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  • 1
    Language: English
    In: Nature, 10 September 2015, Vol.525(7568), pp.251-5
    Description: Understanding the development and function of an organ requires the characterization of all of its cell types. Traditional methods for visualizing and isolating subpopulations of cells are based on messenger RNA or protein expression of only a few known marker genes. The unequivocal identification of a specific marker gene, however, poses a major challenge, particularly if this cell type is rare. Identifying rare cell types, such as stem cells, short-lived progenitors, cancer stem cells, or circulating tumour cells, is crucial to acquire a better understanding of normal or diseased tissue biology. To address this challenge we first sequenced the transcriptome of hundreds of randomly selected cells from mouse intestinal organoids, cultured self-organizing epithelial structures that contain all cell lineages of the mammalian intestine. Organoid buds, like intestinal crypts, harbour stem cells that continuously differentiate into a variety of cell types, occurring at widely different abundances. Since available computational methods can only resolve more abundant cell types, we developed RaceID, an algorithm for rare cell type identification in complex populations of single cells. We demonstrate that this algorithm can resolve cell types represented by only a single cell in a population of randomly sampled organoid cells. We use this algorithm to identify Reg4 as a novel marker for enteroendocrine cells, a rare population of hormone-producing intestinal cells. Next, we use Reg4 expression to enrich for these rare cells and investigate the heterogeneity within this population. RaceID confirmed the existence of known enteroendocrine lineages, and moreover discovered novel subtypes, which we subsequently validated in vivo. Having validated RaceID we then applied the algorithm to ex vivo-isolated Lgr5-positive stem cells and their direct progeny. We find that Lgr5-positive cells represent a homogenous abundant population of stem cells mixed with a rare population of Lgr5-positive secretory cells. We envision broad applicability of our method for discovering rare cell types and the corresponding marker genes in healthy and diseased organs.
    Keywords: Sequence Analysis, RNA ; Single-Cell Analysis ; Cell Separation -- Methods ; Intestine, Small -- Cytology ; RNA, Messenger -- Genetics
    ISSN: 00280836
    E-ISSN: 1476-4687
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  • 2
    Language: English
    In: Nature, 18 June 2015, Vol.522(7556), pp.324-6
    Description: Interplanetary dust particles hit the surfaces of airless bodies in the Solar System, generating charged and neutral gas clouds, as well as secondary ejecta dust particles. Gravitationally bound ejecta clouds that form dust exospheres were recognized by in situ dust instruments around the icy moons of Jupiter and Saturn, but have hitherto not been observed near bodies with refractory regolith surfaces. High-altitude Apollo 15 and 17 observations of a 'horizon glow' indicated a putative population of high-density small dust particles near the lunar terminators, although later orbital observations yielded upper limits on the abundance of such particles that were a factor of about 10(4) lower than that necessary to produce the Apollo results. Here we report observations of a permanent, asymmetric dust cloud around the Moon, caused by impacts of high-speed cometary dust particles on eccentric orbits, as opposed to particles of asteroidal origin following near-circular paths striking the Moon at lower speeds. The density of the lunar ejecta cloud increases during the annual meteor showers, especially the Geminids, because the lunar surface is exposed to the same stream of interplanetary dust particles. We expect all airless planetary objects to be immersed in similar tenuous clouds of dust.
    Keywords: Sciences (General) ; Physics;
    ISSN: 00280836
    E-ISSN: 1476-4687
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  • 3
    In: Nature, 2017, Vol.546(7657), p.293
    Description: The timing and location of the emergence of our species and of associated behavioural changes are crucial for our understanding of human evolution. The earliest fossil attributed to a modern form of Homo sapiens comes from eastern Africa and is approximately 195 thousand years old1,2, therefore the emergence of modern human biology is commonly placed at around 200 thousand years ago3,4. The earliest Middle Stone Age assemblages come from eastern and southern Africa but date much earlier5-7. Here we report the ages, determined by thermoluminescence dating, of fire-heated flint artefacts obtained from new excavations at the Middle Stone Age site of Jebel Irhoud, Morocco, which are directly associated with newly discovered remains of H. sapiens8. A weighted average age places these Middle Stone Age artefacts and fossils at 315 34 thousand years ago. Support is obtained through the recalculated uranium series with electron spin resonance date of 286 32 thousand years ago for a tooth from the Irhoud 3 hominin mandible. These ages are also consistent with the faunal and microfaunal9 assemblages and almost double the previous age estimates for the lower part of the deposits10,11. The north African site of Jebel Irhoud contains one of the earliest directly dated Middle Stone Age assemblages, and its associated human remains are the oldest reported for H. sapiens. The emergence of our species and of the Middle Stone Age appear to be close in time, and these data suggest a larger scale, potentially pan-African, origin for both.
    Keywords: Morocco ; Artifacts ; Fossils ; Origins ; Uranium ; Electron Paramagnetic Resonance ; Emergence ; Stone Age ; Series (Mathematics) ; Age ; Evolution ; Dating ; Uranium ; Chronology ; Mandible ; Evolution ; Resonance ; Fossils ; Artefacts ; Uranium ; Thermoluminescence ; Teeth ; Stone ; Estimates ; Electron Spin ; Spin Resonance ; Thermoluminescence ; Teeth ; Fossils ; Human Behavior ; Biology ; Stone Age ; Evolution ; Fossils ; Paleontology ; Hominids ; Time Measurement;
    ISSN: 0028-0836
    E-ISSN: 1476-4687
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  • 4
    In: Geophysical Research Letters, 28 December 2011, Vol.38(24), pp.n/a-n/a
    Description: Impact ejecta and collisional debris from the Edgeworth‐Kuiper Belt are the dominant source of micron‐sized grains in the outer solar system, as they slowly migrate inwards through the outer solar system before most grains are ejected during close encounters with Jupiter. These grains drive several phenomena in the outer solar system, including the generation of impact ejecta clouds at airless bodies, the formation of ionospheric layers and neutral gases in the atmospheres of the giant planets due to meteoric ablation, the generation of tenuous outer planetary ring systems and the spatial and compositional alteration of Saturn's main rings. Previous analyses have offered estimates of the net mass production rate from the Edgeworth‐Kuiper Belt both theoretically and observationally. In order to improve upon these estimates, we compare measurements of the interplanetary dust density in the outer solar system by both the Pioneer 10 meteoroid detector and the New Horizons Student Dust Counter with a dynamical dust grain tracing model. Our best estimates for the net mass production rate and the ejecta mass distribution power law exponent are (8.9 ± 0.5) × 10 g/s and 3.02 ± 0.04, respectively. Dust grains produced in the Kuiper Belt migrate inward Dynamical dust grain tracing code is used to establish relative dust densities Measurements by Pioneer 10 and New Horizons constrain dust production rates
    Keywords: Edgeworth‐Kuiper Belt ; Dynamical Dust Model ; Interplanetary Dust
    ISSN: 0094-8276
    E-ISSN: 1944-8007
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  • 5
    In: Geophysical Research Letters, 28 March 2012, Vol.39(6), pp.n/a-n/a
    Description: In the vicinity of Enceladus, a geologically active moon of Saturn, the modeled spacecraft potential is significantly more negative than indicated by the Cassini Langmuir probe measurements. To understand this potential difference, we introduce two new dust–related charging currents: a) the dust ram current; and b) the dust impact–plasma current, in addition to the customary collection of electrons and ions, and photoemission. Our results show that these dust currents are important at high relative speeds between the spacecraft and the dust, or in regions with a low plasma‐to‐dust ratio, and can lead to reduced spacecraft charging. Two dust currents are introduced for the spacecraft charging calculation The spacecraft potential is neutralized by the dust currents Dust impact plasma may affect in‐situ thermal plasma measurements
    Keywords: Cassini ; Enceladus ; Saturn ; Dust
    ISSN: 0094-8276
    E-ISSN: 1944-8007
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  • 6
    In: Geophysical Research Letters, 28 June 2016, Vol.43(12), pp.6103-6110
    Description: We report on laboratory experiments to shed light on dust charging and transport that have been suggested to explain a variety of unusual phenomena on the surfaces of airless planetary bodies. We have recorded micron‐sized insulating dust particles jumping to several centimeters high with an initial speed of ~0.6 m/s under ultraviolet illumination or exposure to plasmas, resulting in an equivalent height of ~0.11 m on the lunar surface that is comparable to the height of the so‐called lunar horizon glow. Lofted large aggregates and surface mobilization are related to many space observations. We experimentally show that the emission and re‐absorption of photoelectron and/or secondary electron at the walls of microcavities formed between neighboring dust particles below the surface are responsible for generating unexpectedly large negative charges and intense particle‐particle repulsive forces to mobilize and lift off dust particles. Micron‐sized insulating dust particles are recorded to hop and mobilize under UV illumination or exposure to plasmas in laboratory The emission and re‐absorption of photoelectron/secondary electron at dusty surfaces generate unexpectedly large charges and repulsive forces Electrostatic processes are efficient on the surfaces of all airless bodies in space to redistribute fine dust particles
    Keywords: Dust ; Plasma ; Photoelectrons ; Secondary Electrons ; Electrostatic Transport ; Airless Bodies
    ISSN: 0094-8276
    E-ISSN: 1944-8007
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  • 7
    Language: English
    In: Journal of Applied Physics, 01 May 2010, Vol.107(9)
    Description: The thermal stability of nanocrystalline diamond films with 10–30 nm grain size deposited by microwave enhanced chemical vapor deposition on silicon substrate was investigated as a function of annealing temperature up to 1200   ° C . The thermal stability of the surface-upper atomic layers was studied with near edge x-ray absorption fine structure (NEXAFS) spectroscopy recorded in the partial electron yield mode. This technique indicated substantial thermally induced graphitization of the film within a close proximity to the surface. While in the bulk region of the film no graphitization was observed with either Raman spectroscopy or NEXAFS spectroscopy recorded in total electron yield mode, even after annealing to 1200   ° C . Raman spectroscopy did detect the complete disappearance of transpolyacetylene (t-PA)-like ν 1 and ν 3 modes following annealing at 1000   ° C . Secondary ion mass spectroscopy, applied to investigate this relative decrease in hydrogen atom concentration detected only a ∼ 30 % decrease in the bulk content of hydrogen atoms. This enhanced stability of sp 3 hybridized atoms within the bulk region with respect to graphitization is discussed in terms of carbon bond rearrangement due to the thermal decomposition of t-PA-like fragments.
    Keywords: Articles
    ISSN: 0021-8979
    E-ISSN: 1089-7550
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  • 8
    In: Nature, 2016
    Description: The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley. Such matter is generally thought to have originated in the interstellar medium, but it might have formed in the solar nebula-the cloud of gas and dust that was left over after the Sun formed. This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization. Many gaseous organic molecules, however, have been observed; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei. These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula. Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov-Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites. The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites' parent bodies. We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.
    Keywords: Atoms & Subatomic Particles ; Comets ; Organic Chemicals ; Dust;
    ISSN: 0028-0836
    E-ISSN: 1476-4687
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  • 9
    In: Nature, 2016, Vol.529(7585), p.208
    Description: Sulawesi is the largest and oldest island within Wallacea, a vast zone of oceanic islands separating continental Asia from the Pleistocene landmass of Australia and Papua (Sahul). By one million years ago an unknown hominin lineage had colonized Flores immediately to the south (1), and by about 50 thousand years ago, modern humans (Homo sapiens) had crossed to Sahul (2,3). On the basis of position, oceanic currents and biogeographical context, Sulawesi probably played a pivotal part in these dispersals (4). Uranium-series dating of speleothem deposits associated with rock art in the limestone karst region of Maros in southwest Sulawesi has revealed that humans were living on the island at least 40 thousand years ago (ref. 5). Here we report new excavations at Talepu in the Walanae Basin northeast of Maros, where in situ stone artefacts associated with fossil remains of megafauna (Bubalus sp., Stegodon and Celebochoerus) have been recovered from stratified deposits that accumulated from before 200 thousand years ago until about 100 thousand years ago. Our findings suggest that Sulawesi, like Flores, was host to a long-established population of archaic hominins, the ancestral origins and taxonomic status of which remain elusive.
    Keywords: Uranium Series Disequilibrium Dating – Usage ; Uranium – Research ; Uranium – Health Aspects ; Hominids – Research;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 10
    In: Nature, 2016, Vol.530(7588), p.63
    Description: Cometary nuclei consist mostly of dust and water ice1. Previous observations have found nuclei to be low-density and highly porous bodies2-4, but have only moderately constrained the range of allowed densities because of the measurement uncertainties. Here we report the precise mass, bulk density, porosity...
    Keywords: Space Exploration ; Dust ; Porosity ; Comets ; Astronomy;
    ISSN: 0028-0836
    E-ISSN: 14764687
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