Differential expression and sex chromosome association of CHD3/4 and CHD5 during spermatogenesis

ATP-dependent nucleosome remodelers of the CHD family play important roles in chromatin regulation during development and differentiation. The ubiquitously expressed CHD3 and CHD4 proteins are essential for stem cell function and serve to orchestrate gene expression in different developmental settings. By contrast, the closely related CHD5 is predominantly expressed in neural tissue and its role is believed to be restricted to neural differentiation. Indeed, loss of CHD5 contributes to neuroblastoma. In this study, we first demonstrate that CHD5 is a nucleosome-stimulated ATPase. We then compare CHD3/4 and CHD5 expression in mouse brain and show that CHD5 expression is restricted to a subset of cortical and hippocampal neurons whereas CHD3/4 expression is more widespread. We also uncover high levels of CHD5 expression in testis. CHD5 is transiently expressed in differentiating germ cells. Expression is first detected in nuclei of postmeiotic round spermatids, reaches a maximum in stage VIII spermatids and then falls to undetectable levels in stage IX spermatids. Surprisingly, CHD3/4 and CHD5 show complementary expression patterns during spermatogenesis with CHD3/ 4 levels progressively decreasing as CHD5 expression increases. In spermatocytes, CHD3/4 localizes to the pseudoautosomal region, the X centromeric region and then spreads into the XY body chromatin. In postmeiotic cells, CHD5 colocalises with macroH2A1.2 in association with centromeres and part of the Y chromosome. The subnuclear localisations of CHD4 and CHD5 suggest specif

Statistical anisotropy of magnetohydrodynamic turbulence

Direct numerical simulations of decaying and forced magnetohydrodynamic (MHD) turbulence without and with mean magnetic field are analyzed by higher-order two-point statistics. The turbulence exhibits statistical anisotropy with respect to the direction of the local magnetic field even in the case of global isotropy. A mean magnetic field reduces the parallel-field dynamics while in the perpendicular direction a gradual transition towards two-dimensional MHD turbulence is observed with $k^{-3/2}$ inertial-range scaling of the perpendicular energy spectrum. An intermittency model based on the Log-Poisson approach, $\zeta_p=p/g^2 +1 -(1/g)^{p/g}$, is able to describe the observed structure function scalings.Comment: 4 pages, 3 figures. To appear in Phys.Rev.

Identification et caractérisation fonctionnelle de gènes impliqués dans l'induction et la régulation de la réaction hypersensible et la résistance locale acquise chez la tabac

La réaction d hypersensibilité (HR) est l un des mécanismes de défense les plus efficaces dont dispose la plante pour lutter contre l attaque par des agents pathogènes. Phénotypiquement, la HR correspond à la mort programmée des cellules percevant l infection. Dans les cellules adjacentes, on observe une forte induction de réponses de défense. Cette zone correspond à la part vivante de la HR, que nous appelons résistance locale acquise ou LAR en références aux travaux de Ross au début des années 1960. HR et LAR participent ensembles au confinement de l infection au site d attaque. Alors que la HR est induite par des signaux exogènes issus de l agent pathogène, la LAR est induite par des signaux endogènes libérés par les cellules en état de HR. Ainsi, les gènes inducteurs du phénomène LAR, dont aucun n était connu, présentent un patron d expression spécifique de la HR. Le premier objectif de ma thèse a été de mettre en œuvre une stratégie permettant de selectionner des gènes potentiellement impliqués dans l induction du phénomène LAR. Un criblage par Differential Display Reverse Transcript Polymerase Chain Reaction a permis de sélectionner 24 ESTs (expressed sequence tag), parmi 5000 à 10000 transcripts analysés, présentant une expression spécifique au cours de la HR induite par infiltration d élicitine dans les feuilles de tabac. Le deuxième objectif de ma thèse a été de mettre en œuvre une analyse fonctionnelle de gain et de perte de fonction pour tester le rôle potentiel dans la mise en place du phénomène LAR de trois gènes parmi les vingt quatre issus du crible. J ai pu montrer que, parmi les 3 gènes, l extinction par Virus-Induced Gene Silencing du gène NtRING1, codant une E3 ligase putative à domaine RING, retarde la mise en place de la HR et l induction de gènes de défense. Parmi les cinq gènes issus du crible et analysés fonctionnellement jusqu à présent, NtRING1 et NtLRP1 semblent impliqués dans l exécution de la HR.The hypersensitive response (HR) is one of the most efficient plant defense mechanisms against pathogens. Phenotypically, the HR corresponds to the lesions developing at the infection sites. In the narrow zone surrounding the cells undergoing the HR cell death, a strong activation of defense responses occurs contributing to a local, highly inhospitable environment for the invading pathogen. This latter phenomenon was called localized acquired resistance (LAR). It corresponds to the living component of the HR. Whereas the HR is induced by exogenous signals issuing from the pathogen, LAR is triggerred by endogenous signals issuing from the plant cells undergoing the HR. Consequently, the genes inducing LAR, whose none are known yet, should be characterized by a HR-specific expression profile. The first part of this work consisted in the set-up of a strategy aimed to isolated such latter genes. A screening by Differential Display Reverse Transcript Polymerase Chain Reaction allowed to isolate 24 ESTs (expressed sequence tag) with such an expression profile. A second part of the work consisted in the functional characterization, by loss- and gain-of-function experiements, of 3 genes issuing from that screen. Among the three genes, silencing by Virus-Induced Gene Silencing of NtRING1, encoding a putative E3 ligase with a RING-finger motive delays the HR in tobacco induced by ß-megaspemin, a well as the expression of different defense-related genes. Among the 5 genes issuing from the screen and so far analyzed at the fonctional level, NtRING1 and NtLRP1 appeared involved in the execution of the HR.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Search for multimessenger sources of gravitational waves and high-energy neutrinos with Advanced LIGO during its first observing run, ANTARES, and IceCube

Astrophysical sources of gravitational waves, such as binary neutron star and black hole mergers or core-collapse supernovae, can drive relativistic outflows, giving rise to non-thermal high-energy emission. High-energy neutrinos are signatures of such outflows. The detection of gravitational waves and high-energy neutrinos from common sources could help establish the connection between the dynamics of the progenitor and the properties of the outflow. We searched for associated emission of gravitational waves and high-energy neutrinos from astrophysical transients with minimal assumptions using data from Advanced LIGO from its first observing run O1, and data from the Antares and IceCube neutrino observatories from the same time period. We focused on candidate events whose astrophysical origins could not be determined from a single messenger. We found no significant coincident candidate, which we used to constrain the rate density of astrophysical sources dependent on their gravitational-wave and neutrino emission processes

Multi-messenger Observations of a Binary Neutron Star Merger

International audienceOn 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta