Genome Architecture Shapes Transcriptional Responses to DNASupercoiling in a Multicellular Organism

Abstract

DNA supercoiling is an intrinsic consequence of transcription that must be resolved to maintain proper gene expression. How DNA supercoiling shapes transcription dynamics in chromatinized animal genomes remains unclear. Here, we acutely depleted topoisomerases I and II in Caenorhabditis elegans and applied nascent transcription profiling, nuclear and total RNA-seq, histone modification mapping, and long-read sequencing to capture the immediate transcriptional and chromatin responses to topological stress. We show that the genomic context influences the effect of supercoiling on transcription initiation, elongation and coordinated expression of adjacent genes. The impact of supercoiling on transcription initiation is not uniformly repressive but instead depends on the orientation and proximity of neighboring genes. We find that negative supercoiling promotes coordinated expression of divergent gene pairs, while positive supercoiling inhibits and uncouples expression of convergent genes. DNA supercoiling hinders transcription elongation globally resulting in reduced production of longer transcripts and overall shortening of poly(A) tails. While DNA supercoiling generated by neighboring transcription impacts initiation, elongation defects are driven by local supercoiling generated by the genes own transcription. These elongation effects are not accompanied by global changes in elongation-associated histone modifications but coincide with modest reductions in promoter and enhancer marks. Our findings reveal a directional mechanism by which genome architecture shapes transcriptional responses to DNA supercoiling, uncovering a DNA topological basis for coordinated gene expression in a multicellular organism.