133 research outputs found
The Initial Mass Function and Disk Frequency of the Rho Ophiuchi Cloud: An Extinction-Limited Sample
We have completed an optical spectroscopic survey of an unbiased,
extinction-limited sample of candidate young stars covering 1.3 square degrees
of the Rho Ophiuchi star forming region. While infrared, X-ray, and optical
surveys of the cloud have identified many young stellar objects (YSOs), these
surveys are biased towards particular stages of stellar evolution and are not
optimal for studies of the disk frequency and initial mass function.We have
obtained over 300 optical spectra to help identify 135 association members
based on the presence of H-alpha in emission, lithium absorption, X-ray
emission, a mid-infrared excess, a common proper motion, reflection nebulosity,
and/or extinction considerations. Spectral types along with R and I band
photometry were used to derive effective temperatures and bolometric
luminosities for association members to compare with theoretical tracks and
isochrones for pre-main-sequence stars. An average age of 3.1 Myr is derived
for this population which is intermediate between that of objects embedded in
the cloud core of Rho Ophiuchi and low mass stars in the Upper Scorpius
subgroup. Consistent with this age we find a circumstellar disk frequency of
27% plus or minus 5%. We also constructed an initial mass function for an
extinction-limited sample of 123 YSOs (A_v less than or equal to 8 mag), which
is consistent with the field star initial mass function for YSOs with masses >
0.2 M_sun. There may be a deficit of brown dwarfs but this result relies on
completeness corrections and requires confirmation.Comment: 46 pages, 7 figures, 4 table
Recommended from our members
In vivo characterization of glutamine metabolism identifies therapeutic targets in clear cell renal cell carcinoma
Targeting metabolic vulnerabilities has been proposed as a therapeutic strategy in renal cell carcinoma (RCC). Here, we analyzed the metabolism of patient-derived xenografts (tumorgrafts) from diverse subtypes of RCC. Tumorgrafts from VHL-mutant clear cell RCC (ccRCC) retained metabolic features of human ccRCC and engaged in oxidative and reductive glutamine metabolism. Genetic silencing of isocitrate dehydrogenase-1 or isocitrate dehydrogenase-2 impaired reductive labeling of tricarboxylic acid (TCA) cycle intermediates in vivo and suppressed growth of tumors generated from tumorgraft-derived cells. Glutaminase inhibition reduced the contribution of glutamine to the TCA cycle and resulted in modest suppression of tumorgraft growth. Infusions with [amide-15N]glutamine revealed persistent amidotransferase activity during glutaminase inhibition, and blocking these activities with the amidotransferase inhibitor JHU-083 also reduced tumor growth in both immunocompromised and immunocompetent mice. We conclude that ccRCC tumorgrafts catabolize glutamine via multiple pathways, perhaps explaining why it has been challenging to achieve therapeutic responses in patients by inhibiting glutaminase
A nearby m star with three transiting super-earths discovered by k2
I. J. M. Crossfied, âA Nearby M Star with Three Transiting Super-Earths Discovered by K2â, The Astrophysical Journal, Vol 804(1), April 2015. © 2015. The American Astronomical Society.Small, cool planets represent the typical end-products of planetary formation. Studying the architectures of these systems, measuring planet masses and radii, and observing these planets' atmospheres during transit directly informs theories of planet assembly, migration, and evolution. Here we report the discovery of three small planets orbiting a bright (Ks = 8.6 mag) M0 dwarf using data collected as part of K2, the new ecliptic survey using the re-purposed Kepler spacecraft. Stellar spectroscopy and K2 photometry indicate that the system hosts three transiting planets with radii 1.5-2.1 , straddling the transition region between rocky and increasingly volatile-dominated compositions. With orbital periods of 10-45 days the planets receive just 1.5-10x the flux incident on Earth, making these some of the coolest small planets known orbiting a nearby star; planet d is located near the inner edge of the system's habitable zone. The bright, low-mass star makes this system an excellent laboratory to determine the planets' masses via Doppler spectroscopy and to constrain their atmospheric compositions via transit spectroscopy. This discovery demonstrates the ability of K2 and future space-based transit searches to find many fascinating objects of interest.Peer reviewe
Crystal structure of human NADK2 reveals a dimeric organization and active site occlusion by lysine acetylation
Submitted documentInternational audienceNAD+ kinases (NADKs) are metabolite kinases that phosphorylate NAD+ molecules to make NADP+, a limiting substrate for the generation of reducing power NADPH. NADK2 sustains mitochondrial NADPH production that enables proline biosynthesis and antioxidant defense. However, its molecular architecture and mechanistic regulation remain undescribed. Here, we report the crystal structure of human NADK2, revealing a new substrate-driven mode of activation. We find that NADK2 presents an unexpected dimeric organization instead of the typical tetrameric assemblage observed for other NADKs. A specific extended segment (aa 325-365) is crucial for NADK2 dimerization and activity. Moreover, we find that NADK2 is decorated with numerous acetylation events, including those on Lys76 and Lys304, which reside near the active site and are critical for mitochondrial NADP(H) production, proline synthesis, and cell growth. These findings reveal new molecular insight into the structure and regulation of a vital enzyme in mitochondrial NADPH and proline metabolism
HILIC and ERLIC Enrichment of Glycopeptides Derived from Breast and Brain Cancer Cells
Aberrant
glycosylation has been linked to many different cancer
types. The bloodâbrain barrier (BBB) is a region of the brain
that regulates the entrance of ions, diseases, toxins, and so on.
However, in breast cancer metastasis, the BBB fails to prevent the
crossing of the cancer cells into the brain. Here we present a study
of identifying and quantifying the glycosylation of six breast and
brain cancer cell lines using hydrophilic interaction liquid chromatography
(HILIC) and electrostatic repulsion liquid chromatography (ERLIC)
enrichments and LCâMS/MS analysis. Qualitative and quantitative
analyses of N-linked glycosylation were performed by both enrichment
techniques for individual and complementary comparison. Potential
cancer glycopeptide biomarkers were identified and confirmed by chemometric
and statistical evaluations. A total of 497 glycopeptides were characterized,
of which 401 were common glycopeptides (80.6% overlap) identified
from both enrichment techniques. HILIC enrichment yielded 320 statistically
significant glycopeptides in 231BR relative to the other cell lines
out of 494 unique glycopeptides, and sequential HILIC-ERLIC enrichment
yielded 214 statistically significant glycopeptides in 231BR compared
with the other cell lines out of 404 unique glycopeptides. The results
provide the first comprehensive glycopeptide listing for these six
cell lines
Using arterialâvenous analysis to characterize cancer metabolic consumption in patients
Cellular metabolism is altered in many cancer types and the advent of metabolomics has allowed us to understand more about how this is dysregulated. Here, the authors report a method named CARVE to analyse the arterial supply and venous drainage of glioma patients during surgery and identify the metabolites that may be consumed and produced by the cancer
Autophagy Regulation of Metabolism Is Required for CD8+ T Cell Anti-tumor Immunity
Summary: Autophagy is a cell survival process essential for the regulation of immune responses to infections. However, the role of T cell autophagy in anti-tumor immunity is less clear. Here, we demonstrate a cell-autonomous role for autophagy in the regulation of CD8+ T-cell-mediated control of tumors. Mice deficient for the essential autophagy genes Atg5, Atg14, or Atg16L1 display a dramatic impairment in the growth of syngeneic tumors. Moreover, T cells lacking Atg5 have a profound shift to an effector memory phenotype and produce greater amounts of interferon-Îł (IFN-Îł) and tumor necrosis factor α (TNF-α). Mechanistically, Atg5â/â CD8+ T cells exhibit enhanced glucose metabolism that results in alterations in histone methylation, increases in H3K4me3 density, and transcriptional upregulation of both metabolic and effector target genes. Nonetheless, glucose restriction is sufficient to suppress Atg5-dependent increases in effector function. Thus, autophagy-dependent changes in CD8+ T cell metabolism directly regulate anti-tumor immunity. : DeVorkin et al. show that loss of autophagy enhances CD8+ T-cell-mediated rejection of tumors. Mechanistically, suppression of autophagy shifts T cells to a glycolytic phenotype and causes a reduction in S-adenosylmethionine. As a consequence, autophagy-deficient T cells transcriptionally reprogram immune response genes to an effector memory state. Keywords: autophagy, CD8+ T cells, anti-tumor immunity, glycolysis, lactate, SAM, methylatio
Integrated Transcriptomic and Glycomic Profiling of Glioma Stem Cell Xenografts
Bone
marrow-derived human mesenchymal stem cells (BM-hMSCs) have
the innate ability to migrate or home toward and engraft in tumors
such as glioblastoma (GBM). Because of this unique property of BM-hMSCs,
we have explored their use for cell-mediated therapeutic delivery
for the advancement of GBM treatment. Extravasation, the process by
which blood-borne cellsîžsuch as BM-hMSCsîženter the tissue,
is a highly complex process but is heavily dependent upon glycosylation
for glycanâglycan and glycanâprotein adhesion between
the cell and endothelium. However, in a translationally significant
preclinical glioma stem cell xenograft (GSCX) model of GBM, BM-hMSCs
demonstrate unequal tropism toward these tumors. We hypothesized that
there may be differences in the glycan compositions between the GSCXs
that elicit homing (âattractorsâ) and those that do
not (ânon-attractorsâ) that facilitate or impede the
engraftment of BM-hMSCs in the tumor. In this study, glycotranscriptomic
analysis revealed significant heterogeneity within the attractor phenotype
and the enrichment of high mannose type <i>N</i>-glycan
biosynthesis in the non-attractor phenotype. Orthogonal validation
with topical PNGase F deglycosylation on the tumor regions of xenograft
tissue, followed by nLCâESIâMS, confirmed the presence
of increased high mannose type <i>N</i>-glycans in the non-attractors.
Additional evidence provided by our glycomic study revealed the prevalence
of terminal sialic acid-containing <i>N</i>-glycans in non-attractors
and terminal galactose and <i>N</i>-acetyl-glucosamine <i>N</i>-glycans in attractors. Our results provide the first evidence
for differential glycomic profiles in attractor and non-attractor
GSCXs and extend the scope of molecular determinates in BM-hMSC homing
to glioma
Functional Assessment of Lipoyltransferase-1 Deficiency in Cells, Mice, and Humans
Summary: Inborn errors of metabolism (IEMs) link metabolic defects to human phenotypes. Modern genomics has accelerated IEM discovery, but assessing the impact of genomic variants is still challenging. Here, we integrate genomics and metabolomics to identify a cause of lactic acidosis and epilepsy. The proband is a compound heterozygote for variants in LIPT1, which encodes the lipoyltransferase required for 2-ketoacid dehydrogenase (2KDH) function. Metabolomics reveals abnormalities in lipids, amino acids, and 2-hydroxyglutarate consistent with loss of multiple 2KDHs. Homozygous knockin of a LIPT1 mutation reduces 2KDH lipoylation in utero and results in embryonic demise. In patient fibroblasts, defective 2KDH lipoylation and function are corrected by wild-type, but not mutant, LIPT1 alleles. Isotope tracing reveals that LIPT1 supports lipogenesis and balances oxidative and reductive glutamine metabolism. Altogether, the data extend the role of LIPT1 in metabolic regulation and demonstrate how integrating genomics and metabolomics can uncover broader aspects of IEM pathophysiology. : Ni et al. investigate human LIPT1 deficiency, which results in developmental delay, epilepsy, and broad metabolic abnormalities, including lactic acidosis, L- and D-2-hydroxyglutaric aciduria, defective lipogenesis, and an altered balance between oxidative and reductive glutamine metabolism. Keywords: inborn errors of metabolism, metabolomics, genomics, lactic acidosis, epilepsy,developmental delay, 2-ketoacid dehydrogenase, lipoylation, lipogenesis, fatty acid oxidatio
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