Mapping Human Transient Transcriptomes Using Single Nucleotide Resolution 4sU Sequencing (SNU-Seq)

Abstract

AbstractGenomes are pervasively transcribed leading to stable and unstable transcripts that define functional regions of genomes and contribute to cellular phenotypes. Defining comprehensive nascent transcriptomes is pivotal to understand gene regulation, disease processes, and the impact of extracellular signals on cells. However, currently employed methods are laborious, technically challenging and costly. We developed single-nucleotide resolution 4sU-sequencing (SNU-Seq), involving pulse labelling, biotinylation and direct isolation of nascent transcripts. Artificial poly-(A)-tailing of the 3’ most nucleotide of nascent transcripts ensures oligo-d(T) primer-based library preparation and sequencing using commercial 3’ RNA-Seq kits. We show that SNU-Seq is a cost-effective new method generating even read profiles across transcription units. We used SNU-Seq to identify transcription elongation parameters, to map usage of polyadenylation (PAS) sites and novel enhancers. Remarkably, 4sU labelled nascent RNA accumulates short ∼100nt transcripts that map to the 5’ end of genes. We show that isolation of these short nascent RNA and sequencing the 5’ and 3’ ends using size-selected SNU-Seq (ssSNU-Seq) provides highly sensitive annotations of mapped and novel TSSs, promoter-proximal pause/termination sites. Thus, SNU-seq and ssSNU-seq combined yield comprehensive transcriptomics data at low cost with high spatial and temporal resolution.Highlights-SNU-Seq maps nascent transcripts at base-pair resolution, with high sensitivity and low cost-SNU-Seq detects comprehensive polyadenylation sites.-SNU-Seq maps the promoter proximal pause 60-80 nt from the TSS.-Size-selected SNU-Seq yields highly sensitive and novel TSS annotations