Untranslated Region Of DMPK Gene Research Articles

Aberrant Expression of a Non-muscle RBFOX2 Isoform Triggers Cardiac Conduction Defects in Myotonic Dystrophy.

Myotonic dystrophy type 1 (DM1) is a multisystemic genetic disorder caused by the CTG repeat expansion in the 3'-untranslated region of DMPK gene. Heart dysfunctions occur in ∼80% of DM1 patients and are the second leading cause of DM1-related deaths. Herein, we report that upregulation of a non-muscle splice isoform of RNA-binding protein RBFOX2 in DM1 heart tissue-due to altered splicing factor and microRNA activities-induces cardiac conduction defects in DM1 individuals. Mice engineered to express the non-muscle RBFOX240 isoform in heart via tetracycline-inducible transgenesis, or CRISPR/Cas9-mediated genome editing, reproduced DM1-related cardiac conduction delay and spontaneous episodes of arrhythmia. Further, by integrating RNA binding with cardiac transcriptome datasets from DM1 patients and mice expressing the non-muscle RBFOX2 isoform, we identified RBFOX240-driven splicing defects in voltage-gated sodium and potassium channels, which alter their electrophysiological properties. Thus, our results uncover a trans-dominant role for an aberrantly expressed RBFOX240 isoform in DM1 cardiac pathogenesis.

Short antisense-locked nucleic acids (all-LNAs) correct alternative splicing abnormalities in myotonic dystrophy.

Myotonic dystrophy type 1 (DM1) is an autosomal dominant multisystemic disorder caused by expansion of CTG triplet repeats in 3′-untranslated region of DMPK gene. The pathomechanism of DM1 is driven by accumulation of toxic transcripts containing expanded CUG repeats (CUGexp) in nuclear foci which sequester several factors regulating RNA metabolism, such as Muscleblind-like proteins (MBNLs). In this work, we utilized very short chemically modified antisense oligonucleotides composed exclusively of locked nucleic acids (all-LNAs) complementary to CUG repeats, as potential therapeutic agents against DM1. Our in vitro data demonstrated that very short, 8- or 10-unit all-LNAs effectively bound the CUG repeat RNA and prevented the formation of CUGexp/MBNL complexes. In proliferating DM1 cells as well as in skeletal muscles of DM1 mouse model the all-LNAs induced the reduction of the number and size of CUGexp foci and corrected MBNL-sensitive alternative splicing defects with high efficacy and specificity. The all-LNAs had low impact on the cellular level of CUGexp-containing transcripts and did not affect the expression of other transcripts with short CUG repeats. Our data strongly indicate that short all-LNAs complementary to CUG repeats are a promising therapeutic tool against DM1.

Detection for trinucleotide repeats in myotonic dystrophy type 1

To establish an efficient method which can be easily used for detecting CTG trinucleotide repeats in myotonic dystrophy type 1 (DM1). Tri-primer polymerase chain reaction (TP-PCR) combined with electropherogram was used to detect CTG repeats in the 3'-untranslated region of DMPK gene. Twenty non-related DM1 patients and 24 healthy controls were selected. All patients were found to have carried pathologic alleles containing more than 100 CTG repeats, while the healthy controls have carried 5-37 CTG repeats. TP-PCR combined with electropherograms may provide a highly sensitive, specific and accurate method which is less time-consuming and easier to perform for the detection of pathologic alleles in DM1 patients.

Abstract P104: Reactivation of Embryonic Gene Program due to CUG Repeat RNA Expression in Myotonic Dystrophy

Myotonic dystrophy type 1 (DM1) is a dominantly inherited disease that affects multiple organ systems. Cardiac involvement, which is characterized by conduction defects and arrhythmias, is the second leading cause of death in DM1 patients. The causative mutation is a CTG expansion in the 3' untranslated region of DMPK gene resulting in aberrant expression of CUG repeat RNA that accumulates into nuclear foci and causes misregulation in alternative splicing. Here we show that heart-specific and inducible expression of CUG repeat RNA in a DM1 mouse model results in global reactivation of embryonic gene expression program in adult heart that is distinct from a general hypertrophic stress response. Using q-PCR TaqMan arrays, we identified 54 miRNAs that were differentially expressed in DM1 mouse hearts one week following induction of CUG repeat RNA. Interestingly, 83% (45/54) of them exhibited a developmental shift in expression towards the embryonic pattern. Because over 90% (41/45) of them were down regulated within 72 hr after induction of repeat RNA and only 2/22 examined decreased in two unrelated mouse models of heart disease, we conclude their reduced expression is specific to DM1 and not simply a general response to cardiac injury. Microarray studies revealed a developmental switch not only in the miRNA expression patterns but also a pervasive shift in mRNA steady state levels of a number of genes to embryonic stage. Intriguingly, we found that loss of MBNL1 or gain of CELF1 activity, two major RNA binding proteins disrupted in DM1, are not driving the miRNA misregulation since their expression is indistinguishable between wild type, MBNL1 knock out and CELF1 over expressing mice. Moreover, comparable decrease in ten out of ten primary miRNA transcripts examined suggests loss of expression is not due to a processing defect. Instead, we discovered that adult-to-embryonic shift in expression of select micro- and messenger RNAs in DM1 heart occurs due to specific inactivation of a Mef2 transcriptional program. We are currently determining causal contributions of this Mef2-miRNA circuitry in the developmental reprogramming of gene expression in DM1 as well as its direct role in cardiac manifestations of this disease.

Clinical, familial and hereditary analysis of myotonic dystrophy

To analyze the clinical, familial and hereditary features of myotonic dystrophy to improve the knowledge and provide molecule evidence for gene diagnosis and prenatal diagnosis of myotonic dystrophy or dystrophia myotonia (DM) families. Clinical data of 2 DM families were collected based on the probands. The number of trinucleotide CTG repeat in the 3' untranslated region of myotonic dystrophy protein kinase (DMPK) gene on chromosome 19 was determined by DNA sequence and repeat fragment. Except for 1 subclinical patient, another 5 patients progressed slowly with the features of myotonic muscular weakness and atrophy. One patient had hatchet face, 1 had cataract and diabetes mellitus, and the other 3 were bald. Electromyologram showed 3 patients had myotonic discharge and myopathic abnormalities. The number of trinucleotide CTG repeat in the 3' untranslated region of DMPK gene of 5 patients exceeded 50. DM can be anticipated. Gene analysis can verify the disease and identify subclinical patients. It helps to prevent the DM births by hereditary consultation performing prenatal diagnosis.

Normal myogenesis and increased apoptosis in myotonic dystrophy type-1 muscle cells

Myotonic dystrophy (DM) is caused by a (CTG)(n) expansion in the 3'-untranslated region of DMPK gene. Mutant transcripts are retained in nuclear RNA foci, which sequester RNA binding proteins thereby misregulating the alternative splicing. Controversy still surrounds the pathogenesis of the DM1 muscle distress, characterized by myotonia, weakness and wasting with distal muscle atrophy. Eight primary human cell lines from adult-onset (DM1) and congenital (cDM1) patients, (CTG)(n) range 90-1800, were successfully differentiated into aneural-immature and contracting-innervated-mature myotubes. Morphological, immunohistochemical, RT-PCR and western blotting analyses of several markers of myogenesis indicated that in vitro differentiation-maturation of DM1 myotubes was comparable to age-matched controls. In all pathological muscle cells, (CTG)(n) expansions were confirmed by long PCR and RNA fluorescence in situ hybridization. Moreover, the DM1 myotubes showed the splicing alteration of insulin receptor and muscleblind-like 1 (MBNL1) genes associated with the DM1 phenotype. Considerable myotube loss and atrophy of 15-day-differentiated DM1 myotubes indicated activated catabolic pathways, as confirmed by the presence of apoptotic (caspase-3 activation, cytochrome c release, chromatin fragmentation) and autophagic (P62/LC3) markers. Z-VAD treatment significantly reduced the decrease in myonuclei number and in average width in 15-day-differentiated DM1 myotubes. We thus propose that the muscle wasting typical in DM1 is due to impairment of muscle mass maintenance-regeneration, through premature apoptotic-autophagic activation, rather than altered myogenesis.

D.P.4.07 In vitro study of DM1 primary myotubes

Myotonic Dystrophy is the most common form of adult muscular dystrophy, with a prevalence of 1/8000. Type 1, accounting for the 98% of total cases, is caused by a (CTG)n triplet expansion in 3′-untranslated region of DMPK gene. In muscle tissue myotonia and insulin resistance have been associated to altered splicing of chloride channel-1 (ClC-1) and insulin receptor (IR) mRNAs, due to pleiotropic effect of mutant DMPK. An inhibition of differentiation in DM1 myoblasts, maybe due to anomalous interactions between mutant RNA and many key myogenic factors, was supposed to be the primary determinant of muscle wasting and weakness.

Differences in CTG triplet repeat expansion in leukemic cells and normal lymphocytes from a 14‐year‐old female with congenital myotonic dystrophy

We describe a rare case of acute lymphoblastic leukemia in a 14-year-old female with congenital myotonic dystrophy manifested as mental retardation, extensive contractures of multiple joints of the lower extremities, and severe scoliosis. Because of the potential toxicity of chemotherapy and the patient's poor performance status, a modified chemotherapy regimen was administered. Analysis of the greatly expanded number of CTG repeats at the 3' untranslated region of DMPK gene showed that the number of repeats was 233 greater in leukemic cells than in normal lymphocytes; this elongation may have occurred during the cellular proliferation of leukemic clones.

Altered phosphorylation and intracellular distribution of a (CUG)n triplet repeat RNA-binding protein in patients with myotonic dystrophy and in myotonin protein kinase knockout mice.

Myotonic dystrophy (DM) is associated with expansion of CTG repeats in the 3'-untranslated region of the myotonin protein kinase (DMPK) gene. The molecular mechanism whereby expansion of the (CUG)n repeats in the 3'-untranslated region of DMPK gene induces DM is unknown. We previously isolated a protein with specific binding to CUG repeat sequences (CUG-BP/hNab50) that possibly plays a role in mRNA processing and/or transport. Here we present evidence that the phosphorylation status and intracellular distribution of the RNA CUG-binding protein, identical to hNab50 protein (CUG-BP/hNab50), are altered in homozygous DM patient and that CUG-BP/hNab50 is a substrate for DMPK both in vivo and in vitro. Data from two biological systems with reduced levels of DMPK, homozygous DM patient and DMPK knockout mice, show that DMPK regulates both phosphorylation and intracellular localization of the CUG-BP/hNab50 protein. Decreased levels of DMPK observed in DM patients and DMPK knockout mice led to the elevation of the hypophosphorylated form of CUG-BP/hNab50. Nuclear concentration of the hypophosphorylated CUG-BP/hNab50 isoform is increased in DMPK knockout mice and in homozygous DM patient. DMPK also interacts with and phosphorylates CUG-BP/hNab50 protein in vitro. DMPK-mediated phosphorylation of CUG-BP/hNab50 results in dramatic reduction of the CUG-BP2, hypophosphorylated isoform, accumulation of which was observed in the nuclei of DMPK knockout mice. These data suggest a feedback mechanism whereby decreased levels of DMPK could alter phosphorylation status of CUG-BP/hNab50, thus facilitating nuclear localization of CUG-BP/hNab50. Our results suggest that DM pathophysiology could be, in part, a result of sequestration of CUG-BP/hNab50 and, in part, of lowered DMPK levels, which, in turn, affect processing and transport of specific subclass of mRNAs.