Project description:A functional study of genes that might play a role in DNA repair/recombination and in the response to oxidative stress (Microarrays expression studies, Microbiological assays, In planta functional studies). Which Arabidopsis thaliana genes are induced by ionising radiations? Comparison of SADE transcriptome data (Af1999083) and micro-arrays transcriptome data.
Project description:Meiotic recombination is carried out through a specialized pathway for the formation and repair of DNA double-strand breaks (DSBs) made by the Spo11 protein. The present study shed light on the functional role of Cyclin, CYC2, in Tetrahymena thermophila which has transcriptionally high expression level during meiosis process. Knocking out the CYC2 gene results in arrest of meiotic conjugation process at 2.5â??3.5 h after conjugation initiation, before the meiosis division starts, and in company with the absence of DSBs. To investigate the underlying mechanism of this phenomenon, a complete transcriptome profile was performed between wild-type strain and CYC2 knock-out strain. Functional analysis of RNA-Seq results identifies related differentially expressed genes (DEGs) including SPO11 and these DEGs are enriched in DNA repair/mismatch repair (MMR) terms in homologous recombination (HR), which indicates that CYC2 could play a crucial role in meiosis by regulating SPO11 and participating in HR. We performed mRNA profiling on both wild-type strains and CYC2-knocking out strains at four different stages during meiosis prohase of Tetrahymena thermophila.
Project description:Immunoglobulin (Ig) and T cell receptor (TCR) V(D)J gene recombination relies on non-homologous end-joining (NHEJ), which repairs DNA double-strand breaks (DSBs) introduced by the RAG1/2 nuclease complex. Functional redundancies exist between NHEJ and the ATM kinase-dependent chromatin DSB response, likely masking the activity of additional factors. Here, we performed targeted CRISPR/Cas9 knockout screens (+/- ATM kinase inhibition) in pro-B cells and identified Senataxin (SETX) as a novel player in V(D)J recombination. We show that SETX supports V(D)J recombination, particularly when the ATM kinase is inhibited or in an XLF-deficient background. Furthermore, we show that SETX suppresses the formation of aberrant coding end-to-signal end hybrid joints during V(D)J recombination, both in vitro and in vivo. Finally, SETX prevents the aberrant joining of AID-induced DNA ends during class switch recombination (CSR). Overall, our work reveals an important role for SETX in promoting recombination fidelity and suppressing genome instability during antigen receptor gene diversification.
Project description:Background: Cells deficient in DNA repair factors breast cancer susceptibility 1/2 (BRCA1/2) or ataxia-telangiectasia mutated (ATM) are sensitive to poly-ADP ribose polymerase (PARP) inhibitors. Building on our previous findings, we asked how the lysine methyltransferase SETD1A contributed to PARP inhibitor-mediated cell death and determined the mechanisms responsible. Methods: We used cervical, breast, lung and ovarian cancer cells bearing mutations in BRCA1 or ATM and depleted SETD1A using siRNA or CRISPR/Cas9. We assessed the effects of the PARPi Olaparib on cell viability, homologous recombination, and DNA repair. We assessed underlying transcriptional perturbations using RNAseq. We also used data from The Cancer Genomics Atlas (TCGA) to investigate overall patient survival. Results: Loss of SETD1A from both BRCA1-deficient and ATM-deficient cancer cells was associated with resistance to Olaparib, explained by an partial restoration of homologous recombination. Mechanistically, SETD1A-dependent transcription of the crossover junction endonuclease EME1 correlated with sensitivity to Olaparib in these cells. Accordingly, when SETD1A or EME1 was lost, BRCA1 or ATM-mutated cells became resistant to Olaparib, and homologous recombination was partially restored. Conclusions: Loss of SETD1A or EME1 may explain why patients develop resistance to PARP inhibitors in the clinic.
Project description:Homologous recombination-mediated DNA repair deficiency (HRD) predisposes to cancer development, but also provides therapeutic opportunities. Here, we identified an HRD gene signature that robustly predicted HRD status. Unexpectedly, concurrent loss of PTEN in BRCA1-deficient cells might extensively rewire the HR repair network and confer resistance to PARP inhibitor, partially through over-expression of TTK. We used the HRD gene signature as a drug discovery tool and found several PARP-inhibitor-synergizing agents through the connectivity map. Thus gene expression profiling can be used to define the functional status of the HR repair network providing prognostic and therapeutic information. Various shRNAs that target genes involved in homologous recombination (HR) were transfected in MCF-10A non-transformed breast cells lines. Stable HR gene knockdown MCF-10A cells were seeded 200000 at 10 cm plate. Cells were harvested after 48 hours culturing and used for gene expression profiling. The shRNAs that target ATM, ATR, CHK1, CHK2, and 53BP1 genes were transfected in MCF-10A non-transformed breast cell line by lentiviral particles and selected stable ATM, ATR, CHK1, CHK2, and 53BP1 knockdown MCF-10A cells. Scrambled control shRNA-transfected and wild type MCF-10A cells were applying as control. All knockdown and control MCF-10A cells were seeded with 2 x 10^5 cells at 10 cm culture plate. Cells were cultured in MCF-10A medium and harvested after 48 hours culturing. mRNA was extracted from collected cells and performing gene expression profiling. Three biological replicates were applied.
Project description:Mutations in the ATM tumor suppressor gene confer cellular hypersensitivity to various DNA-damaging chemotherapeutic agents. To explore genetic resistance mechanisms towards such drugs, we performed genome-wide CRISPR-Cas9 loss-of-function screens in cells treated with the DNA topoisomerase I poison topotecan. Our ensuing characterizations of hits established that loss of terminal components of the non-homologous end joining (NHEJ) machinery or components of the BRCA1-A complex specifically confer topotecan resistance to ATM-deficient cells. Our findings indicate that hypersensitivity of ATM-mutant cells to topotecan or the poly-(ADP-ribose) polymerase (PARP) inhibitor olaparib is due to delayed engagement of homologous recombination repair (HRR) at a subset of DNA-replication-fork associated single ended double-strand breaks (seDSBs), which allows non-homologous end joining (NHEJ) mediated repair, resulting in toxic chromosome fusions. Thus, restoration of legitimate repair in ATM-deficient cells – either by preventing the DNA ligation step of NHEJ or by enhancing HRR engagement by deregulating the BRCA1-A complex – markedly suppresses this toxicity. We conclude that the crucial role for ATM at seDSBs is to prevent toxic LIG4-mediated NHEJ at damaged replication forks. Furthermore, our observation that suppressor mutations in ATM-mutant backgrounds are fundamentally different to those that operate in BRCA1-mutant scenarios suggests new opportunities for patient stratification in the clinic, as well as additional therapeutic vulnerabilities that might be exploited in drug-resistant cancers.