Spindle Assembly in Xenopus Egg Extracts: Respective Roles of Centrosomes and Microtubule Self-Organization

In Xenopus egg extracts, spindles assembled around sperm nuclei contain a centrosome at each pole, while those assembled around chromatin beads do not. Poles can also form in the absence of chromatin, after addition of a microtubule stabilizing agent to extracts. Using this system, we have asked (a) how are spindle poles formed, and (b) how does the nucleation and organization of microtubules by centrosomes influence spindle assembly? We have found that poles are morphologically similar regardless of their origin. In all cases, microtubule organization into poles requires minus end–directed translocation of microtubules by cytoplasmic dynein, which tethers centrosomes to spindle poles. However, in the absence of pole formation, microtubules are still sorted into an antiparallel array around mitotic chromatin. Therefore, other activities in addition to dynein must contribute to the polarized orientation of microtubules in spindles. When centrosomes are present, they provide dominant sites for pole formation. Thus, in Xenopus egg extracts, centrosomes are not necessarily required for spindle assembly but can regulate the organization of microtubules into a bipolar array

HIV-1 Buds Predominantly at the Plasma Membrane of Primary Human Macrophages

HIV-1 assembly and release are believed to occur at the plasma membrane in most host cells with the exception of primary macrophages, for which exclusive budding at late endosomes has been reported. Here, we applied a novel ultrastructural approach to assess HIV-1 budding in primary macrophages in an immunomarker-independent manner. Infected macrophages were fed with BSA-gold and stained with the membrane-impermeant dye ruthenium red to identify endosomes and the plasma membrane, respectively. Virus-filled vacuolar structures with a seemingly intracellular localization displayed intense staining with ruthenium red, but lacked endocytosed BSA-gold, defining them as plasma membrane. Moreover, HIV budding profiles were virtually excluded from gold-filled endosomes while frequently being detected on ruthenium red–positive membranes. The composition of cellular marker proteins incorporated into HIV-1 supported a plasma membrane–derived origin of the viral envelope. Thus, contrary to current opinion, the plasma membrane is the primary site of HIV-1 budding also in infected macrophages

Three-dimensional architecture and biogenesis of membrane structures associated with hepatitis C virus replication

All positive strand RNA viruses are known to replicate their genomes in close association with intracellular membranes. In case of the hepatitis C virus (HCV), a member of the family Flaviviridae, infected cells contain accumulations of vesicles forming a membranous web (MW) that is thought to be the site of viral RNA replication. However, little is known about the biogenesis and three-dimensional structure of the MW. In this study we used a combination of immunofluorescence- and electron microscopy (EM)-based methods to analyze the membranous structures induced by HCV in infected cells. We found that the MW is derived primarily from the endoplasmic reticulum (ER) and contains markers of rough ER as well as markers of early and late endosomes, COP vesicles, mitochondria and lipid droplets (LDs). The main constituents of the MW are single and double membrane vesicles (DMVs). The latter predominate and the kinetic of their appearance correlates with kinetics of viral RNA replication. DMVs are induced primarily by NS5A whereas NS4B induces single membrane vesicles arguing that MW formation requires the concerted action of several HCV replicase proteins. Three-dimensional reconstructions identify DMVs as protrusions from the ER membrane into the cytosol, frequently connected to the ER membrane via a neck-like structure. In addition, late in infection multi-membrane vesicles become evident, presumably as a result of a stress-induced reaction. Thus, the morphology of the membranous rearrangements induced in HCV-infected cells resemble those of the unrelated picorna-, corona- and arteriviruses, but are clearly distinct from those of the closely related flaviviruses. These results reveal unexpected similarities between HCV and distantly related positive-strand RNA viruses presumably reflecting similarities in cellular pathways exploited by these viruses to establish their membranous replication factories

Fusion between Phagosomes, Early and Late Endosomes: A Role for Actin in Fusion between Late, but Not Early Endocytic Organelles

Actin is implicated in membrane fusion, but the precise mechanisms remain unclear. We showed earlier that membrane organelles catalyze the de novo assembly of F-actin that then facilitates the fusion between latex bead phagosomes and a mixture of early and late endocytic organelles. Here, we correlated the polymerization and organization of F-actin with phagosome and endocytic organelle fusion processes in vitro by using biochemistry and light and electron microscopy. When membrane organelles and cytosol were incubated at 37°C with ATP, cytosolic actin polymerized rapidly and became organized into bundles and networks adjacent to membrane organelles. By 30-min incubation, a gel-like state was formed with little further polymerization of actin thereafter. Also during this time, the bulk of in vitro fusion events occurred between phagosomes/endocytic organelles. The fusion between latex bead phagosomes and late endocytic organelles, or between late endocytic organelles themselves was facilitated by actin, but we failed to detect any effect of perturbing F-actin polymerization on early endosome fusion. Consistent with this, late endosomes, like phagosomes, could nucleate F-actin, whereas early endosomes could not. We propose that actin assembled by phagosomes or late endocytic organelles can provide tracks for fusion-partner organelles to move vectorially toward them, via membrane-bound myosins, to facilitate fusion

Prospective evaluation of quality of life effects in patients undergoing palliative radiotherapy for brain metastases

Background: Recently published results of quality of life (QoL) studies indicated different outcomes of palliative radiotherapy for brain metastases. This prospective multi-center QoL study of patients with brain metastases was designed to investigate which QoL domains improve or worsen after palliative radiotherapy and which might provide prognostic information. Methods: From 01/2007-01/2009, n=151 patients with previously untreated brain metastases were recruited at 14 centers in Germany and Austria. Most patients (82 %) received whole-brain radiotherapy. QoL was measured with the EORTC-QLQ-C15-PAL and brain module BN20 before the start of radiotherapy and after 3 months. Results: At 3 months, 88/142 (62 %) survived. Nine patients were not able to be followed up. 62 patients (70.5 % of 3-month survivors) completed the second set of questionnaires. Three months after the start of radiotherapy QoL deteriorated significantly in the areas of global QoL, physical function, fatigue, nausea, pain, appetite loss, hair loss, drowsiness, motor dysfunction, communication deficit and weakness of legs. Although the use of corticosteroid at 3 months could be reduced compared to pre-treatment (63 % vs. 37 %), the score for headaches remained stable. Initial QoL at the start of treatment was better in those alive than in those deceased at 3 months, significantly for physical function, motor dysfunction and the symptom scales fatigue, pain, appetite loss and weakness of legs. In a multivariate model, lower Karnofsky performance score, higher age and higher pain ratings before radiotherapy were prognostic of 3-month survival. Conclusions: Moderate deterioration in several QoL domains was predominantly observed three months after start of palliative radiotherapy for brain metastases. Future studies will need to address the individual subjective benefit or burden from such treatment. Baseline QoL scores before palliative radiotherapy for brain metastases may contain prognostic information

Characterization of Chromosomal Instability in Murine Colitis-Associated Colorectal Cancer

Patients suffering from ulcerative colitis (UC) bear an increased risk for colorectal cancer. Due to the sparsity of colitis-associated cancer (CAC) and the long duration between UC initiation and overt carcinoma, elucidating mechanisms of inflammation-associated carcinogenesis in the gut is particularly challenging. Adequate murine models are thus highly desirable. For human CACs a high frequency of chromosomal instability (CIN) reflected by aneuploidy could be shown, exceeding that of sporadic carcinomas. The aim of this study was to analyze mouse models of CAC with regard to CIN. Additionally, protein expression of p53, beta-catenin and Ki67 was measured to further characterize murine tumor development in comparison to UC-associated carcinogenesis in men.The AOM/DSS model (n = 23) and IL-10(-/-) mice (n = 8) were applied to monitor malignancy development via endoscopy and to analyze premalignant and malignant stages of CACs. CIN was assessed using DNA-image cytometry. Protein expression of p53, beta-catenin and Ki67 was evaluated by immunohistochemistry. The degree of inflammation was analyzed by histology and paralleled to local interferon-γ release.CIN was detected in 81.25% of all murine CACs induced by AOM/DSS, while all carcinomas that arose in IL-10(-/-) mice were chromosomally stable. Beta-catenin expression was strongly membranous in IL-10(-/-) mice, while 87.50% of AOM/DSS-induced tumors showed cytoplasmatic and/or nuclear translocation of beta-catenin. p53 expression was high in both models and Ki67 staining revealed higher proliferation of IL-10(-/-)-induced CACs.AOM/DSS-colitis, but not IL-10(-/-) mice, could provide a powerful murine model to mechanistically investigate CIN in colitis-associated carcinogenesis

The force of the sign. Terrorism as a symbolic phenomenon

Seit der radikalen Änderung der weltpolitischen Lage durch das Selbstmordattentat islamistischer Terroristen auf die Supermacht U.S.A. am 11.9.01 versucht die Weltöffentlichkeit, dem Phänomen des Terrorismus durch die verschiedensten Erklärungsstrategien Herr zu werden. Man führt den Kampf der Kulturen oder Religionen an, verweist auf die Ausbeutung der Peripherie des kapitalistischen Weltsystems durch den Hegemon U.S.A. oder pathologisiert bzw. dämonisiert die Taten der Terroristen. Uns scheinen diese Erklärungsstrategien den Machtkonstellationen der postmodernen Gesellschaften nicht gerecht zu werden, da sie ein zentrales soziales Phänomen der vergangenen Jahrzehnte nicht beachten: das Unbehagen an der pluralistischen Gesellschaft und der konsensuell-repräsentativen Demokratie. Um dieses Unbehagen angemessen beschreiben zu können, wollen wir uns ihm aus einer zeichentheoretischen Perspektive nähern, die soziale Formationen nicht durch (kooperative) Arbeit determiniert sieht, sondern durch die Instanz des Codes. Für Jean Baudrillard ist die Wahl des Ziels der beiden Türme bedeutend, die sich wechselseitig reflektieren und das System nach allen Seiten hin abschließen. Mit ihnen wurde das neuralgische Zentrum des Systems getroffen, das sich auf einem binären Code gründet. Die Twintowers bedeuteten nicht nur das Ende jedweder originalen Referenz, sondern auch den Abschluss des Bezeichneten durch die Wiederholung des Zeichens. Der Code führt eine symbolische Verteilung der gesellschaftlichen Körper durch und zielt auf eine möglichst genaue Übereinstimmung der Gemeinschaft mit sich selbst gemäß eines arithmetischen und geometrischen Kalküls. Die integrative Kraft dieses auf dem Identitätsprinzip basierenden Systems scheint immer häufiger nicht mehr in der Lage zu sein, das negative Potential antagonistischer Strategien binden zu können, die in Form von zivilem Ungehorsam, Politik von Minoritäten oder terroristischen Akten die symbolische Ordnung der westlichen Gesellschaften unterhöhlen. In diesem Tagungsband diskutieren wir das Ausmaß der Krise der konsensuellen Demokratie und ihrer Institutionen. Die Aufsätze behandeln folgende Themen: • Die Krise der pluralistischen Gesellschaft: Wie verständlich ist das kulturelle, politische und religiöse Unbehagen am westlichen Wertekanon? • Die Funktion der Medien in der konsensuellen Demokratie; die gesellschaftliche Wirkung der medialen Reproduktion terroristischer Akte; das Bild des Terrorismus in der Populärkultur • Ästhetischer Terror: Die Vernichtung von Sinn und Bedeutung in der zeitgenössischen Kunst und Kunsttheorie • Die politische Logik des Terrorismus (Ziele, Bedingungen u. Legitimität des Terrorismus in Abgrenzung zu alternativen politischen Ausdrucksformen wie z.B. dem zivilen Ungehorsam; die Bedeutung des terroristischen Opfertodes) • Geschichte des Terrorismus (speziell der Terrorismus der RAF) • Terror als irrationale Gewalt (der ontologische Status des Terrorismus)Since the radical changes in international politics caused by the suicide attacks on the USA by Islamic terrorists on the 11th of September in 2001, the world public tries to grasp the phenomenon of „Terrorism“ through different explanatory strategies. These include referring to the clash of cultures and of religions, to the exploitation of the periphery by the capitalist system incarnated by the USA, or pathologizing as well as demonizing the deeds of the terrorists. All these explanatory attempts do not seem to do justice to the actual constellations of power in postmodern societies, because they do not take a widespread social phenomenon of the past decades in consideration: the discomfort with the pluralistic society and with the concurrent-representative democracy. In order to describe this discomfort adequately we would like to approach the phenomenon from a semiotic perspective which does not consider social formations as determined by cooperative work but rather by the authority of the code. For Jean Baudrillard the target was meaningful since the two towers not only reflect each other but also completely close the system. With them the neuralgic center which is based upon the binary code was severely hit. The twin towers not only meant the end of every original reference but also the completion of the signified by the reduplication of the sign. The code conducts a symbolic distribution of the social bodies and aims at an as accurate as possible identification of the community with itself corresponding to an arithmetic and geometric calculus. The system which is based upon the principle of identity does not seem to have the ability to integrate antagonist energies properly. So these antagonist powers undermine the symbolic order of western societies in terms of civil disobedience, politics of minorities or terroristic acts. In this conference transcript we discuss the degree of crisis of consensual democracy and ist institutions. The essays cover the following topics: • The crisis of the pluralistic society: How comprehensible and justified is the cultural, political, and religious discomfort with western values? • The function of mass media in democratic systems: What is the impact of the reproduction of terrorist acts on society? How does popular culture deal with terrorism? • Aesthetic terror: the destruction of sense and meaning in contemporary arts and art theory • The political logic of terrorism (aims, legitimacy of terrorism as opposed to other forms of opposition like civil disobedience; the meaning of the terrorist self-sacrifice death) • History of terrorism (e.g. The German terrorism of the RAF) • Terrorism as an irrational power (ontological status of terrorism

Cryo Electron Tomography of Native HIV-1 Budding Sites

The structure of immature and mature HIV-1 particles has been analyzed in detail by cryo electron microscopy, while no such studies have been reported for cellular HIV-1 budding sites. Here, we established a system for studying HIV-1 virus-like particle assembly and release by cryo electron tomography of intact human cells. The lattice of the structural Gag protein in budding sites was indistinguishable from that of the released immature virion, suggesting that its organization is determined at the assembly site without major subsequent rearrangements. Besides the immature lattice, a previously not described Gag lattice was detected in some budding sites and released particles; this lattice was found at high frequencies in a subset of infected T-cells. It displays the same hexagonal symmetry and spacing in the MA-CA layer as the immature lattice, but lacks density corresponding to NC-RNA-p6. Buds and released particles carrying this lattice consistently lacked the viral ribonucleoprotein complex, suggesting that they correspond to aberrant products due to premature proteolytic activation. We hypothesize that cellular and/or viral factors normally control the onset of proteolytic maturation during assembly and release, and that this control has been lost in a subset of infected T-cells leading to formation of aberrant particles