3'-UTR transcripts disrupt C2C12 myogenic differentiation by compromising MyoD.

Myotonic dystrophy (DM) is caused by two similar noncoding repeat expansion mutations (DM1 and DM2). It is thought that both mutations produce pathogenic RNA molecules that accumulate in nuclear foci. The DM1 mutation is a CTG expansion in the 3' untranslated region (3'-UTR) of dystrophia myotonica protein kinase (DMPK). In a cell culture model, mutant transcripts containing a (CUG)200 DMPK 3'-UTR disrupt C2C12 myoblast differentiation; a phenotype similar to what is observed in myoblast cultures derived from DM1 patient muscle. Here, we have used our cell culture model to investigate how the mutant 3'-UTR RNA disrupts differentiation. We show that MyoD protein levels are compromised in cells that express mutant DMPK 3'-UTR transcripts. MyoD, a transcription factor required for the differentiation of myoblasts during muscle regeneration, activates differentiation-specific genes by binding E-boxes. MyoD levels are significantly reduced in myoblasts expressing the mutant 3'-UTR RNA within the first 6 h under differentiation conditions. This reduction correlates with blunted E-box-mediated gene expression at time points that are critical for initiating differentiation. Importantly, restoring MyoD levels rescues the differentiation defect. We conclude that mutant DMPK 3'-UTR transcripts disrupt myoblast differentiation by reducing MyoD levels below a threshold required to activate the differentiation program.

3' Untranslated Regions↗