MBNL2 dysfunction in outer radial glial cells is associated with disrupted corticogenesis in congenital myotonic dystrophy [eCLIP]

However, the role of MBNL in neurodevelopmental disorders associated with severe forms of DM1 remains poorly understood. We used enhanced crosslinking and immunoprecipitation (eCLIP) to study MBNL2-RNA binding sites in 70-day-old forebrain organoids derived from an apparently healthy individual, a patient with congenital myotonic dystrophy (CDM) carrying approximately 2,000 CTG repeats, and an isogenic control in which the pathogenic repeat expansion had been removed.

Using Skipper, a workflow allowing improved discovery of protein–RNA binding sites, including in annotated repetitive elements, we identified reproducible enriched windows for the DMPK 3′ UTR in CDM organoids compared to the corresponding input controls. In contrast, no significant binding in the same region was detected in either the unaffected or the isogenic control. This finding supports a physical interaction between MBNL2 and the CUG-expanded DMPK mRNA, observed specifically in neural stem cells of late-stage forebrain organoids by immunostaining and fluorescence in situ hybridization (FISH).