Transient Physical Effects in Electron Beam Sintering

The extensive use of the electron beam in manufacturing processes like welding or perforating revealed the high potentials for also using it for solid freeform fabrication. First approaches like feeding wire into a melt pool have successfully shown the technical feasibility. Among other features, the electron beam exhibits high scanning speed, high power output, and beam density. While in laser-based machines the fabrication is working in a stable way, transient physical effects in the electron beam process can be observed, which still restrict process stability. For instance, a high power input of the electron beam can result in sudden scattering of the metal powder. The authors have developed an electron beam freeform fabrication system and examined the above mentioned effects. Thus, the paper provides methods in order to identify, isolate and avoid these effects, and to finally realize a reproducible process.Mechanical Engineerin

Layer Formations in Electron Beam Sintering

Among direct metal processing manufacturing technologies (Rapid Manufacturing), Electron Beam Sintering (EBS) exhibits a high application potential. Especially, the fast beam deflection provided by electromagnetic lenses allows the realization of considerable building speeds and minor residual stresses. Therefore, this paper aims to examine and utilize the given potential for additive layer manufacturing. In this context, the deployed scanning strategy is a very important aspect. By means of an increasing computer power, innovative and flexible patterns for the solidification of the powder can be implemented. Thus, different patterns are being examined and evaluated. Finally, occurring effects in the exposed zone are introduced.Mechanical Engineerin

Spotlight on Geminin

In the previous issue of Breast Cancer Research, Gardner and co-workers describe a novel interaction between Geminin, a protein that prevents reinitiation of DNA replication, and Topoisomerase IIα (TopoIIα), an enzyme essential for removing catenated intertwines between sister chromatids. Geminin facilitates the action of TopoIIα, thereby promoting termination of DNA replication at the same time it inhibits initiation. In this manner, Geminin ensures that cells duplicate their genome once, but only once, each time they divide. Remarkably, either depletion of Geminin or over-expression of Geminin inhibits the action of TopoIIα, thereby making Geminin an excellent target for cancer chemotherapy

Single Bead Affinity Detection (SINBAD) for the Analysis of Protein-Protein Interactions

We present a miniaturized pull-down method for the detection of protein-protein interactions using standard affinity chromatography reagents. Binding events between different proteins, which are color-coded with quantum dots (QDs), are visualized on single affinity chromatography beads by fluorescence microscopy. The use of QDs for single molecule detection allows the simultaneous analysis of multiple protein-protein binding events and reduces the amount of time and material needed to perform a pull-down experiment

Molecular architecture of the Nup84–Nup145C–Sec13 edge element in the nuclear pore complex lattice

Nuclear pore complexes (NPCs) facilitate all nucleocytoplasmic transport. These massive protein assemblies are modular, with a stable structural scaffold supporting more dynamically attached components. The scaffold is made from multiple copies of the heptameric Y complex and the heteromeric Nic96 complex. We previously showed that members of these core subcomplexes specifically share an ACE1 fold with Sec31 of the COPII vesicle coat, and we proposed a lattice model for the NPC based on this commonality. Here we present the crystal structure of the heterotrimeric 134-kDa complex of Nup84–Nup145C–Sec13 of the Y complex. The heterotypic ACE1 interaction of Nup84 and Nup145C is analogous to the homotypic ACE1 interaction of Sec31 that forms COPII lattice edge elements and is inconsistent with the alternative 'fence-like' NPC model. We construct a molecular model of the Y complex and compare the architectural principles of COPII and NPC lattices.National Institutes of Health (U.S.) (Grant GM77537)Pew Charitable Trusts (Scholar Award

Pom121 links two essential subcomplexes of the nuclear pore complex core to the membrane

Pom121 anchors core structures of the NPC to the membrane through its binding to the β-propeller domains of Nup155 and Nup160

Inter- and intrachromosomal asynchrony of cell division cycle events in root meristem cells of Allium cepa: possible connection with gradient of cyclin B-like proteins

Alternate treatments of Allium cepa root meristems with hydroxyurea (HU) and caffeine give rise to extremely large and highly elongated cells with atypical images of mitotic divisions, including internuclear asynchrony and an unknown type of interchromosomal asynchrony observed during metaphase-to-anaphase transition. Another type of asynchrony that cannot depend solely on the increased length of cells was observed following long-term incubation of roots with HU. This kind of treatment revealed both cell nuclei entering premature mitosis and, for the first time, an uncommon form of mitotic abnormality manifested in a gradual condensation of chromatin (spanning from interphase to prometaphase). Immunocytochemical study of polykaryotic cells using anti-β tubulin antibodies revealed severe perturbations in the microtubular organization of preprophase bands. Quantitative immunofluorescence measurements of the control cells indicate that the level of cyclin B-like proteins reaches the maximum at the G2 to metaphase transition and then becomes reduced during later stages of mitosis. After long-term incubation with low doses of HU, the amount of cyclin B-like proteins considerably increases, and a significant number of elongated cells show gradients of these proteins spread along successive regions of the perinuclear cytoplasm. It is suggested that there may be a direct link between the effects of HU-mediated deceleration of S- and G2-phases and an enhanced concentration of cyclin B-like proteins. In consequence, the activation of cyclin B-CDK complexes gives rise to an abnormal pattern of premature mitotic chromosome condensation with biphasic nuclear structures having one part of chromatin decondensed, and the other part condensed

Meiosis genes in Daphnia pulex and the role of parthenogenesis in genome evolution

<p>Abstract</p> <p>Background</p> <p>Thousands of parthenogenetic animal species have been described and cytogenetic manifestations of this reproductive mode are well known. However, little is understood about the molecular determinants of parthenogenesis. The <it>Daphnia pulex </it>genome must contain the molecular machinery for different reproductive modes: sexual (both male and female meiosis) and parthenogenetic (which is either cyclical or obligate). This feature makes <it>D. pulex </it>an ideal model to investigate the genetic basis of parthenogenesis and its consequences for gene and genome evolution. Here we describe the inventory of meiotic genes and their expression patterns during meiotic and parthenogenetic reproduction to help address whether parthenogenesis uses existing meiotic and mitotic machinery, or whether novel processes may be involved.</p> <p>Results</p> <p>We report an inventory of 130 homologs representing over 40 genes encoding proteins with diverse roles in meiotic processes in the genome of <it>D. pulex</it>. Many genes involved in cell cycle regulation and sister chromatid cohesion are characterized by expansions in copy number. In contrast, most genes involved in DNA replication and homologous recombination are present as single copies. Notably, <it>RECQ2 </it>(which suppresses homologous recombination) is present in multiple copies while <it>DMC1 </it>is the only gene in our inventory that is absent in the <it>Daphnia </it>genome. Expression patterns for 44 gene copies were similar during meiosis <it>versus </it>parthenogenesis, although several genes displayed marked differences in expression level in germline and somatic tissues.</p> <p>Conclusion</p> <p>We propose that expansions in meiotic gene families in <it>D. pulex </it>may be associated with parthenogenesis. Taking into account our findings, we provide a mechanistic model of parthenogenesis, highlighting steps that must differ from meiosis including sister chromatid cohesion and kinetochore attachment.</p