STAG2 promotes the myelination transcriptional program in oligodendrocytes

SUMMARYCohesin folds chromosomes via DNA loop extrusion. Cohesin-mediated chromosome loops regulate transcription by shaping long-range enhancer-promoter interactions, among other mechanisms. Mutations of cohesin subunits and regulators cause human developmental diseases termed cohesinopathy. Vertebrate cohesin consists of SMC1, SMC3, RAD21, and either STAG1 or STAG2. To probe the physiological functions of cohesin, we created conditional knockout (cKO) mice with Stag2 deleted in the nervous system. Stag2 cKO mice exhibit growth retardation, neurological defects, and premature death, in part due to insufficient myelination of nerve fibers. Stag2 cKO oligodendrocytes exhibit delayed maturation and downregulation of myelination-related genes. Stag2 loss reduces promoter-anchored loops at downregulated genes in oligodendrocytes. Thus, STAG2-cohesin generates promoter-anchored loops at myelination-promoting genes to facilitate their transcription. Our study implicates defective myelination as a contributing factor to cohesinopathy and establishes oligodendrocytes as a relevant cell type to explore the mechanisms by which cohesin regulates transcription.

Establishment of a Large Collection of Cells from Major Depressive Disorder Patients to Model Disease and Therapy Response in Vitro

Major Depressive Disorder (MDD) is a multifactorial psychiatric condition that affects 4.4% of the world population, causing substantial personal suffering, disability and social costs. Current pharmacological treatments for MDD do not effect remission in 30% of patients. The development of in vitro models for MDD will aid the understanding of this disorder, its pharmacogenomics, and the development of new therapies. Although hiPSCs from 6 MDD patients have been established, given the complexity and heterogeneity of the disease much larger sample sizes may be needed to fully model the disorder in vitro. To this end, we established a collection of 66 primary cells and 10 induced pluripotent stem cells (hiPSCs) from a sample of clinically well-characterized MMD patients, who were participants of a clinical study that compared the effect of transcranial direct current stimulation (tCDS) versus escitalopram on the treatment of MDD. Cells were differentiated in vitro into serotoninergic neurons, a clinically relevant cell type for MMD. This collection of cells increases significantly the number of available samples from MDD patients, and thus will contribute to research into the molecular basis of depression.

Cell freezing protocol optimized for ATAC-Seq on motor neurons derived from human induced pluripotent stem cells

In recent years, the assay for transposase-accessible chromatin using sequencing (ATAC-Seq) has become a fundamental tool of epigenomic research. However, it has proven difficult to perform this technique on frozen samples because freezing cells before extracting nuclei impairs nuclear integrity and alters chromatin structure. We describe a protocol for freezing cells that is compatible with ATAC-Seq, producing results that compare well with those generated from fresh cells. We found that while flash-frozen samples are not suitable for ATAC-Seq, the assay is successful with slow-cooled cryopreserved samples. Using this method, we were able to isolate high quality, intact nuclei, and we verified that epigenetic results from fresh and cryopreserved samples agree quantitatively. We developed our protocol on a disease-relevant cell type, namely motor neurons differentiated from induced pluripotent stem cells from a patient affected by spinal muscular atrophy.