Inferring cell-type-specific causal gene regulatory networks during human neurogenesis

BackgroundGenetic variation influences both chromatin accessibility, assessed in chromatin accessibility quantitative trait loci (caQTL) studies, and gene expression, assessed in expression QTL (eQTL) studies. Genetic variants can impact either nearby genes (local eQTLs) or distal genes (trans eQTLs). Colocalization between caQTL and eQTL, or local- and distant-eQTLs suggests that they share causal variants. However, pairwise colocalization between these molecular QTLs does not guarantee a causal relationship. Mediation analysis can be applied to assess the evidence supporting causality versus independence between molecular QTLs. Given that the function of QTLs can be cell-type-specific, we performed mediation analyses to find epigenetic and distal regulatory causal pathways for genes within two major cell types of the developing human cortex, progenitors and neurons. ResultsWe found that expression of 168 and 38 genes were mediated by chromatin accessibility in progenitors and neurons, respectively. We also found that the expression of 781 and 200 downstream genes were mediated by upstream genes in progenitors and neurons. Moreover, we discovered that a genetic locus associated with inter-individual differences in brain structure showed evidence for mediation of SLC26A7 through chromatin accessibility, identifying molecular mechanisms of a common variant association to a brain trait. ConclusionsIn this study, we identified cell-type-specific causal gene regulatory networks whereby the impacts of variants on gene expression were mediated by chromatin accessibility or distal gene expression. Identification of these causal paths will enable identifying and prioritizing actionable regulatory targets perturbing these key processes during neurodevelopment.