CTG Trinucleotide Repeat “Big Jumps”: Large Expansions, Small Mice

Trinucleotide repeat expansions are the genetic cause of numerous human diseases, including fragile X mental retardation, Huntington disease, and myotonic dystrophy type 1. Disease severity and age of onset are critically linked to expansion size. Previous mouse models of repeat instability have not recreated large intergenerational expansions (“big jumps”), observed when the repeat is transmitted from one generation to the next, and have never attained the very large tract lengths possible in humans. Here, we describe dramatic intergenerational CTG•CAG repeat expansions of several hundred repeats in a transgenic mouse model of myotonic dystrophy type 1, resulting in increasingly severe phenotypic and molecular abnormalities. Homozygous mice carrying over 700 trinucleotide repeats on both alleles display severely reduced body size and splicing abnormalities, notably in the central nervous system. Our findings demonstrate that large intergenerational trinucleotide repeat expansions can be recreated in mice, and endorse the use of transgenic mouse models to refine our understanding of triplet repeat expansion and the resulting pathogenesis

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Céramiques communes brunes de Provence occidentale : réactualisation de la typologie

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La Beauvalle : un établissement agricole antique (Aix-en-Provence, Bouches-du-Rhône).

International audienceLa Beauvalle,agriculture,antiquité,Aix-en-Provence, Bouches-du-Rhôn

Sense and Antisense <i>DMPK</i> RNA Foci Accumulate in DM1 Tissues during Development

<div><p>Myotonic dystrophy type 1 (DM1) is caused by an unstable expanded CTG repeat located within the <i>DMPK</i> gene 3’UTR. The nature, severity and age at onset of DM1 symptoms are very variable in patients. Different forms of the disease are described, among which the congenital form (CDM) is the most severe. Molecular mechanisms of DM1 are well characterized for the adult form and involve accumulation of mutant <i>DMPK</i> RNA forming foci in the nucleus. These RNA foci sequester proteins from the MBNL family and deregulate CELF proteins. These proteins are involved in many cellular mechanisms such as alternative splicing, transcriptional, translational and post-translational regulation miRNA regulation as well as mRNA polyadenylation and localization. All these mechanisms can be impaired in DM1 because of the deregulation of CELF and MBNL functions. The mechanisms involved in CDM are not clearly described. In order to get insight into the mechanisms underlying CDM, we investigated if expanded RNA nuclear foci, one of the molecular hallmarks of DM1, could be detected in human DM1 fetal tissues, as well as in embryonic and neonatal tissues from transgenic mice carrying the human <i>DMPK</i> gene with an expanded CTG repeat. We observed very abundant RNA foci formed by sense <i>DMPK</i> RNA and, to a lesser extent, antisense <i>DMPK</i> RNA foci. Sense <i>DMPK</i> RNA foci clearly co-localized with MBNL1 and MBNL2 proteins. In addition, we studied <i>DMPK</i> sense and antisense expression during development in the transgenic mice. We found that <i>DMPK</i> sense and antisense transcripts are expressed from embryonic and fetal stages in heart, muscle and brain and are regulated during development. These results suggest that mechanisms underlying DM1 and CDM involved common players including toxic expanded RNA forming numerous nuclear foci at early stages during development.</p></div

Transcriptionally Repressive Chromatin Remodelling and CpG Methylation in the Presence of Expanded CTG-Repeats at the DM1 Locus

An expanded CTG-repeat in the 3′ UTR of the DMPK gene is responsible for myotonic dystrophy type I (DM1). Somatic and intergenerational instability cause the disease to become more severe during life and in subsequent generations. Evidence is accumulating that trinucleotide repeat instability and disease progression involve aberrant chromatin dynamics. We explored the chromatin environment in relation to expanded CTG-repeat tracts in hearts from transgenic mice carrying the DM1 locus with different repeat lengths. Using bisulfite sequencing we detected abundant CpG methylation in the regions flanking the expanded CTG-repeat. CpG methylation was postulated to affect CTCF binding but we found that CTCF binding is not affected by CTG-repeat length in our transgenic mice. We detected significantly decreased DMPK sense and SIX5 transcript expression levels in mice with expanded CTG-repeats. Expression of the DM1 antisense transcript was barely affected by CTG-repeat expansion. In line with altered gene expression, ChIP studies revealed a locally less active chromatin conformation around the expanded CTG-repeat, namely, decreased enrichment of active histone mark H3K9/14Ac and increased H3K9Me3 enrichment (repressive chromatin mark). We also observed binding of PCNA around the repeats, a candidate that could launch chromatin remodelling cascades at expanded repeats, ultimately affecting gene transcription and repeat instability

Sense and antisense <i>DMPK</i> RNA levels in transgenic mice.

<p>qRT-PCR were performed in heart, skeletal muscle and brain from DMSXL and DM20 embryos and neonates at embryonic E14.5 to postnatal P29 stages. Levels of sense <i>DMPK</i> (left panels) and antisense transcripts (right panels) were reported on graphs using 18S as internal control, in arbitrary units (a.u.) with standard deviation of the mean for repeated experiments.</p