Synthetic heterochromatin bypasses RNAi and centromeric repeats to establish functional centromeres

In the central domain of fission yeast centromeres, the kinetochore is assembled on CENP-A cnp1 nucleosomes. Normally, small interfering RNAs generated from flanking outer repeat transcripts direct histone H3 lysine 9 methyltransferase Clr4 to homologous loci to form heterochromatin. Outer repeats, RNA interference (RNAi), and centromeric heterochromatin are required to establish CENP-A Cnpl chromatin. We demonstrated that tethering Clr4 via DNA-binding sites at euchromatic loci induces heterochromatin assembly, with or without active RNAi. This synthetic heterochromatin completely substitutes for outer repeats on plasmid-based minichromosomes, promoting de novo CENP-A Cnpl and kinetochore assembly, to allow their mitotic segregation, even with RNAi inactive. Thus, the role of outer repeats in centromere establishment is simply the provision of RNAi substrates to direct heterochromatin formation; H3K9 methylation-dependent heterochromatin is alone sufficient to form functional centromeres.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Solar-like oscillations in the G8 V star tau Ceti

We used HARPS to measure oscillations in the low-mass star tau Cet. Although the data were compromised by instrumental noise, we have been able to extract the main features of the oscillations. We found tau Cet to oscillate with an amplitude that is about half that of the Sun, and with a mode lifetime that is slightly shorter than solar. The large frequency separation is 169 muHz, and we have identified modes with degrees 0, 1, 2, and 3. We used the frequencies to estimate the mean density of the star to an accuracy of 0.45% which, combined with the interferometric radius, gives a mass of 0.783 +/- 0.012 M_sun (1.6%).Comment: accepted for publication in A&

Executive functioning in preschool children affected by autism spectrum disorder: A pilot study

Introduction: Autism spectrum disorders (ASD) are a complex set of neurological dysfunction and development characterized by deficits in social and non-verbal interaction. Few studies have explored the executive functioning in ASD preschoolers. The aim of this pilot study is the assessment of executive functioning in preschool children with ASD. Material and methods: 8 ASD children (7 males, 1 female) mean age 3.09 (SD \ub1 0.83 years) were enrolled in the study and compared with a control group of 15 typically developing children (12 males, 3 females) (mean age 24.3 \ub1 0.61). All subjects underwent assessment of executive functioning with the BRIEF-P test. Results: The two groups were matched for age (p = 0.625) and gender (p = 0.900). Table 1 shows the comparison between the two groups at the BRIEF-P, with significantly higher scores on all subscales of ASD children compared with controls. Conclusions: Despite the small sample examined the results of this study agree with what is already known in the literature confirm the presence of a significant deficit in executive functions of subjects with ASD emphasizing for the first time the emergence of such problems at an early stage of development, but demanding further studies to confirm this

Monoclonal anti-CD18 antibody prevents transcellular biosynthesis of cysteinyl leukotrienes in vitro and in vivo and protects against leukotriene-dependent increase in coronary vascular resistance and myocardial stiffness

Background - Cysteinyl leukotrienes (cys-LT) can constrict small and large vessels and increase vascular permeability. Formation of cys-LT arising from polymorphonuclear leukocytes (PMNL) and endothelial cell cooperation (transcellular synthesis) led to the hypothesis that PMNL-endothelial cell adhesion may represent a key step toward the formation of vasoactive cys-LT. Methods and Results - We studied the effect of pretreatment with a monoclonal antibody directed against the CD18 subunit of PMNL \u3b22-integrin on the synthesis of cys-LT in a PMNL-perfused isolated rabbit heart in vitro and in a model of permanent ligature of the left descending coronary artery in the rabbit in vivo. Challenge of PMNL-perfused rabbit hearts with formyl-met-leu- phe (0.3 \u3bcmol/L) caused synthesis of cys-LT and increase in coronary perfusion pressure that were prevented by the anti-CD18 antibody. Similar results were obtained with the use of A-23187 (0.5 \u3bcmol/L) as a challenge. Persistence of PMNL-associated myeloperoxidase activity in the perfusion buffer was observed in the presence of the anti-CD18 antibody, indicating decreased PMNL infiltration. Coronary artery ligature in vivo increased urinary excretion of leukotriene E4, supporting the activation of the 5- lipoxygenase pathway during experimental acute myocardial infarction. Pretreatment with the anti-CD18 antibody (1 mg/kg) prevented the increase in leukotriene E4 excretion. Conclusions - These data support the importance of adhesion in promoting cys-LT formation, originating from PMNL-endothelial cell cooperation, and contributing to myocardial stiffness and increased coronary resistance

Ultra-precise Masses and Magnitudes for the Gliese 268 M-dwarf Binary

Recent advances in astrometry using interferometry and precision radial velocity techniques combined allow for a significant improvement in the precision of masses of M‐dwarf stars in visual systems. We report recent astrometric observations of Gliese 268, an M‐dwarf binary with a 10.4 day orbital period, with the IOTA interferometer and radial velocity observations with the ELODIE instrument. Combining these measurements leads to preliminary masses of the constituent stars with uncertainties of 0.4%. The masses of the components are 0.22596±0.00084 M_⊙ for the primary and 0.19230±0.00071 M_⊙ for the secondary. The system parallax is determined by these observations to be 0.1560±.0030 arcsec (2.0% uncertainty) and is within Hipparcos error bars (0.1572±.0033). We tested these physical parameters, along with the near‐infrared luminosities of the stars, against stellar evolution models for low‐mass stars. Discrepancies between the measured and theoretical values point toward a low‐level departure from the predictions. These results are among the most precise masses measured for visual binaries

A near-infrared interferometric survey of debris disc stars. II. CHARA/FLUOR observations of six early-type dwarfs

High-precision interferometric observations of six early-type main sequence stars known to harbour cold debris discs have been obtained in the near-infrared K band with the FLUOR instrument at the CHARA Array. The measured squared visibilities are compared to the expected visibility of the stellar photospheres based on theoretical photospheric models taking into account rotational distortion, searching for potential visibility reduction at short baselines due to circumstellar emission. Our observations bring to light the presence of resolved circumstellar emission around one of the six target stars (zeta Aql) at the 5 sigma level. The morphology of the emission source cannot be directly constrained because of the sparse spatial frequency sampling of our interferometric data. Using complementary adaptive optics observations and radial velocity measurements, we find that the presence of a low-mass companion is a likely origin for the excess emission. The potential companion has a K-band contrast of four magnitudes, a most probable mass of about 0.6 Msun, and is expected to orbit between about 5.5 AU and 8 AU from its host star assuming a purely circular orbit. Nevertheless, by adjusting a physical debris disc model to the observed Spectral Energy Distribution of the zeta Aql system, we also show that the presence of hot dust within 10 AU from zeta Aql, producing a total thermal emission equal to 1.69 +- 0.31% of the photospheric flux in the K band, is another viable explanation for the observed near-infrared excess. Our re-interpretation of archival near- to far-infrared photometric measurements shows however that cold dust is not present around zeta Aql at the sensitivity limit of the IRS and MIPS instruments onboard Spitzer, and urges us to remove zeta Aql from the category of bona fide debris disc stars.Comment: 14 pages, accepted for publication in A&

Hot circumstellar material resolved around β Pic with VLTI/PIONIER

Aims. We aim at resolving the circumstellar environment around β Pic in the near-infrared in order to study the inner planetary system (<200 mas, i.e., ~4 AU). Methods. Precise interferometric fringe visibility measurements were obtained over seven spectral channels dispersed across the H band with the four-telescope VLTI/PIONIER interferometer. Thorough analysis of interferometric data was performed to measure the stellar angular diameter and to search for circumstellar material. Results. We detected near-infrared circumstellar emission around β Pic that accounts for 1.37% ± 0.16% of the near-infrared stellar flux and that is located within the field-of-view of PIONIER (i.e., ~200 mas in radius). The flux ratio between this excess and the photosphere emission is shown to be stable over a period of 1 year and to vary only weakly across the H band, suggesting that the source is either very hot (≳1500 K) or dominated by the scattering of the stellar flux. In addition, we derive the limb-darkened angular diameter of β Pic with an unprecedented accuracy (θ_LD= 0.736 ± 0.019 mas). Conclusions. The presence of a small H-band excess originating in the vicinity of β Pic is revealed for the first time thanks to the high-precision visibilities enabled by VLTI/PIONIER. This excess emission is likely due to the scattering of stellar light by circumstellar dust and/or the thermal emission from a yet unknown population of hot dust, although hot gas emitting in the continuum cannot be firmly excluded

A Submillimetre Search for Cold Extended Debris Disks in the Beta Pictoris Moving Group

The Beta Pictoris Moving Group is a nearby stellar association of young (12Myr) co-moving stars including the classical debris disk star beta Pictoris. Due to their proximity and youth they are excellent targets when searching for submillimetre emission from cold, extended, dust components produced by collisions in Kuiper-Belt-like disks. They also allow an age independent study of debris disk properties as a function of other stellar parameters. We observed 7 infrared-excess stars in the Beta Pictoris Moving Group with the LABOCA bolometer array, operating at a central wavelength of 870 micron at the 12-m submillimetre telescope APEX. The main emission at these wavelengths comes from large, cold dust grains, which constitute the main part of the total dust mass, and hence, for an optically thin case, make better estimates on the total dust mass than earlier infrared observations. Fitting the spectral energy distribution with combined optical and infrared photometry gives information on the temperature and radial extent of the disk. From our sample, beta Pic, HD181327, and HD172555 were detected with at least 3-sigma certainty, while all others are below 2-sigma and considered non-detections. The image of beta Pic shows an offset flux density peak located near the south-west extension of the disk, similar to the one previously found by SCUBA at the JCMT. We present SED fits for detected sources and give an upper limit on the dust mass for undetected ones. We find a mean fractional dust luminosity f_dust=11x10^{-4} at t=12Myr, which together with recent data at 100Myr suggests an f_dust propto t^{-alpha} decline of the emitting dust, with alpha > 0.8.Comment: 11 pages, 3 figures, 3 tables; accepted for publication in Astronomy & Astrophysic