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Telomere attrition and mitochondrial DNA variations are implicated in the biological aging process and genomic stability can be influenced by nutritional factors. This study aims to analyze the relative telomere length (rTL) and mitochondrial DNA copy number (mtCN) in aged individuals and their association with plasma folate and vitamin B12 levels. This community-based cross-sectional study involves 428 subjects (60 years: 242≥60 years: 186). Quantitative real-time PCR was used to measure rTL and mtCN variation, and radioimmunoassay to measure plasma folate and vitamin B12 levels. The subjects in the ≥60 years age group have significantly shorter telomeres and lower mtCN compared to the60 years age group. A significant positive correlation was observed between the rTL and mtCN, and both of them were positively associated with plasma folate and vitamin B12 levels. In the ≥60 age group; folate and vitamin B12 positively correlated with rTL and vitamin B12 with mtCN. The study revealed a decline of rTL and mtCN with age in the Indian population and their association suggests that they may co-regulate each other with age. In conclusion, folate and vitamin B12 may delay aging by preventing the reduction in rTL length and mtCN.

Poly(ADP-ribosyl)ation (PARylation) is a reversible post-translational modification regulating various biological pathways including DNA damage repair (DDR). Rapid turnover of PARylation is critically important for an optimal DNA damage response and maintaining genomic stability. Recent studies show that PARylation is tightly regulated by a group of enzymes that can erase the ADP-ribose (ADPR) groups from target proteins. The aim of this review is to present a comprehensive understanding of dePARylation enzymes, their substrates and roles in DDR. Special attention will be laid on the role of these proteins in the development of cancer and their feasibility in anticancer therapeutics.

In this issue, Li et al. (2019) report a previously unknown Ca2+-CaMKK2-AMPK signaling cascade that protects stalled forks from degradation by phosphorylating and inhibiting the EXO1 nuclease, revealing a surprising role for Ca2+ influx in the maintenance of genomic stability.

Helicases and translocases comprise one of the largest and highly conserved gene families in eukaryotic organisms, including plant. Members of this gene family are involved in a plethora of molecular processes related to DNA and RNA metabolism that are crucial for the maintenance of normal cellular functions. In this review, we bring together three major groups under this gene family – RNA helicases, DNA helicases, chromatin remodelers and highlight the key roles played by these well-known members in plant growth, development, and stress tolerance. We summarize this extensive information in a broader context and provide novel insights into helicases and translocases as multifunctional gene modules using in-silico approaches. We briefly highlight the stress-specific expression pattern of Arabidopsis helicases and how tissue-specific expression of DNA helicases vary from their counterparts in the monocot rice, a behaviour that likely reflects an evolutionary divergence in expression pattern. Overall, this review will serve as a framework for future studies and facilitate the identification and selection of promising helicases for developing stress-tolerant and developmentally resilient plants with the help of modern breeding and genetic engineering technologies.

The tumor suppressor p53 is one of the most important proteins for protection of genomic stability and cancer prevention. Cancers often inactivate it by either mutating its gene or disabling its function. Thus, activating p53 becomes an attractive approach for the development of molecule-based anti-cancer therapy. The past decade and half have witnessed tremendous progress in this area. This essay offers readers with a grand review on this progress with updated information about small molecule activators of p53 either still at bench work or in clinical trials.

DNA end resection is a critical step in the repair of DNA double strand breaks. It controls the way the lesion is going to be repaired, thus its regulation has a great importance in maintaining genomic stability. In this review, we focus in recent discoveries in the field that point to a modulation of resection by RNA molecules and RNA-related proteins. Moreover, we aim to reconcile contradictory reports on the positive or negative effect of DNA:RNA hybrids in the resection process., pH laboratory is financed by the Spanish Ministry of Economy and Competitivity (SAF2016-74855-P) and by the European Union Regional Funds (FEDER). RP-C was funded with an FPU fellowship from the Spanish Ministry of Education. CABIMER is supported by the regional government of Andalucía (Junta de Andalucía).

DNA carries the genetic information that directs complex biological processes; thus, maintaining a stable genome is critical for individual growth and development and for human health. DNA repair is a fundamental and conserved mechanism responsible for mending damaged DNA and restoring genomic stability, while its deficiency is closely related to multiple human disorders. In recent years, remarkable progress has been made in the field of DNA repair and aging. Here, we will extensively discuss the relationship among DNA damage, DNA repair, aging and aging-associated diseases based on the latest research. In addition, the possible role of DNA repair in several potential rejuvenation strategies will be discussed. Finally, we will also review the emerging methods that may facilitate future research on DNA repair.

Summary Human embryonic stem cells (hESC) show great promise for clinical and research applications, but their well-known proneness to genomic instability hampers the development to their full potential. Here, we demonstrate that medium acidification linked to culture density is the main cause of DNA damage and genomic alterations in hESC grown on feeder layers, and this even in the short time span of a single passage. In line with this, we show that increasing the frequency of the medium refreshments minimizes the levels of DNA damage and genetic instability. Also, we show that cells cultured on laminin-521 do not present this increase in DNA damage when grown at high density, although the (long-term) impact on their genomic stability remains to be elucidated. Our results explain the high levels of genome instability observed over the years by many laboratories worldwide, and show that the development of optimal culture conditions is key to solving this problem., Graphical Abstract, Highlights • Increased culture density induces DNA damage and genomic alterations in hESC • Medium acidification due to lactic acid accumulation is the main driver • More frequent medium refreshments rescues genomic integrity in high-density culture • Laminin-521 reduces DNA damage but has no clear effect on genomic instability, In this article, Spits and colleagues show that the culture density of hESC is directly correlated to increased DNA damage and genomic instability. This is caused by medium acidification and can be countered by more frequent medium refreshments. When cultured on laminin-521, hESC show less DNA damage than in the feeder-based system, but no clear difference in genomic instability was found.

DNA mismatch repair (MMR) maintains genomic stability primarily by correcting replication errors. Defects in MMR lead to cancers and cause resistance to many chemotherapeutic drugs. Emerging evidence reveals that MMR is coupled with replication and precisely regulated in the context of chromatin; strikingly, tumors defective in MMR are highly responsive to immune checkpoint blockade therapy. As a tribute to Dr. Samuel Wilson for his many scientific contributions to the field of DNA repair and his leadership as Editor-in-Chief of the journal DNA Repair, we summarize recent developments in research on MMR at the chromatin level, its implications for tumorigenesis, and its therapeutic potential.

Background Although once considered a homologous recombination DNA repair gene, CDK12 is now thought to have a distinct role in maintaining genomic stability. In prostate cancer, inactivating CDK12 mutations lead to gene fusion-induced neoantigens and possibly sensitivity to PD1 inhibitors. Methods We conducted a retrospective multicenter study to identify advanced prostate cancer patients with loss-of-function CDK12 mutations. We characterized their clinical features and therapeutic outcomes, including sensitivity to PARP and PD1 inhibitors. Results 58 men with at least monoallelic CDK12 alterations were identified from 9 academic centers; 28 (48%) had biallelic inactivation. Tissue for genomics was from primary tumors in 45 cases (77%) and from metastatic sites in 13 cases (23%). All CDK12 mutations were somatic-only. Median age at diagnosis was 60 y (41–78 y), 71%/29% were white/nonwhite, 79% had Gleason sum 9-10, 10% had ductal/intraductal histology, 76% had stage T3/T4 disease, 47% had metastases at diagnosis, and the median PSA was 24 ng/mL. Of those undergoing primary ADT (± Abi, ± Doce) for advanced disease (n = 54), only 85% had a PSA50 response, with median PFS of 11.8 (95% CI 8.3–15.4) mo; OS from ADT initiation was 40.8 (95% CI 18.7–53) mo. Of those receiving first-line Abi/Enza for mCRPC (n = 34), only 47% had a PSA50 response, with median PFS of 4.3 (95% CI 2.6–6.0) mo. Of those receiving a first Taxane agent for mCRPC (n = 20), only 35% had a PSA50 response, with median PFS of 4.0 (95% CI 2.6–5.3) mo. Eleven men received a PARP inhibitor (10 Olaparib, 1 Rucaparib): none had a PSA50 response, and median PFS was 3.6 (95% CI 3.0–4.2) mo. Eight men received a PD1 inhibitor as 4th to 6th-line mCRPC therapy (5 Pembro, 3 Nivo): 38% had a PSA50 response, and median PFS was 6.6 (95% CI 2.3–10.8) mo. Conclusions CDK12-altered prostate cancer is an aggressive subtype presenting at young age, with high Gleason grade, and often with de novo M1 disease at diagnosis. Outcomes to hormonal and taxane therapies are poor, and PARP inhibitors are also ineffective. A proportion of these patients respond favorably to PD1 inhibitors, implicating CDK12 deficiency in immunotherapy responsiveness. Legal entity responsible for the study Emmanuel S. Antonarakis. Funding Has not received any funding. Disclosure E.S. Antonarakis: Advisory / Consultancy, Research grant / Funding (institution): Janssen; Advisory / Consultancy, Research grant / Funding (institution): Astellas; Advisory / Consultancy, Research grant / Funding (institution): Sanofi; Advisory / Consultancy, Research grant / Funding (institution): Dendreon; Advisory / Consultancy, Research grant / Funding (institution): Medivation; Advisory / Consultancy: ESSA; Advisory / Consultancy, Research grant / Funding (institution): AstraZeneca; Advisory / Consultancy, Research grant / Funding (institution): Clovis; Advisory / Consultancy, Research grant / Funding (institution): Merck; Research grant / Funding (institution): Johnson & Johnson; Research grant / Funding (institution): Genentech; Research grant / Funding (institution): Novartis; Advisory / Consultancy, Research grant / Funding (institution): Bristol-Myers Squibb; Advisory / Consultancy: Eli Lilly; Licensing / Royalties: Qiagen. N. Agarwal: Advisory / Consultancy: Astellas; Advisory / Consultancy, Research grant / Funding (institution): AstraZeneca; Advisory / Consultancy: Argos; Advisory / Consultancy, Research grant / Funding (institution): Bristol-Myers Squibb; Advisory / Consultancy, Research grant / Funding (institution): Clovis; Advisory / Consultancy, Research grant / Funding (institution): Eisai; Advisory / Consultancy, Research grant / Funding (institution): Exelixis; Advisory / Consultancy, Research grant / Funding (institution): EMD Serono; Advisory / Consultancy, Research grant / Funding (institution): Eli Lilly; Advisory / Consultancy: Foundation One; Advisory / Consultancy, Research grant / Funding (institution): Genentech; Advisory / Consultancy, Research grant / Funding (institution): Janssen; Advisory / Consultancy, Research grant / Funding (institution): Merck; Advisory / Consultancy, Research grant / Funding (institution): Medivation; Advisory / Consultancy, Research grant / Funding (institution): Novartis; Advisory / Consultancy, Research grant / Funding (institution): Nektar; Advisory / Consultancy, Research grant / Funding (institution): Pfizer; Research grant / Funding (institution): Bavarian Nordic; Research grant / Funding (institution): Calithera; Research grant / Funding (institution): Celldex. B.L. Maughan: Advisory / Consultancy: Peloton Therapeutics; Advisory / Consultancy: Bristol-Myers Squibb; Advisory / Consultancy: Tempus; Advisory / Consultancy: Bayer; Advisory / Consultancy: Exelixis; Advisory / Consultancy: Janssen; Advisory / Consultancy: Astellas. M. Hussain: Advisory / Consultancy, Research grant / Funding (institution): AstraZeneca; Advisory / Consultancy, Research grant / Funding (institution): Pfizer; Advisory / Consultancy, Research grant / Funding (institution): Bayer; Honoraria (self), Research grant / Funding (institution): Genentech; Honoraria (self): Sanofi Genzyme; Honoraria (self): Research To Practice; Honoraria (self): Aptitude Health; Honoraria (self): Epics. All other authors have declared no conflicts of interest.

Long noncoding RNAs (lncRNAs) have emerged as regulators of diverse biological processes. Here we describe the initial functional analysis of a poorly characterized human lncRNA (LINC00657) that is induced after DNA damage, which we termed Noncoding RNA Activated by DNA Damage or NORAD. NORAD is highly conserved and abundant, with expression levels of approximately 500–1,000 copies per cell. Remarkably, inactivation of NORAD triggers dramatic aneuploidy in previously karyotypically-stable cell lines. NORAD maintains genomic stability by sequestering PUMILIO proteins, which repress the stability and translation of messenger RNAs to which they bind. In the absence of NORAD, PUMILIO proteins drive chromosomal instability by hyperactively repressing mitotic, DNA repair, and DNA replication factors. These findings introduce a mechanism that regulates the activity of a deeply conserved and highly dosage-sensitive family of RNA binding proteins and reveal unanticipated roles for a lncRNA and PUMILIO proteins in the maintenance of genomic stability.

Acute pulmonary injury, or acute respiratory distress syndrome, has a high incidence in elderly individuals and high mortality in its most severe degree, becoming a challenge to public health due to pathophysiological complications and increased economic burden. Acute pulmonary injury can develop from sepsis, septic shock, and pancreatitis causing reduction of alveolar airspace due to hyperinflammatory response. Oxidative stress acts directly on the maintenance of inflammation, resulting in tissue injury, as well as inducing DNA damages. Once the DNA is damaged, enzymatic DNA repair mechanisms act on lesions in order to maintain genomic stability and, consequently, contribute to cell viability and homeostasis. Although palliative treatment based on mechanical ventilation and antibiotic using have a kind of efficacy, therapies based on modulation of DNA repair and genomic stability could be effective for improving repair and recovery of lung tissue in patients with acute pulmonary injury.

Summary: H2AX safeguards genomic stability in a dose-dependent manner; however, mechanisms governing its proteostasis are poorly understood. Here, we identify a PRMT5-RNF168-SMURF2 cascade that regulates H2AX proteostasis. We show that PRMT5 sustains the expression of RNF168, an E3 ubiquitin ligase essential for DNA damage response (DDR). Suppression of PRMT5 occurs in methylthioadenosine phosphorylase (MTAP)-deficient glioblastoma cells and attenuates the expression of RNF168, leading to destabilization of H2AX by E3 ubiquitin ligase SMURF2. RNF168 and SMURF2 serve as a stabilizer and destabilizer of H2AX, respectively, via their dynamic interactions with H2AX. In supporting an important role of this signaling cascade in regulating H2AX, MTAP-deficient glioblastoma cells display higher levels of DNA damage spontaneously or in response to genotoxic agents. These findings reveal a regulatory mechanism of H2AX proteostasis and define a signaling cascade that is essential to DDR and that is disrupted by the loss of a metabolic enzyme in tumor cells. : Du et al. identify a signaling cascade that regulates the abundance of H2AX, an essential protein in mediating the DNA damage response. The study links the effect of MTAP loss, a common genetic alteration in cancers, to cancer cells’ response to DNA damage insults (e.g., genotoxic agents). Keywords: H2AX, PRMT5, RNF168, SMURF2, MTAP, glioblastoma

Background & Aim Human pluripotent stem cells (hPSCs) hold great promise for disease modeling, drug discovery and clinical applications. Therefore, working with highly pluripotent, well characterized and quality controlled cell stocks during development is crucial to ensure reproducible experimental conditions. Methods, Results & Conclusion Here, we established a workflow encompassing stable expansion of hPSCs using a xeno-free cultivation medium, assessment of pluripotency using a defined marker combination and assessment of differentiation potential based on lineage-specific, complete media both combined with quantitative, multicolor flow cytometry analysis to characterize and quality control the cultivated hPSCs, as well as cryopreservation of hPSCs using an animal component-free, chemically defined cryopreservation media. Following this workflow, hPSCs could be stably expanded over 20 passages with persistent, high expression of pluripotency markers (>92%) TRA-1-60, SSEA-4, SSEA-5, Oct-4, Sox2 and almost no expression of differentiation maker SSEA-1, showed a homogenous morphology and also retained a stable karyotype. Quantitative, flow cytometry–based analysis reproducibly proved their differentiation potential into ectoderm, mesoderm, and endoderm. Cells cultivated under the same conditions showed a reproducible recovery after cryopreservation and thawing resulting in a 8-12 fold expansion in passage 1, high pluripotency marker expression as well as genomic stability confirmed 5 passages post thaw. Thus, the workflow shown here assures a standardized, robust expansion of hPSCs, includes characterization and quality control of the expanded cells, as well as efficient cryopreservation. The flow based QC strategy was also successfully applied for characterization of cells cultivated under standardized, automated, closed system conditions using the CliniMACS Prodigy Instrument which is of major relevance for generation of master cell banks (MCB) and working cell banks (WCB) for future clinical cell manufacturing.

Because of the ability to manipulate their genome, mice are the experimental tool of choice for many areas of scientific investigation. Moreover, established experimental mouse models of human disease are widely available and offer a valuable resource to obtain proof-of-concept for many cell-based therapies. Nevertheless, efforts to establish reliable methods to isolate mesenchymal stromal cells (MSCs) from mouse bone marrow have been elusive. Indeed, a variety of physical and genetic approaches have been described to fractionate MSCs from other cell lineages in bone marrow, but few have achieved high yields or purity while maintaining the genomic integrity of the cells. We provide a historic overview of published procedures dedicated to the isolation of mouse MSCs from bone marrow and compact bone. We also review current findings indicating that growth-restrictive conditions imposed by atmospheric oxygen promotes immortalization of mouse MSCs and how expansion in a low-oxygen environment enhances cell yields and maintains genomic stability. Finally, we provide basic recommendations for isolating primary mouse MSCs and discuss potential pitfalls associated with these isolation methods.

Endogenous processes or genotoxic agents can induce many types of single DNA damage (single-strand breaks, oxidized bases and abasic sites). In addition, ionizing radiation induces complex lesions such as double-strand breaks and clustered damage. To preserve the genomic stability and prevent carcinogenesis, distinct repair pathways have evolved. Despite this, complex DNA damage can cause severe problems and is believed to contribute to the biological consequences observed in cells exposed to genotoxic stress. In this review, the current knowledge of formation and repair of complex DNA damage is summarized and the risks and biological consequences associated with their repair are discussed.

The genetic stability of induced pluripotent stem (iPS) cells has a significant impact on their potential use in regenerative medicine and basic research. Analysis of the genomic integrity of iPS cells suggests a tendency to develop aberrations ranging from whole chromosome trisomies to single nucleotide mutations. Furthermore, fluctuations in telomere elongation and changes in mitochondrial DNA are also observed. Some mutations may already exist in the founder cells or result from prolonged culturing, however, many of the mutations occur during the reprogramming event. Thus, great care should be given to the initial characterization and subsequent culturing of new iPS cell lines in order to avoid the use of potentially aberrant cells.

In this study we assessed the genomic stability of Mycobacterium bovis BCG Moreau seed lots used in Poland for BCG vaccine production since 1955 by pulsed field gel electrophoresis (PFGE), amplified fragment length polymorphism (AFLP) and random amplification of polymorphic DNA (RAPD). BCG vaccine lots were more closely related the original lot -M. bovis BCG Rio de Janeiro Moreau compared with seeds used before 1980, which is consistent with seed lot distribution recorded in the archives. We confirmed the presence of RD8, RD2, senX3-regX3, RD14, DU2-I, whiB3, trcR, the second copy of IS6110 inserted in the promoter region of phoP, mutation D322G in phoR, ΔRD1, and ΔfadD26-ppsA in M. bovis BCG Moreau used for BCG production in Poland. However, unlike the Rio de Janeiro parent BCG, the BCG Moreau substrain used in Poland does not harbour a deletion in Rv3887c, a region that is involved in the membrane transport protein that is part of the ESX-2 type VII secretion system. Differences in the distribution of BCG Moreau for its subsequent use for manufacturing influenced the microevolution of BCG Moreau used in Brazil and Poland.

Many metals serve as micronutrients which protect against genomic instability. Chromium is most abundant in its trivalent and hexavalent forms. Trivalent chromium has historically been considered an essential element, though recent data indicate that while it can have pharmacological effects and value, it is not essential. There are no data indicating that trivalent chromium promotes genomic stability and, instead may promote genomic instability. Hexavalent chromium is widely accepted as highly toxic and carcinogenic with no nutritional value. Recent data indicate that it causes genomic instability and also has no role in promoting genomic stability.

The 2009 Nobel Prize for Physiology and Medicine was awarded to Elizabeth H. Blackburn, Carol W. Greider and Jack K. Szostak for their work on telomeres and telomerase. This prize acknowledges their pionneering discoveries on chromosomal extremities. Telomeres are the nucleoproteic complexes that may be found at the ends of linear chromosomes. They are essential for genomic stability and are involved in aging and tumorogenesis.

Cancer cells utilize complex mechanisms to remodel their bioenergetic properties. We exploited the intrinsic genomic stability of xeroderma pigmentosum C (XPC) to understand the inter-relationships between genomic instability, reactive oxygen species (ROS) generation, and metabolic alterations during neoplastic transformation. We showed that knockdown of XPC (XPC KD ) in normal human keratinocytes results in metabolism remodeling through NADPH oxidase-1 (NOX-1) activation, which in turn leads to increased ROS levels. While enforcing antioxidant defenses by overexpressing catalase, CuZnSOD, or MnSOD could not block the metabolism remodeling, impaired NOX-1 activation abrogates both alteration in ROS levels and modifications of energy metabolism. As NOX-1 activation is observed in human squamous cell carcinomas (SCCs), the blockade of NOX-1 could be a target for the prevention and the treatment of skin cancers. This article is part of a Special Issue entitled: Bioenergetics of Cancer.

Chromosome instability (CIN), a common feature of solid tumors, promotes tumor evolution and increases drug resistance during therapy. We previously demonstrated that loss of the pRB tumor suppressor causes changes in centromere structure and generates CIN. However, the reason for, and significance of, this change was unclear. Here we show that defects in cohesion are key to the pRB-loss phenotype. pRB loss alters H4K20 methylation, a prerequisite for efficient establishment of cohesion at centromeres. Changes in cohesin regulation are first evident during S-phase where they compromise replication and increase DNA damage. Ultimately such changes compromise mitotic fidelity in pRB-deficient cells. Remarkably, increasing cohesion suppressed all of these phenotypes and dramatically reduced CIN in cancer cells lacking functional pRB. These data explain how loss of pRB undermines genomic integrity. Given the frequent functional inactivation of pRB in cancer, conditions that increase cohesion may provide a general strategy to suppress CIN.

The recent decade has engendered a convergence of the otherwise distinct fields of DNA replication, recombination, and repair, as we are learning how these essential transactions can operate in coordination to achieve genomic stability and to ensure cellular viability. In the next decade, we can anticipate a functional understanding of the roles of posttranslational protein modifications in the regulation and prioritizing of pathways for genomic maintenance. The fundamental knowledge gained should lead to more effective clinical intervention in human disease.

Polyploidization, the addition of a complete set of chromosomes to the genome, represents one of the most dramatic mutations known to occur. Nevertheless, polyploidy is well tolerated in many groups of eukaryotes. Indeed, the majority of flowering plants and vertebrates have descended from polyploid ancestors. This Review examines the short-term effects of polyploidization on cell size, body size, genomic stability, and gene expression and the long-term effects on rates of evolution.

The human DNA helicase RECQL4 interacts in an array of intracellular regulatory pathways from the initiation of DNA replication, through maintaining genomic stability, to the N-end rule pathway. Interestingly, mutations in RECQL4 have recently been revealed not only in Rothmund-Thomson-, but RAPADILINO-, and cases of Baller-Gerold syndrome also. Although these disorders represent distinct genetic entities, clinical observations have delineated highly variable expressivity and significant overlaps in the associated phenotypic manifestations. Consequently, it is especially difficult to draw precise genotype-phenotype correlations in RECQL4 related syndromes. This is likely due to the complex and multiple cellular networks RECQL4 is associated with.

The protective "cap" that assembles at chromosome ends recruits and controls an intricate network of biochemical activities, each one critical for telomere structure and the maintenance of genomic stability. Recent studies have uncovered the components of telomere caps and have started to define the pathways that lead from telomere dysfunction to chromosomal catastrophe.

Since it is not always possible to reduce human exposure to mutagens, attempts have been directed to identify potential antimutagens and anticarcinogens for use in protecting the population against environmental disease. The purpose of this paper is to provide the reader with information about the antimutagenic and anticarcinogenic potentials of some dietary constituents and foods widely consumed in Brazil, and to reinforce diet as a key factor in determining genomic stability and preventing human diseases. In this report, we have summarized data that show interactive effects between some dietary components and specific chemical mutagens or carcinogens using in vitro and in vivo short- or medium-term assays. The summary indicates that certain dietary compounds may be useful agents for disease prevention.

The p53 tumour suppressor is crucial for the ability of the cell to either arrest cell cycle progression or activate apoptosis in response to stimuli that may impinge on genomic stability. p53 activation is controlled by mechanisms involving post-translational modifications, protein interactions and modulation of subcellular localisation. Recently, p53 was identified within nuclear bodies, particular subnuclear structures that can provide a 'platform' where interaction of p53 with specific cofactors is favoured. Modulation of recruitment/release of some of these components and modifications might be required for directing p53 toward one or another of its downstream response pathways.

Accurate chromosome segregation is essential to ensure genomic stability because the aneuploidy that results from segregation errors leads to birth defects and contributes to the development of cancer. Chromosome segregation is directed by the kinetochore, the chromosomal site of attachment to dynamic polymers called microtubules (MTs). Although the fidelity of chromosome segregation depends on precise interactions between kinetochores and MTs, it is still unclear how this interaction is mediated and regulated. Here we discuss current progress in determining how kinetochores assemble and attach to MTs during mitosis as well as how they correct errors.

The evolutionarily conserved Hus1 proteins function in DNA damage response pathways that serve to maintain genomic stability [1, 2]. Cells lacking mouse Hus1 are hypersensitive to certain genotoxins [3], and we have explored the molecular basis for this defect by examining how Hus1 inactivation affects genotoxin-induced signaling events. p53 accumulation and activation in response to DNA damage appeared normal in Hus1 null cells. Likewise, Hus1 was dispensable for genotoxin-induced Chk2 phosphorylation. In contrast, Chk1 phosphorylation after genotoxic stress was greatly reduced in the absence of Hus1, but was restored in Hus1 null fibroblasts complemented by infection with a Hus1 -expressing retrovirus. These results demonstrate that mouse Hus1 is required for a specific subset of DNA damage signaling events and functions to promote genotoxin-induced Chk1 phosphorylation.

BRCA1 contributes to the response to UV irradiation. Utilizing its BRCT motifs, it is recruited during S/G2 to UV-damaged sites in a DNA replication-dependent, but nucleotide excision repair- independent manner. More specifically, at UV- stalled replication forks, it promotes photoproduct excision, suppression of translesion synthesis, and the localization and activation of replication factor C complex (RFC) subunits. The last function, in turn, triggers post-UV checkpoint activation and post- replicative repair. These BRCA1 functions differ from those required for DSBR.

We have characterized the susceptibility and genetic stability of varicella-zoster viruses (VZV) isolated from skin lesions of three patients with herpes zoster and six patients with varicella treated with conventional short-term acyclovir (ACV) administration. The susceptibilities to ACV of the serial isolates from the patients were examined, and there was no significant difference in the susceptibility to ACV among the isolates before and during the ACV treatment, indicating that conventional short-term ACV treatment did not generate ACV-resistant VZV infections. Polymerase chain reaction (PCR) analyses of these as well as seven thymidine kinase-deficient VZV strains derived from in vitro ACV treatment were carried out to examine their genomic stability. Five regions containing tandem direct reiterations (R1-R5) were amplified by PCR and compared, and the region containing the Pst I-site was also examined. PCR analyses demonstrated that the R1, R5 and the Pst I-sites were stable and useful in epidemiological studies even after ACV treatment. The R2, R3 and R4 sites were far less stable in these experimental conditions. In this paper we discuss the results of the PCR analyses with regard to the dynamics of VZV population in patients with VZV infection treated with conventional short-term ACV administration.

This meeting served to juxtapose the fundamental studies on the distinct pathways which maintain genomic stability with work that addresses the phenotypic consequences of loss of genomic stability in humans. This created an exciting environment where we were prompted to think about the links between fundamental and applied research. It was also a forum where new ideas could be formed that will hopefully fuel interesting research in human disease. As we place the genome projects into perspective, the ideas arising from meetings such as the 1st MRC Human Genetics Symposium might be expected to guide studies that will reveal the molecular defects which underlie some of the more impenetrable phenotypes of human diseases.

Telomeres protect the ends of chromosomes and are important for genomic stability. Telomeric DNA is double stranded with a single strand overhang and contains the same sequence repeated over and over. This G rich DNA can fold into G-quadruplex structures, which can contribute to the regulation and maintenance of telomere length. Telomeric G-quadruplex structures, containing the human telomeric repeat TTAGGG, fold under many different conformations depending on their environment. They show large conformational diversity in solutions containing KCl and the different conformations interconnect dynamically one with another with time constants that depend on salt concentration. We investigate here different telomeric G-quadruplex structures using single molecule FRET microscopy to obtain a direct insight into their structural polymorphism and dynamics. Experimental conditions are carefully chosen and adjusted to yield G-quadruplex foldings with both large and low conformational heterogeneity. This study allows a clear identification of FRET efficiency signatures for different G-quadruplex conformations.

Cellular metabolic rates might regulate aging by impinging on genomic stability through the DNA repair pathways. A new study published in Cell (Mostoslavsky et al., 2006) reports that deficiency in one of the mammalian Sir2 homologs, SIRT6, results in genome instability through the DNA base excision repair pathway and leads to aging-associated degenerative phenotypes.

Magnetic Tweezers are a powerful, highly parallelizable, single-molecule technique that allows the conformational manipulation of individual, double-strand DNA molecules. It allows the user to measure mechanical or enzymatic work done on DNA by proteins present in the solution. Total-Internal Reflection Fluorescence (TIRF) Microscopy is another prolific single-molecule technique which allows the user to detect and localize individual proteins in real-time. We have constructed an apparatus which combines the two techniques, allowing the user to simultaneously detect both the localization of proteins on DNA and the subsequent action of these proteins on the DNA. We apply this novel technique to study properties of the mismatch repair system embodied by the MutS, MutL, and MutH proteins. During genome replication, single-nucleotide errors are inadvertently created in the daughter-strand sequence. The detection and elimination of these errors is essential in maintaining an organism's genomic stability. In E. coli, MutS, MutL and MutH are the three proteins responsible for detecting error-induced mismatches in the double-strand DNA and then initiating the excision process that will remove the mismatch. MutS recognizes the mismatch, MutL links MutS to MutH and MutH cuts the error-containing daughter strand, initiating the mismatch's removal by downstream agents. Although the roles of these proteins are crucial to quenching replication mutations, the process by which they assemble onto the DNA remains unknown. Using the combined Magnetic Tweezers and TIRF techniques we are able to probe the recruitment of these proteins and measure the kinetics of their assembly onto DNA, their movement along it, and their eventual nicking of one of the strands.