Trinucleotide-repeat expanded and normal DMPK transcripts contain unusually long poly(A) tails despite differential nuclear residence

Abstract

In yeast and higher eukaryotes nuclear retention of transcripts may serve in control over RNA decay, nucleocytoplasmic transport and premature cytoplasmic appearance of mRNAs. Hyperadenylation of RNA is known to be associated with nuclear retention, but the cause-consequence relationship between hyperadenylation and regulation of RNA nuclear export is still unclear. We compared polyadenylation status between normal and expanded DMPK transcripts in muscle cells and tissues derived from unaffected individuals and patients with myotonic dystrophy type 1 (DM1). DM1 is an autosomal dominant disorder caused by (CTG)n repeat expansion in the DMPK gene. DM1 etiology is characterized by an almost complete block of nuclear export of DMPK transcripts carrying a long (CUG)n repeat, including aberrant sequestration of RNA-binding proteins. We show here by use of cell fractionation, RNA size separation and analysis of poly(A) tail length that a considerable fraction of transcripts from the normal DMPK allele is also retained in the nucleus (~30%). They carry poly(A) tails with an unusually broad length distribution, ranging between a few dozen to >500 adenosine residues. Remarkably, expanded DMPK (CUG)n transcripts from the mutant allele, almost exclusively nuclear, carry equally long poly(A) tails. Our findings thus suggest that nuclear retention may be a common feature of regulation of DMPK RNA expression. The typical forced nuclear residence of expanded DMPK transcripts affects this regulation in tissues of DM1 patients, but not through hyperadenylation.

Value of insoluble PABPN1 accumulation in the diagnosis of oculopharyngeal muscular dystrophy

“…Like OPMD, it is considered a neurodegenerative RNA pathology [22]. Positivity for nuclear insoluble aggregation of PABPN1 in DM1 muscle samples could be the result of a nonspecific linkage between abnormal nuclear mRNA accumulations and PABPN1 residues [23][24][25]. However, positivity was found in only two of 10 DM1 samples and none was detected in other spliceopathies examined in this cohort (i.e.…”

Phase-separated stress granules and processing bodies are compromised in Myotonic Dystrophy Type 1

“…The hallmark cellular defect in DM1 is the presence of CUGexp RNA foci formed by mutant DMPK transcripts in the cell nucleus. While some DMPK mRNA is clearly exported to the cytoplasm and translated (Gudde et al, 2017), the global effect of the presence of CTGexp RNA and formation of nuclear CUGexp foci on cellular RNA metabolism is not understood, although the sequestration of the multi-functional RBP, MBNL1, within the foci is thought to be a major cause of DM1 pathology. Lens cataract is the most prevalent symptom in DM1 (Romeo, 2012; Smith and Gutmann, 2016).…”

Implications of Poly(A) Tail Processing in Repeat Expansion Diseases

“…Mutated transcripts are mainly localized in the nucleus, where they form RNA foci and sequester RBPs such as MBNL1, -2, and -3; HNRNPH1; CUGBP1; and STAU1 [ 117 , 118 ]. This leads to the trans-deregulation of RNA metabolism-especially APA, miRNA processing, and alternative splicing processes [ 119 , 120 ]. MBNL’s implications in alternative splicing and APA are well-documented [ 121 , 122 , 123 , 124 ].…”