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Massively Parallel Reporter Assay of human-specific substitutions in neurodevelopmental enhancers

ABSTRACT: We performed a Massively Parallel Reporter Assay (MPRA) to screen >30,000 human-specific substitutions in ChIP-seq-identified Human Gain Enhancers (HGEs) and Human Accelerated Regions (HARs), highly conserved non-coding regions that show accelerated sequence evolution in humans. After comparing human and chimpanzee reference alleles, we used a second MPRA to deconvolute individual substitutions within differentially active enhancers from substitutions in the same fragment and from other variants (human segregating variants or chimpanzee-specific variants) to isolate their specific effects on enhancer activity.

ORGANISM(S): Homo sapiens Pan troglodytes

PROVIDER: GSE140983 | GEO | 2019/11/26

REPOSITORIES: GEO

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Project description:Genome-wide association studies (GWAS) have successfully identified 145 genomic regions that contribute to schizophrenia risk, but linkage disequilibrium (LD) makes it challenging to discern causal variants. Computational finemapping prioritized thousands of credible variants, ~98% of which lie within poorly characterized non-coding regions. To functionally validate their regulatory effects, we performed a massively parallel reporter assay (MPRA) on 5,173 finemapped schizophrenia GWAS variants in primary human neural progenitors (HNPs). We identified 440 variants with allelic regulatory effects (MPRA-positive variants), with 72% of GWAS loci containing at least one MPRA-positive variant. Transcription factor binding had modest predictive power for predicting the allelic activity of MPRA-positive variants, while GWAS association, finemap posterior probability, enhancer overlap, and evolutionary conservation failed to predict MPRA-positive variants. Furthermore, 64% of MPRA-positive variants did not exhibit eQTL signature, suggesting that MPRA could identify yet unexplored variants with regulatory potentials. MPRA-positive variants differed from eQTLs, as they were more frequently located in distal neuronal enhancers. Therefore, we leveraged neuronal 3D chromatin architecture to identify 273 genes that physically interact with MPRA-positive variants. These genes annotated by chromatin interactome displayed higher mutational constraints and regulatory complexity than genes annotated by eQTLs, recapitulating a recent finding that eQTL- and GWAS-detected variants map to genes with different properties. Finally, we propose a model in which allelic activity of multiple variants within a GWAS locus can be aggregated to predict gene expression by taking chromatin contact frequency and accessibility into account. In conclusion, we demonstrate that MPRA can effectively identify functional regulatory variants and delineate previously unknown regulatory principles of schizophrenia.

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Massively Parallel Reporter Assay of human-specific substitutions in neurodevelopmental enhancers

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