Ptf1a Promoter-Driven Cre Expression During Spermatogenesis Causes Germline Recombination.

OBJECTIVES: Two independently developed Ptf1a-Cre mouse lines, Ptf1atm1(cre)Hnak and Ptf1atm1(Cre)Cvw, are widely used in pancreatic research. Recently, Ptf1atm1(cre)Hnak line was reported to transmit unwanted paternal recombination. We aimed to investigate whether this exists in the Ptf1atm1(Cre)Cvw line. METHODS: Ptf1atm1(Cre)Cvw mice were crossed with R26-LSL-LacZ reporter mice. DNA recombination and gene expression were examined by recombination-specific polymerase chain reaction, reverse transcription-polymerase chain reaction, and X-Gal staining. RESULTS: R26 locus recombination was detected in the pancreas as well as the testes and sperm of the double transgenic mice. Positive ptf1a mRNA expression from testes revealed that there was endogenous Ptf1a promoter activity in this extrapancreatic tissue. Of the 15 progenies that inherited LacZ from the male double transgenic mice, 4 (26.7%) were positive for complete whole-body recombination. The presence of recombination in R26 only mice suggested that the recombination occurred before meiosis. CONCLUSIONS: Paternal germline recombination exists in the Ptf1atm1(Cre)Cvw mouse line. Ptf1a promoter-driven Cre expression during spermatogenesis before meiosis is the cause of germline recombination. Therefore, when male Ptf1a-Cre mice are used in compound mice breeding, it is necessary to genotype not only floxed alleles but also recombined alleles to examine unwanted recombinations.

Saccharomyces cerevisiae DNA repair pathways involved in repair of lesions induced by mixed ternary mononuclear Cu(II) complexes based on valproic acid with 1,10-phenanthroline or 2,2'- bipyridine ligands.

The sodium valproate has been largely used as an anti-epilepsy drug and, recently, as a putative drug in cancer therapy. However, the treatment with sodium valproate has some adverse effects. In this sense, more effective and secure complexes than sodium valproate should be explored in searching for new active drugs. This study aims to evaluate the cytotoxicity of sodium valproate, mixed ternary mononuclear Cu(II) complexes based on valproic acid (VA) with 1,10-phenanthroline (Phen) or 2,2'- bipyridine (Bipy) ligands - [Cu2(Valp)4], [Cu(Valp)2Phen] and [Cu(Valp)2Bipy] - in yeast Saccharomyces cerevisiae, proficient or deficient in different repair pathways, such as base excision repair (BER), nucleotide excision repair (NER), translesion synthesis (TLS), DNA postreplication repair (PRR), homologous recombination (HR) and non-homologous end-joining (NHEJ). The results indicated that the Cu(II) complexes have higher cytotoxicity than sodium valproate in the following order: [Cu(Valp)2Phen] > [Cu(Valp)2Bipy] > [Cu2(Valp)4] > sodium valproate. The treatment with Cu(II) complexes and sodium valproate induced mutations in S. cerevisiae. The data indicated that yeast strains deficient in BER (Ogg1p), NER (complex Rad1p-Rad10p) or TLS (Rev1p, Rev3p and Rad30p) proteins are associated with increased sensitivity to sodium valproate. The BER mutants (ogg1Δ, apn1Δ, rad27Δ, ntg1Δ and ntg2Δ) showed increased sensitivity to Cu(II) complexes. DNA damage induced by the complexes requires proteins from NER (Rad1p and Rad10p), TLS (Rev1p, Rev3p and Rad30p), PRR (Rad6 and Rad18p) and HR (Rad52p and Rad50p) for efficient repair. Therefore, Cu(II) complexes display enhanced cytotoxicity when compared to the sodium valproate and induce distinct DNA lesions, indicating a potential application as cytotoxic agents.

Complex Mechanisms of Antimony Genotoxicity in Budding Yeast Involves Replication and Topoisomerase I-Associated DNA Lesions, Telomere Dysfunction and Inhibition of DNA Repair.

Antimony is a toxic metalloid with poorly understood mechanisms of toxicity and uncertain carcinogenic properties. By using a combination of genetic, biochemical and DNA damage assays, we investigated the genotoxic potential of trivalent antimony in the model organism Saccharomyces cerevisiae. We found that low doses of Sb(III) generate various forms of DNA damage including replication and topoisomerase I-dependent DNA lesions as well as oxidative stress and replication-independent DNA breaks accompanied by activation of DNA damage checkpoints and formation of recombination repair centers. At higher concentrations of Sb(III), moderately increased oxidative DNA damage is also observed. Consistently, base excision, DNA damage tolerance and homologous recombination repair pathways contribute to Sb(III) tolerance. In addition, we provided evidence suggesting that Sb(III) causes telomere dysfunction. Finally, we showed that Sb(III) negatively effects repair of double-strand DNA breaks and distorts actin and microtubule cytoskeleton. In sum, our results indicate that Sb(III) exhibits a significant genotoxic activity in budding yeast.

The coronavirus proofreading exoribonuclease mediates extensive viral recombination.

Recombination is proposed to be critical for coronavirus (CoV) diversity and emergence of SARS-CoV-2 and other zoonotic CoVs. While RNA recombination is required during normal CoV replication, the mechanisms and determinants of CoV recombination are not known. CoVs encode an RNA proofreading exoribonuclease (nsp14-ExoN) that is distinct from the CoV polymerase and is responsible for high-fidelity RNA synthesis, resistance to nucleoside analogues, immune evasion, and virulence. Here, we demonstrate that CoVs, including SARS-CoV-2, MERS-CoV, and the model CoV murine hepatitis virus (MHV), generate extensive and diverse recombination products during replication in culture. We show that the MHV nsp14-ExoN is required for native recombination, and that inactivation of ExoN results in decreased recombination frequency and altered recombination products. These results add yet another critical function to nsp14-ExoN, highlight the uniqueness of the evolved coronavirus replicase, and further emphasize nsp14-ExoN as a central, completely conserved, and vulnerable target for inhibitors and attenuation of SARS-CoV-2 and future emerging zoonotic CoVs.

DNA repair pathways important for the survival of Escherichia coli to hydrogen peroxide mediated killing.

Escherichia coli exposed to 1-3 mM hydrogen peroxide undergo killing which is designated as the mode-one killing which is a result of oxidative DNA damage. Oxidative stress mediated DNA damage can be repaired by various DNA repair pathways like base excision repair, nucleotide excision repair and homologous recombination repair. In this study we have investigated the role of multiple DNA repair pathways in survival to oxidative killing and assessed their relative importance. Results show that both nucleotide excision repair pathway as well as the RecF pathway of recombination repair are important for repair of the DNA damage caused by exposure to hydrogen peroxide. The study also provides the evidence that RecG helicase which is known for the resolution of Holliday junction intermediates plays a critical role in the survival of mode-one killing by peroxide. There is a severe impact on the survival of repair mutants when parameters like aeration and growth medium are changed. Low aeration and growth in minimal medium provide significant protection from the mode-one killing suggesting that under natural conditions Escherichia coli cells are likely to be protected from the oxidative stress mediated DNA damage.

Genetic recombination in disgust-associated bitter taste-responsive neurons of the central nucleus of amygdala in male mice.

A bitter substance induces specific orofacial and somatic behavioral reactions such as gapes in mice as well as monkeys and humans. These reactions have been proposed to represent affective disgust, and therefore, understanding the neuronal basis of the reactions would pave the way to understand affective disgust. It is crucial to identify and access the specific neuronal ensembles that are activated by bitter substances, such as quinine, the intake of which induces disgust reactions. However, the method to access the quinine-activated neurons has not been fully established yet. Here, we show evidence that a targeted recombination in active populations (TRAP) method, induces genetic recombination in the quinine-activated neurons in the central nucleus of the amygdala (CeA). CeA is one of the well-known emotional centers of the brain. We found that the intraoral quinine infusion, that resulted in disgust reactions, increased both cFos-positive cells and Arc-positive cells in the CeA. By using Arc-CreER;Ai3 TRAP mice, we induced genetic recombination in the quinine-activated neurons and labelled them with fluorescent protein. We confirmed that the quinine-TRAPed fluorescently-labelled cells preferentially coexpressed Arc after quinine infusion. Our results suggest that the TRAP method can be used to access specific functional neurons in the CeA.

A DNA repair player, ring finger protein 43, relieves etoposide-induced topoisomerase II poisoning.

Ring finger protein 43 (RNF43) is an E3 ubiquitin ligase which is well-known for its role in negative regulation of the Wnt-signaling pathway. However, the function in DNA double-strand break repairs has not been investigated. In this study, we used a lymphoblast cell line, DT40, and mouse embryonic fibroblast as cellular models to study DNA double-strand break (DSB) repairs. For this purpose, we created RNF43 knockout, RNF43-/- DT40 cell line to investigate DSB repairs. We found that deletion of RNF43 does not interfere with cell proliferation. However, after exposure to various types of DNA-damaging agents, RNF43-/- cells become more sensitive to topoisomerase II inhibitors, etoposide, and ICRF193, than wild type cells. Our results also showed that depletion of RNF43 results in apoptosis upon etoposide-mediated DNA damage. The delay in resolution of γH2AX and 53BP1 foci formation after etoposide treatment, as well as epistasis analysis with DNAPKcs, suggested that RNF43 might participate in DNA repair of etoposide-induced DSB via non-homologous end joining. Disturbed γH2AX foci formation in MEFs following pulse etoposide treatment supported the notion that RNF43 also functions DNA repair in mammalian cells. These findings propose two possible functions of RNF43, either participating in NHEJ or removing the blockage of 5' topo II adducts from DSB ends.

Development of an ObLiGaRe Doxycycline Inducible Cas9 system for pre-clinical cancer drug discovery.

The CRISPR-Cas9 system has increased the speed and precision of genetic editing in cells and animals. However, model generation for drug development is still expensive and time-consuming, demanding more target flexibility and faster turnaround times with high reproducibility. The generation of a tightly controlled ObLiGaRe doxycycline inducible SpCas9 (ODInCas9) transgene and its use in targeted ObLiGaRe results in functional integration into both human and mouse cells culminating in the generation of the ODInCas9 mouse. Genomic editing can be performed in cells of various tissue origins without any detectable gene editing in the absence of doxycycline. Somatic in vivo editing can model non-small cell lung cancer (NSCLC) adenocarcinomas, enabling treatment studies to validate the efficacy of candidate drugs. The ODInCas9 mouse allows robust and tunable genome editing granting flexibility, speed and uniformity at less cost, leading to high throughput and practical preclinical in vivo therapeutic testing.

Radioprotective effect of chloropyllin, protoporphyrin-IX and bilirubin compared with amifostine® in Drosophila melanogaster.

The identification of substances that prevent or minimize the detrimental effects of ionizing radiation is an essential undertaking. The aim of this paper was to evaluate and compare the radioprotective potential of chlorophyllin, protoporphyrin and bilirubin, with amifostine®, an US Food & Drug Administration approved radioprotector Using the somatic mutation and recombination assay in the Drosophila melanogaster wing, it was found that pretreatment (1-9 h) with any of the porphyrins or amifostine® alone, did not affect the larva-adult viability or the basal frequency of mutation. However, they were associated with significant reductions in frequency of somatic mutation and recombination compared with the gamma-irradiated (20 Gy) control as follows: bilirubin (69.3 %)> chlorophyllin (40.0 %)> protoporphyrin (39.0 %)> amifostine® (19.7 %). Bilirubin also caused a 16 % increase in larva-adult viability with 3 h of pretreatment respect to percentage induced in 20 Gy control group. Whilst amifostine® was associated with lower genetic damage after pre-treatment of 1 and 3 h, this did not attain significance. These findings suggest that the tested porphyrins may have some potential as radioprotectant agents.

Thermus thermophilus Argonaute Functions in the Completion of DNA Replication.

In many eukaryotes, Argonaute proteins, guided by short RNA sequences, defend cells against transposons and viruses. In the eubacterium Thermus thermophilus, the DNA-guided Argonaute TtAgo defends against transformation by DNA plasmids. Here, we report that TtAgo also participates in DNA replication. In vivo, TtAgo binds 15- to 18-nt DNA guides derived from the chromosomal region where replication terminates and associates with proteins known to act in DNA replication. When gyrase, the sole T. thermophilus type II topoisomerase, is inhibited, TtAgo allows the bacterium to finish replicating its circular genome. In contrast, loss of gyrase and TtAgo activity slows growth and produces long sausage-like filaments in which the individual bacteria are linked by DNA. Finally, wild-type T. thermophilus outcompetes an otherwise isogenic strain lacking TtAgo. We propose that the primary role of TtAgo is to help T. thermophilus disentangle the catenated circular chromosomes generated by DNA replication.

Occupational benzene exposure and the risk of genetic damage: a systematic review and meta-analysis.

BACKGROUND: Benzene, an important component of organic solvents, is commonly used in industry. Meanwhile, benzene is a human carcinogen leading to leukemia. Although the links between benzene and various types of genetic damage indicators have been evaluated in several studies, but their results remain inconsistent. So we conducted a meta-analysis, and to explore the influence of low concentration benzene exposure on workers' genetic damage indicators using 3.25 mg/m3 as the boundary value, in order to provide a basis for improved prevention and control of the harm from benzene exposure to the occupational population. METHODS: We conducted a search of five databases, including Pub Med, Web of Science, China National Knowledge Infrastructure (CNKI), Wan Fang Data and Chongqing VIP, to identify relevant articles up to December 25, 2018. Two researchers independently extracted and evaluated the data according to the inclusion and exclusion criteria of the literature. The imported articles were managed by Endnote X7, and the data were extracted and sorted by Excel 2013. We utilized Stata 12.0 software to perform the meta-analysis in the present study. RESULTS: A total of 68 eligible articles were finally included for the synthetic analyses. The meta-analysis results showed that occupational benzene exposure led to significantly increased Micronucleus (MN) frequency, Sister chromatid exchange (SCE) frequency, Chromosome aberration (CA) frequency, Olive Tail moment (OTM), Tail moment (TM), Tail length (TL), and Tail DNA% (T DNA%) compared to the control group (P < 0.05), and the pooled effect value estimates were 1.36, 0.98, 0.76, 1.06, 0.96, 1.78, and 1.42, respectively. Subsequent analysis of the effect of low concentration benzene exposure on genetic damage found significantly increased MN frequency increased compared with the control group (P < 0.05). CONCLUSIONS: Occupational benzene exposure can affect multiple genetic damage indicators. Even at an exposure concentration lower than 3.25 mg/m3, benzene exposure has genotoxicity. These data provide an important scientific basis for the further revision of occupational disease prevention strategies. At the same time, increased attention should be focused on the health monitoring of the occupational population exposed to benzene, and health management should be strengthened to improve the health of the occupational population.

Polyamines stimulate RecA-mediated recombination by condensing duplex DNA and stabilizing intermediates.

Polyamines are naturally occurring cationic molecules in cells. In addition to their roles in modulating gene expression and cell proliferation, they have been shown to stimulate DNA recombination. The molecular mechanism for stimulation is not clear. We utilized single-molecule tethered particle motion (TPM) experiments to investigate how polyamines stimulate RecA-mediated recombination. We showed that natural polyamines, spermine and spermidine, condense duplex DNA, but with different efficiencies. While ∼300 µM of spermine condenses 50% of duplex DNA, 2.0 mM of spermidine is required to achieve the same level of condensation. The condensation takes place in a stepwise manner, and is reversible upon removal of polyamines. We also showed that addition of polyamines stimulates the duplex capture activity of RecA filament and stabilizes the intermediates with longer dwell time. Through condensing duplex DNA and stabilizing the complex of RecA filaments and duplex DNA, polyamines stimulate the formation of functional intermediates by ∼20-fold, and promote recombination progression.

Mismatch repair systems might facilitate the chromosomal recombination induced by N-nitrosodimethylamine, but not by N-nitrosodiethylamine, in Drosophila.

Mismatch repair (MMR) systems play important roles in maintaining the high fidelity of genomic DNA. It is well documented that a lack of MMR increases the mutation rate, including base exchanges and small insertion/deletion loops; however, it is unknown whether MMR deficiency affects the frequency of chromosomal recombination in somatic cells. To investigate the effects of MMR on chromosomal recombination, we used the Drosophila wing-spot test, which efficiently detects chromosomal recombination. We prepared MMR (MutS)-deficient flies (spel1(-/-)) using a fly line generated in this study. The spontaneous mutation rate as measured by the wing-spot test was slightly higher in MutS-deficient flies than in wild-type (spel1(+/-)) flies. Previously, we showed that N-nitrosodimethylamine (NDMA)-induced chromosomal recombination more frequently than N-nitrosodiethylamine (NDEA) in Drosophila. When the wing-spot test was performed using MMR-deficient flies, unexpectedly, the rate of NDMA-induced mutation was significantly lower in spel1(-/-) flies than in spel1(+/-) flies. In contrast, the rate of mutation induced by NDEA was higher in spel1(-/-) flies than in spel1(+/-) flies. These results suggest that in Drosophila, the MutS homologue protein recognises methylated DNA lesions more efficiently than ethylated ones, and that MMR might facilitate mutational chromosomal recombination due to DNA double-strand breaks via the futile cycle induced by MutS recognition of methylated lesions.

The Wing-Spot and the Comet Tests as Useful Assays for Detecting Genotoxicity in Drosophila.

In spite of its pioneer use in detecting mutational processes, Drosophila still plays an important role in those studies aiming to detect and quantify the induction of DNA damage. Here we describe two assays, one detecting primary damage (the Comet assay) and the other detecting somatic mutation and recombination effects (wing-spot test). It is important to emphasize that somatic recombination is a key event in cancer development and no assays exist at present to detect and quantify somatic recombination processes, other than the spot tests developed in Drosophila.

Evaluation of mutagenic activity of platinum complexes in somatic cells of Drosophila melanogaster.

Cisplatin, carboplatin, and oxaliplatin are some of the most often used alkylating chemotherapeutic agents. In view of the paucity of data on the genotoxicity of oxaliplatin, this study compares the mutagenic activity of cisplatin (0.006, 0.012, 0.025, 0.05 mM), carboplatin (0.1, 0.2, 0,5, 1.0 mM), and oxaliplatin (0.1, 0.2, 0,5, 1.0 mM) using the somatic mutation and recombination test (SMART) in Drosophila melanogaster. Standard and high-bioactivation crosses of the drosophilid were used, which present basal and high levels of cytochrome P450 (CYP450) metabolization enzymes, respectively. All concentrations of cisplatin and carboplatin induced lesions in genetic material in both crosses, while oxaliplatin was mutagenic only to high bioactivation flies treated with 0.1, 0.5 and 1 mM of the compound. No significant differences were observed between genotoxicity values of cisplatin and carboplatin. However, CYP450 enzymes may have affected the mutagenic action of oxaliplatin. Carboplatin induced mainly mutation events, while cisplatin triggered mostly mutation and recombination events when low and high doses were used. Most events induced by oxaliplatin were generated by somatic recombination. Important differences were observed in genotoxic potential of platinum chemotherapeutic compounds, possibly due to the origin and type of the lesions induced in DNA and the repair mechanisms involved.

p-Coumaric acid inhibits the Listeria monocytogenes RecA protein functions and SOS response: An antimicrobial target.

Bacterial RecA plays an important role in the evaluation of antibiotic resistance via stress-induced DNA repair mechanism; SOS response. Accordingly, RecA became an important therapeutic target against antimicrobial resistance. Small molecule inhibitors of RecA may prevent adaptation of antibiotic resistance mutations and the emergence of antimicrobial resistance. In our study, we observed that phenolic compound p-Coumaric acid as potent RecA inhibitor. It inhibited RecA driven biochemical activities in vitro such as ssDNA binding, strand exchange, ATP hydrolysis and RecA coprotease activity of E. coli and L. monocytogenes RecA proteins. The mechanism underlying such inhibitory action of p-Coumaric acid involves its ability to interfere with the DNA binding domain of RecA protein. p-Coumaric acid also potentiates the activity of ciprofloxacin by inhibiting drastic cell survival of L. monocytogenes as well as filamentation process; the bacteria defensive mechanism in response to DNA damage. Additionally, it also blocked the ciprofloxacin induced RecA expression leading to suppression of SOS response in L. monocytogenes. These findings revealed that p-Coumaric acid is a potent RecA inhibitor, and can be used as an adjuvant to the existing antibiotics which not only enhance the shelf-life but also slow down the emergence of antibiotic resistance in bacteria.

Mapping the drivers of within-host pathogen evolution using massive data sets.

Differences among hosts, resulting from genetic variation in the immune system or heterogeneity in drug treatment, can impact within-host pathogen evolution. Genetic association studies can potentially identify such interactions. However, extensive and correlated genetic population structure in hosts and pathogens presents a substantial risk of confounding analyses. Moreover, the multiple testing burden of interaction scanning can potentially limit power. We present a Bayesian approach for detecting host influences on pathogen evolution that exploits vast existing data sets of pathogen diversity to improve power and control for stratification. The approach models key processes, including recombination and selection, and identifies regions of the pathogen genome affected by host factors. Our simulations and empirical analysis of drug-induced selection on the HIV-1 genome show that the method recovers known associations and has superior precision-recall characteristics compared to other approaches. We build a high-resolution map of HLA-induced selection in the HIV-1 genome, identifying novel epitope-allele combinations.

Mutagenicity and recombinogenicity evaluation of bupropion hydrochloride and trazodone hydrochloride in somatic cells of Drosophila melanogaster.

The aim of the present study was to appraise the mutagenic and recombinogenic potential of bupropion hydrochloride (BHc) and trazodone hydrochloride (THc). We used standard (ST) and the high bioactivation (HB) crossings from Drosophila melanogaster in the Somatic Mutation and Recombination Test. We treated third-instar larvae from both crossings with different concentrations of BHc and THc (0.9375 to 7.5 mg/mL). BHc significantly increased the frequency of mutant spots in both crossings, except for the lowest concentration in the ST crossing. ST had also the mostly recombinogenic result, and in the HB, BHc was highly mutagenic. On the other hand, THc significantly increased the frequency of mutant spots in both the ST and HB crossings at all concentrations. The three initial concentrations were recombinogenic and the highest concentration was mutagenic for the THc. BHc and THc at high concentrations were toxic, even though their mutagenicity was not dose-related. THc significantly increased the frequency of mutant spots when metabolized, probably as a result of the production of 1-(3'-chlorophenyl) piperazine. BHc was essentially recombinogenic and when metabolized, it became mutagenic. THc was recombinogenic in both crossings. Further studies are needed to clarify the action mechanisms from BHc and THc.

iSuRe-Cre is a genetic tool to reliably induce and report Cre-dependent genetic modifications.

Most biomedical research aimed at understanding gene function uses the Cre-Lox system, which consists of the Cre recombinase-dependent deletion of genes containing LoxP sites. This system enables conditional genetic modifications because the expression and activity of the recombinase Cre/CreERT2 can be regulated in space by tissue-specific promoters and in time by the ligand tamoxifen. Since the precise Cre-Lox recombination event is invisible, methods were developed to report Cre activity and are widely used. However, numerous studies have shown that expression of a given Cre activity reporter cannot be assumed to indicate deletion of other LoxP-flanked genes of interest. Here, we report the generation of an inducible dual reporter-Cre mouse allele, iSuRe-Cre. By significantly increasing Cre activity in reporter-expressing cells, iSuRe-Cre provides certainty that these cells have completely recombined floxed alleles. This genetic tool increases the ease, efficiency, and reliability of conditional mutagenesis and gene function analysis.