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Nature Contents 28 September 2006 (Vol. 443 pp374-480 )
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[自然要览] （选自英国Nature杂志，2006年9月28日出版） 封面故事：固体中或室温下的玻色－爱因斯坦凝聚 Bose–Einstein condensation of exciton polaritons / Bose–Einstein condensation of quasi-equilibrium magnons at room temperature under pumping 玻色－爱因斯坦凝聚（BEC）是首次于1924年假设存在的一种物质形式，已经在 超低温度下、在稀释原子气体中进行了著名的演示试验。现在，科学家正在为寻 找BEC能够出现的固态体系做很多努力。理论上，半导体微腔（光子被束缚在其 中，并与电子激发态耦合在一起，导致偏振子的生成）有可能允许BEC在低温学 中标准的温度下出现。现在，Kasprzak等人报告了偏振子在这样一个微腔中被激 发的实验。 在超过一个临界偏振子密度时，一个宏观量子相的自发形成就会出 现，代表一种固态的BEC。如果光子与固态激发的耦合足够强的话，BEC还应可能 在更高温度下出现。Demokritov等人已经做到了这一点，他们在室温下、在一种 磁振子（一种类型的磁激发）气体中观测到了BEC。（Article p. 409; Letter p. 430; N&V）封面所示为BEC开始形成时的粒子-粒子相互作用。 书评：《性、药物和DNA》（Called to the bar） Science uncut 我们的书评人说，Michael Stebbins的《性、药物和DNA》是用一部书的篇幅侈 谈不敬的生物，是分子生物学家的世界观。Stebbins 所谈的是其他科学家不敢 公开谈论的“狗屁话”。书中的话题从政治腐败和被怀疑销售饮食添加剂到针对 进化的宗教案例无所不包。有些话题是切中要害的，而有些则没有说到点子上。 但如果你要找的是很可能在下班后的生物学家喜欢光顾的某个酒吧中能够听到的 那种即兴的、粗俗的高谈阔论，该书将是适合你看的。（Books and Arts p. 396） 从脚上产丝的毒蜘蛛（Silk root） Biomaterials: Silk-like secretion from tarantula feet 蜘蛛是从被称为腹部喷丝头的器官吐丝的，它们用自己所吐的丝来捕捉猎物、保 护自己、进行繁殖和扩散。科学家发现，名为zebra tarantulas的毒蜘蛛从其脚 上分泌一种像丝的物质，用它来帮助自己附着在光滑的垂直平面上。该发现让我 们知道了一种新的蜘蛛丝来源以及一种新的附着机制，并为研究蜘蛛丝的演化提 供了一个窗口：与产生这种跗骨丝有关的遗传机制应能够表明，蜘蛛丝的最初功 能是增加牵引力、还是后来才用于该目的的。（Brief Communication p. 407） 与干细胞衰老调控有关的蛋白（Stem cell ageing） Stem-cell ageing modified by the cyclin-dependent kinase inhibitor p16INK4a 在本期Nature中，三个实验室分别报告了一种蛋白的发现。该蛋白专门在干细胞 中调控衰老。 这个发现可帮助回答一个根本问题：为什么哺乳动物的祖先细胞 随着年龄增长会逐渐失去其分裂和生成新细胞的能力？Norman Sharpless及其同 事培育出一种剔出了肿瘤抑制因子p16 INK4a的小鼠，该因子是细胞周期控制中 涉及的一种蛋白，已知会以一种依赖于年龄的方式表达。在对该蛋白在血液、胰 腺和大脑的再生中所起作用进行的研究中，三个小组分别发现，p16 INK4a不仅 是一种生物标记，而且是衰老过程的一个促成因子。通过比较p16 INK4a在小鼠 体内表达增多或减少所产生的效应，他们发现，p16 INK4a阻止干细胞的增殖， 但只是在比较老的小鼠体内。综合起来，该研究表明，p16 INK4a通过肿瘤抑制 因子的行动减少癌症的发病，与此同时通过降低干细胞功能对衰老做出贡献。该 研究还表明，2-型糖尿病也许与胰岛失去再生能力有关，阻断该蛋白在某些组织 中的作用，也许能够抵抗衰老的某些效应。（Article p. 421; Letters pp. 448, 453; N&V） 高质量恒星的质量怎样增长？（Stars in the making） Infall of gas as the formation mechanism of stars up to 20 times more massive than the Sun 高质量或OB-型恒星能支配星系的出现和演化，并且肯定会合成重元素和通过高 能风和超新星影响星际介质。但当前关于恒星形成的模型无法解释它们的存在。 低质量恒星最初通过从周围物质中吸收气体来增长。但对一颗比太阳质量大10倍 以上的恒星，强大的恒星辐射预计会抑制其吸收物质，并限制其质量的增长。现 在，对朝向一个高质量恒星形成区域的一条氨线所做的观测，为认为高质量恒星 通过非球状增长来形成的理论提供了支持：气体似乎是朝向一颗非常年轻的、约 为太阳质量20倍的恒星内降落来帮助其增长的。（Letter p. 427） 流体并非不可压缩（Go without the flow） Violation of the incompressibility of liquid by simple shear flow 多年来成功用来描述气流和液流的标准流体动力学理论有一大假设：流体是注定 不能压缩的。过去人们认为，对大多数体系，在流速接近声速之前，这个假设是 成立的。但现在，研究表明，如果将粘度对密度的依赖考虑进去的话，即便对简 单的剪切流，不可压缩的条件也会被违反。这些结果也许会为了解与低雷诺数下 液体机械不稳定性相关的各种不同现象提供线索，包括在如金属气体和地幔等非 常粘的液体中所看到的剪切带效应。（Letter p. 434） 大气中甲烷水平变化的原因（Methane glut postponed） Contribution of anthropogenic and natural sources to atmospheric methane variability 过去20年里大气甲烷水平的变化有很好的记录，但这些变化的原因仍然不确定。 Bousquet等人采用倒转的（即从上到下的）模拟方法来对1983和2004年间不同来 源的甲烷排放所发生的变化进行量化。他们发现，上个世纪90年代大气甲烷增长 速度的下降是由人为因素造成的排放的下降引起的，但人为因素造成的排放1999 年以来又再次增加了。迄今，这种趋势一直被湿地排放的巧合降低所掩盖，但它 有可能引起不远的将来甲烷总量再次增加。（Letter p. 439; N&V） 亚马逊/圭亚那地盾地区的生物数据库（An overview of the Amazon） Continental-scale patterns of canopy tree composition and function across Amazonia 在亚马逊流域/圭亚那地盾地区从事研究工作的研究人员积累了大量生态学数据 集。现在，这项研究工作已经被综合在一个数据库中，内容涵盖25万棵树，它所 提供的信息能够明显帮助我们认识亚马逊生态系统的生物多样性及其在全球气候 系统中的位置。整个亚马逊地区树木组成和功能中两个主导梯度很明显，反映了 土壤肥沃程度的分布和旱季长度的差别。这些数据还表明，圭亚那地盾中豆类的 主导地位是由于它们的种子质量大，所受到的干扰小，而不是由于它们的根部能 够适应贫瘠的土壤。（Letter p. 444） 油菜类固醇和茁长素之间的相互作用（Plant hormones linked） BRX mediates feedback between brassinosteroid levels and auxin signalling in root growth 油菜类固醇和茁长素是植物生长的重要调控因子，这两个通道经常调控同样基因 的事实表明，它们之间一定有某种相互作用。而它们到底是怎样相互作用的却仍 然是个谜，但新的证据表明，它们是在相当早的时候就有相互作用，甚至在胚根 生长的最初阶段，它们就通过一个反馈环进行交流，这个反馈环以一种依赖于茁 长素的方式维持油菜类固醇的水平。反过来，油菜类固醇会限制由茁长素诱导产 生的转录响应的速度。对油菜类固醇水平敏感的拟南芥基因数量要比以前所认为 的多很多，已知调控根部细胞增殖和伸长的BREVIS RADIX基因，被发现在油菜类 固醇/茁长素相互作用中是一个重要参与者。（Letter p. 458） 细胞溶解酶颗粒真正的输送方式（Special delivery） Centrosome polarization delivers secretory granules to the immunological synapse 细胞毒性T-淋巴细胞是免疫系统的一个重要部分，在免疫突触上通过释放分泌性 溶酶体中的内容来杀死目标。人们一般假设（通过与黑素细胞进行比较），细胞 溶解酶颗粒是通过短的、加号端朝前的微管从微管组织中心向肌动蛋白细胞骨架 运动的，目的是到达免疫突触。但实际上不是这样。现在，细胞毒性T-淋巴细胞 被发现独立于肌动蛋白或加号端微管马达，而是利用一种由中心体的运动控制的 新机制来输送致命的细胞溶解酶颗粒。（Letter p. 462） 酵母细胞中的“沙漏”（Picture Caption Hourglass figures） Structural insights into yeast septin organization from polarized fluorescence microscopy 在重要的亚微米尺度上来研究细胞结构的分析方法几乎没有。Alina Vrabioiu 和 Timothy Mitchison已经研究出一种新方法，并用它来解决关于正在分裂的酵 母细胞中的“沙漏”特征的结构的一个长期存在的争论。刚性附着的GFP的偏振 荧光显微镜观测结果，被用来确定septin细丝的组织和septin的动态。Septin是 与细胞分裂密切相关的一种聚合GTP酶。研究人员观察到，这些细丝在活酵母中 形成有序组合，并在胞质分裂(cytokinesis)前转动90°。（Letter p. 466） ATP酶泵离子的工作方式（Ion pumps: the outside story） Ion permeation through the Na+,K+-ATPase P-型ATP酶离子泵存在于几乎所有细胞膜中，推动离子逆其浓度梯度穿过细胞 膜。结构研究在近年来取得巨大进展，现在我们对离子泵里面是什么样子已经知 道了很多，但仍然不清楚它们是怎样在一侧收集离子而在另一侧释放它们。现 在，通过利用海洋毒素palytoxin来解耦Na+、K+-ATP酶的泵离子转位通道的控制 门，从而将该泵转变成一种阳离子通道，Nicolás Reyes 和 David Gadsby获得 了关于离子泵作用方式的一个新观点。在细胞外侧，离子通道以一个又深、又宽 的门廊的形式开始，这个门廊突然变窄，形成一个阳离子选择性过滤器，由酸性 侧链组成。引人注目的是，将它们当中仅仅一个的负电荷逆转，就会将该通道从 阳离子选择性通道变成阴离子选择性通道。（Letter p. 470） |
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---------------------- NEWS AND VIEWS ---------------------- Ecology: A pitcher of things to come Big conclusions can be drawn from the tiny ecosystems that flourish in carnivorous pitcher plants. Manipulating habitat size and predator abundance reveals which is more important to ecosystem dynamics. Jonathan B Shurin 10.1038/443399a http://www.nature.com/nature/journal/v443/n7110/full/443399a.html Chemistry: Hydrogen at the flick of a switch Before hydrogen can be used as a transportation fuel, a safe storage system for the gas must be found. Metal clusters that release hydrogen in response to an electric current may be a step in the right direction. Masanori Takimoto and Zhaomin Hou 10.1038/443400a http://www.nature.com/nature/journal/v443/n7110/full/443400a.html Evolution: Different paths to the same end Genetic dissection of a yeast gene-regulatory pathway shows that the logical output of such a pathway can remain the same even though the molecular mechanisms underlying the output have diverged remarkably. Antonis Rokas 10.1038/443401a http://www.nature.com/nature/journal/v443/n7110/full/443401a.html Condensed-matter physics: Coherent questions Bose-Einstein condensation occurs when many particles enter into the same, coherent quantum state, and is now claimed to occur in various systems of 'quasiparticles' in solids. But is it the right term to use here? David Snoke 10.1038/443403a http://www.nature.com/nature/journal/v443/n7110/full/443403a.html Ageing: Balancing regeneration and cancer The proliferation of cells must balance the longevity assured by tissue renewal against the risk of developing cancer. The tumour-suppressor protein p16INK4a seems to act at the pivot of this delicate equilibrium. Christian M Beausejour and Judith Campisi 10.1038/nature05221 http://www.nature.com/nature/jou ... ll/nature05221.html Climate change: A nasty surprise in the greenhouse The Kyoto Protocol aims to reduce emissions of greenhouse gases such as methane. But it seems that the fall in human-induced methane emissions in the 1990s was only transitory, and atmospheric methane might rise again. Jos Lelieveld 10.1038/443405a http://www.nature.com/nature/journal/v443/n7110/full/443405a.html ---------------------- BRIEF COMMUNICATIONS ---------------------- Biomaterials: Silk-like secretion from tarantula feet Stanislav N Gorb et al. 10.1038/443407a Abstract: http://www.nature.com/nature/journal/v443/n7110/abs/443407a. html Article: http://www.nature.com/nature/journal/v443/n7110/full/443407a. html BRIEF COMMUNICATIONS ARISING Plant genetics: Increased outcrossing in hothead mutants Peng Peng, Simon W.-L. Chan, Govind A. Shah and Steve E. Jacobsen 10.1038/nature05251 Abstract: http://www.nature.com/nature/jou ... bs/nature05251.html Article: http://www.nature.com/nature/jou ... ll/nature05251.html Increased outcrossing in hothead mutants (Reply) Susan J. Lolle, Robert E. Pruitt, J. L. Victor and J. M. Young 10.1038/nature05252 Abstract: http://www.nature.com/nature/jou ... bs/nature05252.html Article: http://www.nature.com/nature/jou ... ll/nature05252.html ---------------------- ARTICLES ---------------------- Bose-Einstein condensation of exciton polaritons This paper presents a comprehensive set of experiments in which polaritons are excited in a semiconductor microcavity. Above a critical density of polaritons, massive occupation of the ground state at 19 K is observed and various pieces of experimental evidence point to a spontaneous onset of a macroscopic quantum phase. J. Kasprzak et al. 10.1038/nature05131 Abstract: http://www.nature.com/nature/jou ... bs/nature05131.html Article: http://www.nature.com/nature/jou ... ll/nature05131.html Evolution of alternative transcriptional circuits with identical logic A detailed molecular analysis of related yeast species shows that progressively opposed genetic logics can evolve while resulting in a conserved phenotypic output:mating-type determination. This is the first clear demonstration of the 'genetic drift' principle at a molecular level. Annie E. Tsong, Brian B. Tuch, Hao Li and Alexander D. Johnson 10.1038/nature05099 Abstract: http://www.nature.com/nature/jou ... bs/nature05099.html Article: http://www.nature.com/nature/jou ... ll/nature05099.html Stem-cell ageing modified by the cyclin-dependent kinase inhibitor p16INK4a Three separate labs report that p16INK4a, a protein known to be expressed in an age-dependent manner regulates ageing specifically in stem cells. Studying its role in regeneration of three different tissues, the blood, pancreas, and brain, the three groups separately found that p16INK4a is not only a biomarker, but an effector of ageing. Viktor Janzen et al. 10.1038/nature05159 Abstract: http://www.nature.com/nature/jou ... bs/nature05159.html Article: http://www.nature.com/nature/jou ... ll/nature05159.html ---------------------- LETTERS ---------------------- Infall of gas as the formation mechanism of stars up to 20 times more massive than the Sun Observations of an ammonia line towards a high-mass star forming region indicate that the gas is falling inwards towards a very young star of ~20 times more massive than the Sun, in line with theoretical predictions of non-spherical accretion. Maria T. Beltran et al. 10.1038/nature05074 Abstract: http://www.nature.com/nature/jou ... bs/nature05074.html Article: http://www.nature.com/nature/jou ... ll/nature05074.html Bose-Einstein condensation of quasi-equilibrium magnons at room temperature under pumping Bose-Einstein condensation, the formation of a collective quantum state of identical particles, called bosons, is observed at room temperature in a gas of magnons, which are a type of magnetic excitation. S. O. Demokritov et al. 10.1038/nature05117 Abstract: http://www.nature.com/nature/jou ... bs/nature05117.html Article: http://www.nature.com/nature/jou ... ll/nature05117.html Violation of the incompressibility of liquid by simple shear flow This paper details that the incompressibility of fluids can be violated for even simple shear flows if the density dependence of the viscosity is taken into account. The results may shed light on various phenomena associated with the mechanical instabilities of liquids at low Reynolds number. Akira Furukawa and Hajime Tanaka 10.1038/nature05119 Abstract: http://www.nature.com/nature/jou ... bs/nature05119.html Article: http://www.nature.com/nature/jou ... ll/nature05119.html Contribution of anthropogenic and natural sources to atmospheric methane variability Inverse modelling is used to quantify variations in methane emissions from different sources from 1983-2004 reveals that a decrease in the growth rate of atmospheric methane during the 1990s was caused by a decrease in anthropogenic emissions, but that anthropogenic emissions have increased again since 1999. P. Bousquet et al. 10.1038/nature05132 Abstract: http://www.nature.com/nature/jou ... bs/nature05132.html Article: http://www.nature.com/nature/jou ... ll/nature05132.html Continental-scale patterns of canopy tree composition and function across Amazonia Two dominant gradients in tree composition and function across the Amazon reflect patterns of soil fertility and differences in the length of the dry season length. The dominance of legumes in the Guiana shield may be due to high seed mass and low rates of disturbance, rather than root adaptations to poor soils. Hans ter Steege et al. 10.1038/nature05134 Abstract: http://www.nature.com/nature/jou ... bs/nature05134.html Article: http://www.nature.com/nature/jou ... ll/nature05134.html Increasing p16INK4a expression decreases forebrain progenitors and neurogenesis during ageing Three separate labs report that p16INK4a, a protein known to be expressed in an age-dependent manner regulates ageing specifically in stem cells. Studying its role in regeneration of three different tissues, the blood, pancreas, and brain, the three groups separately found that p16INK4a is not only a biomarker, but an effector of ageing. Anna V. Molofsky et al. 10.1038/nature05091 Abstract: http://www.nature.com/nature/jou ... bs/nature05091.html Article: http://www.nature.com/nature/jou ... ll/nature05091.html p16INK4a induces an age-dependent decline in islet regenerative potential Three separate labs report that p16INK4a, a protein known to be expressed in an age-dependent manner regulates ageing specifically in stem cells. Studying its role in regeneration of three different tissues, the blood, pancreas, and brain, the three groups separately found that p16INK4a is not only a biomarker, but an effector of ageing. Janakiraman Krishnamurthy et al. 10.1038/nature05092 Abstract: http://www.nature.com/nature/jou ... bs/nature05092.html Article: http://www.nature.com/nature/jou ... ll/nature05092.html BRX mediates feedback between brassinosteroid levels and auxin signalling in root growth New evidence suggests that as early as in embryogenic root growth, brassinosteriods and auxin communicate through a feedback loop that maintains brassinosteroid levels in an auxin-dependent manner. In turn, brassinosteroid levels are rate-limiting for auxin-induced transcriptional responses. Celine F. Mouchel, Karen S. Osmont and Christian S. Hardtke 10.1038/nature05130 Abstract: http://www.nature.com/nature/jou ... bs/nature05130.html Article: http://www.nature.com/nature/jou ... ll/nature05130.html Centrosome polarization delivers secretory granules to the immunological synapse In cytotoxic T lymphocytes, polarized granule delivery occurs by a mechanism that does not require actin or plus-end microtubule motors, but only minus-end directed granule transport. It is also controlled by movement of the centrosome to contact the plasma membrane at the immunological synapse. Jane C. Stinchcombe et al. 10.1038/nature05071 Abstract: http://www.nature.com/nature/jou ... bs/nature05071.html Article: http://www.nature.com/nature/jou ... ll/nature05071.html Structural insights into yeast septin organization from polarized fluorescence microscopy Polarized fluorescence microscopy of green fluorescent protein rigidly attached to septin was used to determine septin filament organization and dynamics. The filaments form ordered assemblies in living yeast and undergo a 90-degree rotation before the onset of cytokinesis. This suggests that septins play a mechanical role in cell division. Alina M. Vrabioiu and Timothy J. Mitchison 10.1038/nature05109 Abstract: http://www.nature.com/nature/jou ... bs/nature05109.html Article: http://www.nature.com/nature/jou ... ll/nature05109.html Ion permeation through the Na+,K+-ATPase Nicolas Reyes and David C. Gadsby 10.1038/nature05129 Abstract: http://www.nature.com/nature/jou ... bs/nature05129.html Article: http://www.nature.com/nature/jou ... ll/nature05129.html |
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