BRCA1 Balances the Action of a Transcription Elongation Factor In Mammary Gland Development and Tumorigenesis (sequencing)

Work from our mouse models showed that COBRA1, the B subunit of NELF, could facilitate R-loop (DNA:RNA hybrid) accumulation in the BRCA1-deficient mouse mammary epithelium. Since NELF could promoter RNA PolII pausing at promoter proximal regions, we asked whether COBRA1-mediated RNA Pol II pausing could contribute to accumulated R-loops. To answer this question, we performed chromatin immunoprecipitation-sequencing (ChIP-seq) for RNA Pol II, as well as two NELF subunits, NELF-A and NELF-B (COBRA1) in mouse primary mammary epithelium cells. To locate R-loops in the same cell population, we performed DNA:RNA immunoprecipitation-sequencing (DRIP-seq) with or without treatment of RNase H, a nuclease that specifically degrades RNA in the R-loop structure. Our sequencing results showed that RNA Pol II, NELF and R-loops are all enriched at transcription start sites (TSSs). Notably, genes with TSS R-loop accumulation are significantly enriched for COBRA1 binding. Taken together, the genomic data lent additional support to the notion that COBRA1-mediated RNAPII pausing contributes to R-loop dynamics in mammary epithelium. Overall design: Examination of RNA Pol II, NELF and R-loop distribution in the mouse mammary genome.