Loss of an oligodendrocyte specific silencer element provides a framework to assess the pathogenic impact of lamin B1 structural variants
The role of non-coding regulatory elements and how they might contribute to tissue type specificity of disease phenotypes is poorly understood. Autosomal Dominant Leukodystrophy (ADLD) is a fatal, adult-onset, neurological disorder that is characterized by extensive CNS demyelination. Most cases of ADLD are caused by tandem genomic duplications involving the lamin B1 gene (LMNB1) while a small subset are caused by genomic deletions upstream of the gene. Utilizing data from recently identified families that carry LMNB1 gene duplications but that do not exhibit demyelination, ADLD patient tissues, CRISPR modified cell lines and mouse models, we have identified a novel silencer element that is lost in ADLD patients and that specifically targets overexpression only to oligodendrocytes. This element consists of CTCF binding sites that mediate three-dimensional chromatin looping involving the LMNB1 and the recruitment of the PRC2 repressor complex.  Loss of the silencer element in ADLD identifies a previously unknown role for silencer elements in tissue specificity and disease causation. Overall design: CUT&RUN experiments in human fibroblast cells and oligodendrocytes from Mus musculus