Cellular heterogeneity in the developing forebrain masks transcriptional outcomes and principles of Evf2 enhancer lncRNA-Dlx5/6UCE-gene guidance

Abstract

During mouse embryonic brain development, the Evf2 ultraconserved enhancer (UCE) lncRNA guides the Dlx5/6UCE to [~]129 sites across chr6. However, previous work identified only 4 transcriptionally regulated targets associated with Evf2-Dlx5/6UCE enhancer-gene guided sites (EGGs), raising questions about the significance of the majority of Evf2-EGGs. Here, single cell transcriptomics (scRNAseq) shows that Evf2-EGGs on chr6 coincide with subpopulation-specific Evf2 transcriptional targets, revealing far greater alignment between EGGs and transcriptional targets than previously reported. Surprisingly, subpopulation-specific Evf2 regulated gene networks in embryonic progenitors predict adult synaptic and seizure defects. Evf2 regulation of EGGs to gene bodies (GB, Dlx5/6UCE locations within {+/-}5kb of the target gene) divides chr6 into short-range (<10Mb distant), highly activated genes, and long/super-long-range (10-129Mb), moderately repressed genes. Clustering of Evf2 transcriptionally regulated chr6 targets in populations where Evf2 is first activated supports that Evf2-EGG transcriptional effects can occur from EGG shifts as far as 3Mb, uncoupling enhancer shift distance and transcriptional direction from transcriptional outcome. Evf2 RNA binding sites (RBSs) divide chr6 into 4 major regions, consistent with a role for RBS chromosomal spacing in long-and super-long-range EGG selectivity. Surprisingly, 95% of 147 RBSs genome-wide potentially form inter-chromosomal DNA loops. Evf2-regulated combinatorial recruitment of Evf2-ribonucleoproteins at EGGs and RBSs, together with effects on homeodomain transcription factor DNA motif recognition, support a novel model of lncRNA directed multi-modal EGG selectivity during intra- and inter-chromosomal gene regulation.