Identity of Leu-19 (CD56) leukocyte differentiation antigen and neural cell adhesion molecule.

Neural cell adhesion molecule (N-CAM) is a membrane glycoprotein expressed on neural and muscle tissues that is involved in homotypic adhesive interactions. We have demonstrated that N-CAM also is expressed on hematopoietic cells, and is recognized by the anti-Leu-19 mAb. Leu-19 is preferentially expressed on NK cells and T lymphocytes that mediate MHC-unrestricted cytotoxicity, but is also present on some myeloid leukemia cell lines. On NK cells, T cells, the KG1a.5 hematopoietic cell line, and a neuroblastoma cell line, Leu-19 is a approximately 140-kD polypeptide with N-linked carbohydrates and abundant sialic acid residues. Sequential immunoprecipitation and peptide mapping demonstrated that the Leu-19 and N-CAM molecules expressed on leukocyte and neuroblastoma cell lines are similar structures. These findings suggest that the Leu-19 antigen on leukocytes may be involved in cell adhesion, analogous to the function on N-CAM on neural cells

Protostellar clusters in intermediate-mass (IM) star forming regions

The transition between the low density groups of T Tauri stars and the high density clusters around massive stars occurs in the intermediate-mass (IM) range (M$_*$$\sim$2--8 M$_\odot$). High spatial resolution studies of IM young stellar objects (YSO) can provide important clues to understand the clustering in massive star forming regions. Aims: Our aim is to search for clustering in IM Class 0 protostars. The high spatial resolution and sensitivity provided by the new A configuration of the Plateau de Bure Interferometer (PdBI) allow us to study the clustering in these nearby objects. Methods: We have imaged three IM Class 0 protostars (Serpens-FIRS 1, IC 1396 N, CB 3) in the continuum at 3.3 and 1.3mm using the PdBI. The sources have been selected with different luminosity to investigate the dependence of the clustering process on the luminosity of the source. Results: Only one millimeter (mm) source is detected towards the low luminosity source Serpens--FIRS 1. Towards CB 3 and IC1396 N, we detect two compact sources separated by $\sim$0.05 pc. The 1.3mm image of IC 1396 N, which provides the highest spatial resolution, reveal that one of these cores is splitted in, at least, three individual sources.Comment: 4 pages, 3 figures, accepted for publication in Astronomy and Astrophysics Letters (Special Feature IRAM/PdB

A Keplerian gaseous disk around the B0 star R Mon

We present high-angular resolution observations of the circumstellar disk around the massive Herbig Be star R Mon (M~8 Msun) in the continuum at 2.7mm and 1.3mm and the CO 1->0 and 2->1 rotational lines. Based on the new 1.3mm continuum image we estimate a disk mass (gas+dust) of 0.007 Msun and an outer radius of <150 AU. Our CO images are consistent with the existence of a Keplerian rotating gaseous disk around this star. Up to our knowledge, this is the most clear evidence for the existence of Keplerian disks around massive stars reported thus far. The mass and physical characteristics of this disk are similar to thoseof the more evolved T Tauri stars and indicate a shorter timescale for the evolution and dispersal of circumstellar disks around massive stars which lose most of their mass before the star becomes visible.Comment: 5 page

Apoptotic signaling through CD95 (Fas/Apo-1) activates an acidic sphingomyelinase.

Intracellular pathways leading from membrane receptor engagement to apoptotic cell death are still poorly characterized. We investigated the intracellular signaling generated after cross-linking of CD95 (Fas/Apo-1 antigen), a broadly expressed cell surface receptor whose engagement results in triggering of cellular apoptotic programs. DX2, a new functional anti-CD95 monoclonal antibody was produced by immunizing mice with human CD95-transfected L cells. Crosslinking of CD95 with DX2 resulted in the activation of a sphingomyelinase (SMase) in promyelocytic U937 cells, as well as in other human tumor cell lines and in CD95-transfected murine cells, as demonstrated by induction of in vivo sphingomyelin (SM) hydrolysis and generation of ceramide. Direct in vitro measurement of enzymatic activity within CD95-stimulated U937 cell extracts, using labeled SM vesicles as substrates, showed strong SMase activity, which required pH 5.0 for optimal substrate hydrolysis. Finally, all CD95-sensitive cell lines tested could be induced to undergo apoptosis after exposure to cell-permeant C2-ceramide. These data indicate that CD95 cross-linking induces SM breakdown and ceramide production through an acidic SMase, thus providing the first information regarding early signal generation from CD95, and may be relevant in defining the biochemical nature of intracellular messengers leading to apoptotic cell death

First results from a VLBA proper motion survey of H2O masers in low-mass YSOs: the Serpens core and RNO15-FIR

This article reports first results of a long-term observational program aimed to study the earliest evolution of jet/disk systems in low-mass YSOs by means of VLBI observations of the 22.2 GHz water masers. We report here data for the cluster of low-mass YSOs in the Serpens molecular core and for the single object RNO~15-FIR. Towards Serpens SMM1, the most luminous sub-mm source of the Serpens cluster, the water maser emission comes from two small (< 5 AU in size) clusters of features separated by ~25 AU, having line of sight velocities strongly red-shifted (by more than 10 km/s) with respect to the LSR velocity of the molecular cloud. The two maser clusters are oriented on the sky along a direction that is approximately perpendicular to the axis of the radio continuum jet observed with the VLA towards SMM1. The spatial and velocity distribution of the maser features lead us to favor the interpretation that the maser emission is excited by interaction of the receding lobe of the jet with dense gas in the accretion disk surrounding the YSO in SMM1. Towards RNO~15-FIR, the few detected maser features have both positions and (absolute) velocities aligned along a direction that is parallel to the axis of the molecular outflow observed on much larger angular scales. In this case the maser emission likely emerges from dense, shocked molecular clumps displaced along the axis of the jet emerging from the YSO. The protostar in Serpens SMM1 is more massive than the one in RNO~15-FIR. We discuss the case where a high mass ejection rate can generate jets sufficiently powerful to sweep away from their course the densest portions of circumstellar gas. In this case, the excitation conditions for water masers might preferably occur at the interface between the jet and the accretion disk, rather than along the jet axis.Comment: 18 pages (postscript format); 9 figures; to be published into Astronomy & Astrophysics, Main Journa

Relative Evolutionary Time Scale of Hot Molecular Cores with Respect to Ultra Compact HII Regions

Using the Owens Valley and Nobeyama Radio Observatory interferometers, we carried out an unbiased search for hot molecular cores and ultracompact UC HII regions toward the high-mass star forming region G19.61--0.23. In addition, we performed 1.2 mm imaging with SIMBA, and retrieved 3.5 and 2 cm images from the VLA archive data base. The newly obtained 3 mm image brings information on a cluster of high-mass (proto)stars located in the innermost and densest part of the parsec scale clump detected in the 1.2 mm continuum. We identify a total of 10 high-mass young stellar objects: one hot core (HC) and 9 UC HII regions, whose physical parameters are obtained from model fits to their continuum spectra. The ratio between the current and expected final radii of the UC \HII regions ranges from 0.3 to 0.9, which leaves the possibility that all O-B stars formed simultaneously. Under the opposite assumption -- namely that star formation occurred randomly -- we estimate that HC lifetime is less than $\sim$1/3 of that of UCHII regions on the basis of the source number ratio between them.Comment: 13 pages, 2 figs, including a color fi

New constraints on dust grain size and distribution in CQ Tau

Grain growth in circumstellar disks is expected to be the first step towards the formation of planetary systems. There is now evidence for grain growth in several disks around young stars. Radially resolved images of grain growth in circumstellar disks are believed to be a powerful tool to constrain the dust evolution models and the initial stage for the formation of planets. In this paper we attempt to provide these constraints for the disk surrounding the young star CQ Tau. This system was already suggested from previous studies to host a population of grains grown to large sizes. We present new high angular resolution (0.3-0.9 arcsec) observations at wavelengths from 850um to 3.6cm obtained at the SMA, IRAM-PdBI and NRAO-VLA interferometers. We perform a combined analysis of the spectral energy distribution and of the high-resolution images at different wavelengths using a model to describe the dust thermal emission from the circumstellar disk. We include a prescription for the gas emission from the inner regions of the system. We detect the presence of evolved dust by constraining the disk averaged dust opacity coefficient beta (computed between 1.3 and 7mm) to be 0.6+/-0.1. This confirms the earlier suggestions that the disk contains dust grains grown to significant sizes and puts this on firmer grounds by tightly constraining the gas contamination to the observed fluxes at mm-cm wavelengths. We report some evidence of radial variations in dust properties, but current resolution and sensitivity are still too low for definitive results.Comment: 9 pages, A&A in pres