The ATM protein kinase is centrally involved in the cellular response to ionizing radiation (IR) and other DNA double‐strand‐break‐inducing insults. Although it has been well established that IR exposure activates the ATM kinase domain, the actual mechanism by which ATM responds to damaged DNA has remained enigmatic. Now, a landmark paper provides strong evidence that DNA‐strand breaks trigger widespread activation of ATM through changes in chromatin structure.1 This review discusses a checkpoint activation model in which chromatin perturbations lead to the (...) conversion of inactive ATM domains to phosphorylated, active ATM monomers. The new findings underscore the critical importance of epigenetic events in genome function and surveillance in mammalian cells. BioEssays 25:627–630, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

The concept of regulatory ‘checkpoints’ in the eukaryotic cycle has proved to be a fruitful one. Here, its applicability to the bacterial cell cycle is examined. A primitive DNA damage checkpoint operates in E. coli such that, after exposure to ultraviolet light, while excision repair occurs, chromosome replication continues very slowly with the production of discontinuous daughter strands. The slower the rate of excision of photoproducts, the greater the delay before the normal rate of DNA replication is restored, the (...) additional time for repair ensuring that normal survival is maintained. A model is proposed in which replication rate is controlled by the ratio of RecAcoated to uncoated single stranded regions of DNA in the replication fork. There are also two cell division inhibitors SulA (=SfiA) and SfiC under the control of the SOS system and sensitive to DNA damage, but they are irrelevant to the survival of wild‐type bacteria under normal conditions. In strains where SulA and SfiC do not operate, inhibition is not influenced by the rate of excision repair and so fails one of the criteria for a DNA damage checkpoint, namely the monitoring of the DNA for the level of residual damage. (shrink)

In many animals, early development of the embryo is characterized by synchronous, biphasic cell divisions. These cell divisions are controlled by maternally inherited proteins and RNAs. A critical question in developmental biology is how the embryo transitions to a later pattern of asynchronous cell divisions and transfers the prior maternal control of development to the zygotic genome. The most‐common model regarding how this transition from maternal to zygotic control is regulated posits that this is a consequence of the limitation of (...) maternal gene products, due to their titration during early cell divisions. Here we discuss a recent article by Crest et al.1 that instead proposes that the balance of Cyclin‐dependent Kinase 1 and Cyclin B (Cdk1‐CycB) activity relative to that of the Drosophila checkpoint kinase Chk1 determines when asynchronous divisions begin. BioEssays 29:949–952, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

How chromatin bridges are detected by the abscission checkpoint during mammalian cell division is unknown. Here, we discuss recent findings from our lab showing that the DNA topoisomerase IIα (Top2α) enzyme binds to catenated (“knotted”) DNA next to the midbody and forms abortive Top2‐DNA cleavage complexes (Top2ccs) on chromatin bridges. Top2ccs are then processed by the proteasome to promote localization of the DNA damage sensor protein Rad17 to Top2‐generated double‐strand DNA ends on DNA knots. In turn, Rad17 promotes local recruitment (...) of the MRN protein complex and downstream ATM‐Chk2‐INCENP signaling to delay abscission and prevent chromatin bridge breakage in cytokinesis. (shrink)

In nature, cells face a variety of stresses that cause physical damage to the plasma membrane and cell wall. It is well established that evolutionarily conserved cell cycle checkpoints monitor various cellular perturbations, including DNA damage and spindle misalignment. However, the ability of these cell cycle checkpoints to sense a damaged plasma membrane/cell wall is poorly understood. To the best of our knowledge, our recent paper described the first example of such a checkpoint, using budding yeast as a (...) model. In this review, we will discuss this important question as well as provide hypothetical explanations to be tested in the future. (shrink)

Dependency relationships within the cell cycle allow cells to arrest the cycle reversibly in response to agents or conditions that interfere with specific aspects of its normal progression. In addition, overlapping pathways exist which also arrest the cell cycle in response to DNA damage. Collectively, these control mechanisms have become known as checkpoints. Analysis of checkpoints is facilitated by the fact that dependency relationships within the cell cycle, such as the dependency of mitosis on the completion of DNA (...) synthesis, and the DNA damage checkpoint can be separated genetically. In fission yeast, Schizosaccharomyces pombe, the dependency of mitosis on prior completion of DNA synthesis is mediated through tyrosine‐15 phosphorylation of the ubiquitous mitotic regulator p34cdc2. In contrast, the arrest of mitosis caused by DNA damage acts through a separate mechanism that appears to be independent of tyrosine‐15 phosphorylation. Despite these distinct interactions with the mitotic machinery, the majority of fission yeast mutants that are deficient in mitotic arrest after DNA damage are also unable to respond to inhibition of DNA synthesis. In this essay we survey the current knowledge concerning feedback controls and checkpoints within fission yeast and relate this to information derived from other systems. (shrink)

Three major aspects of G1 regulation acting at START in fission yeast are discussed in this review. Firstly, progression towards S phase in the mitotic cycle. This is controlled by the activation of transcription complexes at START which cause cell cycle‐dependent activation of genes required for DNA synthesis. The second aspect is the regulation of developmental fate occurring during G1. Passage through START appears to inhibit sexual differentiation because the meiotic and mitotic pathways are mutually exclusive. This is brought about (...) because the meiotic pathway is inhibited by the same gene functions that are required for S phase onset. Thirdly, distinct checkpoint, or dependency, controls operate both pre‐ and post‐START in the mitotic cycle to inhibit mitosis in the absence of replicated DNA, and also to limit rounds of DNA replication to one per cell cycle. (shrink)

DNA double‐strand breaks (DSBs) are extremely hazardous lesions for all DNA‐bearing organisms and the mechanisms of DSB repair are highly conserved. In the eukaryotic mitotic cell cycle, DSBs are often present following DNA replication while, in meiosis, hundreds of DSBs are generated as a prelude to the reshuffling of the maternally and paternally derived genomes. In both cases, the DSBs are repaired by a process called homologous recombinational repair (HRR), which utilises an intact DNA molecule as the repair template. Mitotic (...) and meiotic HRR are managed by ‘checkpoints’ that inhibit cell division until DSB repair is complete. Here we attempt to summarise the substantial recent progress in understanding the checkpoint management of HRR in mitosis (focussing mainly on mammals) and then go on to use this information as a framework for understanding the presumed checkpoint management of HRR in mammalian meiosis. BioEssays 29:974–986, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

The RecQ family of DNA helicases have been shown to be important for the maintenance of genomic integrity in all organisms analysed to date. In human cells, representatives of this family include the proteins defective in the cancer predisposition disorder Bloom's syndrome and the premature ageing condition, Werner's syndrome. Several pieces of evidence suggest that RecQ family helicases form associations with one or more of the cellular topoisomerases, and together these heteromeric complexes manipulate DNA structure to effect efficient DNA replication, (...) genetic recombination, or both. Here, we propose that RecQ helicases are required for ensuring that structural abnormalities arising during replication, such as at sites where replication forks encounter DNA lesions, are corrected with high fidelity. In mutants defective in these proteins, not only is replication abnormal, but cells display aberrant responses to DNA-damaging agents or inhibitors of DNA synthesis. We suggest that RecQ helicases may be important for the integration of cellular responses to these insults, such as by linking cell cycle checkpoint responses to recombinational repair. BioEssays 21:286–294, 1999. © 1999 John Wiley & Sons, Inc. (shrink)

Together, DNA repair and checkpoint responses ensure the integrity of the genome. Coordination of cell cycle checkpoints and DNA repair are especially important following genotoxic radiation or chemotherapy, during which unusually high loads of DNA damage are sustained. In mammalian cells, the checkpoint kinase, Cds1 (also known as Chk2) is activated by ATM in response to DNA damage. The role of Cds1 as a checkpoint kinase depends on its ability to phosphorylate cell cycle regulators such p53, Cdc25 and Brca1. (...) A role for Cds1 in repair is suggested by the finding that it interacts with the Holliday junction resolving activity Mus81. This review focuses on the many questions generated by recent progress in understanding the function and regulation of human Cds1. BioEssays 24:502–511, 2002. © 2002 Wiley Periodicals, Inc. (shrink)

DNA replication stress threatens ordinary DNA synthesis. The evolutionarily conserved DNA replication stress response pathway involves sensor kinase Mec1/ATR, adaptor protein Mrc1/Claspin, and effector kinase Rad53/Chk1, which spurs a host of changes to stabilize replication forks and maintain genome integrity. DNA replication forks consist of largely distinct sets of proteins at leading and lagging strands that function autonomously in DNA synthesis in vitro. In this article, we discuss eSPAN and BrdU‐IP‐ssSeq, strand‐specific sequencing technologies that permit analysis of protein localization and (...) DNA synthesis at individual strands in budding yeast. Using these approaches, we show that under replication stress Rad53 stalls DNA synthesis on both leading and lagging strands. On lagging strands, it stimulates PCNA unloading, and on leading strands, it attenuates the replication function of Mrc1‐Tof1. We propose that in doing so, Rad53 couples leading and lagging strand DNA synthesis during replication stress, thereby preventing the emergence of harmful ssDNA. (shrink)

Faithful DNA replication and accurate chromosome segregation are the key machineries of genetic transmission. Disruption of these processes represents a hallmark of cancer and often results from loss of tumor suppressors. PTEN is an important tumor suppressor that is frequently mutated or deleted in human cancer. Loss of PTEN has been associated with aneuploidy and poor prognosis in cancer patients. In mice, Pten deletion or mutation drives genomic instability and tumor development. PTEN deficiency induces DNA replication stress, confers stress tolerance, (...) and disrupts mitotic spindle architecture, leading to accumulation of structural and numerical chromosome instability. Therefore, PTEN guards the genome by controlling multiple processes of chromosome inheritance. Here, we summarize current understanding of the PTEN function in promoting high-fidelity transmission of genetic information. We also discuss the PTEN pathways of genome maintenance and highlight potential targets for cancer treatment. PTEN is a guardian of the genome. However, the role of PTEN in guarding the genome has not been revealed until recently. PTEN controls multiple fundamental processes of genomic transmission. By physically interacting with key molecules in DNA replication, DNA repair/decatenation, and chromosome segregation during the cell cycle, PTEN maintains genomicintegrity and fitness. (shrink)

DNA double‐strand breaks (DSBs) are one of the most deleterious forms of DNA damage and can result in cell inviability or chromosomal aberrations. The Mre11‐Rad50‐Nbs1 (MRN) ATPase‐nuclease complex is a central player in the cellular response to DSBs and is implicated in the sensing and nucleolytic processing of DSBs, as well as in DSB signaling by activating the cell cycle checkpoint kinase ATM. ATP binding to Rad50 switches MRN from an open state with exposed Mre11 nuclease sites to a closed (...) state with partially buried nuclease sites. The functional meaning of this switch remained unclear. A new study shows that ATP binding to Rad50 promotes DSB recognition, tethering, and ATM activation, while ATP hydrolysis opens the nuclease active sites to promote processing of DSBs. MRN thus emerges as functional switch that may coordinate the temporal transition from signaling to processing of DSBs. (shrink)

In response to DNA‐damage, cells have to decide between different cell fate programmes. Activation of the tumour suppressor HIPK2 specifies the DNA damage response (DDR) and tips the cell fate balance towards an apoptotic response. HIPK2 is activated by the checkpoint kinase ATM, and triggers apoptosis through regulatory phosphorylation of a set of cellular key molecules including the tumour suppressor p53 and the anti‐apoptotic corepressor CtBP. Recent work has identified HIPK2 as a regulator of the ultimate step in cytokinesis: the (...) abscission of the mother and daughter cells. Since proper cytokinesis is essential for genome stability and maintenance of correct ploidy, this finding sheds new light on the tumour suppressor function of HIPK2. Here we highlight the molecular mechanisms coordinating HIPK2 function and discuss its emerging role as a tumour suppressor. (shrink)

Cohesin establishes sister‐chromatid cohesion during S phase to ensure proper chromosome segregation in mitosis. It also facilitates postreplicative homologous recombination repair of DNA double‐strand breaks by promoting local pairing of damaged and intact sister chromatids. In G2 phase, cohesin that is not bound to chromatin is inactivated, but its reactivation can occur in response to DNA damage. Recent papers by Koshland's and Sjögren's groups describe the critical role of the known cohesin cofactor Eco1 (Ctf7) and ATR checkpoint kinase in damage‐induced (...) reactivation of cohesin, revealing an intricate mechanism that regulates sister‐chromatid pairing to maintain genome integrity.1,2 BioEssays 30:5–9, 2008. © 2007 Wiley Periodicals, Inc. (shrink)

The correct execution of the DNA replication process is crucially import for the maintenance of genome integrity of the cell. Several types of sources, both endogenous and exogenous, can give rise to DNA damage leading to the DNA replication fork arrest. The processes by which replication blockage is sensed by checkpoint sensors and how the pathway leading to resolution of stalled forks is activated are still not completely understood. However, recent emerging evidence suggests that one candidate for a sensor of (...) replication stress is ATR and that, together with a member of RecQ family helicases, Werner syndrome protein (WRN) and MRE11 complex, can collaborate to promote the restarting of DNA synthesis through the resolution of stalled replication forks. Here, we discuss how WRN, the MRE11 complex and the ATR kinase could work together in response to replication blockage to avoid DNA replication fork collapse and genome instability. BioEssays 26:306–313, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

Homologous recombination (HR) is required to protect and restart stressed replication forks. Paradoxically, the Mrc1 branch of the S phase checkpoints, which is activated by replicative stress, prevents HR repair at breaks and arrested forks. Indeed, the mechanisms underlying HR can threaten genome integrity if not properly regulated. Thus, understanding how cells avoid genetic instability associated with replicative stress, a hallmark of cancer, is still a challenge. Here I discuss recent results that support a model by which HR responds (...) to replication stress through replicative and repair activities that operate at different stages of the cell cycle (S and G2, respectively) and in distinct subnuclear structures. Remarkably, the replication checkpoint appears to control this scenario by inhibiting the assembly of HR repair centers at stressed forks during S phase, thereby avoiding genetic instability. (shrink)

Double strand break (DSB) repair is suppressed during mitosis because RNF8 and downstream DNA damage response (DDR) factors, including 53BP1, do not localize to mitotic chromatin. Discovery of the mitotic kinase‐dependent mechanism that inhibits DSB repair during cell division was recently reported. It was shown that restoring mitotic DSB repair was detrimental, resulting in repair dependent genome instability and covalent telomere fusions. The telomere DDR that occurs naturally during cellular aging and in cancer is known to be refractory to G2/M (...) checkpoint activation. Such DDR‐positive telomeres, and those that occur as part of the telomere‐dependent prolonged mitotic arrest checkpoint, normally pass through mitosis without covalent ligation, but result in cell growth arrest in G1 phase. The discovery that suppressing DSB repair during mitosis may function primarily to protect DDR‐positive telomeres from fusing during cell division reinforces the unique cooperation between telomeres and the DDR to mediate tumor suppression. (shrink)

Chromosome transmission in S. cerevisiae requires the activities of many structural and regulatory proteins required for the replication, repair, recombination and segregation of chromosomal DNA, and co‐ordination of the chromosome cycle with progression through the cell cycle. An important structural domain on each chromosome is the kinetochore (centromere DNA and associated proteins), which provides the site of attachment of chromosomes to the spindle microtubules. Stoler et al.(1) have recently reported the cloning of an essential gene CSE4, mutations in which cause (...) chromosome nondisjunction of a marked chromosome bearing a centromere DNA mutation. The cse4–1 mutation causes cells to arrest in the G2/M phase of the cell cycle with a 2N DNA content in a RAD9 checkpoint‐independent manner. The carboxyl terminus of Cse4p and the human centromere‐localized protein CENP‐A have a high degree of homology to the C‐terminal domain of histone H3. Since both CENP‐A and Cse4p also have biochemical properties similar to histones H3 and H4, it is tempting to speculate that these histone H3‐like proteins are components of specialized nucleosomes, a class of which may be unique to the centromeres. (shrink)

Human individuals often exhibit important differences in their sensitivity to ionising radiation. Extensive literature links radiation sensitivity with impaired DNA repair which is due to a lack of correct functioning in many proteins involved in DNA‐repair pathways and/or in DNA‐damage checkpoint responses. Given that ionising radiation is an important and widespread diagnostic and therapeutic tool, it is important to investigate further those factors and mechanisms that underlie individual radiosensitivity. Recently, evidence is accumulating that telomere function may well be involved in (...) cellular and organism responses to ionising radiation, broadening still further the currently complex and challenging scenario. BioEssays. BioEssays 28: 1172–1180, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

Abstractp53 is a multifunctional protein which plays a role in modulating gene transcription, policing cell cycle checkpoints, activating apoptosis, controlling DNA replication and repair, maintaining genomic stability and responding to genetic insults. Mutation of the p53 gene confers the single greatest known selective advantage favoring cancer formation. Point mutations result not only in the loss of tumor suppressor functions, but also in the gain of tumor promotion functions. These dual circumstances may be unique to p53 and, in part, could (...) explain the relatively powerful force behind this selection pressure. General mechanisms of gain of function by mutated p53 may include alteration in transcriptional modulation and newly acquired targets for transcriptional regulation and protein binding. Despite the direct significance of p53 mutations, loss of the remaining wild‐type allele is usually required for the formation of tumors in the natural setting. Novel applications of the basic scientific knowledge of p53 could lead to an improvement in cancer treatment, hopefully in the not so distant future. (shrink)

Ataxia‐telangiectasia (A‐T) is a pleiotropic recessive disorder characterized cerebellar ataxia, immunodeficiency, specific developmental defects, profound predisposition to cancer and acute radiosensitivity. Functional inactivation of single gene product, ATM, accounts for this compound phenotype. We suggest that ATM acts as a sensor of reactive oxygen species and/or oxidative damage cellular macromolecules, including DNA. In turn, ATM induces signalling through multiple pathways, thereby coordinating acute phase stress responses with cell cycle checkpoint control and repair of oxidative damage. Absence of ATM is proposed (...) to limit the repair of insidious oxidative damage that can occur under normal physiological conditions, ultimately leading to apoptosis of particularly sensitive cells, such as neurons and thymocytes. (shrink)

Major events of the cell cycle—DNA synthesis, mitosis and cell division—are regulated by a complex network of protein interactions that control the activities of cyclin‐dependent kinases. The network can be modeled by a set of nonlinear differential equations and its behavior predicted by numerical simulation. Computer simulations are necessary for detailed quantitative comparisons between theory and experiment, but they give little insight into the qualitative dynamics of the control system and how molecular interactions determine the fundamental physiological properties of cell (...) replication. To that end, bifurcation diagrams are a useful analytical tool, providing new views of the dynamical organization of the cell cycle, the role of checkpoints in assuring the integrity of the genome, and the abnormal regulation of cell cycle events in mutants. These claims are demonstrated by an analysis of cell cycle regulation in fission yeast. BioEssays 24:1095–1109, 2002. © 2002 Wiley‐Periodicals, Inc. (shrink)

Eukaryotic genomes harbor a large number of homologous repeat sequences that are capable of recombining. Their potential to disrupt genome stability highlights the need to understand how homologous recombination processes are coordinated. The Saccharomyces cerevisiae Rad1–Rad10 endonuclease performs an essential role in recombination between repeated sequences, by processing 3′ single‐stranded intermediates formed during single‐strand annealing and gene conversion events. Several recent studies have focused on factors involved in Rad1–Rad10‐dependent removal of 3′ nonhomologous tails during homologous recombination, including Msh2–Msh3, Slx4, and (...) the newly identified Saw1 protein. Together, this new work provides a model for how Rad1–Rad10‐dependent end processing is coordinated: Msh2–Msh3 stabilizes and prepares double‐strand/single‐strand junctions for Rad1–Rad10 cleavage, Saw1 recruits Rad1–Rad10 to 3′ tails, and Slx4 mediates crosstalk between the DNA damage checkpoint machinery and Rad1–Rad10. (shrink)

Bacterial checkpoints, analogous to those proposed to exist in eukaryotic cells, offer insights into the definition of a checkpoint. Examination of bacterial “checkpoint” or arrest phenomena illustrate problems with a too‐casual application of the checkpoint idea to eukaryotic phenomena. The question raised here is whether there are cellular processes that “check” whether a cellular process is completed. It is possible that many eukaryotic “checkpoints” may not have “checking” functions. Some of the ubiquitous checkpoint phenomena widely described may be (...) merely the result of the inherent incompleteness of earlier events preventing the initiation of subsequent events. BioEssays 28: 1035–1039, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

Bacterial checkpoints, analogous to those proposed to exist in eukaryotic cells, offer insights into the definition of a checkpoint. Examination of bacterial “checkpoint” or arrest phenomena illustrate problems with a too‐casual application of the checkpoint idea to eukaryotic phenomena. The question raised here is whether there are cellular processes that “check” whether a cellular process is completed. It is possible that many eukaryotic “checkpoints” may not have “checking” functions. Some of the ubiquitous checkpoint phenomena widely described may be (...) merely the result of the inherent incompleteness of earlier events preventing the initiation of subsequent events. BioEssays 28: 1035–1039, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

Here we discuss a “chromosome separation checkpoint” that might regulate the anaphase‐telophase transition. The concept of cell cycle checkpoints was originally proposed to account for extrinsic control mechanisms that ensure the order of cell cycle events. Several checkpoints have been shown to regulate major cell cycle transitions, namely at G1‐S and G2‐M. At the onset of mitosis, the prophase‐prometaphase transition is controlled by several potential checkpoints, including the antephase checkpoint, while the spindle assembly checkpoint guards the metaphase‐anaphase (...) transition. Our hypothesis is based on the recently uncovered feedback control mechanism that delays chromosome decondensation and nuclear envelope reassembly until effective separation of sister chromatids during anaphase is achieved. A central player in this potential checkpoint is the establishment of a constitutive, midzone‐based Aurora B phosphorylation gradient that monitors the position of chromosomes along the spindle axis. We propose that this surveillance mechanism represents an additional step towards ensuring mitotic fidelity. (shrink)

This Christian sermon uses a DNA lab experience as a basis for theological reflection on ourselves and our offering. Who are we to God? What determines the self that we offer? Can the alphabet of DNA shed light for us on the Word of God in our lives? This first attempt to introduce the language and laboratory environment of genetic testing (represented by DNA fingerprinting) within a parish preaching context juxtaposes liturgical, scientific, and biblical language and settings for fresh insights.

DNA methylation can be considered a component of epigenetic memory with a critical role during embryo development, and which undergoes dramatic reprogramming after fertilization. Though it has been a focus of research for many years, the reprogramming mechanism is still not fully understood. Recent results suggest that absence of maintenance at DNA replication is a major factor, and that there is an unexpected role for TET3-mediated oxidation of 5mC to 5hmC in guarding against de novo methylation. Base-resolution and genome-wide profiling (...) methods are enabling more comprehensive assessments of the extent to which ART might impair DNA methylation reprogramming, and which sequence elements are most vulnerable. Indeed, as we also review here, studies showing the effect of culture media, ovarian stimulation or embryo transfer on the methylation pattern of embryos emphasize the need to face ART-associated defects and search for strategies to mitigate adverse effects on the health of ART-derived children. DNA methylation, critical for embryo development, suffers significant changes after fertilization, including demethylation, remethylation and TET3-mediated oxidation of 5 mC to 5 hmC. In addition to infertility and environmental insults, ART could impact DNA methylation and ART related consequences in the offspring have been reported. (shrink)

The pedagogical function of science teaching may benefit from an analysis of the historical-epistemic dimension, without neglecting the socio-political context in which a given research was carried out. In the case of DNA structure, the background of its discovery is particularly complex. Starting from the analysis of some papers, the view on the circumstances that led to their drafting broadens. We try to answer the fundamental question for any educator: why teach all that? Ethics issues are related to the general (...) organisation of research, increasingly focused on speed and competition. Even teaching is affected by these dynamics, not only in higher education, but also at secondary level; students should be made aware of this trend. The history of science could therefore favour a more general awareness. _SUNTO_ La funzione pedagogica dell’insegnamento scientifico può trarre vantaggio da un’analisi della dimensione storico-epistemica, senza trascurare il contesto socio-politico nel quale una determinata ricerca è stata condotta. Nel caso della struttura del DNA, i retroscena della sua scoperta sono particolarmente complessi. Dopo l’analisi di alcuni articoli, si allarga gradualmente la vista sulle circostanze che hanno condotto alla loro stesura. Si cerca di rispondere a una domanda fondamentale per ogni educatore: perché insegnare tutto ciò? Le questioni etiche riguardano l’organizzazione generale della ricerca, sempre più tesa alla velocità e alla competizione. Persino l’insegnamento è influenzato da dinamiche simili, non solo in ambito accademico, ma anche a livello secondario; gli studenti dovrebbero essere a conoscenza di questa tendenza. La storia della scienza può dunque favorire una maggiore consapevolezza. (shrink)

DNA topoisomerases, capable of manipulating DNA topology, are ubiquitous and indispensable for cellular survival due to the numerous roles they play during DNA metabolism. As we review here, current structural approaches have revealed unprecedented insights into the complex DNA‐topoisomerase interaction and strand passage mechanism, helping to advance our understanding of their activities in vivo. This has been complemented by single‐molecule techniques, which have facilitated the detailed dissection of the various topoisomerase reactions. Recent work has also revealed the importance of topoisomerase (...) interactions with accessory proteins and other DNA‐associated proteins, supporting the idea that they often function as part of multi‐enzyme assemblies in vivo. In addition, novel topoisomerases have been identified and explored, such as topo VIII and Mini‐A. These new findings are advancing our understanding of DNA‐related processes and the vital functions topos fulfil, demonstrating their indispensability in virtually every aspect of DNA metabolism. (shrink)

This paper focuses on the question of whether DNA patents help or hinder scientific discovery and innovation. While DNA patents create a wide variety of possible benefits and harms for science and technology, the evidence we have at this point in time supports the conclusion that they will probably promote rather than hamper scientific discovery and innovation. However, since DNA patenting is a relatively recent phenomena and the biotechnology industry is in its infancy, we should continue to gather evidence about (...) the effects of DNA patenting on scientific innovation and discovery as well the economic, social, and legal conditions relating to intellectual property in biotechnology. We should give the free market, the courts, researchers, and patent offices a chance to settle issues related to innovation and discovery, before we seek legislative remedies, since new laws proposed at this point would lack adequate foresight and could do more harm than good. However, we should be open to new laws or regulations on DNA patents if they are required to in order to deal with some of the biases and limitations of the free market. (shrink)

DNA methylation is a repressive epigenetic mark vital for normal development. Recent studies have uncovered an unexpected role for the DNA methylome in ensuring the correct targeting of the Polycomb repressive complexes throughout the genome. Here, we discuss the implications of these findings for cancer, where DNA methylation patterns are widely reprogrammed. We speculate that cancer‐associated reprogramming of the DNA methylome leads to an altered Polycomb binding landscape, influencing gene expression by multiple modes. As the Polycomb system is responsible for (...) the regulation of genes with key roles in cell fate decisions and cell cycle regulation, DNA methylation induced Polycomb mis‐targeting could directly drive carcinogenesis and disease progression.Editor's suggested further reading in BioEssays Unmasking risk loci: DNA methylation illuminates the biology of cancer predisposition Abstract. (shrink)

Type II DNA topoisomerase activity is required to change DNA topology. It is important in the relaxation of DNA supercoils generated by cellular processes, such as transcription and replication, and it is essential for the condensation of chromosomes and their segregation during mitosis. In mammals this activity is derived from at least two isoforms, termed DNA topoisomerase IIα and β. The α isoform is involved in chromosome condensation and segregation, whereas the role of the β isoform is not yet clear. (...) DNA topoisomerase IIβ was first reported in 1987. Here we review the research on DNA topoisomerase IIβ over the last 10 years. BioEssays 20:215–226, 1998.© 1998 John Wiley & Sons, Inc. (shrink)

Those objecting to human DNA patenting frequently do so on the grounds that the practice violates or threatens human dignity. For example, from 1993 to 1994, more than thirty organizations representing indigenous peoples approved formal declarations objecting to the National Institutes of Health's bid to patent viral DNA taken from subjects in Papua New Guinea and the Solomon Islands. Although these were not patents on human DNA, the organizations argued that the patents could harm and exploit indigenous peoples and violate (...) their cultural values. NIH eventually dropped one of its patent applications.On May 18, 1995, 180 religious leaders, led by biotechnology critic Jeremy Rifkin, held a press conference objecting to DNA patenting in Washington, D.C. In their “Joint Appeal against Human and Animal Patenting,” these leaders decried any attempt to patent nature. Some of the more outspoken members of the Joint Appeal likened DNA patenting to slavery, while others objected to treating human beings as marketable commodities. In his recent book, The Biotech Century, Rifkin rehashed the objections to DNA patenting voiced by members of the Joint Appeal. (shrink)

The regulation of DNA replication is a fascinating biological problem both from a mechanistic angle—How is replication timing regulated?—and from an evolutionary one—Why is replication timing regulated? Recent work has provided significant insight into the first question. Detailed biochemical understanding of the mechanism and regulation of replication initiation has made possible robust hypotheses for how replication timing is regulated. Moreover, technical progress, including high‐throughput, single‐molecule mapping of replication initiation and single‐cell assays of replication timing, has allowed for direct testing of (...) these hypotheses in mammalian cells. This work has consolidated the conclusion that differential replication timing is a consequence of the varying probability of replication origin initiation. The second question is more difficult to directly address experimentally. Nonetheless, plausible hypotheses can be made and one—that replication timing contributes to the regulation of chromatin structure—has received new experimental support. (shrink)

Cell cycle arrest in M phase can be induced by the failure of a single chromosome to attach properly to the mitotic spindle. The same cell cycle checkpoint mediates M phase arrest when cells are treated with drugs that either disrupt or hyperstabilize spindle microtubules. Study of yeast mutants that fail to arrest in the presence of microtubule disruptors identified a set of genes important in this checkpoint pathway. Two recent papers report the cloning of human and Xenopus homologues of (...) one of these yeast genes, called MAD2 (for mitotic arrest deficient‐2)(1,2). Introduction of antibodies to the MAD2 protein into living mammalian cells or Xenopus egg extracts abrogates the M phase arrest induced by microtubule inhibitors. This and other recent developments suggest a model for the M phase checkpoint in which unattached kinetochores inhibit the ubiquitination of proteins whose proteolysis is necessary for chromatid separation and exit from mitosis. (shrink)

The nuclear pore complex (NPC) is emerging as a center for recruitment of a class of “difficult to repair” lesions such as double‐strand breaks without a repair template and eroded telomeres in telomerase‐deficient cells. In addition to such pathological situations, a recent study by Su and colleagues shows that also physiological threats to genome integrity such as DNA secondary structure‐forming triplet repeat sequences relocalize to the NPC during DNA replication. Mutants that fail to reposition the triplet repeat locus to the (...) NPC cause repeat instability. Here, we review the types of DNA lesions that relocalize to the NPC, the putative mechanisms of relocalization, and the types of recombinational repair that are stimulated by the NPC, and present a model for NPC‐facilitated repair. (shrink)

Through analysis of film sequences focusing on DNA in two British Broadcasting Corporation nonfiction science television programs, Wonders of Life and Bang! Goes the Theory, first broadcast in 2013, contrasting “religious” and “secular” representations of science are identified. In the “religious” portrayal, immutable scientific knowledge is revealed to humanity by nature with minimal human intervention. Science provides a creation story, “explanatory omnicompetence,” and makes life existentially meaningful. In the “secular” portrayal, scientific knowledge is changeable; is produced through technical skill in (...) expert communities; and is ambiguous, potentially positive and negative for society. Television representations of science affect audience understandings, and this is particularly the case for nonfiction representations of science, as they are likely to be “taken more seriously” than fictional representations. The consequences of the “religious” representation of science are discussed, and it is argued that a widespread understanding of science as presented in the religious portrayal would negatively impact democracy. (shrink)

Over 30 million people worldwide have taken a commercial at-home DNA test, because they were interested in their genetic ancestry, disease predisposition or inherited traits. Yet, these consumer DNA data are also increasingly used for a very different purpose: to identify suspects in criminal investigations. By matching a suspect’s DNA with DNA from a suspect’s distant relatives who have taken a commercial at-home DNA test, law enforcement can zero in on a perpetrator. Such forensic use of consumer DNA data has (...) been performed in over 200 criminal investigations. However, this practice of so-called investigative genetic genealogy raises ethical concerns. In this paper, we aim to broaden the bioethical analysis on IGG by showing the limitations of an individual-based model. We discuss two concerns central in the debate: privacy and informed consent. However, we argue that IGG raises pressing ethical concerns that extend beyond these individual-focused issues. The very nature of the genetic information entails that relatives may also be affected by the individual customer’s choices. In this respect, we explore to what extent the ethical approach in the biomedical genetic context on consent and consequences for relatives can be helpful for the debate on IGG. We argue that an individual-based model has significant limitations in an IGG context. The ethical debate is further complicated by the international, transgenerational and commercial nature of IGG. We conclude that IGG should not only be approached as an individual but also—and perhaps primarily—as a collective issue. There are no data in this work. (shrink)

Science; Ethics; Politics; Beyond recombinant dna.

DNA barcodes, like traditional sources of taxonomic information, are potentially powerful heuristics in the identification of described species but require mindful analytical interpretation. The role of DNA barcoding in generating hypotheses of new taxa in need of formal taxonomic treatment is discussed, and it is emphasized that the recursive process of character evaluation is both necessary and best served by understanding the empirical mechanics of the discovery process. These undertakings carry enormous ramifications not only for the translation of DNA sequence (...) data into taxonomic information but also for our comprehension of the magnitude of species diversity and its disappearance. This paper examines the potential strengths and pitfalls of integrating DNA sequence data, specifically in the form of DNA barcodes as they are currently generated and analyzed, with taxonomic practice. (shrink)

First the ‘Weismann barrier’ and later on Francis Crick’s ‘central dogma’ of molecular biology nourished the gene-centric paradigm of life, i.e., the conception of the gene/genome as a ‘central source’ from which hereditary specificity unidirectionally flows or radiates into cellular biochemistry and development. Today, due to advances in molecular genetics and epigenetics, such as the discovery of complex post-genomic and epigenetic processes in which genes are causally integrated, many theorists argue that a gene-centric conception of the organism has become problematic. (...) Here, we first explore the causal implications of the following two central dogma-related issues: (1) widespread reverse transcription—arguing for an extension from ‘DNA-genome’ to RNA-encompassing ‘NA-genome’ and, thus, from traditional DNA-centrism to a broader ‘NA-centrism’; and (2) the absence of a mechanism of reverse translation—arguing for the ‘structural primacy’ of NA-sequence over protein in cellular biochemistry. Secondly, we explore whether this latter conclusion can be extended to a ‘functional primacy’ of NA-sequence over protein in cellular biochemistry, which would imply a limited kind of ‘gene/NA-centrism’ confined to the subcellular level of NA/protein-based biochemistry. Finally, we explore the conditions—and their (non)fulfilment—for a more generalised form of gene-centrism extendable to higher levels of biological organisation. We conclude that the higher we go in the biological hierarchy, the more dubious gene-centric claims become. (shrink)