Mapping Chromatin Occupancy ofPpp1r1b-lncRNAGenome-Wide Using Chromatin Isolation by RNA Purification (ChIRP)-seq

Abstract

ABSTRACTLong non-coding RNA (lncRNA) mediated transcriptional regulation is increasingly recognized as an important gene regulatory mechanism during development and disease. LncRNAs are emerging as critical regulators of chromatin state; yet the nature and the extent of their interactions with chromatin remain to be fully revealed. We have previously identifiedPpp1r1b-lncRNAas an essential epigenetic regulator of myogenic differentiation in cardiac and skeletal myocytes in mice and humans. We further demonstrated thatPpp1r1b-lncRNAfunction is mediated by the interaction with the chromatin-modifying complex polycomb repressive complex 2 (PRC2) at the promoter of myogenic differentiation transcription factors,TBX5andMyoD1. Herein, we employed an unbiased chromatin isolation by RNA purification (ChIRP) and high throughput sequencing to map the repertoire ofPpp1r1b-lncRNAchromatin occupancy genome-wide in the mouse muscle myoblast cell line. We uncovered a total of 99732 true peaks corresponding toPpp1r1b-lncRNAbinding sites at high confidence (P-value < 1e-5 and enrichment score ≥ 10). ThePpp1r1b-lncRNA-binding sites averaged 558 bp in length and were distributed widely within the coding and non-coding regions of the genome. Approximately 46% of these true peaks were mapped to gene elements, of which 1180 were mapped to experimentally validated promoter sequences. Importantly, the promoter-mapped binding sites were enriched in myogenic transcription factors and heart development while exhibiting focal interactions with known motifs of proximal promoters and transcription initiation by RNA polII, including TATA, transcription initiator, CCAAT-box, and GC-box, supportingPpp1r1b-lncRNArole in transcription initiation of myogenic regulators. Remarkably, nearly 40% ofPpp1r1b-lncRNA-binding sites mapped to gene introns, were enriched with the Homeobox family of transcription factors, and exhibited TA-rich motif sequences, suggesting potential motif specificPpp1r1b-lncRNA-bound introns. Lastly, more than 136521enhancer sequences were detected inPpp1r1b-lncRNA-occupancy sites at high confidence. Among these enhancers,12% exhibited cell type/tissue-specific enrichment in fetal heart and muscles. Together, our findings provide further insights into the genome-widePpp1r1b-lncRNA:Chromatin interactome that may potentially dictate its function in myogenic differentiation and potentially other cellular and biological processes.