557 research outputs found
Rapid kinetics of agonist binding and permeability response analyzed in parallel on acetylcholine receptor rich membranes from Torpedo marmorata
No full textHeidmann T, Bernhardt J, Neumann E, Changeux JP. Rapid kinetics of agonist binding and permeability response analyzed in parallel on acetylcholine receptor rich membranes from Torpedo marmorata. Biochemistry. 1983;22(23):5452-5459
Applied and fundamental aspects of BABY BOOM-mediated regeneration
No full textKeywords: Somatic embryogenesis, Transcription factor, AINTEGUMENTA-LIKE, BABY BOOM, BBM, Sweet Pepper Transformation Title: Applied and Fundamental Aspects of BBM-mediated Regeneration Author: Iris Heidmann Catergories: Plant regeneration, Plant transformation, transcription factor, somatic embryogenesis Plant regeneration from tissues or single cells is essential for plant propagation. Efficient regeneration can be archieved through somatic embryogenesis using the plant growth regulator auxin or overexpression of specific transcription factors, but the underlying mechanisms are poorly understood. The potency of the BABY BOOM (BBM) AINTEGUMENTA-LIKE transcription factor to induce somatic embryogenesis in crop (sweet pepper) and model species (tobacco) was investigated. It was found that the introduction of BBM into sweet pepper, which is recalcitrant for transformation, enhanced the regeneration of transgenic plants. Exogenous cytokinin was necessary to induce somatic embryogenesis in both tobacco and sweet pepper. The mechanism underlying BBM-mediated somatic embryogenesis was studied in Arabidopsis by identifying BBM target genes (ChIPSeq). Genes controlling zygotic embryo identity and maturation (LAFL), as well as auxin biosynthesis (TAA1, YUCCA) and transport (PIN) are BBM targets. Mutant analysis and chemical inhibition studies showed that these genes play positive roles in BBM-induced somatic embryogenesis. </p
Vaccination directed against the human endogenous retrovirus-K envelope protein inhibits tumor growth in a murine model system
No full textHuman endogenous retrovirus (HERV) genomes are chromosomally integrated in all cells of an individual. They are normally transcriptionally silenced and transmitted only vertically. Enhanced expression of HERV-K accompanied by the emergence of anti-HERV-K-directed immune responses has been observed in tumor patients and HIV-infected individuals. As HERV-K is usually not expressed and immunological tolerance development is unlikely, it is an appropriate target for the development of immunotherapies. We generated a recombinant vaccinia virus (MVA-HKenv) expressing the HERV-K envelope glycoprotein (ENV), based on the modified vaccinia virus Ankara (MVA), and established an animal model to test its vaccination efficacy. Murine renal carcinoma cells (Renca) were genetically altered to express E. coli beta-galactosidase (RLZ cells) or the HERV-K ENV gene (RLZ-HKenv cells). Intravenous injection of RLZ-HKenv cells into syngenic BALB/c mice led to the formation of pulmonary metastases, which were detectable by X-gal staining. A single vaccination of tumor-bearing mice with MVA-HKenv drastically reduced the number of pulmonary RLZ-HKenv tumor nodules compared to vaccination with wild-type MVA. Prophylactic vaccination of mice with MVA-HKenv precluded the formation of RLZ-HKenv tumor nodules, whereas wild-type MVA-vaccinated animals succumbed to metastasis. Protection from tumor formation correlated with enhanced HERV-K ENV-specific killing activity of splenocytes. These data demonstrate for the first time that HERV-K ENV is a useful target for vaccine development and might offer new treatment opportunities for diverse types of cancer
A Preliminary Numerical Study on the Effect of High Freestream Turbulence on Anti-Vortex Film Cooling Design at High Blowing Ratio
No full textResearchers at NASA Glenn Research Center have developed and investigated a novel film cooling design, the anti-vortex hole (AVH), which has been shown to cancel or counter the vorticity generated by conventional holes and increase film effectiveness at high blowing ratios and low turbulence levels. This paper presents preliminary CFD results on the film effectiveness and net heat flux reduction at high blowing ratio and elevated freestream turbulence levels for the adjacent AVH. Baseline cases at low turbulence levels of 5% intensity and length scale of Λx/dm = 1 with a nominal blowing ratio of 2 and a density ratios of 1 and 2 were compared to previous results reported by Heidmann [1]. Higher freestream turbulence cases were investigated with a turbulence intensity and length scale of 10% and Λx/dm = 1 and 3, respectively. Results showed that higher freestream turbulence improves adiabatic effectiveness for the AVH design.</jats:p
Optomechanical coupling between ultracold atoms and a membrane oscillator
No full textIn this thesis, I report on the realization of a hybrid optomechanical system in which ultracold atoms are coupled to a micromechanical membrane. The atoms are trapped in the intensity maxima of an optical standing wave formed by retroreflection of a laser beam from the membrane surface. Vibrations of the membrane displace the standing wave, thus coupling to the center-of-mass motion of the atomic ensemble. Conversely, atoms imprint their motion onto the laser light, thereby modulating the radiation pressure force on the membrane. In this way, the laser light mediates a long-distance, coherent coupling between the two systems.
When the trap frequency of the atoms is matched to the membrane frequency, we observe resonant energy transfer. In addition, by applying simultaneous laser cooling to the atoms, we can dissipate energy from the coupled system leading to sympathetic cooling of the membrane mode. The experimental data follows the theoretical estimations that predict the coupling to scale with the number of trapped atoms. Furthermore, by including the finite temperature of the atoms and their spatially inhomogeneous trapping potential in the theoretical model of the optomechanical coupling, we can accurately describe the width and shape of the resonance.
In an improved experimental setup, the membrane is enclosed in a cavity while the atoms are trapped in the standing wave lattice outside the cavity. The presence of the cavity results in a considerable enhancement of the coupling strength in proportion to the cavity finesse. So far we have observed sympathetic cooling of the membrane mode by a factor of 32 starting from room temperature. Theoretical estimates show that in such a setup ground-state cooling of the membrane mode should be possible, allowing one to access the quantum coherent coupling regime
Observation of a kilogram-scale oscillator near its quantum ground state
No full textWe introduce a novel cooling technique capable of approaching the quantum ground state of a kilogram-scale system—an interferometric gravitational wave detector. The detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO) operate within a factor of 10 of the standard quantum limit (SQL), providing a displacement sensitivity of 10<sup>−18</sup> m in a 100 Hz band centered on 150 Hz. With a new feedback strategy, we dynamically shift the resonant frequency of a 2.7 kg pendulum mode to lie within this optimal band, where its effective temperature falls as low as 1.4 μK, and its occupation number reaches about 200 quanta. This work shows how the exquisite sensitivity necessary to detect gravitational waves can be made available to probe the validity of quantum mechanics on an enormous mass scale
Molecular virology of a functionnal human endogenous retrovirus
No full textEnviron 8% du génome humain est constitué de rétrovirus endogènes (HERV). La famille de bétarétrovirus HERV-K(HML2), l'une des plus actives chez l'homme, est entrée il y a 45 millions d'années dans le génome des primates et s'est amplifiée efficacement depuis, et ce malgré l'existence de nombreuses protéines cellulaires, appelées facteurs de restriction, qui s'opposent à la réplication du virus dans la cellule hôte. La Tetherin/BST2, l'un d'entre eux, est une protéine membranaire capable de bloquer le relargage des virions dans le milieu extracellulaire et est active sur la plupart des virus enveloppés testés jusqu'à présent, en particulier HERV-K(HML2). Nous avons tout d'abord mis en évidence que l'enveloppe (Env) de la famille HML2 est un antagoniste de la Tetherin, propriété qui a pu contribuer au succès de l'amplification de la famille HERV¬K(HML2) dans les génomes. Plusieurs domaines de l'enveloppe coopèrent pour s'opposer à l'action du facteur de restriction : la SU (domaine d'interaction), ainsi que la partie transmembranaire, alors que la queue cytoplasmique n'est pas indispensable. Le mécanisme de cette inhibition n'a pas été encore complètement élucidé, mais l'on sait, comme pour la glycoprotéine d'Ebola, que l'Env HERV-K(HML2) n'induit ni relocalisation, ni dégradation de la Tetherin. Etant donné le grand polymorphisme insertionnel de la famille HERV-K(1-IML2), il est très probable que cette activité anti-Tetherin endogène soit variable entre les individus, ce qui pourrait avoir des conséquences dans les pathologies où les éléments HERV-K(HML2) sont spécifiquement induits. Parmi ces pathologies, les cancers de la peau, du sein et de la lignée germinale présentent une association particulièrement forte avec l'expression de l'Env HERV-K(HML2), que nous avons voulu mieux comprendre dans la suite de ces travaux de thèse. Nous avons dans un premier temps montré que l'expression de l'Env dans des cellules humaines non transformées de l'épithélium de sein (MCF10A), induit la transition vers un phénotype mésenchymateux (EMT, transition épithélio-mésenchymateuse), caractéristique de l'apparition de métastases dans les cancers. Cette transition est associée à une augmentation de la mobilité des cellules (mise en évidence dans des tests Transwell), à un changement de morphologie des cellules et à une modification du profil d'expression de quelques marqueurs moléculaires caractéristiques (E-cadherin, N-cadherin, vimentin, fibronectin). Grâce à une étude transcriptomique en cellules 293T, nous avons mis en évidence que l'expression de l'Env HERV-K induit fortement plusieurs facteurs de transcription : ETV4, ETVS, ainsi que EGR1, qui ont été identifiés comme des marqueurs du processus de tumorigénèse dans différents modèles. Nous avons également montré que l'Env HERV-K active la voie des MAP kinases via ERK 1/2 —dérégulée dans un grand nombre de cancers- en amont de la kinase Raf. Ces phénomènes d'induction de la transduction de signal requièrent la présence de la queue cytoplasmique de l'enveloppe. De façon remarquable, seule l'enveloppe du bétarétrovirus de mouton JSRV, oncogénique in vivo, est capable d'activer les mêmes voies de signalisation, ce qui renforce l'hypothèse d'une implication de l'Env HERV-K(HML2) dans la tumorigenèse.Human endogenous retroviruses (HERV) represent about 8% of our genomic content. HERV-K(HML2) betaretroviral family is one of the most active in humans. Although it entered 45 million years ago in the primate genomes, its members have amplified quite recently despite the existence of restriction factors, which are host proteins blocking viral replication in cells. Tetherin/BST2 is one of them and acts by keeping the viral particles attached to the cell surface. It targets most enveloped viruses tested so far including HERV-K(HML2). We show that the envelope protein (Env) of HML2 family is an antagonist of Tetherin retriction, property that probably helped the endogenous retrovirus to efficiently amplify in the genomes. We mapped several domains required for antagonism : the surface subunit of Env (SU), which interacts with Tetherin, and the transmembrane. We also show that the cytoplasmic tail is dispensable for counteraction. Similar to Ebola glycoprotein, HERV-K(HML2) Env does not mediate Tetherin degradation or cell surface removal; therefore, it uses a yet-undescribed mechanism to inactivate the restriction factor. Due to their recent amplification, HERV-K(HML2) elements are extremely polymorphic in the human population, and it is likely that individuals will not all possess the same anti-Tetherin potential. This could have functional consequences in pathologies where HERV-K(HML2) is specifically induced. Among them, melanomas, breast cancers and germ line tumors display a strong association with HML2 Env expression, that we wanted to better analyse. We first show that Env expression in a model of epithelial human breast cancer cells induces the so-called EMT (epithelial mesenchymal transition), critical for cancer progression and the process of metastasis. This includes enhanced migratory capacities (shown by transwell assays), changes in cell morphology and characteristic modifications in a set of molecular markers (e.g. E-cadherin, N-cadherin, vimentin, fibronectin). Microarray experiments performed in 293T cells revealed that HERV-K(HML2) Env is a strong inducer of several transcription factors, namely ETV4, ETVS and EGRI, which have been associated with cellular transformation. Importantly, we also show that HERV-K(HML2) Env activates the MAP kinase pathway via ERK 1/2, key player in numerous cancers. This induction occurs upstream of the kinase Raf and involves the cytoplasmic tail of HERV-K(HML2) Env. In addition, this phenomenon is very specific, being absent with every other Env tested, except for JSRV Env which is already known to have transforming properties in vivo
Restriction by APOBEC3 proteins of endogenous retroviruses with an extracellular life cycle: <it>ex vivo </it>effects and <it>in vivo </it>"traces" on the murine IAPE and human HERV-K elements
No full textAbstract Background APOBEC3 cytosine deaminases have been demonstrated to restrict infectivity of a series of retroviruses, with different efficiencies depending on the retrovirus. In addition, APOBEC3 proteins can severely restrict the intracellular transposition of a series of retroelements with a strictly intracellular life cycle, including the murine IAP and MusD LTR-retrotransposons. Results Here we show that the IAPE element, which is the infectious progenitor of the strictly intracellular IAP elements, and the infectious human endogenous retrovirus HERV-K are restricted by both murine and human APOBEC3 proteins in an ex vivo assay for infectivity, with evidence in most cases of strand-specific G-to-A editing of the proviruses, with the expected signatures. In silico analysis of the naturally occurring genomic copies of the corresponding endogenous elements performed on the mouse and human genomes discloses "traces" of APOBEC3-editing, with the specific signature of the murine APOBEC3 and human APOBEC3G enzymes, respectively, and to a variable extent depending on the family member. Conclusion These results indicate that the IAPE and HERV-K elements, which can only replicate via an extracellular infection cycle, have been restricted at the time of their entry, amplification and integration into their target host genomes by definite APOBEC3 proteins, most probably acting in evolution to limit the mutagenic effect of these endogenized extracellular parasites.</p
cber richtungsbewegungen, hervorgerufen durch Verletzungen und Assimilationshemmung
No full textVolume: 122Start Page: 1227End Page: 125
Cytochrome oxidase subunit VI of Trypanosoma brucei is imported without a cleaved presequence and is developmentally regulated at both RNA and protein levels
No full textMitochondrial respiration in the African trypanosome undergoes dramatic developmental stage regulation. This requires co-ordinated control of components encoded by both the nuclear genome and the kinetoplast, the unusual mitochondrial genome of these parasites. As a model for understanding the co-ordination of these genomes, we have examined the regulation and mitochondrial import of a nuclear-encoded component of the cytochrome oxidase complex, cytochrome oxidase subunit VI (COXVI). By generating transgenic trypanosomes expressing intact or mutant forms of this protein, we demonstrate that COXVI is not imported using a conventional cleaved presequence and show that sequences at the N-terminus of the protein are necessary for correct mitochondrial sorting. Analyses of endogenous and transgenic COXVI mRNA and protein expression in parasites undergoing developmental stage differentiation demonstrates a temporal order of control involving regulation in the abundance of, first, mRNA and then protein. This represents the first dissection of the regulation and import of a nuclear-encoded protein into the cytochrome oxidase complex in these organisms, which were among the earliest eukaryotes to possess a mitochondrion
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