Variants in the zinc transporter TMEM163 cause a hypomyelinating leukodystrophy.

Hypomyelinating leukodystrophies comprise a subclass of genetic disorders with deficient myelination of the CNS white matter. Here we report four unrelated families with a hypomyelinating leukodystrophy phenotype harbouring variants in TMEM163 (NM_030923.5). The initial clinical presentation resembled Pelizaeus-Merzbacher disease with congenital nystagmus, hypotonia, delayed global development and neuroimaging findings suggestive of significant and diffuse hypomyelination. Genomic testing identified three distinct heterozygous missense variants in TMEM163 with two unrelated individuals sharing the same de novo variant. TMEM163 is highly expressed in the CNS particularly in newly myelinating oligodendrocytes and was recently revealed to function as a zinc efflux transporter. All the variants identified lie in highly conserved residues in the cytoplasmic domain of the protein, and functional in vitro analysis of the mutant protein demonstrated significant impairment in the ability to efflux zinc out of the cell. Expression of the mutant proteins in an oligodendroglial cell line resulted in substantially reduced mRNA expression of key myelin genes, reduced branching and increased cell death. Our findings indicate that variants in TMEM163 cause a hypomyelinating leukodystrophy and uncover a novel role for zinc homeostasis in oligodendrocyte development and myelin formation.

Enhanced differentiation of the mouse oli-neu oligodendroglial cell line using optimized culture conditions.

OBJECTIVE: Oligodendrocytes (OL) are the glial cell type in the CNS that are responsible for myelin formation. The ability to culture OLs in vitro has provided critical insights into the mechanisms underlying their function. However, primary OL cultures are tedious to obtain, difficult to propagate and are not easily conducive to genetic manipulation. To overcome these obstacles, researchers have generated immortalized OL like cell lines derived from various species. One such cell line is the mouse Oli-neu line which is thought to recapitulate characteristics of OLs in early stages of maturity. They have been extensively utilized in multiple studies as surrogates for OLs, especially in analyzing epigenetic modifications and regulatory pathways in the OL lineage. RESULTS: In this report we present the development of optimized culture media and growth conditions that greatly facilitate the differentiation of Oli-neu cells. Oli-neu cells differentiated using these new protocols exhibit a higher expression of myelin related genes and increased branching, both of which are defining characteristics of mature OLs, when compared to previous culture protocols. We envision that these new culture conditions will greatly facilitate the use of Oli-neu cells and enhance their ability to recapitulate the salient features of primary OLs.

An oligodendrocyte silencer element underlies 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 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 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.