审校：赵维杰 半夏 邓卓 访冬 史静雯
Real-time spectral interferometry probes the internal dynamics of femtosecond soliton molecules
G. Herink, F. Kurtz, B. Jalali, D. R. Solli, C. Ropers
（导读 肖坤） 孤子束缚态与分子束缚态类似，然而其形成机制与内部动力学尚未在实验中直接观察过。本研究采用时域展宽技术，得到了周期量级锁模激光器谐振腔中孤子分子的飞秒级演化过程，孤子束缚态在谐振腔中往返轨迹表明其动力学可能受拓扑保护。这些发现凸显了超快实时探测的重要作用。
Solitons, particle-like excitations ubiquitous in many fields of physics, have been shown to exhibit bound states akin to molecules. The formation of such temporal soliton bound states and their internal dynamics have escaped direct experimental observation. By means of an emerging time-stretch technique, we resolve the evolution of femtosecond soliton molecules in the cavity of a few-cycle mode-locked laser. We track two- and three-soliton bound states over hundreds of thousands of consecutive cavity roundtrips, identifying fixed points and periodic and aperiodic molecular orbits. A class of trajectories acquires a path-dependent geometrical phase, implying that its dynamics may be topologically protected. These findings highlight the importance of real-time detection in resolving interactions in complex nonlinear systems, including the dynamics of soliton bound states, breathers, and rogue waves.
Femtosecond x-ray spectroscopy of an electrocyclic ring-opening reaction
Andrew R. Attar, Aditi Bhattacherjee, C. D. Pemmaraju, Kirsten Schnorr, Kristina D. Closser, David Prendergast, Stephen R. Leone
（导读 肖坤） 超快光激发的1,3-环己二烯电环化开环反应通常需要通过中间激发态最小值进行，而这会导致非绝热弛豫到光产物基态的异构化。本研究在近碳K边（~284 电子伏特）使用飞秒软X射线光谱法直接探测出该瞬态中间态的价电子结构，该结构在紫外光激发后60±20 fs内出现，而衰减时间常数为110±60 fs。
The ultrafast light-activated electrocyclic ring-opening reaction of 1,3-cyclohexadiene is a fundamental prototype of photochemical pericyclic reactions. Generally, these reactions are thought to proceed through an intermediate excited-state minimum (the so-called pericyclic minimum), which leads to isomerization via nonadiabatic relaxation to the ground state of the photoproduct. Here, we used femtosecond (fs) soft x-ray spectroscopy near the carbon K-edge (~284 electron volts) on a tabletop apparatus to directly reveal the valence electronic structure of this transient intermediate state. The core-to-valence spectroscopic signature of the pericyclic minimum observed in the experiment was characterized, in combination with time-dependent density functional theory calculations, to reveal overlap and mixing of the frontier valence orbital energy levels. We show that this transient valence electronic structure arises within 60 ± 20 fs after ultraviolet photoexcitation and decays with a time constant of 110 ± 60 fs.
Long-range hot-carrier transport in hybrid perovskites visualized by ultrafast microscopy
Zhi Guo, Yan Wan, Mengjin Yang, Jordan Snaider, Kai Zhu, Libai Huang（黄立白，普渡大学）
（导读 王腾） 热载流子如果可以在热化之前被捕获，则太阳能电池的效率有望可以突破Shockley-Queisser极限。本研究利用超快速瞬态显微吸收光谱(TAM)直接观察了CH3NH3PbI3薄膜中热载流子的迁移，揭示了热载流子三种不同的输运方式。研究结果揭示了基于混合钙钛矿的热载流子器件的潜在应用价值。
The Shockley-Queisser limit for solar cell efficiency can be overcome if hot carriers can be harvested before they thermalize. Recently, carrier cooling time up to 100 picoseconds was observed in hybrid perovskites, but it is unclear whether these long-lived hot carriers can migrate long distance for efficient collection. We report direct visualization of hot-carrier migration in methylammonium lead iodide (CH3NH3PbI3) thin films by ultrafast transient absorption microscopy, demonstrating three distinct transport regimes. Quasiballistic transport was observed to correlate with excess kinetic energy, resulting in up to 230 nanometers transport distance that could overcome grain boundaries. The nonequilibrium transport persisted over tens of picoseconds and ~600 nanometers before reaching the diffusive transport limit. These results suggest potential applications of hot-carrier devices based on hybrid perovskites.
Adam G. Kelly, Toby Hallam, Claudia Backes…Georg S. Duesberg, Jonathan N. Coleman
（导读 王腾） 由相互连接的各类二维纳米片组成的全印刷晶体管是纳米科学的一个重要目标。本研究利用电解门控制制备了全印刷垂直堆叠晶体管。该晶体管的电极和沟道由石墨烯和过渡金属二硫化物所构成，并表现出良好的器件性能。这些特性允许在相对低的驱动电压下承载更大的电流。
All-printed transistors consisting of interconnected networks of various types of two-dimensional nanosheets are an important goal in nanoscience. Using electrolytic gating, we demonstrate all-printed, vertically stacked transistors with graphene source, drain, and gate electrodes, a transition metal dichalcogenide channel, and a boron nitride (BN) separator, all formed from nanosheet networks. The BN network contains an ionic liquid within its porous interior that allows electrolytic gating in a solid-like structure. Nanosheet network channels display on:off ratios of up to 600, transconductances exceeding 5 millisiemens, and mobilities of >0.1 square centimeters per volt per second. Unusually, the on-currents scaled with network thickness and volumetric capacitance. In contrast to other devices with comparable mobility, large capacitances, while hindering switching speeds, allow these devices to carry higher currents at relatively low drive voltages.
Unequivocal determination of complex molecular structures using anisotropic NMR measurements
Yizhou Liu, Josep Saurí, Emily Mevers…Gary E. Martin, R. Thomas Williamson http://science.sciencemag.org/content/356/6333/eaam5349
（导读 马欢） 利用核磁共振（NMR）数据解析复杂分子的结构时可能出现错误。本研究提供了一种新的方法，将各向异性NMR参数，特别是残余偶极耦合（RDC）和残留化学位移各向异性（RCSA）与计算机辅助结构说明（CASE）程序、密度泛函理论（DFT）计算相结合，该方法可以有效地确定复杂分子三维结构，是对传统NMR技术的重要改进。
Assignment of complex molecular structures from nuclear magnetic resonance (NMR) data can be prone to interpretational mistakes. Residual dipolar couplings and residual chemical shift anisotropy provide a spatial view of the relative orientations between bonds and chemical shielding tensors, respectively, regardless of separation. Consequently, these data constitute a reliable reporter of global structural validity. Anisotropic NMR parameters can be used to evaluate investigators’ structure proposals or structures generated by computer-assisted structure elucidation. Application of the method to several complex structure assignment problems shows promising results that signal a potential paradigm shift from conventional NMR data interpretation, which may be of particular utility for compounds not amenable to x-ray crystallography.
High-performance vitrimers from commodity thermoplastics through dioxaborolane metathesis
Max Röttger, Trystan Domenech, Rob van der Weegen, Antoine Breuillac, Renaud Nicolaÿ, Ludwik Leibler
（导读 卓思琪） Vitrimers是兼顾强度和可重复利用性的新型塑料。本文报道了一种快速高效二氧杂戊硼烷置换方法，可利用此方法处理聚甲基丙烯酸甲酯、聚苯乙烯和高密度聚乙烯等商品化热塑性塑料，在其分子间形成动态交联但维持热塑性，得到vitrimers塑料。该策略对碳-碳单键为主干的多聚物适用。
Windmills, cars, and dental restoration demand polymer materials and composites that are easy to process, assemble, and recycle while exhibiting outstanding mechanical, thermal, and chemical resistance. Vitrimers, which are polymer networks able to shuffle chemical bonds through exchange reactions, could address these demands if they were prepared from existing plastics and processed with fast production rates and current equipment. We report the metathesis of dioxaborolanes, which is rapid and thermally robust, and use it to prepare vitrimers from polymers as different as poly(methyl methacrylate), polystyrene, and high-density polyethylene that, although permanently cross-linked, can be processed multiple times by means of extrusion or injection molding. They show superior chemical resistance and dimensional stability and can be efficiently assembled. The strategy is applicable to polymers with backbones made of carbon-carbon single bonds.
Tungsten-182 heterogeneity in modern ocean island basalts
Andrea Mundl, Mathieu Touboul, Matthew G. Jackson, James M. D. Day, Mark D. Kurz, Vedran Lekic, Rosalind T. Helz, Richard J. Walker
（导读 赵维娜） 现代大洋岛玄武岩（OIB）钨同位素数据具有变化的182W/184W，且与3He/4He负相关，说明OIB接近太阳系最初6000万年形成的地球内部区域，分析显示其含有金属且富含惰性气体。其最可能的源区是位于Hawaii, Samoa 和 Iceland下方的一些超低速带，而非具有正常182W及低3He/4He的热点OIB下方。
New tungsten isotope data for modern ocean island basalts (OIB) from Hawaii, Samoa, and Iceland reveal variable 182W/184W, ranging from that of the ambient upper mantle to ratios as much as 18 parts per million lower. The tungsten isotopic data negatively correlate with 3He/4He. These data indicate that each OIB system accesses domains within Earth that formed within the first 60 million years of solar system history. Combined isotopic and chemical characteristics projected for these ancient domains indicate that they contain metal and are repositories of noble gases. We suggest that the most likely source candidates are mega–ultralow-velocity zones, which lie beneath Hawaii, Samoa, and Iceland but not beneath hot spots whose OIB yield normal 182W and homogeneously low 3He/4He.
The applied value of public investments in biomedical research
Danielle Li, Pierre Azoulay, Bhaven N. Sampat
（导读 郭思瑶） 科学上的公共投资是否有实际应用是科学家与决策者长期争论的话题。研究人员利用27年间专利数据与美国国家健康研究所（NIH）资助间的联系，发现10%的资助直接产生专利但30%的资助产生被专利人引用的学术文章。NIH大量的研究成果对于专利的影响是间接的。
Scientists and policy-makers have long argued that public investments in science have practical applications. Using data on patents linked to U.S. National Institutes of Health (NIH) grants over a 27-year period, we provide a large-scale accounting of linkages between public research investments and subsequent patenting. We find that about 10% of NIH grants generate a patent directly but 30% generate articles that are subsequently cited by patents. Although policy-makers often focus on direct patenting by academic scientists, the bulk of the effect of NIH research on patenting appears to be indirect. We also find no systematic relationship between the “basic” versus “applied” research focus of a grant and its propensity to be cited by a patent.
Giant viruses with an expanded complement of translation system components
Frederik Schulz, Natalya Yutin, Natalia N. Ivanova…Eugene V. Koonin, Tanja Woyke
（导读 卓思琪） 巨型病毒的发现模糊了病毒和细胞生命的界限。本文报道了元基因组数据中一类名为Klosneuviruses的巨型病毒，可编码一种扩展的翻译组件。系统基因组学分析发现，Klosneuviruses并不源自细胞的祖先，而是由小病毒获取大量宿主基因后形成的。
The discovery of giant viruses blurred the sharp division between viruses and cellular life. Giant virus genomes encode proteins considered as signatures of cellular organisms, particularly translation system components, prompting hypotheses that these viruses derived from a fourth domain of cellular life. Here we report the discovery of a group of giant viruses (Klosneuviruses) in metagenomic data. Compared with other giant viruses, the Klosneuviruses encode an expanded translation machinery, including aminoacyl transfer RNA synthetases with specificities for all 20 amino acids. Notwithstanding the prevalence of translation system components, comprehensive phylogenomic analysis of these genes indicates that Klosneuviruses did not evolve from a cellular ancestor but rather are derived from a much smaller virus through extensive gain of host genes.
De novo assembly of the Aedes aegypti genome using Hi-C yields chromosome-length scaffolds
Olga Dudchenko, Sanjit S. Batra, Arina D. Omer…Aviva Presser Aiden, Erez Lieberman Aiden
（导读 卓思琪） 本研究通过结合Hi-C数据和已有组装草图开发了染色体长度支架的生成方法，并得到了埃及伊蚊（Ae.aegypti）和致倦库蚊（Culex quinquefasciatus）的基因组组装，显示了所有基因重排都发生在染色体臂内部而非之间。该基因组装程序快、准、方便，可多物种应用。
The Zika outbreak, spread by the Aedes aegypti mosquito, highlights the need to create high-quality assemblies of large genomes in a rapid and cost-effective way. Here we combine Hi-C data with existing draft assemblies to generate chromosome-length scaffolds. We validate this method by assembling a human genome, de novo, from short reads alone (67× coverage). We then combine our method with draft sequences to create genome assemblies of the mosquito disease vectors Ae. Aegypti and Culex quinquefasciatus, each consisting of three scaffolds corresponding to the three chromosomes in each species. These assemblies indicate that almost all genomic rearrangements among these species occur within, rather than between, chromosome arms. The genome assembly procedure we describe is fast, inexpensive, and accurate, and can be applied to many species.
Engrams and circuits crucial for systems consolidation of a memory
Takashi Kitamura, Sachie K. Ogawa, Dheeraj S. Roy, Teruhiro Okuyama, Mark D. Morrissey, Lillian M. Smith, Roger L. Redondo, Susumu Tonegawa
（导读 李骏） 情景记忆的形成需要海马具有快速的突触可塑性，而其永久储存则依赖于新皮层网络中的逐步巩固。然而，支持新皮层进行记忆巩固的机制尚不明确。本研究发现新皮层前额叶的记忆痕迹细胞在初始学习中快速生成。信号产生后，前额叶承载记忆痕迹的神经元在海马记忆痕迹神经元的支持下，随着时间逐渐成熟。海马细胞的记忆痕迹逐渐消退，而基底外侧杏仁核的记忆痕迹则继续维持。
Episodic memories initially require rapid synaptic plasticity within the hippocampus for their formation and are gradually consolidated in neocortical networks for permanent storage. However, the engrams and circuits that support neocortical memory consolidation have thus far been unknown. We found that neocortical prefrontal memory engram cells, which are critical for remote contextual fear memory, were rapidly generated during initial learning through inputs from both the hippocampal–entorhinal cortex network and the basolateral amygdala. After their generation, the prefrontal engram cells, with support from hippocampal memory engram cells, became functionally mature with time. Whereas hippocampal engram cells gradually became silent with time, engram cells in the basolateral amygdala, which were necessary for fear memory, were maintained. Our data provide new insights into the functional reorganization of engrams and circuits underlying systems consolidation of memory.
Deconstructing behavioral neuropharmacology with cellular specificity
Brenda C. Shields, Elizabeth Kahuno, Charles Kim, Pierre F. Apostolides, Jennifer Brown, Sarah Lindo, Brett D. Mensh, Joshua T. Dudman, Luke D. Lavis, Michael R. Tadross
（导读 李骏） 行为由分子、细胞、环路层面上的机制决定。然而，由于许多蛋白在脑内广泛地表达，在特定细胞上操纵它们变得困难。本研究实现了将药理学的速度和分子特异性与细胞类型特异性相结合。DART（Drugs Acutely Restricted by Tethering）技术可将药物迅速地定位到特定细胞的表面，且无需事先对靶点做修饰。研究人员研制了一种AMPA受体拮抗DART，并用其揭示了帕金森造模小鼠的运动缺陷与AMPA受体的关系。
Behavior has molecular, cellular, and circuit determinants. However, because many proteins are broadly expressed, their acute manipulation within defined cells has been difficult. Here, we combined the speed and molecular specificity of pharmacology with the cell type specificity of genetic tools. DART (drugs acutely restricted by tethering) is a technique that rapidly localizes drugs to the surface of defined cells, without prior modification of the native target. We first developed an AMPAR antagonist DART, with validation in cultured neuronal assays, in slices of mouse dorsal striatum, and in behaving mice. In parkinsonian animals, motor deficits were causally attributed to AMPARs in indirect spiny projection neurons (iSPNs) and to excess phasic firing of tonically active interneurons (TANs). Together, iSPNs and TANs (i.e., D2 cells) drove akinesia, whereas movement execution deficits reflected the ratio of AMPARs in D2 versus D1 cells. Finally, we designed a muscarinic antagonist DART in one iteration, demonstrating applicability of the method to diverse targets.
Reovirus infection triggers inflammatory responses to dietary antigens and development of celiac disease
Romain Bouziat, Reinhard Hinterleitner, Judy J. Brown…Terence S. Dermody, Bana Jabri
（导读 郭思瑶） 病毒感染可能引起乳糜泻和辅助性T细胞1(TH1)对抗食用麸质的免疫活动，本研究构建了一个病毒感染模型来验证这一观点。呼肠孤病毒是一种无毒性的病原体，但是结果显示它能通过抑制外周性调节T细胞(pTreg)转换和促进TH1免疫来破坏肠道内免疫内稳态；人体试验则显示呼肠孤病毒可能引发乳糜泄。
Viral infections have been proposed to elicit pathological processes leading to the initiation of T helper 1 (TH1) immunity against dietary gluten and celiac disease (CeD). To test this hypothesis and gain insights into mechanisms underlying virus-induced loss of tolerance to dietary antigens, we developed a viral infection model that makes use of two reovirus strains that infect the intestine but differ in their immunopathological outcomes. Reovirus is an avirulent pathogen that elicits protective immunity, but we discovered that it can nonetheless disrupt intestinal immune homeostasis at inductive and effector sites of oral tolerance by suppressing peripheral regulatory T cell (pTreg) conversion and promoting TH1 immunity to dietary antigen. Initiation of TH1 immunity to dietary antigen was dependent on interferon regulatory factor 1 and dissociated from suppression of pTreg conversion, which was mediated by type-1 interferon. Last, our study in humans supports a role for infection with reovirus, a seemingly innocuous virus, in triggering the development of CeD.
Causal role for inheritance of H3K27me3 in maintaining the OFF state of a Drosophila HOX gene
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. Hence, in this context, the inheritance of H3K27 trimethylation conveys epigenetic memory.
Propagation of Polycomb-repressed chromatin requires sequence-specific recruitment to DNA
Friederike Laprell, Katja Finkl, Jürg Müller
（导读 卓思琪） 多梳蛋白抑制复合物2（PRC2）传递组蛋白H3K27三甲基化（H3K27me3）一般被认为不依赖于DNA序列。本研究发现H2K27me3传递到新的核小体上需要将PRC2序列特异性地靶向到多梳响应元件（PRE）DNA上，但标记后的核小体在复制过程中以序列非依赖的模式传递给子细胞。
Epigenetic inheritance models posit that during Polycomb repression, Polycomb repressive complex 2 (PRC2) propagates histone H3 lysine 27 trimethylation (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. After excision in replication-stalled cells, H3K27me3 levels stay high and repression persists. H3K27me3-marked nucleosomes therefore provide a memory of repression that is transmitted in a sequence-independent manner to daughter strand DNA during replication. In contrast, propagation of H3K27 trimethylation to newly incorporated nucleosomes requires sequence-specific targeting of PRC2 to PRE DNA.
Xiaoyi Wang, Danesh Moazed
（导读 吴媛媛） 组蛋白H3K9甲基化的顺式基因沉默状态究竟是如何稳定地遗传的？研究人员利用酵母证实，除了序列非依赖的机制外，基因沉默的表观遗传依赖CREB家族转录因子的结合位点，因此DNA序列在可遗传的基因沉默中发挥着关键作用。
Epigenetic inheritance mechanisms play fundamental roles in maintaining cellular memory of gene expression states. In fission yeast, histone H3 lysine 9 (H3K9) is methylated (H3K9me) at heterochromatic domains. These domains can be epigenetically inherited when epe1+, 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. We show that in epe1+ cells, in addition to sequence-independent mechanisms that propagate H3K9me, epigenetic inheritance of silencing requires binding sites for sequence-dependent activating transcription factor (ATF)–adenosine 3′,5′-monophosphate (cAMP) response element–binding protein (CREB) family transcription factors within their native chromosomal context. Thus, specific DNA sequences contribute to cis inheritance of H3K9me and silent epigenetic states.
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