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https://www.readbyqxmd.com/read/28325842/surface-changes-on-comet-67p-churyumov-gerasimenko-suggest-a-more-active-past
#1
M Ramy El-Maarry, O Groussin, N Thomas, M Pajola, A-T Auger, B Davidsson, X Hu, S F Hviid, J Knollenberg, C Güttler, C Tubiana, S Fornasier, C Feller, P Hasselmann, J-B Vincent, H Sierks, C Barbieri, P Lamy, R Rodrigo, D Koschny, H U Keller, H Rickman, M F A'Hearn, M A Barucci, J-L Bertaux, I Bertini, S Besse, D Bodewits, G Cremonese, V Da Deppo, S Debei, M De Cecco, J Deller, J D P Deshapriya, M Fulle, P J Gutierrez, M Hofmann, W-H Ip, L Jorda, G Kovacs, J-R Kramm, E Kührt, M Küppers, L M Lara, M Lazzarin, Z-Yi Lin, J J Lopez Moreno, S Marchi, F Marzari, S Mottola, G Naletto, N Oklay, A Pommerol, F Preusker, F Scholten, X Shi
The Rosetta spacecraft spent ~2 years orbiting comet 67P/Churyumov-Gerasimenko, most of it at distances that allowed surface characterization and monitoring at submeter scales. From December 2014 to June 2016, numerous localized changes were observed, which we attribute to cometary-specific weathering, erosion, and transient events driven by exposure to sunlight and other processes. While the localized changes suggest compositional or physical heterogeneity, their scale has not resulted in substantial alterations to the comet's landscape...
March 21, 2017: Science
https://www.readbyqxmd.com/read/28302795/causal-role-for-inheritance-of-h3k27me3-in-maintaining-the-off-state-of-a-drosophila-hox-gene
#2
Rory T Coleman, Gary Struhl
Many eukaryotic cells can respond to transient environmental or developmental stimuli with heritable changes in gene expression that are associated with nucleosome modifications. However, it remains uncertain whether modified nucleosomes play a causal role in transmitting such epigenetic memories, as opposed to controlling or merely reflecting transcriptional states inherited by other means. Here, we provide in vivo evidence that H3K27 trimethylated nucleosomes, once established at a repressed Drosophila HOX gene, remain heritably associated with that gene and can carry the memory of the silenced state through multiple rounds of replication, even when the capacity to copy the H3K27me3 mark to newly incorporated nucleosomes is diminished or abolished...
March 16, 2017: Science
https://www.readbyqxmd.com/read/28302794/dna-sequence-dependent-epigenetic-inheritance-of-gene-silencing-and-histone-h3k9-methylation
#3
Xiaoyi Wang, Danesh Moazed
Epigenetic inheritance mechanisms play fundamental roles in maintaining cellular memory of gene expression states. In fission yeast, histone H3 lysine 9 (H3K9me) is methylated at heterochromatic domains. These domains can be epigenetically inherited when epi1+, encoding an enzyme that promotes H3K9 demethylation, is deleted. How native epigenetic states are stably maintained in epe1(+) cells remains unknown. Here, we developed a system to examine the role of DNA sequence and genomic context in propagation of a cis-heritable H3K9me-dependent silenced state...
March 16, 2017: Science
https://www.readbyqxmd.com/read/28302793/anticancer-sulfonamides-target-splicing-by-inducing-rbm39-degradation-via-recruitment-to-dcaf15
#4
Ting Han, Maria Goralski, Nicholas Gaskill, Emanuela Capota, Jiwoong Kim, Tabitha C Ting, Yang Xie, Noelle S Williams, Deepak Nijhawan
Indisulam is an aryl sulfonamide drug with selective anticancer activity. Its mechanism of action and the basis for its selectivity are unknown. Here we show that indisulam promotes the recruitment of RBM39 (RNA binding motif protein 39) to the CUL4-DCAF15 E3 ubiquitin ligase, leading to RBM39 polyubiquitination and proteasomal degradation. Mutations in RBM39 that prevent its recruitment to CUL4-DCAF15 increase RBM39 stability and confer resistance to indisulam's cytotoxicity. RBM39 associates with pre-mRNA splicing factors, and inactivation of RBM39 by indisulam causes aberrant pre-mRNA splicing...
March 16, 2017: Science
https://www.readbyqxmd.com/read/28302792/propagation-of-polycomb-repressed-chromatin-requires-sequence-specific-recruitment-to-dna
#5
Friederike Laprell, Katja Finkl, Jürg Müller
Epigenetic inheritance models posit that during Polycomb repression, Polycomb Repressive Complex 2 (PRC2) propagates histone H3K27 tri-methylation (H3K27me3) independently of DNA sequence. We show that insertion of Polycomb Response Element (PRE) DNA into the Drosophila genome creates extended domains of H3K27me3-modified nucleosomes in the flanking chromatin and causes repression of a linked reporter gene. After excision of PRE DNA, H3K27me3 nucleosomes become diluted with each round of DNA replication and reporter gene repression is lost, whereas in replication-stalled cells, H3K27me3 levels stay high and repression persists...
March 16, 2017: Science
https://www.readbyqxmd.com/read/28254785/notch-jagged-complex-structure-implicates-a-catch-bond-in-tuning-ligand-sensitivity
#6
Vincent C Luca, Byoung Choul Kim, Chenghao Ge, Shinako Kakuda, Di Wu, Mehdi Roein-Peikar, Robert S Haltiwanger, Cheng Zhu, Taekjip Ha, K Christopher Garcia
Notch receptor activation initiates cell fate decisions, and is distinctive in its reliance on mechanical force and protein glycosylation. The 2.5 angstrom crystal structure of the extracellular interacting regions of Notch1 complexed with an engineered, high-affinity variant of Jagged1 (Jag1) reveals a binding interface that extends ~120 angstroms along five consecutive domains of each protein. O-Linked fucose modifications on Notch1 EGF domains 8 and 12 engage the EGF3 and C2 domains of Jag1, respectively, and different Notch domains are favored in binding to Jag1 compared to those that bind to the Delta-like 4 ligand...
March 2, 2017: Science
https://www.readbyqxmd.com/read/28254784/assembly-of-embryonic-and-extra-embryonic-stem-cells-to-mimic-embryogenesis-in-vitro
#7
Sarah Ellys Harrison, Berna Sozen, Neophytos Christodoulou, Christos Kyprianou, Magdalena Zernicka-Goetz
Mammalian embryogenesis requires intricate interactions between embryonic and extra-embryonic tissues to orchestrate and coordinate morphogenesis with changes in developmental potential. Here, we combine mouse embryonic stem cells (ESCs) and extra-embryonic trophoblast stem cells (TSCs) in a 3D-scaffold to generate structures whose morphogenesis is remarkably similar to natural embryos. By using genetically-modified stem cells and specific inhibitors, we show embryogenesis of ESC- and TSC-derived embryos, ETS-embryos, depends on crosstalk involving Nodal signaling...
March 2, 2017: Science
https://www.readbyqxmd.com/read/28254783/deepstack-expert-level-artificial-intelligence-in-heads-up-no-limit-poker
#8
Matej Moravčík, Martin Schmid, Neil Burch, Viliam Lisý, Dustin Morrill, Nolan Bard, Trevor Davis, Kevin Waugh, Michael Johanson, Michael Bowling
Artificial intelligence has seen several breakthroughs in recent years, with games often serving as milestones. A common feature of these games is that players have perfect information. Poker is the quintessential game of imperfect information, and a longstanding challenge problem in artificial intelligence. We introduce DeepStack, an algorithm for imperfect information settings. It combines recursive reasoning to handle information asymmetry, decomposition to focus computation on the relevant decision, and a form of intuition that is automatically learned from self-play using deep learning...
March 2, 2017: Science
https://www.readbyqxmd.com/read/28232581/cryo-em-structures-of-the-triheteromeric-nmda-receptor-and-its-allosteric-modulation
#9
Wei Lü, Juan Du, April Goehring, Eric Gouaux
N-methyl-D-aspartate receptors (NMDARs) are heterotetrameric ion channels assembled as diheteromeric or triheteromeric complexes. Here, we report structures of the triheteromeric GluN1/GluN2A/GluN2B receptor in the absence or presence of the GluN2B-specific allosteric modulator Ro 25-6981 (Ro), determined by cryogenic electron microscopy (cryo-EM). In the absence of Ro, the GluN2A and GluN2B amino terminal domains (ATD) adopt "closed" and "open" clefts, respectively. Upon binding Ro, the GluN2B ATD clamshell transitions from an open to a closed conformation...
February 23, 2017: Science
https://www.readbyqxmd.com/read/28209640/quantized-thermal-transport-in-single-atom-junctions
#10
Longji Cui, Wonho Jeong, Sunghoon Hur, Manuel Matt, Jan C Klöckner, Fabian Pauly, Peter Nielaba, Juan Carlos Cuevas, Edgar Meyhofer, Pramod Reddy
Thermal transport in individual atomic junctions and chains is of great fundamental interest due to unique quantum effects expected to arise in them. Here, by employing novel, custom-fabricated, picowatt-resolution calorimetric scanning probes, we measure the thermal conductance of gold and platinum metallic wires down to single-atom junctions. Our work reveals that the thermal conductance of gold single atom junctions is quantized at room temperature and shows that the Wiedemann-Franz law relating thermal and electrical conductance is satisfied even in single-atom contacts...
February 16, 2017: Science
https://www.readbyqxmd.com/read/28209639/a-macrophage-relay-for-long-distance-signaling-during-postembryonic-tissue-remodeling
#11
Dae Seok Eom, David M Parichy
Macrophages have diverse functions in immunity as well as development and homeostasis. Here we identify a function for these cells in long distance communication during postembryonic tissue remodeling. Ablation of macrophages in zebrafish prevented melanophores from coalescing into adult pigment stripes. Melanophore organization depends on signals provided by cells of the yellow xanthophore lineage via airinemes, long filamentous projections with vesicles at their tips. We show that airineme extension from originating cells, and vesicle deposition on target cells, depend on interactions with macrophages...
February 16, 2017: Science
https://www.readbyqxmd.com/read/28183998/scalable-manufactured-randomized-glass-polymer-hybrid-metamaterial-for-daytime-radiative-cooling
#12
Yao Zhai, Yaoguang Ma, Sabrina N David, Dongliang Zhao, Runnan Lou, Gang Tan, Ronggui Yang, Xiaobo Yin
Passive radiative cooling draws heat from surfaces and radiates it into space as infrared radiation to which the atmosphere is transparent. However, the energy density mismatch between solar irradiance and the low infrared radiation flux from a near-ambient-temperature surface require materials that strongly emit thermal energy and barely absorb sunlight. We embedded resonant polar dielectric microspheres randomly in a polymeric matrix, resulting in a metamaterial that is fully transparent to the solar spectrum while having an infrared emissivity greater than 0...
February 9, 2017: Science
https://www.readbyqxmd.com/read/28183997/a-key-malaria-metabolite-modulates-vector-blood-seeking-feeding-and-susceptibility-to-infection
#13
S Noushin Emami, Bo G Lindberg, Susanna Hua, Sharon Hill, Raimondas Mozuraitis, Philipp Lehmann, Göran Birgersson, Anna-Karin Borg-Karlson, Rickard Ignell, Ingrid Faye
Malaria infection renders humans more attractive to Anopheles gambiae sensu lato mosquitoes than uninfected people. The mechanisms remain unknown. Here, we show that an isoprenoid precursor produced by Plasmodium falciparum, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), affects A. gambiae s.l. blood meal seeking and feeding behaviors, as well as susceptibility to infection. HMBPP acts indirectly by triggering human red blood cells to increase the release of CO2, aldehydes, and monoterpenes, which together enhance vector attraction, and stimulate vector feeding...
February 9, 2017: Science
https://www.readbyqxmd.com/read/28183995/structure-of-a-eukaryotic-voltage-gated-sodium-channel-at-near-atomic-resolution
#14
Huaizong Shen, Qiang Zhou, Xiaojing Pan, Zhangqiang Li, Jianping Wu, Nieng Yan
Voltage-gated sodium (Nav) channels are responsible for the initiation and propagation of action potentials. They are associated with a variety of channelopathies and are targeted by multiple pharmaceutical drugs and natural toxins. Here, we report the cryo-EM structure of a putative Nav channel from American cockroach (designated NavPaS) at 3.8-Å resolution. The voltage sensing domains (VSDs) of the four repeats exhibit distinct conformations. The entrance to the asymmetric selectivity filter vestibule is guarded by heavily glycosylated and disulfide bond-stabilized extracellular loops...
February 9, 2017: Science
https://www.readbyqxmd.com/read/28154242/efficient-and-stable-solution-processed-planar-perovskite-solar-cells-via-contact-passivation
#15
Hairen Tan, Ankit Jain, Oleksandr Voznyy, Xinzheng Lan, F Pelayo García de Arquer, James Z Fan, Rafael Quintero-Bermudez, Mingjian Yuan, Bo Zhang, Yicheng Zhao, Fengjia Fan, Peicheng Li, Li Na Quan, Yongbiao Zhao, Zheng-Hong Lu, Zhenyu Yang, Sjoerd Hoogland, Edward H Sargent
Planar perovskite solar cells made entirely via solution-processing at low temperatures (<150°C) offer promise for simple manufacturing, compatibility with flexible substrates, and perovskite-based tandem devices; however, they require an electron-selective layer that performs well with similar processing. We report a contact passivation strategy using chlorine-capped TiO2 colloidal nanocrystal (NC) film that mitigates interfacial recombination and improves interface binding in low-temperature planar solar cells...
February 2, 2017: Science
https://www.readbyqxmd.com/read/28126728/observation-of-the-wigner-huntington-transition-to-metallic-hydrogen
#16
Ranga P Dias, Isaac F Silvera
Producing metallic hydrogen has been a great challenge to condensed matter physics. Metallic hydrogen may be a room temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 GPa hydrogen becomes metallic with reflectivity as high as 0.91. We fit the reflectance using a Drude free electron model to determine the plasma frequency of 32.5 ± 2...
January 26, 2017: Science
https://www.readbyqxmd.com/read/28082413/a-paralogous-decoy-protects-phytophthora-sojae-apoplastic-effector-psxeg1-from-a-host-inhibitor
#17
Zhenchuan Ma, Lin Zhu, Tianqiao Song, Yang Wang, Qi Zhang, Yeqiang Xia, Min Qiu, Yachun Lin, Haiyang Li, Liang Kong, Yufeng Fang, Wenwu Ye, Yan Wang, Suomeng Dong, Xiaobo Zheng, Brett M Tyler, Yuanchao Wang
The extracellular space (apoplast) of plant tissue represents a critical battleground between plants and attacking microbes. Here we show that a pathogen-secreted apoplastic Xyloglucan-specific EndoGlucanase PsXEG1 is a focus of this struggle in the Phytophthora sojae-soybean interaction. We show that soybean produces an apoplastic Glucanase Inhibitor Protein, (GmGIP1), that binds to PsXEG1 to block its contribution to virulence. P. sojae however, secretes a paralogous PsXEG1-Like Protein (PsXLP1) that has lost enzyme activity but binds to GmGIP1 more tightly than does PsXEG1, thus freeing PsXEG1 to support P...
January 12, 2017: Science
https://www.readbyqxmd.com/read/28059713/time-resolved-x-ray-absorption-spectroscopy-with-a-water-window-high-harmonic-source
#18
Yoann Pertot, Cédric Schmidt, Mary Matthews, Adrien Chauvet, Martin Huppert, Vit Svoboda, Aaron von Conta, Andres Tehlar, Denitsa Baykusheva, Jean-Pierre Wolf, Hans Jakob Wörner
Time-resolved X-ray absorption spectroscopy (TR-XAS) has so far practically been limited to large-scale facilities, to sub-picosecond temporal resolution and to the condensed phase. Here, we report the realization of TR-XAS with a temporal resolution in the low femtosecond range by developing a table-top high-harmonic source reaching up to 350 eV, thus partially covering the spectral region of 280 to 530 eV, where water is transmissive. We use this source to follow previously unexamined light-induced chemical reactions in the lowest electronic states of isolated CF4(+) and SF6(+) molecules in the gas phase...
January 5, 2017: Science
https://www.readbyqxmd.com/read/28302861/step-out-of-the-lab-and-engage
#19
Gabrielle Kardon
No abstract text is available yet for this article.
March 17, 2017: Science
https://www.readbyqxmd.com/read/28302860/mobile-mute-specifies-subsidiary-cells-to-build-physiologically-improved-grass-stomata
#20
Michael T Raissig, Juliana L Matos, M Ximena Anleu Gil, Ari Kornfeld, Akhila Bettadapur, Emily Abrash, Hannah R Allison, Grayson Badgley, John P Vogel, Joseph A Berry, Dominique C Bergmann
Plants optimize carbon assimilation while limiting water loss by adjusting stomatal aperture. In grasses, a developmental innovation-the addition of subsidiary cells (SCs) flanking two dumbbell-shaped guard cells (GCs)-is linked to improved stomatal physiology. Here, we identify a transcription factor necessary and sufficient for SC formation in the wheat relative Brachypodium distachyon. Unexpectedly, the transcription factor is an ortholog of the stomatal regulator AtMUTE, which defines GC precursor fate in Arabidopsis The novel role of BdMUTE in specifying lateral SCs appears linked to its acquisition of cell-to-cell mobility in Brachypodium Physiological analyses on SC-less plants experimentally support classic hypotheses that SCs permit greater stomatal responsiveness and larger range of pore apertures...
March 17, 2017: Science
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