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Nature Contents 8 June 2006 (Vol. 441 pp.667-784)
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[自然要览] （选自英国Nature杂志，2006年6月8日出版） 封面故事：“太古代”地球上存在生命的证据 Stromatolite reef from the Early Archaean era of Australia “太古代”（距今25亿年前）地球上是否存在生命一直是一个激烈争论的问题。这种争 论在很大程度上集中在被称为“叠层石”(stromatolites)的分层沉积结构是否像今天 那样反映群居微生物的活动或反映一些非生物过程。现在，对澳大利亚西部一个引人注 目的10公里长的裸露岩层所做的一项新的分析，为认为那个时候地球上存在生命的观点 提供了支持。这里的“叠层石”已有大约34.30亿年，显示出与在较年轻的微生物礁石 中发现的“叠层石”类似的特点：它不是一系列彼此孤立的化石，却更像以化石形势存 在的一个完整的生态系统。看来，那个时候地球上不但存在生命，而且生命还很兴旺。 封面图片所示为一个来自裸露礁石的锥形“叠层石”：虽然没有刻度标尺，但从Nature 杂志标识底下来看其留下的阴影，就能知道它有多大。（摄影：A. Allwood） （Article p. 716; News and Views） 世界上腿最多的动物再次被发现（Leg work） Biodiversity hotspots: Rediscovery of the world's leggiest animal 世界上腿最多的动物，即一种自其最初于1928年被描述以来一直没有再报道过的千足 虫，去年秋季在其惟一已知栖息地“加利福尼亚植物省”生物多样性热点被再次发现。 一个成年的Illacme plenipes有多达750条腿，而大多数千足虫只有300条左右的腿。其 他相关的和同样稀少的物种在印尼、印度-缅甸和南非的类似热点地区也被发现，这更 加说明了这些地区是生物多样性异常丰富的宝库，是一些极为古老的物种的最后一片家 园。（Brief Communication p. 707） Notch信号通道维持胚胎内“时钟”机制（Notch in the body clock） Noise-resistant and synchronized oscillation of the segmentation clock 一个发育中的胚胎分割成各个部分是由一个“时钟”机制控制的，这个机制由整个胚胎 各个部分中基因转录的同步振荡组成。将计算机模拟和活体移植结合起来所进行的一项 研究显示，Notch信号作用通道维持这些一致的振荡，使早期胚胎中的基因表达噪音静 下来。（Article p. 721; News and Views） 碳在恒星周围气体稳定性中所起的作用（Carbon adds steel） Stabilization of the disk around Pictoris by extremely carbon-rich gas 我们附近的年轻恒星b-Pictoris周围的侧向圆盘是一个原型“碎片盘”，由固体行星类 天体解体后所产生的物质组成，而这些行星类天体可能曾经与太阳系的彗星和小行星相 似。以前的研究工作得出的结论是，该恒星周围的气体应被迅速吹走，这与观测结果是 相反的。来自NASA的FUSE卫星的新的远红外数据，为这种矛盾提供了一个可能的解释： 该圆盘的气体碳含量极高，这使得它很稳定，不会被吹走。（Letter p. 724） 描述粒状物质流动状态的新模型（Truth of grains） A constitutive law for dense granular flows 描述粒状物质怎样在剪切力作用下运动的方程式仍然是一个有争论的问题。Jop等人现 在提出一个新模型，来解释三维体系中致密的颗粒流。他们的模型受到牙膏等粘塑性流 体的行为的启发。该模型研究的结果可以成为地球物理或工业应用中模拟复杂流动的一 个基础工具。（Letter p. 727） 含有扭曲氨基键的化合物的合成（Amides with a twist） Synthesis and structural analysis of 2-quinuclidonium tetrafluoroborate 氨基-氨基键在化学和生物中很普遍。在非环化合物中，氨基键经常是平面的。然而， 在双环“桥头堡”内酰胺中，氨基官能团是高度扭曲的，1938年捷克化学家Rudolf Lukes的一篇著作引起人们对这些“扭曲的氨基”的有趣性质的注意。有趣倒是有趣， 但要生成它们却很难。现在，Kousuke Tani 和 Brian Stoltz报告了他们对一种含有一 个扭曲的氨基键的化合物的首次明确的合成、分离和X-射线晶体定性。他们的合成方法 避开了形成氨基键的传统路径，而用这种方法合成的化合物的获得将使我们对氨基键的 性质有更深了解。（Letter p. 731; News and Views） 动态应力在余震中的作用得到证实（Aftershock tactics） Decay of aftershock density with distance indicates triggering by dynamic stress 余震是最常见的地震类型，过去被认为是由早先的一次“主震”诱导的静态应力诱发 的。最近的研究工作说明，动态应力或晃动也可能是一个因素，而对1984-2002年南加 州地震目录上的地震位置所做的一项分析研究证实了该观点。对余震密度随距主震距离 而减小的情况所做的精密测量显示，余震的概率与在0.2公里至50公里处的地震晃动的 最大幅度是一致的。（Letter p. 735; News and Views） 蜥脚类恐龙也有矮小种类（Small dinosaurs at large） Bone histology indicates insular dwarfism in a new Late Jurassic sauropod dinosaur 认为矮的物种往往在岛屿种群中演化的观点，最近在关于弗洛瑞斯人(Homo floresiensis)和在弗洛瑞斯岛上发现的矮小动物（主要是大象）的讨论中受到很多关 注。现在，似乎同样的事情也曾发生在蜥脚类恐龙身上。在德国北部新发现的化石已被 鉴定为是矮小成年蜥脚类恐龙，可能是在下萨克森盆地的岛屿上从它们体形更大的大陆 同类演化来的。以前，蜥脚类恐龙被认为几乎都是很大的，它们包括“梁龙” （Diplodocus）和“无法龙”（Titanosaurus），而所有较小的蜥脚类恐龙骨头都被假 设为来自未成年的个体。在这些新发现的化石中，是骨头组织学研究证明了它们是成年 个体的。（Letter p. 739） 所有脊椎动物的咽结构的确都同源（Neural crest patterning） Importance of SoxE in neural crest development and the evolution of the pharynx 神经脊细胞（Neural crest cells）是脊椎动物的一个定义特点，它们在胚胎中确定脸 部、头部的很多地方、以及咽部或腮部的特征。然而，在被称为七鳃鳗的原始无颚脊椎 动物身上，咽的结构与有颚脊椎动物很不相同，这便提出了关于神经脊细胞在同源结构 的成形中扮演什么角色的问题。用SoxE基因（该基因确定脊椎动物的头部形状）的定向 错误表达所做的一个实验证实，它们在七鳃鳗身上起类似作用。所以，不管结构上有什 么不同，所有脊椎动物的咽结构的确都是同源的。（Letter p. 750） 大脑蘑菇体在睡眠调控中的作用（Sleep regulation） A dynamic role for the mushroom bodies in promoting sleep in Drosophila 果蝇是睡眠研究的一个成熟的遗传模型。果蝇具有与我们称之为睡眠的行为相似的行为 模式，但睡眠典型的标志性EEG变化及其阶段尚没有被识别出来，所以不可能说果蝇的 睡眠是否是一个神经过程，以及如果是，涉及到什么神经基质。回答这一问题，是解释 基因影响睡眠的机制的一个重要步骤。现在，两个小组已经解决了这一问题，他们都识 别出，被称为蘑菇体的结构是大脑参与睡眠调控的部分。这一发现使我们从神经角度对 果蝇的睡眠有了一个认识，并且还将睡眠与蘑菇体的其他已知功能——学习和记忆联系 了起来。（Letters pp. 753, 757） 皮层神经通信的另一种机制（A slice of the action） Modulation of intracortical synaptic potentials by presynaptic somatic membrane potential 大脑皮层的神经元之间的迅速通信，涉及一个动作电位的传播，但关于这个动作电位是 皮层神经通信的惟一形式的假设却可能需要修正。整细胞记录表明，可能存在另一种机 制。膜电位的变化，如与轴突活动相关的膜电位变化，也可能沿轴突传播，并可明显改 变联会后电位的平均幅度。这种类型的神经信号可能有重要后果，如在感官刺激、清醒 到睡眠的过渡、以及癫痫发作等条件下，膜电位会发生很大变化。（Letter p. 761） 基因在细胞核中的位置会影响其表达（In the right place） SAGA interacting factors confine sub-diffusion of transcribed genes to the nuclear envelope/ Nuclear pore association confers optimal expression levels for an inducible yeast gene 有这样一个事实正在变得清楚：基因在细胞核中的位置会影响它们的表达，两个小组在 本期Nature上报告了酵母中的这种事例。Cabal等人发现，GAL基因的激活会将它们限制 在核外围。Taddei等人报告，仅仅通过阻断或鼓励HXK1基因与核外围的联系来移动该基 因，就能明显改变它的表达。（Letters pp. 770, 774） |
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木虫 (正式写手)
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---------------------- NEWS AND VIEWS ---------------------- Chemistry: Synthesis with a twist Amide bonds underpin protein stability, but distortion from their preferred geometry makes them reactive. An archetypal twisted amide has at last been made, and its chemistry will be revelatory. Harry H. Wasserman http://www.nature.com/nature/journal/v441/n7094/full/441699a.html Palaeontology: Respect for stromatolites Is it time to stop worrying over whether the ancient structures called stromatolites are of microbial origin? ‘Yes’ is the answer to emerge from field and lab work on a 3,430-million-year-old marine ecosystem. Stanley M. Awramik http://www.nature.com/nature/journal/v441/n7094/full/441700a.html Photonics: Transparency on an optical chip A two-laser trick that renders opaque media transparent can be achieved in systems of tiny optical resonators -- with potentially profound consequences for optical communication and information processing. Robert W. Boyd and Daniel J. Gauthier http://www.nature.com/nature/journal/v441/n7094/full/441701a.html Neurobiology: Extending influence Rather than merely firing in a digital on-off fashion, vertebrate neurons may have an analogue aspect to their signalling too -- a finding that will not surprise many who have worked on invertebrate neurons. Eve Marder http://www.nature.com/nature/journal/v441/n7094/full/441702a.html Earthquakes: A hand on the aftershock trigger Received wisdom relates that static stress change associated with an earthquake mainshock is the prime mover of its aftershocks. But a fresh look at the data points the finger at wave-surfing dynamic stress. Ian Main http://www.nature.com/nature/journal/v441/n7094/full/441704a.html Chemical technology: All together now A method that combines techniques for performing chemical synthesis, separation and measurement on a single device illustrates the considerable potential of integrated lab-on-a-chip technology. Stephen J. Haswell http://www.nature.com/nature/journal/v441/n7094/full/441705a.html ---------------------- BRIEF COMMUNICATIONS ---------------------- Biodiversity hotspots: Rediscovery of the world's leggiest animal This ancient animal, found only in a tiny stretch of California, is close to being a true millipede. Paul E. Marek and Jason E. Bond Abstract: http://www.nature.com/nature/journal/v441/n7094/abs/441707a.html Article: http://www.nature.com/nature/journal/v441/n7094/full/441707a.html BRIEF COMMUNICATIONS ARISING Molecular spectroscopy: Complexity of excited-state dynamics in DNA Dimitra Markovitsi, Francis Talbot, Thomas Gustavsson, Delphine Onidas, Elodie Lazzarotto and Sylvie Marguet Abstract: http://www.nature.com/nature/jou ... bs/nature04903.html Article: http://www.nature.com/nature/jou ... ll/nature04903.html Molecular spectroscopy: Complexity of excited-state dynamics in DNA (Reply) Carlos E. Crespo-Hernandez, Boiko Cohen and Bern Kohler Abstract: http://www.nature.com/nature/jou ... bs/nature04904.html Article: http://www.nature.com/nature/jou ... ll/nature04904.html ---------------------- ARTICLES ---------------------- Titan Radar Mapper observations from Cassini's T3 fly-by C. Elachi, S. Wall, M. Janssen, E. Stofan, R. Lopes, R. Kirk, R. Lorenz, J. Lunine, F. Paganelli, L. Soderblom, C. Wood, L. Wye, H. Zebker, Y. Anderson, S. Ostro, M. Allison, R. Boehmer, P. Callahan, P. Encrenaz, E. Flamini, G. Francescetti, Y. Gim, G. Hamilton, S. Hensley, W. Johnson, K. Kelleher, D. Muhleman, G. Picardi, F. Posa, L. Roth, R. Seu, S. Shaffer, B. Stiles, S. Vetrella and R. West Abstract: http://www.nature.com/nature/jou ... bs/nature04786.html Article: http://www.nature.com/nature/jou ... ll/nature04786.html Stromatolite reef from the Early Archaean era of Australia Abigail C. Allwood, Malcolm R. Walter, Balz S. Kamber, Craig P. Marshall and Ian W. Burch Abstract: http://www.nature.com/nature/jou ... bs/nature04764.html Article: http://www.nature.com/nature/jou ... ll/nature04764.html Noise-resistant and synchronized oscillation of the segmentation clock A combination of computer modelling and in vivo transplants demonstrates that the Notch signalling pathway maintains coherent oscillations in gene transcription -- silencing the ‘noisy’ gene expression present in the early embryo. Kazuki Horikawa, Kana Ishimatsu, Eiichi Yoshimoto, Shigeru Kondo and Hiroyuki Takeda Abstract: http://www.nature.com/nature/jou ... bs/nature04861.html Article: http://www.nature.com/nature/jou ... ll/nature04861.html ---------------------- LETTERS ---------------------- Stabilization of the disk around β Pictoris by extremely carbon-rich gas The detection of singly and doubly ionized carbon and neutral atomic oxygen explains the presence of the edge-on disk surrounding the β Pictoris star -- as carbon is extremely overabundant relative to every other measured element, the carbon overabundance should keep the gas disk in keplerian rotation. Aki Roberge, Paul D. Feldman, Alycia J. Weinberger, Magali Deleuil and Jean-Claude Bouret Abstract: http://www.nature.com/nature/jou ... bs/nature04832.html Article: http://www.nature.com/nature/jou ... ll/nature04832.html A constitutive law for dense granular flows A new model is proposed for dense granular flows in three dimensions, inspired by the behaviour of visco-plastic fluids such as toothpaste -- the results could serve as a basic tool for modelling complex flows in geophysical or industrial applications. Pierre Jop, YoA?l Forterre and Olivier Pouliquen Abstract: http://www.nature.com/nature/jou ... bs/nature04801.html Article: http://www.nature.com/nature/jou ... ll/nature04801.html Synthesis and structural analysis of 2-quinuclidonium tetrafluoroborate The first chemical synthesis, isolation and full characterization of bicyclic bridgehead lactams -- those containing a twisted amide bond -- was successful due to the decision to generate the compound by a route other than classical amide bond formation. Kousuke Tani and Brian M. Stoltz Abstract: http://www.nature.com/nature/jou ... bs/nature04842.html Article: http://www.nature.com/nature/jou ... ll/nature04842.html Decay of aftershock density with distance indicates triggering by dynamic stress K. R. Felzer and E. E. Brodsky Abstract: http://www.nature.com/nature/jou ... bs/nature04799.html Article: http://www.nature.com/nature/jou ... ll/nature04799.html Bone histology indicates insular dwarfism in a new Late Jurassic sauropod dinosaur P. Martin Sander, OctA?vio Mateus, Thomas Laven and Nils Knotschke Abstract: http://www.nature.com/nature/jou ... bs/nature04633.html Article: http://www.nature.com/nature/jou ... ll/nature04633.html Intensity of sexual selection along the anisogamy-isogamy continuum Adam Bjork and Scott Pitnick Abstract: http://www.nature.com/nature/jou ... bs/nature04683.html Article: http://www.nature.com/nature/jou ... ll/nature04683.html Social interactions among epithelial cells during tracheal branching morphogenesis Genetic mosaic analysis in Drosophila melanogaster shows that there are two classes of cells in the budding tracheal branches: those that migrate to the tip, and those that follow these lead cells and form a tube. The position of the cell results from competition within the population, with those expressing the highest level of FGF taking the lead positions at the tip, and the others forming the branch stalk. Amin S. Ghabrial and Mark A. Krasnow Abstract: http://www.nature.com/nature/jou ... bs/nature04829.html Article: http://www.nature.com/nature/jou ... ll/nature04829.html Importance of SoxE in neural crest development and the evolution of the pharynx David W. McCauley and Marianne Bronner-Fraser Abstract: http://www.nature.com/nature/jou ... bs/nature04691.html Article: http://www.nature.com/nature/jou ... ll/nature04691.html A dynamic role for the mushroom bodies in promoting sleep in Drosophila Jena L. Pitman, Jermaine J. McGill, Kevin P. Keegan and Ravi Allada Abstract: http://www.nature.com/nature/jou ... bs/nature04739.html Article: http://www.nature.com/nature/jou ... ll/nature04739.html Sleep in Drosophila is regulated by adult mushroom bodies William J. Joiner, Amanda Crocker, Benjamin H. White and Amita Sehgal Abstract: http://www.nature.com/nature/jou ... bs/nature04811.html Article: http://www.nature.com/nature/jou ... ll/nature04811.html Modulation of intracortical synaptic potentials by presynaptic somatic membrane potential Yousheng Shu, Andrea Hasenstaub, Alvaro Duque, Yuguo Yu and David A. McCormick Abstract: http://www.nature.com/nature/jou ... bs/nature04720.html Article: http://www.nature.com/nature/jou ... ll/nature04720.html Germline transmission of genetically modified primordial germ cells Primordial germ cells (PGCs) can be isolated from chicken blood, propagated in culture indefinitely, and genetically modified to make transgenic chickens -- in addition, the chicken PGCs can be induced in vivo to differentiate into embryonic germ cells that contribute to somatic tissues. Marie-Cecile van de Lavoir, Jennifer H. Diamond, Philip A. Leighton, Christine Mather-Love, Babette S. Heyer, Renee Bradshaw, Allyn Kerchner, Lisa T. Hooi, Terri M. Gessaro, Susan E. Swanberg, Mary E. Delany and Robert J. Etches Abstract: http://www.nature.com/nature/jou ... bs/nature04831.html Article: http://www.nature.com/nature/jou ... ll/nature04831.html SAGA interacting factors confine sub-diffusion of transcribed genes to the nuclear envelope The dynamic motility of GAL genes becomes confined at the nuclear periphery after activation -- components of the SAGA histone acetyltransferase complex are required for this confinement, as well as an mRNA export factor. Ghislain G. Cabal, Auguste Genovesio, Susana Rodriguez-Navarro, Christophe Zimmer, Olivier Gadal, Annick Lesne, Henri Buc, Frank Feuerbach-Fournier, Jean-Christophe Olivo-Marin, Eduard C. Hurt and Ulf Nehrbass Abstract: http://www.nature.com/nature/jou ... bs/nature04752.html Article: http://www.nature.com/nature/jou ... ll/nature04752.html Nuclear pore association confers optimal expression levels for an inducible yeast gene Interfering with localization of the HXK1 gene -- by antagonizing its association with the nuclear periphery or promoting it -- can affect gene expression. Angela Taddei, Griet Van Houwe, Florence Hediger, Veronique Kalck, Fabien Cubizolles, Heiko Schober and Susan M. Gasser Abstract: http://www.nature.com/nature/jou ... bs/nature04845.html Article: http://www.nature.com/nature/jou ... ll/nature04845.html ***** |
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