The intersection of DNA replication with antisense 3' RNA processing in Arabidopsis FLC chromatin silencing.

Funder: Wellcome TrustHow noncoding transcription influences chromatin states is still unclear. The Arabidopsis floral repressor gene FLC is quantitatively regulated through an antisense-mediated chromatin silencing mechanism. The FLC antisense transcripts form a cotranscriptional R-loop that is dynamically resolved by RNA 3' processing factors (FCA and FY), and this is linked to chromatin silencing. Here, we investigate this silencing mechanism and show, using single-molecule DNA fiber analysis, that FCA and FY are required for unimpeded replication fork progression across the Arabidopsis genome. We then employ the chicken DT40 cell line system, developed to investigate sequence-dependent replication and chromatin inheritance, and find that FLC R-loop sequences have an orientation-dependent ability to stall replication forks. These data suggest a coordination between RNA 3' processing of antisense RNA and replication fork progression in the inheritance of chromatin silencing at FLC

Repriming DNA synthesis: an intrinsic restart pathway that maintains efficient genome replication

To bypass a diverse range of fork stalling impediments encountered during genome replication, cells possess a variety of DNA damage tolerance (DDT) mechanisms including translesion synthesis, template switching, and fork reversal. These pathways function to bypass obstacles and allow efficient DNA synthesis to be maintained. In addition, lagging strand obstacles can also be circumvented by downstream priming during Okazaki fragment generation, leaving gaps to be filled post-replication. Whether repriming occurs on the leading strand has been intensely debated over the past half-century. Early studies indicated that both DNA strands were synthesised discontinuously. Although later studies suggested that leading strand synthesis was continuous, leading to the preferred semi-discontinuous replication model. However, more recently it has been established that replicative primases can perform leading strand repriming in prokaryotes. An analogous fork restart mechanism has also been identified in most eukaryotes, which possess a specialist primase called PrimPol that conducts repriming downstream of stalling lesions and structures. PrimPol also plays a more general role in maintaining efficient fork progression. Here, we review and discuss the historical evidence and recent discoveries that substantiate repriming as an intrinsic replication restart pathway for maintaining efficient genome duplication across all domains of life

PRIMPOL ensures robust handoff between on-the-fly and post-replicative DNA lesion bypass

Acknowledgements: We would like to thank Kim Liu and Consuelo Perez for help with Illumina sequencing, the LMB flow cytometry facility and members of the Sale lab for discussions.The primase/polymerase PRIMPOL restarts DNA synthesis when replication is arrested by template impediments. However, we do not have a comprehensive view of how PRIMPOL-dependent repriming integrates with the main pathways of damage tolerance, REV1-dependent ‘on-the-fly’ lesion bypass at the fork and PCNA ubiquitination-dependent post-replicative gap filling. Guided by genome-wide CRISPR/Cas9 screens to survey the genetic interactions of PRIMPOL in a non-transformed and p53-proficient human cell line, we find that PRIMPOL is needed for cell survival following loss of the Y-family polymerases REV1 and POLη in a lesion-dependent manner, while it plays a broader role in promoting survival of cells lacking PCNA K164-dependent post-replicative gap filling. Thus, while REV1- and PCNA K164R-bypass provide two layers of protection to ensure effective damage tolerance, PRIMPOL is required to maximise the effectiveness of the interaction between them. We propose this is through the restriction of post-replicative gap length provided by PRIMPOL-dependent repriming

PRIMPOL ensures robust handoff between on-the-fly and post-replicative DNA lesion bypass.

Acknowledgements: We would like to thank Kim Liu and Consuelo Perez for help with Illumina sequencing, the LMB flow cytometry facility and members of the Sale lab for discussions.The primase/polymerase PRIMPOL restarts DNA synthesis when replication is arrested by template impediments. However, we do not have a comprehensive view of how PRIMPOL-dependent repriming integrates with the main pathways of damage tolerance, REV1-dependent 'on-the-fly' lesion bypass at the fork and PCNA ubiquitination-dependent post-replicative gap filling. Guided by genome-wide CRISPR/Cas9 screens to survey the genetic interactions of PRIMPOL in a non-transformed and p53-proficient human cell line, we find that PRIMPOL is needed for cell survival following loss of the Y-family polymerases REV1 and POLη in a lesion-dependent manner, while it plays a broader role in promoting survival of cells lacking PCNA K164-dependent post-replicative gap filling. Thus, while REV1- and PCNA K164R-bypass provide two layers of protection to ensure effective damage tolerance, PRIMPOL is required to maximise the effectiveness of the interaction between them. We propose this is through the restriction of post-replicative gap length provided by PRIMPOL-dependent repriming

Effect of childhood general traumas on suicide attempt depends on TPH2 and ADARB1 variants in psychiatric patients

Suicidal behavior has been associated with a deficient serotonin neurotransmission which is likely a consequence of individual genetic architecture, exposure to environmental factors and interactions of those factors. We examined whether the interaction of child abuse, TPH2 (tryptophan hydroxylase 2) variant rs4290270, affecting alternative splicing and editing of TPH2 pre-mRNAs, and ADARB1 (adenosine deaminase acting on RNA B1) variants rs4819035 and rs9983925 may influence the risk for suicide attempt in psychiatric patients. TPH2 rs4290270 was genotyped in 165 suicide attempters and 188 suicide non-attempters diagnosed with major depressive disorder, bipolar disorder and schizophrenia. Genotyping data for ADARB1 variants were taken over from our previous study. Child abuse before the age of 18 years was assessed using the Early Trauma Inventory-Self Report. Generalized linear models and backward selection were applied to identify the main and interacting effects of environmental and genetic factors, including psychiatric diagnoses, patients’ gender and age as covariates. Childhood general traumas were independently associated with suicide attempt. Two-way interaction between TPH2 rs4290270 and general traumas revealed that TT homozygotes with a history of general traumas had an increased risk for suicide attempt. Three-way interaction of general traumas, TPH2 rs4290270 and ADARB1 rs4819035 indicated that the highest predisposition to suicide attempt was observed in individuals who experienced general traumas and were TT homozygote for rs4290270 and TT homozygote for rs4819035. Our findings suggest that the risk for suicide attempt in psychiatric patients exposed to an adverse childhood environment may depend on TPH2 and ADARB1 variants.This is a post-peer-review, pre-copyedit version of an article published in Journal of Neural Transmission. The final authenticated version is available online at: [http://dx.doi.org/10.1007/s00702-017-1677-z]Journal of Neural Transmission (2017

Simultaneous inhibition of DNA-PK and Polϴ improves integration efficiency and precision of genome editing

Abstract Genome editing, specifically CRISPR/Cas9 technology, has revolutionized biomedical research and offers potential cures for genetic diseases. Despite rapid progress, low efficiency of targeted DNA integration and generation of unintended mutations represent major limitations for genome editing applications caused by the interplay with DNA double-strand break repair pathways. To address this, we conduct a large-scale compound library screen to identify targets for enhancing targeted genome insertions. Our study reveals DNA-dependent protein kinase (DNA-PK) as the most effective target to improve CRISPR/Cas9-mediated insertions, confirming previous findings. We extensively characterize AZD7648, a selective DNA-PK inhibitor, and find it to significantly enhance precise gene editing. We further improve integration efficiency and precision by inhibiting DNA polymerase theta (Polϴ). The combined treatment, named 2iHDR, boosts templated insertions to 80% efficiency with minimal unintended insertions and deletions. Notably, 2iHDR also reduces off-target effects of Cas9, greatly enhancing the fidelity and performance of CRISPR/Cas9 gene editing