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ARID1B is a Dosage-sensitive Regulator of Polycomb Repressive Complex Distribution and HOX Gene Regulation in Patient-derived Neural Progenitors

ABSTRACT: Recent unbiased exome and whole-genome sequencing studies have identified ARID1B (originally BAF250b) as the most frequently mutated gene in human de novo neurodevelopmental disorders and a high confidence autism gene. ARID1B is a subunit of the multimeric SWI/SNF or Brg/Brahma-Associated Factor (BAF) ATP-dependent chromatin remodeling complex. Studies of Arid1b+/- mice as well as other BAF subunit mutants have found defects in neural progenitor proliferation and activity-dependent neuronal dendritogenesis; however, to date, the molecular impact of ARID1B mutations on the human neural lineage has not been investigated. Remarkably, ARID1B is required for expression of HOX genes, including anterior HOX genes necessary for brain development. Despite the high homology with ARID1A and the fact that ARID1A is expressed at about 3-fold higher levels, it is unable to compensate for heterozygous loss of ARID1B. These changes in gene expression were paralleled by dosage-sensitive altered deposition of histone H3 lysine-27 trimethylation (H3K27me3) and histone H2A lysine-119 ubiquitination (H2AK119ub) indicating that an evolutionarily conserved pathway of HOX gene regulation underlies the neurodevelopmental defects accompanying ARID1B haploinsufficiency. Using FIRE-Cas9, we show that the unmutated ARID1B allele can be activated to near normal and potentially therapeutic levels.

ORGANISM(S): Homo sapiens

PROVIDER: GSE188883 | GEO | 2021/11/20

REPOSITORIES: GEO

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Project description:Signaling by the cytokine LIF and its downstream transcription factor, STAT3, prevents differentiation of pluripotent embryonic stem cells (ESCs) by opposing MAP kinase signaling. This contrasts with most cell types where STAT3 signaling induces differentiation. We find that STAT3 binding across the pluripotent genome is dependent upon Brg, the ATPase subunit of a specialized chromatin remodeling complex (esBAF) found in ESCs. Brg is required to establish chromatin accessibility at STAT3 binding targets, in essence preparing these sites to respond to LIF signaling. Moreover, Brg deletion leads to rapid Polycomb (PcG) binding and H3K27me3-mediated silencing of many Brg-activated targets genome-wide, including the target genes of the LIF signaling pathway. Hence, one crucial role of Brg in ESCs involves its ability to potentiate LIF signaling by opposing PcG. Contrary to expectations, Brg also facilitates PcG function at classical PcG target including all four Hox loci, reinforcing their repression in ESCs. These findings reveal that esBAF does not simply antagonize PcG, but rather, the two chromatin regulators act both antagonistically and synergistically with the common goal of supporting pluripotency. Brg conditional embryonic stem cell (ESC) line was prepared from Brg(lox/lox);Actin-CreER mice that allow conditional deletion of Brg upon addition of 4-hydroxytamoxifen (4OHT, Sigma). Brg conditional ESCs were treated with 4-OHT for 72 hours to delete Brg. Brg protein levels completely abolished only at 48 hours (Brg-KO). RNA from Brg conditional ESCs (WT), Brg-KO ESCs, Brg conditional ESCs starved of LIF (Lif-WD) for 48 hours were extracted using Trizol reagent (Invitrogen), followed by RNeasy kit with DNaseI digestion to eliminate genomic DNA. Purified RNA was processed and hybridized onto Affymetrix Mouse MOE 4.0 3’ expression arrays according to the manufacturer's instructions. ChIP-Seq was used to detect and measure STAT3 occupancy and levels of H3K27me3 in the genome before and after the removal of the SWI/SNF ATPase Brg in mouse ESCs. Total of 4 samples (WT and KO STAT3; WT and KO H3K27me3). Input DNA was sequenced as control.

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ARID1B is a Dosage-sensitive Regulator of Polycomb Repressive Complex Distribution and HOX Gene Regulation in Patient-derived Neural Progenitors

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