Molecular consequences of myotonic dystrophy type 2-causing cctg DNA repeats

This Project Grant award from the National Institute of General Medical Sciences (NIGMS) under the Biomedical Research and Research Training Program (CFDA 93.859) provides $434,750 to California State University San Marcos Corp to conduct research on the molecular mechanisms underlying myotonic dystrophy type 2 (DM2). The project aims to elucidate the causes of CCTG repeat instability and large-scale contractions in the CNBP gene, which are associated with DM2. Key objectives include evaluating the role of mismatch repair genes on CCTG repeat contractions, analyzing how genomic location and DNA replication dynamics affect CCTG repeat fragility, and characterizing the differential effects of repeat length and orientation on gene expression and RNA splicing. This research has important implications for understanding the etiology of tetranucleotide expansion diseases like DM2 and may inform potential therapeutic approaches. The award period runs from August 1, 2024 to July 31, 2027.

Abstract

Myotonic dystrophy type 2 is a genetic disorder characterized by progressive muscle wasting and weakness that is caused by long cctg DNA repeats. Individuals can have up to 11,000 cctg repeats within the cnbp gene responsible for disease. The proposed project will elucidate the molecular mechanisms of cctg repeat instability with a specific focus on large-scale contractions and DNA breakage using budding yeast s. Cerevisiae as a model organism. Understanding the molecular mechanisms of contractions is important to evaluate whether manipulating this process would be a viable approach to treat repeat expansion disease. We will evaluate the role of genes involved in the mismatch repair pathway on large-scale contractions. We will carry out genetic analysis of double mutants and specific point mutants that are candidates for study because of their role in protein binding domains or implications from human genome wide association studies. Recently, my lab showed that disease-associated lengths of cctg repeats cause chromosomal fragility in vivo. This project will elucidate how variables such as genomic location and DNA replication dynamics affect cctg DNA fragility, which has important implications for understanding the mechanisms of expansions and chromosomal translocations. Finally, we will investigate cctg repeat-associated gene expression from a distinct angle by characterizing differential effects of repeat length and orientation on steady-state transcript levels and RNA splicing. Altogether, the proposed studies will provide fundamental insights into the molecular mechanisms of DNA replication, repair, and transcription that underlie the etiology of the tetranucleotide expansion disease DM2.