Impact des variations de séquence au sein de l'expansion CTG sur l'instabilité des répétitions et les mécanismes moléculaires impliqués dans la dystrophie myotonique de type 1 // Impact of sequence variations within the CTG repeat expansion on repeat inst

DM1 is an incurable and multi-system neuromuscular disease caused by an unstable CTG repeat expansion in the 3'UTR of the DMPK gene, whose length typically increases across generations and continues to expand over time in somatic tissues. The expanded DMPK mRNAs containing toxic CUG repeats are abnormally retained in the nucleus as aggregates (foci) and interfere with the activity of RNA-binding proteins, leading to misregulation of several downstream RNA transcripts, mainly through abnormal alternative splicing (1). In DM1, longer expanded alleles are usually associated with a worsening of clinical severity and an earlier age of onset. Previous studies have shown that CTG repeat instability depends on repeat length and the presence of variant triplets (interruptions) within repeat expansion. Instability is also influenced by transcription, DNA methylation, chromatin structure, and the DNA replication and repair machinery (2,3). In DM1 population, around 10% of the DM1 population carries interruptions, which exhibit variations in type (CCG, CAG, CTC, and CGG), frequency and position within the repeats (4,5). Interruptions are frequently associated with intergenerational contractions and stabilization of the repeat in tissues through mechanisms that remain to be identified. In addition, CCG interruptions are also linked to milder and later-onset form of DM1 (6). The dynamics of interruptions in patients and their impacts on molecular pathogenesis remain largely unexplored, primarily due to the absence of appropriate models and robust methods for repeat analysis. The PhD project aims to address these gaps by investigating how sequence variations modulate CTG repeat instability and its key molecular consequences in DM1.
In this project, the PhD candidate will take advantage of unique cellular models (Fibroblasts and MYOD-converted fibroblasts) and third-generation long-read sequencing technologies to decipher the role of interrupted repeats in DM1 addressing two questions: 1- What mechanisms are responsible for the stabilization and/or contraction of interrupted expanded allele? 2- How do interruptions affect the molecular pathogenesis and clinical features of DM1?
To explore the mechanisms involved in the stabilization or contraction of the expanded allele in the context of interruptions, the PhD candidate will work with several DM1 fibroblast cell lines carrying either CCG-interrupted expansions or pure CTG repeats. In addition, the candidate will generate isogenic fibroblast lines in which all types of triplet interruptions can be analyzed. This approach will control for patient-specific genetic background variability and overcome limitations imposed by sample availability. Using both the patient-derived fibroblasts and the newly generated isogenic lines, the PhD candidate will investigate the roles of DNA repair and DNA methylation in the stabilization/ contraction of the repeats. Multiple complementary techniques will be employed, including Pacific Biosciences long-read sequencing to analyze repeat instability and DNA methylation patterns, a novel EdU-based assay coupled with droplet digital PCR to assess DNA repair, and epigenetic editing approaches to directly evaluate the impact of methylation on repeat dynamics.
Interruptions within the CTG repeat tract may modulate the DM1 phenotype by stabilizing expanded alleles and/or altering RNA-mediated pathogenic mechanisms. Because these interruptions are transcribed, they may modify RNA secondary structure, thereby influencing toxic RNA foci formation, sequestration of RNA-binding proteins such as MBNL1, and alternative splicing regulation. To address these hypotheses, the PhD candidate will quantify DMPK expression (RT-qPCR) and assess nuclear RNA foci formation (FISH), MBNL1 localization (immunocytochemistry), and alternative splicing of key DM1 target transcripts (RT-PCR, RNA-seq) in fibroblasts and myo-converted fibroblasts carrying either pure or interrupted expansions.
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DM1 is an incurable and multi-system neuromuscular disease caused by an unstable CTG repeat expansion in the 3'UTR of the DMPK gene, whose length typically increases across generations and continues to expand over time in somatic tissues. The expanded DMPK mRNAs containing toxic CUG repeats are abnormally retained in the nucleus as aggregates (foci) and interfere with the activity of RNA-binding proteins, leading to misregulation of several downstream RNA transcripts, mainly through abnormal alternative splicing (1). In DM1, longer expanded alleles are usually associated with a worsening of clinical severity and an earlier age of onset. Previous studies have shown that CTG repeat instability depends on repeat length and the presence of variant triplets (interruptions) within repeat expansion. Instability is also influenced by transcription, DNA methylation, chromatin structure, and the DNA replication and repair machinery (2,3). In DM1 population, around 10% of the DM1 population carries interruptions, which exhibit variations in type (CCG, CAG, CTC, and CGG), frequency and position within the repeats (4,5). Interruptions are frequently associated with intergenerational contractions and stabilization of the repeat in tissues through mechanisms that remain to be identified. In addition, CCG interruptions are also linked to milder and later-onset form of DM1 (6). The dynamics of interruptions in patients and their impacts on molecular pathogenesis remain largely unexplored, primarily due to the absence of appropriate models and robust methods for repeat analysis. The PhD project aims to address these gaps by investigating how sequence variations modulate CTG repeat instability and its key molecular consequences in DM1.
In this project, the PhD candidate will take advantage of unique cellular models (Fibroblasts and MYOD-converted fibroblasts) and third-generation long-read sequencing technologies to decipher the role of interrupted repeats in DM1 addressing two questions: 1- What mechanisms are responsible for the stabilization and/or contraction of interrupted expanded allele? 2- How do interruptions affect the molecular pathogenesis and clinical features of DM1?
To explore the mechanisms involved in the stabilization or contraction of the expanded allele in the context of interruptions, the PhD candidate will work with several DM1 fibroblast cell lines carrying either CCG-interrupted expansions or pure CTG repeats. In addition, the candidate will generate isogenic fibroblast lines in which all types of triplet interruptions can be analyzed. This approach will control for patient-specific genetic background variability and overcome limitations imposed by sample availability. Using both the patient-derived fibroblasts and the newly generated isogenic lines, the PhD candidate will investigate the roles of DNA repair and DNA methylation in the stabilization/ contraction of the repeats. Multiple complementary techniques will be employed, including Pacific Biosciences long-read sequencing to analyze repeat instability and DNA methylation patterns, a novel EdU-based assay coupled with droplet digital PCR to assess DNA repair, and epigenetic editing approaches to directly evaluate the impact of methylation on repeat dynamics.
Interruptions within the CTG repeat tract may modulate the DM1 phenotype by stabilizing expanded alleles and/or altering RNA-mediated pathogenic mechanisms. Because these interruptions are transcribed, they may modify RNA secondary structure, thereby influencing toxic RNA foci formation, sequestration of RNA-binding proteins such as MBNL1, and alternative splicing regulation. To address these hypotheses, the PhD candidate will quantify DMPK expression (RT-qPCR) and assess nuclear RNA foci formation (FISH), MBNL1 localization (immunocytochemistry), and alternative splicing of key DM1 target transcripts (RT-PCR, RNA-seq) in fibroblasts and myo-converted fibroblasts carrying either pure or interrupted expansions.
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Début de la thèse : 01/10/2026

Public funding alone (i.e. government, region, European, international organization research grant)

Concours pour un contrat doctoral

Sorbonne Université SIS (Sciences, Ingénierie, Santé)

515 Complexité du vivant

Knowledge • Required knowledge in molecular and cellular biology • Basic knowledge of bioinformatics and statistics • Understanding of neuromuscular diseases and genome instability Skills • Molecular biology techniques (PCR, QRT-PCR, DNA and RNA extractions, bacteriology, etc.) • Cellular biology techniques Abilities • Motivation, creativity, and enthusiasm • Ability to work in a team
Knowledge • Required knowledge in molecular and cellular biology • Basic knowledge of bioinformatics and statistics • Understanding of neuromuscular diseases and genome instability Skills • Molecular biology techniques (PCR, QRT-PCR, DNA and RNA extractions, bacteriology, etc.) • Cellular biology techniques Abilities • Motivation, creativity, and enthusiasm • Ability to work in a team