602 research outputs found
Phosphorylated MARCKS: A novel centrosome component that also defines a peripheral subdomain of the cortical actin cap in mouse eggs
AbstractMARCKS (myristoylated alanine-rich C-kinase substrate) is a major substrate for protein kinase C (PKC), a kinase that has multiple functions during oocyte maturation and egg activation, for example, spindle function and cytoskeleton reorganization. We examined temporal and spatial changes in p-MARCKS localization during maturation of mouse oocytes and found that p-MARCKS is a novel centrosome component based its co-localization with pericentrin and γ-tubulin within microtubule organizing centers (MTOCs). Like pericentrin, p-MARCKS staining at the MI spindle poles was asymmetric. Based on this asymmetry, we found that one end of the spindle was preferentially extruded with the first polar body. At MII, however, the spindle poles had symmetrical p-MARCKS staining. p-MARCKS also was enriched in the periphery of the actin cap overlying the MI or MII spindle to form a ring-shaped subdomain. Because phosphorylation of MARCKS modulates its actin crosslinking function, this localization suggests p-MARCKS functions as part of the contractile apparatus during polar body emission. Our finding that an activator of conventional and novel PKC isoforms did not increase the amount of p-MARCKS suggested that an atypical isoform was responsible for MARCKS phosphorylation. Consistent with this idea, immunostaining revealed that the staining patterns of p-MARCKS and the active form of the atypical PKC ζ/λ isoform(s) were very similar. These results show that p-MARCKS is a novel centrosome component and also defines a previously unrecognized subdomain of the actin cap overlying the spindle
Indirect ultraviolet photodesorption from CO:N2 binary ices - an efficient grain-gas process
UV ice photodesorption is an important non-thermal desorption pathway in many
interstellar environments that has been invoked to explain observations of cold
molecules in disks, clouds and cloud cores. Systematic laboratory studies of
the photodesorption rates, between 7 and 14 eV, from CO:N2 binary ices, have
been performed at the DESIRS vacuum UV beamline of the synchrotron facility
SOLEIL. The photodesorption spectral analysis demonstrates that the
photodesorption process is indirect, i.e. the desorption is induced by a photon
absorption in sub-surface molecular layers, while only surface molecules are
actually desorbing. The photodesorption spectra of CO and N2 in binary ices
therefore depend on the absorption spectra of the dominant species in the
subsurface ice layer, which implies that the photodesorption efficiency and
energy dependence are dramatically different for mixed and layered ices
compared to pure ices. In particular, a thin (1-2 ML) N2 ice layer on top of CO
will effectively quench CO photodesorption, while enhancing N2 photodesorption
by a factors of a few (compared to the pure ices) when the ice is exposed to a
typical dark cloud UV field, which may help to explain the different
distributions of CO and N2H+ in molecular cloud cores. This indirect
photodesorption mechanism may also explain observations of small amounts of
complex organics in cold interstellar environments.Comment: 21 pages 5 figure
La pensée de Raymond Aron: essais et interpretations
Raymond Aron fut un homme de grand savoir, qui perfectionnait sans cesse sa maĂźtrise des sciences sociales, en ajoutant Ă la sociologie, Ă lâĂ©conomie et Ă la stratĂ©gie, la science et la philosophie politiques. Tandis quâil prenait plaisir Ă analyser les subtilitĂ©s thĂ©oriques de ces sciences, Ă dĂ©terminer leurs relations et leurs limites respectives, contribuant ainsi Ă instruire et Ă©clairer les publics variĂ©s de ses lecteurs et auditeurs, il ne perdait jamais de vue leur portĂ©e pratique et politique. Il fut cet oiseau rare, un homme thĂ©orique qui prenait trĂšs au sĂ©rieux le domaine de lâaction. Dâun cĂŽtĂ©, il ne se lassait pas dâinterroger les limites de la connaissance historique, ou la relation entre lâĂ©conomie et la politique, ou la possibilitĂ© dâune science des relations internationales ; de lâautre cĂŽtĂ©, non sans anxiĂ©tĂ©, il ne cessait de poser la question pratique par excellence : « que faire ? » Le but de sa plus profonde ambition Ă©tait dâĂ©laborer ce quâil appelait une « praxĂ©ologie », soit une thĂ©orie de lâaction, dont la thĂ©orie de la guerre de Clausewitz fournissait Ă la fois lâesquisse et le modĂšle. En des termes plus traditionnels, nous dirons que lâoeuvre multiforme dâAron reprĂ©sente un des plus grands efforts conduits au XXe siĂšcle pour Ă©laborer une philosophie politique pratique.info:eu-repo/semantics/publishedVersio
LES DETERMINANTS MECANIQUES ET NEUROPHYSIOLOGIQUES DE LA PERFORMANCE EN TIR A LâARC : INCIDENCES SUR LâENTRAINEMENT
International audienceLâobjectif de ce travail est de caractĂ©riser les stratĂ©gies musculaires intervenant dans le tir Ă lâarc, mais Ă©galement de dĂ©terminer leur Ă©volution au dĂ©cours de la fatigue. Ainsi lâinfluencede lâapparition dâun phĂ©nomĂšne de fatigue neuro-musculaire sur la performance en tir Ă lâarcpourra ĂȘtre dĂ©terminĂ©e. Une programmation spĂ©cifique de renforcement musculaire pourraalors ĂȘtre Ă©tablie dans le double objectif dâamĂ©liorer la performance, mais Ă©galement derĂ©duire les risques de pathologie de lâĂ©paule
Link between laboratory and astrophysical radiative shocks
This work provides analytical solutions describing the post-shock structure
of radiative shocks growing in astrophysics and in laboratory. The equations
including a cooling function are solved for any values of the exponents , and
. This modeling is appropriate to astrophysics as the observed
radiative shocks arise in optically thin media. In contrast, in laboratory,
radiative shocks performed using high-power lasers present a radiative
precursor because the plasma is more or less optically thick. We study the
post-shock region in the laboratory case and compare with astrophysical shock
structure. In addition, we attempt to use the same equations to describe the
radiative precursor, but the cooling function is slightly modified. In future
experiments we will probe the PSR using X-ray diagnostics. These new
experimental results will allow to validate our astrophysical numerical codes
Wavelength-Dependent UV Photodesorption of Pure and Ices
Context: Ultraviolet photodesorption of molecules from icy interstellar grains can explain observations of cold gas in regions where thermal desorption is negligible. This non-thermal desorption mechanism should be especially important where UV fluxes are high. Aims: and are expected to play key roles in astrochemical reaction networks, both in the solid state and in the gas phase. Measurements of the wavelength-dependent photodesorption rates of these two infrared-inactive molecules provide astronomical and physical-chemical insights into the conditions required for their photodesorption.
Methods: Tunable radiation from the DESIRS beamline at the SOLEIL synchrotron in the astrophysically relevant 7 to 13.6 eV range is used to irradiate pure and thin ice films. Photodesorption of molecules is monitored through quadrupole mass spectrometry. Absolute rates are calculated by using the well-calibrated CO photodesorption rates. Strategic and isotopolog mixtures are used to investigate the importance of dissociation upon irradiation. Results: photodesorption mainly occurs through excitation of the state and subsequent desorption of surface molecules. The observed vibronic structure in the photodesorption spectrum, together with the absence of formation, supports that the photodesorption mechanism of is similar to CO, i.e., an indirect DIET (Desorption Induced by Electronic Transition) process without dissociation of the desorbing molecule. In contrast, photodesorption in the 7â13.6 eV range occurs through dissociation and presents no vibrational structure. Conclusions: Photodesorption rates of and integrated over the far-UV field from various star-forming environments are lower than for CO. Rates vary between and photodesorbed molecules per incoming photon.Astronom
X-ray photodesorption of complex organic molecules in protoplanetary disks -- I. Acetonitrile CH3CN
X-rays emitted from pre-main-sequence stars at the center of protoplanetary
disks can induce nonthermal desorption from interstellar ices populating the
cold regions. This X-ray photodesorption needs to be quantified for complex
organic molecules (COMs), including acetonitrile CH3CN, which has been detected
in several disks. We experimentally estimate the X-ray photodesorption yields
of neutral species from pure CH3CN ices and from interstellar ice analogs for
which CH3CN is mixed either in a CO- or H2O-dominated ice. The ices were
irradiated at 15 K by soft X-rays (400-600 eV) from synchrotron light (SOLEIL
synchrotron). X-ray photodesorption was probed in the gas phase via quadrupole
mass spectrometry. X-ray photodesorption yields were derived from the mass
signals and were extrapolated to higher X-ray energies for astrochemical
models. X-ray photodesorption of the intact CH3CN is detected from pure CH3CN
ices and from mixed 13CO:CH3CN ices, with a yield of about 5x10^(-4)
molecules/photon at 560 eV. When mixed in H2O-dominated ices, X-ray
photodesorption of the intact CH3CN at 560 eV is below its detection limit,
which is 10^(-4) molecules/photon. Yields associated with the desorption of
HCN, CH4 , and CH3 are also provided. The derived astrophysical yields
significantly depend on the local conditions expected in protoplanetary disks.
They vary from 10^(-4) to 10(-6) molecules/photon for the X-ray photodesorption
of intact CH3CN from CO-dominated ices. Only upper limits varying from
5x10^(-5) to 5x10^(-7) molecules/photon could be derived for the X-ray
photodesorption of intact CH3CN from H2O-dominated ices. X-ray photodesorption
of intact CH3CN from interstellar ices might in part explain the abundances of
CH3CN observed in protoplanetary disks. The desorption efficiency is expected
to vary with the local physical conditions, hence with the disk region
The dorsoventral regulatory gene cassette spÀtzle/Toll/cactus controls the potent antifungal response in Drosophila adults
The cytokine-induced activation cascade of NF-kappaB in mammals and the activation of the morphogen dorsal in Drosophila embryos show striking structural and functional similarities (Toll/IL-1, Cactus/I-kappaB, and dorsal/NF-kappaB). Here we demonstrate that these parallels extend to the immune response of Drosophila. In particular, the intracellular components of the dorsoventral signaling pathway (except for dorsal) and the extracellular Toll ligand, spÀtzle, control expression of the antifungal peptide gene drosomycin in adults. We also show that mutations in the Toll signaling pathway dramatically reduce survival after fungal infection. Antibacterial genes are induced either by a distinct pathway involving the immune deficiency gene (imd) or by combined activation of both imd and dorsoventral pathways
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