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Evidence That Masking of Synapsis Imperfections Counterbalances Quality Control to Promote Efficient Meiosis  [PDF]
Susanna Mlynarczyk-Evans,Baptiste Roelens,Anne M. Villeneuve
PLOS Genetics , 2013, DOI: 10.1371/journal.pgen.1003963
Abstract: Reduction in ploidy to generate haploid gametes during sexual reproduction is accomplished by the specialized cell division program of meiosis. Pairing between homologous chromosomes and assembly of the synaptonemal complex at their interface (synapsis) represent intermediate steps in the meiotic program that are essential to form crossover recombination-based linkages between homologs, which in turn enable segregation of the homologs to opposite poles at the meiosis I division. Here, we challenge the mechanisms of pairing and synapsis during C. elegans meiosis by disrupting the normal 1:1 correspondence between homologs through karyotype manipulation. Using a combination of cytological tools, including S-phase labeling to specifically identify X chromosome territories in highly synchronous cohorts of nuclei and 3D rendering to visualize meiotic chromosome structures and organization, our analysis of trisomic (triplo-X) and polyploid meiosis provides insight into the principles governing pairing and synapsis and how the meiotic program is “wired” to maximize successful sexual reproduction. We show that chromosomes sort into homologous groups regardless of chromosome number, then preferentially achieve pairwise synapsis during a period of active chromosome mobilization. Further, comparisons of synapsis configurations in triplo-X germ cells that are proficient or defective for initiating recombination suggest a role for recombination in restricting chromosomal interactions to a pairwise state. Increased numbers of homologs prolong markers of the chromosome mobilization phase and/or boost germline apoptosis, consistent with triggering quality control mechanisms that promote resolution of synapsis problems and/or cull meiocytes containing synapsis defects. However, we also uncover evidence for the existence of mechanisms that “mask” defects, thus allowing resumption of prophase progression and survival of germ cells despite some asynapsis. We propose that coupling of saturable masking mechanisms with stringent quality controls maximizes meiotic success by making progression and survival dependent on achieving a level of synapsis sufficient for crossover formation without requiring perfect synapsis.
Failure of homologous synapsis and sex-specific reproduction problems  [PDF]
Hiroki Kurahashi
Frontiers in Genetics , 2012, DOI: 10.3389/fgene.2012.00112
Abstract: The prophase of meiosis I ensures the correct segregation of chromosomes to each daughter cell. This includes the pairing, synapsis, and recombination of homologous chromosomes. A subset of chromosomal abnormalities, including translocation and inversion, disturbs these processes, resulting in the failure to complete synapsis. This activates the meiotic pachytene checkpoint, and the gametes are fated to undergo cell cycle arrest and subsequent apoptosis. Spermatogenic cells appear to be more vulnerable to the pachytene checkpoint, and male carriers of chromosomal abnormalities are more susceptible to infertility. In contrast, oocytes tend to bypass the checkpoint and instead generate other problems, such as chromosome imbalance that often leads to recurrent pregnancy loss in female carriers. Recent advances in genetic manipulation technologies have increased our knowledge about the pachytene checkpoint and surveillance systems that detect chromosomal synapsis. This review focuses on the consequences of synapsis failure in humans and provides an overview of the mechanisms involved. We also discuss the sexual dimorphism of the involved pathways that leads to the differences in reproductive outcomes between males and females.
Meiotic Chromosome Interactions: Nonhomologous Centromere (Un)Coupling and Homologous Synapsis  [PDF]
Amit Bardhan
ISRN Cell Biology , 2012, DOI: 10.5402/2012/890475
Abstract: The fundamental function of meiosis, segregation of the maternal and paternal chromosomes, is facilitated by reciprocal recombination and intimate juxtaposition (synapsis) between the homologous chromosomes in meiotic prophase. Homolog synapsis, mediated by the synaptonemal complex (SC), is preceded by a stage of pairing between the centromeres of nonhomologous chromosomes. This pairing, named nonhomologous centromere coupling (NCC), depends upon the meiotic cohesin Rec8 and the SC protein Zip1. Nonhomologously coupled centromeres (NCCs), if remain tethered, must interfere with complete homolog synapsis (SC formation). Recent experiments demonstrate the existence of a mechanism that regulates NCC. Importantly, this is part of a regulatory network which couples dissolution of the NCCs with SC formation between the homologous chromosomes, thereby ensuring appropriate meiotic chromosome interactions. This paper reviews this network and presents speculations relating to the initiation of SC formation at centromere. 1. Introduction Cell biologists working on meiosis, the cell division that segregates the maternal and paternal chromosomes to produce haploid gametes from diploid parent cells, have ever been fascinated by the ballet between chromosomes that occupy a substantial part of the meiotic prophase (reviewed in [1, 2]). This culminates into initial side-by-side alignment (named pairing) of the two homologous chromosomes, which subsequently converts to intimate physical juxtaposition (named synapsis) of the two homologs along their entire length. Synapsis between the homologous chromosomes is mediated by a complex proteinaceous structure named synaptonemal complex (SC). (SC may also form between nonhomologous chromosomes or segments of chromosomes that are not homologous.) The SC is a tripartite organelle in which a central element (CE) connects two lateral elements (LEs); each LE represents the merged axes formed along the length of the two sister chromatids (reviewed in [3]). In many organisms, homolog synapsis and SC formation are stringently coupled with the programmed induction of meiotic DNA double strand-breaks (DSBs) by the conserved topoisomerase Spo11, which initiates the process of reciprocal interhomolog recombination (reviewed in [4]). A twist in the tale came from the Roeder laboratory [5]. It was demonstrated that, in budding yeast strain lacking Spo11, a stage of pairing, named Nonhomologous Centromere Coupling (NCC), between the centromeres of nonhomologous chromosomes precedes the homology-dependent synapsis. (The nonhomologously
Client Provider Collaboration for Service Bundling  [cached]
LETIA, I. A.,MARGINEAN, A.
Advances in Electrical and Computer Engineering , 2008,
Abstract: The key requirement for a service industry organization to reach competitive advantages through product diversification is the existence of a well defined method for building service bundles. Based on the idea that the quality of a service or its value is given by the difference between expectations and perceptions, we draw the main components of a frame that aims to support the client and the provider agent in an active collaboration meant to co-create service bundles. Following e3-value model, we structure the supporting knowledge around the relation between needs and satisfying services. We deal with different perspectives about quality through an ontological extension of Value Based Argumentation. The dialog between the client and the provider takes the form of a persuasion whose dynamic object is the current best configuration. Our approach for building service packages is a demand driven approach, allowing progressive disclosure of private knowledge.
Exploring the Client–AEC Interface in Building Lifecycle Integration  [PDF]
John M. Kamara
Buildings , 2013, DOI: 10.3390/buildings3030462
Abstract: The creation and management of buildings over their lifecycle involves the cooperation of many organizations, which broadly fall into a client domain and AEC (architecture, engineering, construction) domain. While this mix of expertise is essential, the ineffective management of the boundaries between these organizations can undermine building lifecycle performance. This paper explores client–AEC interactions at the project development and handover stages, with a view to discovering insights into client–AEC interface management for effective building lifecycle integration (BLI). The concept of boundary objects provided the theoretical framework to discuss findings from two case studies on the project development phase of a private finance initiative project, and the asset development process in a repeat client organization. The findings suggest that there are different emphases in boundary crossing activities at different stages, with boundary roles that relate to decision-making and authority to commit resources being more relevant at the project development stage, whereas the need to explain meanings appear to be more relevant at the handover stage. AEC professionals in client organizations play a crucial role in bridging knowledge boundaries about buildings, but this professional/functional strand to BLI needs to be effectively managed alongside the organizational boundaries, since the authority to resource BLI efforts resides within?organizations.
SECURE REMOTE CLIENT AUTHENTICATION
K.Pradeep,,R.Usha Rani,E.Ravi Kumar,K.Nikhila
International Journal of Engineering Science and Technology , 2010,
Abstract: This paper discusses an application of Secure Remote Client Authentication. It presents a Smart Cards and Digitally certification from third party vendors, Smart cards are based on algorithm to provide secure Remote client Authentication. These schemes vary significantly.In relation to today’s security challenges, which includephishing, man-in-the-middle attacks and malicious software. Secure Remote Client authentication plays a key role.
Predicting Client Satisfaction through (E-Mail) Network Analysis: The Communication Score Card  [PDF]
Dirk Brunberg,Peter A. Gloor,Gianni Giacomelli
Computer Science , 2013,
Abstract: This study seeks to better understand the network characteristics of client support teams by analyzing the teams' e-mail communication networks and comparing it to client organization's satisfaction. In collaboration with a large service provider we studied the impact of network properties on the satisfaction of client organizations. In particular, we found that social network metrics correlate with client satisfaction as measured by Net Promoter Score (NPS). A Communication Score Card is suggested as a dashboard to continuously measure client satisfaction, illustrating that data-driven analysis might help improving service providers' service quality management.
Client-to-Client Streaming Scheme for VOD Applications  [PDF]
M. Dakshayini,T. R. Gopala Krishnan Nair
Computer Science , 2010, DOI: 10.5121/ijma.2010.2204
Abstract: In this paper, we propose an efficient client-to-client streaming approach to cooperatively stream the video using chaining technique with unicast communication among the clients. This approach considers two major issues of VoD 1) Prefix caching scheme to accommodate more number of videos closer to client, so that the request-service delay for the user can be minimized. 2) Cooperative proxy and client chaining scheme for streaming the videos using unicasting. This approach minimizes the client rejection rate and bandwidth requirement on server to proxy and proxy to client path. Our simulation results show that the proposed approach achieves reduced client waiting time and optimal prefix caching of videos minimizing server to proxy path bandwidth usage by utilizing the client to client bandwidth, which is occasionally used when compared to busy server to proxy path bandwidth.
Client-to-Client Streaming Scheme for VOD Applications
M Dakshayini,T R Gopala Krishnan Nair
International Journal of Multimedia & Its Applications , 2010,
Abstract: In this paper, we propose an efficient client-to-client streaming approach to cooperatively stream thevideo using chaining technique with unicast communication among the clients. This approach considerstwo major issues of VoD 1) Prefix caching scheme to accommodate more number of videos closer toclient, so that the request-service delay for the user can be minimized. 2) Cooperative proxy and clientchaining scheme for streaming the videos using unicasting. This approach minimizes the client rejectionrate and bandwidth requirement on server to proxy and proxy to client path. Our simulation results showthat the proposed approach achieves reduced client waiting time and optimal prefix caching of videosminimizing server to proxy path bandwidth usage by utilizing the client to client bandwidth, which isoccasionally used when compared to busy server to proxy path bandwidth.
Reproductive relationships and degree of synapsis in the polytene chromosomes of the Drosophila buzzatii species cluster
Machado, L. P. B.;Madi-Ravazzi, L.;Tadei, W. J.;
Brazilian Journal of Biology , 2006, DOI: 10.1590/S1519-69842006000200010
Abstract: the process of speciation occurs through the evolution of any of several forms of reproductive isolation between taxa, including inviability of hybrids. in this work, strains derived from allopatric populations of drosophila buzzatii cluster species were experimentally crossed in order to evaluate their reproductive and cytogenetic relationships, and to contribute toward understanding the reproductive isolation in this group of sibling species. although intrastrain crosses were highly fertile, we consider it relevant to discuss the differences in intra- and interspecific fertility and fecundity here. among 30 interspecific crosses, about 63% were partially or completely sterile. fifty three percent of interspecific f1 crosses (female and male f1 crossed) were also partially or completely sterile, in contrast to only one out of 24 intraspecific f1 crosses that was partially sterile. an analysis of hybrid polytene chromosomes revealed complete synapsis, except in the microchromosomes (vi) and in the proximal region of the x chromosome. the intraspecific divergence observed in this study and the variable degree of chromosome pairing shown here reveal part of the complexity of the speciation process pertinent to drosophila buzzatii cluster, which is consistent with different traits studied in this cluster.
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