DNA-RNA hybrids contribute to the replication dependent genomic instability induced by Omcg1 deficiency
ABSTRACT During S phase, the replisome has to overcome many physical obstacles that can cause replication fork stalling and compromise genome integrity. Transcription is an important source of replicative stress and consequently, maintenance of genome integrity requires the protection of chromosomes from the deleterious effects arising from the interaction between nascent RNAs and template DNA, leading to stable DNA-RNA hybrids (R-loop) formation. We previously reported the essential role of Omcg1 (Ovum Mutant Candidate Gene) for cell cycle progression during early embryonic development. Here, we show that OMCG1 is a target of the cell cycle checkpoint kinases ATR/ATM and is essential for S phase progression in mouse embryonic fibroblasts. Using a conditional gene inactivation strategy, we demonstrate that OMCG1 depletion impairs cell viability as a consequence of DSB formation, checkpoint activation and replication fork collapse. We also show that no chromosome breaks were generated in non-cycling Omcg1-deficient cells. Furthermore, increased RNaseH expression significantly alleviated genomic instability in deficient fibroblasts suggesting that cotranscriptional R-loops formation contributes to the genesis of replication-dependent DSBs in these cells. Together with recent reports describing its participation to complexes involved in cotanscriptional processes, our results suggest that OMCG1 plays a role in the tight coupling between mRNA processing pathways and maintenance of genome integrity during cell cycle progression.
SourceAvailable from: Michel Cohen-Tannoudji[Show abstract] [Hide abstract]
ABSTRACT: Recent studies have shown that factors involved in transcription-coupled mRNA processing are important for the maintenance of genome integrity. How these processes are linked and regulated in vivo remains largely unknown. In this study, we addressed in the mouse model the function of Omcg1, which has been shown to participate in co-transcriptional processes, including splicing and transcription-coupled repair. Using inducible mouse models, we found that Omcg1 is most critically required in intestinal progenitors. In absence of OMCG1, proliferating intestinal epithelial cells underwent abnormal mitosis followed by apoptotic cell death. As a consequence, the crypt proliferative compartment of the small intestine was quickly and totally abrogated leading to the rapid death of the mice. Lack of OMCG1 in embryonic stem cells led to a similar cellular phenotype, with multiple mitotic defects and rapid cell death. We showed that mutant intestinal progenitors and embryonic stem cells exhibited a reduced cell cycle arrest following irradiation, suggesting that mitotic defects may be consecutive to M phase entry with unrepaired DNA damages. These findings unravel a crucial role for pre-mRNA processing in the homeostasis of the small intestine and point to a major role of OMCG1 in the maintenance of genome integrity.07/2012; 1(7):648-57. DOI:10.1242/bio.20121248
Chemical Reviews 04/2013; 113(11). DOI:10.1021/cr400017y · 45.66 Impact Factor
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ABSTRACT: R loops are three-stranded nucleic acid structures that comprise nascent RNA hybridized with the DNA template, leaving the nontemplate DNA single-stranded. R loops form naturally during transcription even though their persistent formation can be a risky outcome with deleterious effects on genome integrity. On the other hand, over the last few years, an increasingly strong case has been built for R loops as potential regulators of gene expression. Therefore, understanding their function and regulation under these opposite situations is essential to fully characterize the mechanisms that control genome integrity and gene expression. Here we review recent findings about these interesting structures that highlight their opposite roles in cellular fitness.Genes & Development 07/2014; 28(13):1384-1396. DOI:10.1101/gad.242990.114 · 12.64 Impact Factor