Search

Since the beginning of its existence mankind is using natural resources and applying them in construction techniques. The anthropogenic pressure induced by humans its clearly influencing the natural environment and so affecting its functional balance. Buildings are anthropogenic objects that enable mankind to inhabit its natural habitat according to their needs.This article discloses the use issues of buildings according to their anthropogenic pressure taken in consideration the example of a selected building.

Nuclear pore complexes (NPCs) are large proteinaceous assemblies that mediate nuclear compartmentalization. NPCs undergo large-scale structural rearrangements during mitosis in metazoans and some fungi. However, our understanding of NPC remodeling beyond mitosis remains limited. Using time-lapse fluorescence microscopy, we discovered that NPCs undergo two mechanistically separable remodeling events during budding yeast meiosis in which parts or all of the nuclear basket transiently dissociate from the NPC core during meiosis I and II, respectively. Meiosis I detachment, observed for Nup60 and Nup2, is driven by Polo kinase-mediated phosphorylation of Nup60 at its interface with the Y-complex. Subsequent reattachment of Nup60-Nup2 to the NPC core is facilitated by a lipid-binding amphipathic helix in Nup60. Preventing Nup60-Nup2 reattachment causes misorganization of the entire nuclear basket in gametes. Strikingly, meiotic nuclear basket remodeling also occurs in the distantly related fission yeast, Schizosaccharomyces pombe. Our study reveals a conserved and developmentally programmed aspect of NPC plasticity, providing key mechanistic insights into the nuclear basket organization., Journal of Cell Biology, 222 (2), ISSN:0021-9525, ISSN:1540-8140

To evaluate the effects of early anticoagulation on functional outcome, recurrent ischaemic events and haemorrhagic complications in Atrial Fibrillation (AF)-related acute ischaemic strokes (AIS). We retrospectively evaluated patients hospitalised in a Stroke Unit due to AF-related AIS. Patients were divided according to anticoagulation initiation timing (0–4 days, 5–14 days, no anticoagulation by the 14th day). We assessed the following outcomes at 3 months: favourable functional outcome [modified Rankin Scale (mRS) score 0–2 or equal to pre-stroke], recurrent ischaemic events and haemorrhagic complications after anticoagulation initiation. We included 395 patients. Anticoagulation was initiated at days 0–4 in 33.9% of patients, days 5–14 in 25.3% and not initiated by the day 14 in 40.8%. Factors associated with earlier anticoagulation included lower previous mRS, valvular AF and lower stroke severity. Favourable functional outcome occurred in 40.2% of patients, with lower odds in those anticoagulated at 5–14 versus 0–4 days (OR: 0.47, 95% CI: 0.23–0.94), independently of age, previous mRS and stroke severity. Recurrent ischaemic events occurred in 8.3% of patients, with higher odds in non-anticoagulated patients by the 14th day, compared to the remainder groups (OR: 3.26, 95% CI: 1.29–8.22 vs. 0–4 days and OR: 8.16, 95% CI: 1.76–37.9 vs. 5–14 days). In patients who started anticoagulation (n = 288), haemorrhagic complications occurred in 10.8%, being more frequent in those who started at 0–4 days vs. > 14 days. However, it did not abolish the 0–4-day initiation’s benefit on functional outcome. Early anticoagulation was associated with lower ischaemic recurrence and better functional outcome at 3 months. Additional studies are needed to better clarify its haemorrhagic risk.

CRISPR-Cas-based genome editing holds great promise for targeting genetic disorders, including inborn errors of hepatocyte metabolism. Precise correction of disease-causing mutations in adult tissues in vivo, however, is challenging. It requires repair of Cas9-induced double-stranded DNA (dsDNA) breaks by homology-directed mechanisms, which are highly inefficient in nondividing cells. Here we corrected the disease phenotype of adult phenylalanine hydroxylase (Pah)enu2 mice, a model for the human autosomal recessive liver disease phenylketonuria (PKU)1, using recently developed CRISPR-Cas-associated base editors2-4. These systems enable conversion of C∙G to T∙A base pairs and vice versa, independent of dsDNA break formation and homology-directed repair (HDR). We engineered and validated an intein-split base editor, which allows splitting of the fusion protein into two parts, thereby circumventing the limited cargo capacity of adeno-associated virus (AAV) vectors. Intravenous injection of AAV-base editor systems resulted in Pahenu2 gene correction rates that restored physiological blood phenylalanine (L-Phe) levels below 120 µmol/l [5]. We observed mRNA correction rates up to 63%, restoration of phenylalanine hydroxylase (PAH) enzyme activity, and reversion of the light fur phenotype in Pahenu2 mice. Our findings suggest that targeting genetic diseases in vivo using AAV-mediated delivery of base-editing agents is feasible, demonstrating potential for therapeutic application.

SummaryDuring prophase of the first meiotic division, cells deliberately break their DNA. These DNA breaks are repaired by homologous recombination, which facilitates proper chromosome segregation and enables reciprocal exchange of DNA segments between homologous chromosomes, thus promoting genetic diversity in the progeny1. A successful completion of meiotic recombination requires nucleolytic processing of recombination intermediates. Genetic and cellular data implicated a pathway dependent on the putative MLH1-MLH3 (MutLγ) nuclease in generating crossovers, but mechanisms that lead to its activation were unclear2–4. Here, we have biochemically reconstituted key elements of this pro-crossover pathway. First, we show that human MSH4-MSH5 (MutSγ), which was known to support crossing over5–7, binds branched recombination intermediates and physically associates with MutLγ. This helps stabilize the ensemble at joint molecule structures and adjacent dsDNA. Second, we show that MutSγ directly stimulates DNA cleavage by the MutLγ endonuclease, which demonstrates a novel and unexpected function for MutSγ in triggering crossing-over. Third, we find that MutLγ activity is further stimulated by EXO1, but only when MutSγ is present. Fourth, we also identify the replication factor C (RFC) and the proliferating cell nuclear antigen (PCNA) as additional components of the nuclease ensemble, and show thatS. cerevisiaestrains expressing PIP box-mutated MutLγ present striking defects in forming crossovers. Finally, we show that the MutLγ-MutSγ-EXO1-RFC-PCNA nuclease ensemble preferentially cleaves DNA with Holliday junctions, but shows no canonical resolvase activity. Instead, the multilayered nuclease ensemble likely processes meiotic recombination intermediates by nicking dsDNA adjacent to junction points8. Since DNA nicking by MutLγ is dependent on its co-factors, the asymmetric distribution of MutSγ and RFC/PCNA on meiotic recombination intermediates may drive biased DNA cleavage. This unique mode of MutLγ nuclease activation might explain crossover-specific processing of Holliday junctions within the meiotic chromosomal context3, 9.

Cryo-electron tomography (cryoET) has become a powerful technique at the interface of structural biology and cell biology, due to its unique ability for imaging cells in their native state and determining structures of macromolecular complexes in their cellular context. A limitation of cryoET is its restriction to relatively thin samples. Sample thinning by cryo-focused ion beam (cryoFIB) milling has significantly expanded the range of samples that can be analyzed by cryoET. Unfortunately, cryoFIB milling is low-throughput, time-consuming and manual. Here, we report a method for fully automated sequential cryoFIB preparation of high-quality lamellae, including rough milling and polishing. We reproducibly applied this method to eukaryotic and bacterial model organisms, and show that the resulting lamellae are suitable for cryoET imaging and subtomogram averaging. Since our method reduces the time required for lamella preparation and minimizes the need for user input, we envision the technique will render previously inaccessible projects feasible., eLife, 9, ISSN:2050-084X

DNA repair by homologous recombination is under stringent cell cycle control. This includes the last step of the reaction, disentanglement of DNA joint molecules (JMs). Previous work has established that JM resolving nucleases are activated specifically at the onset of mitosis. In case of budding yeast Mus81‐Mms4, this cell cycle stage‐specific activation is known to depend on phosphorylation by CDK and Cdc5 kinases. Here, we show that a third cell cycle kinase, Cdc7‐Dbf4 (DDK), targets Mus81‐Mms4 in conjunction with Cdc5—both kinases bind to as well as phosphorylate Mus81‐Mms4 in an interdependent manner. Moreover, DDK‐mediated phosphorylation of Mms4 is strictly required for Mus81 activation in mitosis, establishing DDK as a novel regulator of homologous recombination. The scaffold protein Rtt107, which binds the Mus81‐Mms4 complex, interacts with Cdc7 and thereby targets DDK and Cdc5 to the complex enabling full Mus81 activation. Therefore, Mus81 activation in mitosis involves at least three cell cycle kinases, CDK, Cdc5 and DDK. Furthermore, tethering of the kinases in a stable complex with Mus81 is critical for efficient JM resolution., The EMBO Journal, 36 (5), ISSN:0261-4189, ISSN:1460-2075

Summary The Bloom’s helicase ortholog, Sgs1, orchestrates the formation and disengagement of recombination intermediates to enable controlled crossing-over during meiotic and mitotic DNA repair. Whether its enzymatic activity is temporally regulated to implement formation of noncrossovers prior to the activation of crossover-nucleases is unknown. Here, we show that, akin to the Mus81-Mms4, Yen1, and MutLγ-Exo1 nucleases, Sgs1 helicase function is under cell-cycle control through the actions of CDK and Cdc5 kinases. Notably, however, whereas CDK and Cdc5 unleash nuclease function during M phase, they act in concert to stimulate Sgs1 activity during S phase/prophase I. Mechanistically, CDK-mediated phosphorylation enhances the velocity and processivity of Sgs1, which stimulates DNA unwinding in vitro and joint molecule processing in vivo. Subsequent hyper-phosphorylation by Cdc5 appears to reduce the activity of Sgs1, while activating Mus81-Mms4 and MutLγ-Exo1. These findings suggest a concerted mechanism driving orderly formation of noncrossover and crossover recombinants in meiotic and mitotic cells.

The Bloom’s helicase ortholog, Sgs1, orchestrates the formation and disengagement of DNA joint molecules to enable controlled crossing-over during meiotic and mitotic DNA repair. Whether its enzymatic activity is temporally regulated to implement formation of noncrossovers prior to the activation of crossover-nucleases is unknown. Here, we show that akin to the Mus81-Mms4, Yen1 and MutLγ-Exo1 nucleases, Sgs1 helicase function is under tight cell cycle control through the actions of CDK and Polo kinase Cdc5. Notably, however, whereas CDK and Cdc5 unleash nuclease function during M-phase, they collaboratively delimit Sgs1 activation to S-phase. Mechanistically, CDK-mediated phosphorylation enhances the velocity and processivity of Sgs1, which stimulates DNA unwinding in vitro and joint molecule processing in vivo. Subsequent hyper-phosphorylation by Cdc5 appears to reduce the activity of Sgs1, while activating Mus81-Mms4 and MutLγ-Exo1. These findings suggest a general mechanism that drives orderly formation of noncrossover and crossover recombinants in meiotic and mitotic cells.

Formation of co-transcriptional R-loops underlies replication fork stalling upon head-on transcription-replication encounters. Here, we demonstrate that RAD51-dependent replication fork reversal induced by R-loops is followed by the restart of semiconservative DNA replication mediated by RECQ1 and RECQ5 helicases, MUS81/EME1 endonuclease, RAD52 strand-annealing factor, the DNA ligase IV (LIG4)/XRCC4 complex, and the non-catalytic subunit of DNA polymerase δ, POLD3. RECQ5 disrupts RAD51 filaments assembled on stalled forks after RECQ1-mediated reverse branch migration, preventing a new round of fork reversal and facilitating fork cleavage by MUS81/EME1. MUS81-dependent DNA breaks accumulate in cells lacking RAD52 or LIG4 upon induction of R-loop formation, suggesting that RAD52 acts in concert with LIG4/XRCC4 to catalyze fork religation, thereby mediating replication restart. The resumption of DNA synthesis after R-loop-associated fork stalling also requires active transcription, the restoration of which depends on MUS81, RAD52, LIG4, and the transcription elongation factor ELL. These findings provide mechanistic insights into transcription-replication conflict resolution.

The formation of stable interactions between chromosomes of maternal and paternal origin-homologs-is required for their segregation during meiosis. To achieve this, cells take advantage of the recombination machinery, which promotes formation of reciprocal interhomolog exchanges, called crossovers, from the repair of self-inflicted DNA breaks. Important genetic studies led to the identification of key enzymes that control meiotic recombination. However, characterization of their biochemical properties when purified from meiotic cultures has been difficult to achieve. Here, we describe a simple approach to purify and characterize DNA repair enzymes from meiotic yeast cells. First, we provide a protocol to generate large-scale synchronous cultures. Second, we describe a general method to prepare meiotic extracts from which protein complexes can be immunoaffinity-purified. Finally, we detail how the purified material can be used for: (i) mass spectrometry-based analysis of interaction partners and posttranslational modifications, and (ii) monitoring enzymatic activities using synthetic DNA substrates.

The establishment of stable interactions between chromosomes underpins vital cellular processes such as recombinational DNA repair and bipolar chromosome segregation. On the other hand, timely disengagement of persistent connections is necessary to assure efficient partitioning of the replicated genome prior to cell division. Whereas great progress has been made in defining how cohesin-mediated chromosomal interactions are disengaged as cells prepare to undergo chromosome segregation, little is known about the metabolism of DNA joint molecules (JMs), generated during the repair of chromosomal lesions. Recent work on Mus81 and Yen1/GEN1, two conserved structure-selective endonucleases, revealed unforeseen links between JM-processing and cell cycle progression. Cell cycle kinases and phosphatases control Mus81 and Yen1/GEN1 to restrain deleterious JM-processing during S-phase, while safeguarding chromosome segregation during mitosis.

The efficient separation of two equal DNA masses to the daughter cells is an essential step in mitosis. This process is dependent upon the removal of any remaining recombination or replication intermediates that link sister chromatids, and a failure to resolve these intermediates leads to genome instability. Similarly, a failure to resolve meiotic recombination intermediates that link homologous chromosomes can cause chromosome nondisjunction and aneuploidy. Cleavage of these potentially toxic replication/recombination intermediates requires the Mus81 endonuclease, which is active upon flaps, forks, and more complex secondary structures in DNA such as Holliday junctions. Recent studies of Mus81 revealed that it is regulated throughout the cell cycle: Mus81 activity is controlled in S-phase to limit the cleavage of replication fork structures, whereas it is activated at G2/M to ensure the cleavage of recombination and late replication intermediates. In this chapter, we describe a simple method that can monitor the activity of Mus81, which involves the immunoprecipitation of epitope-tagged Mus81 and use of an on-bead assay for nuclease activity.

DNA replication and homologous recombination involve the formation of branched DNA structures that physically link chromosomes. Such DNA-based connections, which arise during S-phase, are typically disengaged prior to entry into mitosis, in order to ensure proper chromosome segregation. Exceptions can, however, occur: replication stress, or elevated levels of DNA damage, may cause cells to enter mitosis with unfinished replication as well as carrying recombination intermediates, such as Holliday junctions. Hence, cells are equipped with pathways that recognize and process branched DNA structures, and evolved mechanisms to enhance their function when on the verge of undergoing cell division. One of these pathways utilizes the structure-selective endonuclease Mus81, which is thought to facilitate the resolution of replication and recombination intermediates. Mus81 function is known to be enhanced upon entry into M phase in budding yeast and human cells. Based on recent findings, we discuss here an updated model of Mus81 control during the cell cycle.

Holliday junctions (HJs) can be formed between sister chromatids or homologous chromosomes during the recombinational repair of DNA lesions. A variety of pathways act upon HJs to remove them from DNA, in events that are critical for appropriate chromosome segregation. Despite the identification and characterization of multiple enzymes involved in HJ processing, the cellular mechanisms that regulate and implement pathway usage have only just started to be delineated. A conserved network of core cell-cycle kinases and phosphatases modulate HJ metabolism by exerting spatial and temporal control over the activities of two structure-selective nucleases: yeast Mus81-Mms4 (human MUS81-EME1) and Yen1 (human GEN1). These regulatory cycles operate to establish the sequential activation of HJ processing enzymes, implementing a hierarchy in pathway usage that ensure the elimination of chromosomal interactions which would otherwise interfere with chromosome segregation. Mus81-Mms4/EME1 and Yen1/GEN1 emerge to define a special class of enzymes, evolved to satisfy the cellular need of safeguarding the completion of DNA repair when on the verge of chromosome segregation.

Holliday junctions (HJs) are four-way DNA intermediates that form during homologous recombination, and their efficient resolution is essential for chromosome segregation. Here, we show that three structure-selective endonucleases, namely SLX1-SLX4, MUS81-EME1, and GEN1, define two pathways of HJ resolution in human cells. One pathway is mediated by GEN1, whereas SLX1-SLX4 and MUS81-EME1 provide a second and genetically distinct pathway (SLX-MUS). Cells depleted for SLX-MUS or GEN1 pathway proteins exhibit severe defects in chromosome segregation and reduced survival. In response to CDK-mediated phosphorylation, SLX1-SLX4 and MUS81-EME1 associate at the G2/M transition to form a stable SLX-MUS holoenzyme, which can be reconstituted in vitro. Biochemical studies show that SLX-MUS is a HJ resolvase that coordinates the active sites of two distinct endonucleases during HJ resolution. This cleavage reaction is more efficient and orchestrated than that mediated by SLX1-SLX4 alone, which exhibits a potent nickase activity that acts promiscuously upon DNA secondary structures.

The article describes a monitoring system based on Raspberry Pi platform and a multichannel sensing module associated with water quality and air quality measurement parameters. Thus the temperature, conductivity, relative humidity and gas concentration are measured as was as the underwater acoustic signals. The data is stored on the memory of the drone's computational platform, and synchronized with a remote server database. Advanced data processing algorithms were implemented on the server side. Additionally, a mobile application was developed to be used by people working in the field for data visualization and statistical analysis.

In eukaryotic cells, multiple DNA repair mechanisms respond to a wide variety of DNA lesions. Homologous recombination-dependent repair provides a pathway for dealing with DNA double-strand breaks and replication fork demise. A key step in this process is the resolution of recombination intermediates such as Holliday junctions (HJs). Recently, nucleases from yeast (Yen1) and human cells (GEN1) were identified that can resolve HJ intermediates, in a manner analogous to the E. coli HJ resolvase RuvC. Here, we have analyzed the role of Yen1 in DNA repair in S. cerevisiae, and show that while yen1Delta mutants are repair-proficient, yen1Delta mus81Delta double mutants are exquisitely sensitive to a variety of DNA-damaging agents that disturb replication fork progression. This phenotype is dependent upon RAD52, indicating that toxic recombination intermediates accumulate in the absence of Yen1 and Mus81. After MMS treatment, yen1Delta mus81Delta double mutants arrest with a G2 DNA content and unsegregated chromosomes. These findings indicate that Yen1 can act upon recombination/repair intermediates that arise in MUS81-defective cells following replication fork damage.

SummaryMeiosis differs from mitosis in that DNA replication is followed by the segregation of homologous chromosomes but not sister chromatids. This depends on the formation of interhomolog connections through crossover recombination and on the attachment of sister kinetochores to microtubules emanating from the same spindle pole. We show that in yeast, the Dbf4-dependent Cdc7 kinase (DDK) provides a link between premeiotic S phase, recombination, and monopolar attachment. Independently from its established role in initiating DNA replication, DDK promotes double-strand break formation, the first step of recombination, and the recruitment of the monopolin complex to kinetochores, which is essential for monopolar attachment. DDK regulates monopolin localization together with the polo-kinase Cdc5 bound to Spo13, probably through phosphorylation of the monopolin subunit Lrs4. Thus, activation of DDK both initiates DNA replication and commits meiotic cells to reductional chromosome segregation in the first division of meiosis.

DNA strand break repair by homologous recombination leads to the formation of intermediates in which sister chromatids are covalently linked. The efficient processing of these joint molecules, which often contain four-way structures known as Holliday junctions, is necessary for efficient chromosome segregation during mitotic division. Because persistent chromosome bridges pose a threat to genome stability, cells ensure the complete elimination of joint molecules through three independent pathways. These involve (1) BLM-Topoisomerase IIIα-RMI1-RMI2 (BTR complex), (2) SLX1-SLX4-MUS81-EME1 (SLX-MUS complex), and (3) GEN1. The BTR pathway promotes the dissolution of double Holliday junctions, which avoids the formation of crossover products, prevents sister chromatid exchanges, and limits the potential for loss of heterozygosity. In contrast to BTR, the other two pathways resolve Holliday junctions by nucleolytic cleavage to yield crossover and non-crossover products. To avoid competition with BTR, the resolution pathways are restrained until the late stages of the cell cycle. The temporal regulation of the dissolution/resolution pathways is therefore critical for crossover avoidance while also ensuring that all covalent links between chromosomes are resolved before chromosome segregation.

SummaryHomologous recombination leads to the formation of DNA joint molecules (JMs) that must be resolved to allow chromosome segregation, but how resolution is temporally coupled with chromosome segregation is unknown. Here, we have analyzed the role of the cell-cycle kinases Cdk and Cdc5 in coordinating these events through their involvement in the phosphoregulation of the Mus81-Mms4 nuclease. By identifying CDC5 and MMS4 mutants that uncouple Mus81-Mms4 activation from cell-cycle progression, we show that JM disengagement, prior to anaphase initiation, safeguards chromosome segregation. By simultaneously stimulating the cleavage of cohesin and activating Mus81-Mms4 at the G2/M transition, Cdk and Cdc5 coordinate the sequential elimination of all chromosomal interactions in preparation for chromosome segregation. Conversely, untimely Cdc5 expression increases crossover frequency due to premature activation of Mus81-Mms4. Therefore, temporal restriction of JM resolution, imposed by Cdk/Cdc5, minimizes the potential for loss of heterozygosity while preventing chromosome missegregation and aneuploidy.

Analisa a experiência com a implementação do Projeto de Crédito Fundiário e Combate à Pobreza Rural (PCF), tomando, como estudo de caso, o Projeto de Assentamento Bom Conselho, no município de Macaíba, estado do Rio Grande do Norte. Resume as principais contribuições teóricas sobre o processo recente de modernização da agricultura brasileira e destaca as formas de organização da produção que emergiram desse processo de modernização, entre as quais se inclui a agricultura familiar modernizada e integrada aos circuitos de produção e de mercado. Os dados empíricos para elaboração do estudo de caso foram obtidos em pesquisa documental e em levantamento de campo, durante o qual foram realizadas observações diretas dos plantios e criações existentes no assentamento, além entrevistas com os gestores da associação responsável pelo projeto. A análise dos dados empíricos mostrou que a implementação do PCF – integrada com o Programa de Combate a Pobreza Rural (PCPR) e o Programa Nacional de Fortalecimento da Agricultura Familiar (PRONAF) – teve efeitos bastante significativos, tanto do ponto de vista da renda, quanto do emprego e da segurança alimentar no assentamento pesquisado. Além disso, ficou evidente que a agricultura familiar é capaz de incorporar progresso técnico, diversificar a produção, participar dos mercados de produtos agrícolas diretamente ou por intermédio de uma empresa âncora. Por último, mas não menos importante, ficou comprovado que a reestruturação fundiária não é um programa meramente social, mas um elemento estratégico da mais alta relevância para o desenvolvimento rural em bases sustentáveis.

Apresenta os antecedentes das políticas de desenvolvimento territorial e das formas de gestão pública. Identifica, para tanto, as principais contribuições teóricas contemporâneas no campo do desenvolvimento e da análise de políticas públicas. Explora as atuais experiências de integração de políticas e de atores sociais - nas escalas regional, micro-regional e comunitária no estado do Rio Grande do Norte. Elabora estudo de casos, a saber, o Plano de Desenvolvimento Sustentável da Região do Seridó e mais 04 (quatro) experiências de projetos micro-territoriais financiados pelo Projeto de Combate à Pobreza Rural (PCPR) e por outras políticas, de forma integrada. Analisa os principais atores, as organizações participantes e os arranjos institucionais utilizados nos processos de formulação e implementação, em cada um desses casos. Conclui que os arranjos institucionais descentralizados e participativos e a existência de lideranças e assessores técnicos qualificados e comprometidos com as questões do desenvolvimento e da governança local foram decisivos para o êxito das experiências analisadas. Verifica que, apesar disso, os gestores públicos ainda utilizam pouco as lições que podem ser tiradas, tanto do legado histórico - principalmente no campo da formação e da qualificação de lideranças e técnicos -, quanto das experiências bem sucedidas, que podem ser replicadas com sucesso. É possível e desejável que estas últimas experiências se reproduzam, em face de sua ausência e/ou viabilidade, naquele contexto regional.

SummaryCohesion established between sister chromatids during pre-meiotic DNA replication mediates two rounds of chromosome segregation. The first division is preceded by an extended prophase wherein homologous chromosomes undergo recombination. The persistence of cohesion during prophase is essential for recombination and both meiotic divisions. Here we show that Mnd2, a subunit of the anaphase-promoting complex (APC/C) from budding yeast, is essential to prevent premature destruction of cohesion in meiosis. During S- and prophase, Mnd2 prevents activation of the APC/C by a meiosis-specific activator called Ama1. In cells lacking Mnd2 the APC/C-Ama1 enzyme triggers degradation of Pds1, which causes premature sister chromatid separation due to unrestrained separase activity. In vitro, Mnd2 inhibits ubiquitination of Pds1 by APC/C-Ama1 but not by other APC/C holo-enzymes. We conclude that chromosome segregation in meiosis depends on the selective inhibition of a meiosis-specific form of the APC/C.

Background: Cells undergoing meiosis perform two consecutive divisions after a single round of DNA replication. During the first meiotic division, homologous chromosomes segregate to opposite poles. This is achieved by (1) the pairing of maternal and paternal chromosomes via recombination producing chiasmata, (2) coorientation of homologous chromosomes such that sister chromatids attach to the same spindle pole, and (3) resolution of chiasmata by proteolytic cleavage by separase of the meiotic-specific cohesin Rec8 along chromosome arms. Crucially, cohesin at centromeres is retained to allow sister centromeres to biorient at the second division. Little is known about how these meiosis I-specific events are regulated. Results: Here, we show that Spo13, a centromere-associated protein produced exclusively during meiosis I, is required to prevent sister kinetochore biorientation by facilitating the recruitment of the monopolin complex to kinetochores. Spo13 is also required for the reaccumulation of securin, the persistence of centromeric cohesin during meiosis II, and the maintenance of a metaphase I arrest induced by downregulation of the APC/C activator CDC20. Conclusion: Spo13 is a key regulator of several meiosis I events. The presence of Spo13 at centromere-surrounding regions is consistent with the notion that it plays a direct role in both monopolin recruitment to centromeres during meiosis I and maintenance of centromeric cohesion between the meiotic divisions. Spo13 may also limit separase activity after the first division by ensuring securin reaccumulation and, in doing so, preventing precocious removal from chromatin of centromeric cohesin.

In this paper we present a remote utility metering system based on ZigBee used to collect data from residential electricity, gas and water meters. In order to reduce the use of network resources and to evaluate the sensor network performance, a simulation study was carried out with two types of data related to electronic and non electronic metering devices. The study was conducted using a simulator which was developed using the OMNeT++ platform. The results show that for some application scenarios ZigBee is a valid technological solution to the remote utility metering problem.