《Nature》 目录要览：2009-09-03出版
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《Nature》 目录要览：2009-09-03出版
封面故事：两栖动物心室的发育
Reptilian heart development and the molecular basis of cardiac chamber evolution
鸟类、哺乳动物和鳄鱼的心脏都有两个分开的心室，分别服务于单独的肺脏和系统循环。两栖类只有一个心室，但多数爬行类情况却不清楚。对一种蜥蜴（绿变色龙）和一种乌龟（滑龟）所做的一项新的胚胎学研究表明，先祖物种单一心室向两个心室的分化与“T-box转录因子”（ Tbx5）的表达有关。在鸟类和哺乳动物胚胎中，Tbx5表达限于左心室的前体。在乌龟和蜥蜴中，Tbx5最初在整个心室表达，但在乌龟（而非蜥蜴）中它后来限于在心室的左边表达。这说明，被改变的Tbx5表达，是推动胚胎心脏成形、为高能量陆地生活提供关键的适应性变化——完全被隔膜隔开的心脏——的一个可能的进化力量。与这一观点相一致的是，Tbx5功能丧失或扩大的小鼠会形成单一心室——既非左心室也非右心室。本期封面所示为乌龟和蜥蜴心脏的三维图像。（Letter p. 95）封面图片提供：Bogac Kaynak和 Benoit Bruneau。
不同系统临界点逼近前有普遍性警示信号（Tip-offs for tipping points）
Early-warning signals for critical transitions
从生态系统到金融市场和气候在内的很多复杂系统，都会有临界点，在这样的点上可能会发生从稳定态向非稳定态的突变。在这样的临界点到达之前对其进行预测极为困难，但是现在，不同科学领域的研究工作表明，存在普遍性的早期警示信号，对一系列不同体系来说，这些信号会指示一个临界点是否正在逼近。Scheffer等人通过对这项工作进行评估做出了乐观的结论：在怀疑存在一个临界点的情况下，警示标志具有普遍特征的事实表明，它们也许能为一个重要事件发生的概率是否在增加提供有价值的信息。（Review p. 53）
tRNA运输因子Xpo-t的结构被确定（Keeping tRNA in its place）
Structures of the tRNA export factor in the nuclear and cytosolic states
在转录和处理之后，转移RNA（tRNA）被从细胞核输出到细胞质中，在那里发生转录。tRNA被一个名为Xpo-t的运输因子携带穿过核膜中的小孔。现在，Xpo-t的结构已被确定。其结构是在单独情况下和与tRNA及运输所需要的另一个因子Ran-GTP结合的情况下分别被确定的。与tRNA的结合诱导大的构形变化，从而使得Xpo-t将tRNA包围起来，并与其5ʹ端和3ʹ端都发生相互作用。这可解释蛋白合成中质量控制的一个重要机制，按照该机制，具有未成熟端的未被处理的tRNA被阻止，而不能从细胞核中被运送出去。（Article p. 60）
“仙女座”星系M31周围的星系结构（Galactic detritus around M31）
The remnants of galaxy formation from a panoramic survey of the region around M31
对距我们最近的星系邻居、著名的“仙女座”星系M31周围区域所做的一项全景式探测，发现了一些恒星和相干结构，它们几乎肯定是被M31的潮汐场破坏掉的矮星系残留下来的。最亮的伴星“三角座”星系（M 33）被一个以前未知的显著的恒星结构所包围，该结构为最近与M31的一次遭遇提供了证据。关于星系结构的这一新观点与层级宇宙模型是一致的，后者认为，星系是通过吸积更小的星系来增长自己的质量的。（Letter p. 66; News & Views）
设计出的DNA晶体结构（Designer DNA crystals）
From molecular to macroscopic via the rational design of a self-assembled 3D DNA crystal
创造一种具有所期望的微观分子结构的宏观物体（如一种晶体）是一种挑战。一个比较有希望的方法是，使用具有坚固三维模体和粘性端部的大分子，这样将它们彼此搭接起来时，它们就会形成一个周期性排列，通过晶体学技术可对这种排列进行研究。Zhang等人将DNA用于这一目的，DNA分子排列成一个被称为“tensegrity triangle”的结构模体，可生长成200微米大小的晶体，在其中原子的位置可以4埃的分辨率被确定。互补DNA链之间高度针对性的相互作用，使得晶体的单元格有可能实现所期望的、所设计的结构。后者还还具有周期性的洞，这些洞有可能被用来在一个三维周期排列中容纳生物分子，从而使得即使在它们自己不能结晶时也有可能确定它们的结构。（Letter p. 74）
造成海洋中固氮丧失的主要因素（Nitrogen lost at sea）
Denitrification as the dominant nitrogen loss process in the Arabian Sea
固氮的供应量是世界一半以上海洋中初级生产的限制因素。最近的报告表明，造成海洋中氧供应受限区域固氮全部或大部丧失的是氨厌氧氧化（anammox），而非产生双氮气体（N2）的传统反硝化作用。Ward等人发现，在阿拉伯海中主导固氮丧失的是反硝化作用，而非氨厌氧氧化。在这一区域，反硝化细菌比氨厌氧氧化细菌更多，即使当氨厌氧氧化速度很显著时也是如此。这项工作解决了我们对全球氮循环和固氮存量的认识中一大不确定性问题，证实反硝化作用是整个海洋氮循环中的一个主要过程。（Letter p. 78）
手斧在亚洲和欧洲出现的时间间隔被显著缩小（Bridging the gap）
The oldest hand-axes in Europe
技术史上一个关键过渡是，从最早的石器时代的古人类所使用的简单的砍刀一样的工具向被称为手斧的较为精致的、双面制品的过渡。从手斧在亚洲出现到它们在欧洲的最早记录之间有一个非常长的时间间隔，大约为100万年，这个时间间隔长期以来使古人类学家迷惑不解。一般来说，手斧首次在欧洲出现一直被认为是在距今大约50万年前。Gary Scott 和Luis Gibert对西班牙南部两个有手斧的旧石器地点的年代测定重新进行了评估，得出名为La Solana del Zamborino的石屋地点和名为Estrecho del Quípar的石屋地点的年代分别为距今76万年前和距今90万年前，从而将亚洲与欧洲之间的时间间隔显著缩小。（Letter p. 82）
用iPS细胞培育出的小鼠（Mice from iPS cells）
iPS cells produce viable mice through tetraploid complementation / Adult mice generated from induced pluripotent stem cells
自诱导多能干细胞（即iPS细胞）于2006年被首次发现以来，它们的特性以其所模仿的真正的胚胎干细胞为基准得到了测定。最近的一批论文（其中两篇发表在本期|Nature上）报告，从iPS 细胞培育出了能存活的成年小鼠。这是一个引人瞩目的技术成就，它表明，就它们生成构成所有组织和所有器官的潜力来说，这些细胞与胚胎细胞的确非常接近。Zhao等人所采用的一种技术被称为“四倍体互补”，利用该技术，他们从注射的多能细胞生成了嵌合的小鼠，而胚胎组织则完全来自注射的细胞。Boland等人培育出了完全从小鼠胚胎成纤维细胞的可诱导基因重新编程产生的iPS细胞衍生出来的具有生育能力的成年小鼠。这些小鼠的培育成功，为用于研究工作和用于细胞替换疗法应用的、由iPS细胞生成的组织的研究都提供了一个新的资源。（Letters pp. 86, 91）
利用光精确操纵细胞内蛋白活动的新技术（A light touch on proteins）
A genetically encoded photoactivatable Rac controls the motility of living cells
细胞功能的很多方面，取决于各种不同蛋白活动什么时候以及在细胞中的什么地方在分子层面上被打开或关闭。一项利用光来在活细胞内的精确时间和地点操纵某种蛋白活动的新技术，有可能使对蛋白功能的这一基础问题的研究具有可行性。该技术所采用的是Rac1的一个由基因编码的、可用光激发的衍生物。Rac1是一种GTP酶，它调控肌动蛋白细胞骨架动态，可因暴露于激光而被激发。这种局部激发产生精确局部化的细胞突起和皱褶，可引导细胞运动。该方法应能扩展到其他蛋白。（Letter p. 104）
抗氧化剂在某些条件下有利于癌细胞存活（Pro-cancer antioxidants）
Antioxidant and oncogene rescue of metabolic defects caused by loss of matrix attachment
来自试管研究和动物研究的实验证据表明，抗氧化剂也许能抑制癌症形成，尽管有关其在临床条件下的效果还几乎没有结论性证据。然而，发现在某些条件下抗氧化剂能帮助促进癌细胞存活和增殖却有点儿出乎意料。正常表皮细胞如果与在结构上具有支持作用的细胞外基质脱离时就会死亡，但在乳腺癌中，引起癌症的基因如erbB2能为脱离的肿瘤发生细胞提供存活信号。Schafer等人发现，细胞脱离还会引起代谢缺陷，这些缺陷被erbB2和被抗氧化剂都可挽救，抗氧化剂似乎是通过经由脂肪酸氧化提升细胞能量水平来发挥作用的。这些发现指出了一些新的机制，它们有可能被癌细胞利用，来增强自己在被改变的基质环境中的存活能力。（Letter p. 109; News & Views）
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NEWS AND VIEWS
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Astrophysics: Hidden chaos in cosmic order pp43-44
[ldquo]Galaxies, like elephants, have long memories,[rdquo] says an influential article from the 1980s. Tapping into these memories has revealed some surprising facts about the history of our neighbouring Andromeda galaxy.
Nickolay Y. Gnedin
doi:10.1038/461043a
http://www.nature.com/nature/journal/v461/n7260/full/461043a.html
Cancer: The fat and the furious pp44-45
Evidence linking metabolic alterations to cancer progression is accumulating. It seems that cancer cells must sustain their energy production and remain well fed to survive detachment from their normal habitat.
Eyal Gottlieb
doi:10.1038/461044a
http://www.nature.com/nature/journal/v461/n7260/full/461044a.html
Materials science: Pulsating vesicles pp45-47
During her travels through Wonderland, Alice finds several ways of growing and shrinking in size. A polymeric vesicle plays the same trick in response to pH, in a process that might one day be useful for drug delivery.
Jan C. M. van Hest
doi:10.1038/461045a
http://www.nature.com/nature/journal/v461/n7260/full/461045a.html
Structural biology: A channel with a twist pp47-49
Mechanosensitive channels release tension in cell membranes by opening 'pressure relief' pores. The structure of a partially open channel suggests a gating mechanism and delivers an unexpected architectural twist.
Valeria Vasquez and Eduardo Perozo
doi:10.1038/461047a
http://www.nature.com/nature/journal/v461/n7260/full/461047a.html
50 & 100 years ago p48
doi:10.1038/461048a
http://www.nature.com/nature/journal/v461/n7260/full/461048a.html
Nitrogen cycle: Oceans apart pp49-50
Reactive nitrogen is lost from the oceans as dinitrogen [mdash] N2 [mdash] produced by microbial metabolism. The latest twist in an ongoing story is that different pathways dominate in two of the oceanic regions concerned.
Maren Voss and Joseph P. Montoya
doi:10.1038/461049a
http://www.nature.com/nature/journal/v461/n7260/full/461049a.html
Neuroscience: Persistent feedback pp50-51
How does the brain remember the consequences of our actions? Persistent activity in the prefrontal cortex and basal ganglia may be crucial for learning correct actions through experience.
Hyojung Seo and Daeyeol Lee
doi:10.1038/461050a
http://www.nature.com/nature/journal/v461/n7260/full/461050a.html
Correction p51
doi:10.1038/461051a
http://www.nature.com/nature/journal/v461/n7260/full/461051a.html
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REVIEW
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Early-warning signals for critical transitions pp53-59
Marten Scheffer et al.
doi:10.1038/nature08227
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08227.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08227.html
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LETTERS
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The remnants of galaxy formation from a panoramic survey of the region around M31 pp66-69
In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound and distant stars surrounding the galaxy. A panoramic survey of the Andromeda galaxy (M31) now reveals stars and coherent structures that are almost certainly remnants of dwarf galaxies destroyed by the tidal field of M31.
Alan W. McConnachie et al.
doi:10.1038/nature08327
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08327.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08327.html
Laser cooling by collisional redistribution of radiation pp70-73
Collisional redistribution of radiation has been proposed as a cooling mechanism for atomic two-level systems. Here, a proof-of-principle demonstration is reported in which a relative cooling of 66 K is achieved in an ultradense vapour of rubidium atoms and argon buffer gas. This technique may facilitate fundamental studies of supercooling and have applications in optical refrigeration.
Ulrich Vogl and Martin Weitz
doi:10.1038/nature08203
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08203.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08203.html
From molecular to macroscopic via the rational design of a self-assembled 3D DNA crystal pp74-77
Although we live in a macroscopic three-dimensional (3D) world, our best description of the structure of matter is at the atomic and molecular scale. Reconciling these two scales with atomic precision requires high spatial control of the 3D structure of matter, with the simplest practical route to achieving this being to form a crystalline arrangement by self-assembly. Here, the crystal structure of a designed, self-assembled 3D crystal based on the DNA tensegrity triangle is reported.
Jianping Zheng et al.
doi:10.1038/nature08274
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08274.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08274.html
Denitrification as the dominant nitrogen loss process in the Arabian Sea pp78-81
Fixed nitrogen availability limits primary production in over half of the world's oceans. Oceanic oxygen minimum zones (OMZs) are responsible for about 35% of oceanic dinitrogen gas (N2) production and up to half of that occurs in the Arabian Sea. It has recently been argued that anaerobic ammonia oxidation (anammox) alone is responsible for fixed nitrogen loss in the OMZs; however, here it is shown that denitrification rather than anammox dominates the N2 loss term in the Arabian Sea.
B. B. Ward et al.
doi:10.1038/nature08276
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08276.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08276.html
The oldest hand-axes in Europe pp82-85
A key development in the history of technology was the transition to hand-axes and bifacial chopping tools during the Early Pleistocene (about 1.5 million years ago) in Africa. Puzzlingly, the earliest records in Europe of hand-axes lag behind this date by a million years, at around 0.5 million years ago. Here, palaeomagnetic analysis of two sites in southeastern Spain where hand-axes have been found yields revised dates of up to 0.9 million years ago, significantly closing the time gap.
Gary R. Scott and Luis Gibert
doi:10.1038/nature08214
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08214.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08214.html
iPS cells produce viable mice through tetraploid complementation
Induced pluripotent stem (iPS) cells were first created by forced expression of four transcription factors in mouse fibroblasts, a technique that has since been widely used to generate embryonic stem (ES)-cell-like pluripotent cells from a variety of cell types in other species. The generation of several iPS cell lines in mice that are capable of generating viable, fertile live-born progeny by tetraploid complementation [mdash] a technique where chimaeric mice are generated using injected pluripotent cells [mdash] is now reported.
Xiao-yang Zhao et al.
doi:10.1038/nature08267
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08267.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08267.html
Adult mice generated from induced pluripotent stem cells
Differentiated cells can be reprogrammed into induced pluripotent stem (iPS) cells through the transient overexpression of a small number of transcription factors. These iPS cells resemble embryonic stem (ES) cells but, until now, they had not passed the most stringent test of pluripotency by generating full-term or adult mice in tetraploid complementation assays. Here, fertile adult mice derived entirely from iPS cells are reported.
Michael J. Boland et al.
doi:10.1038/nature08310
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08310.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08310.html
Reptilian heart development and the molecular basis of cardiac chamber evolution pp95-98
The hearts of birds, mammals and crocodiles have two ventricles serving separate pulmonary and systemic circulations, whereas the hearts of amphibians have only one ventricle. In most reptiles, however, the situation is unclear, which is of interest in the context of the evolution of cardiac septation. Here, gene expression in the developing ventricles of two reptiles is analysed; the results suggest a role for the T-box transcription factor Tbx5.
Kazuko Koshiba-Takeuchi et al.
doi:10.1038/nature08324
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08324.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08324.html
Coordination of Rho GTPase activities during cell protrusion pp99-103
The Rho GTPase family is involved in the control of cytoskeleton dynamics, but the spatiotemporal coordination of each element (Rac1, RhoA and Cdc42) remains unknown. Here, GTPase coordination in mouse embryonic fibroblasts is examined both through simultaneous visualization of two GTPase biosensors and using a computational approach.
Matthias Machacek et al.
doi:10.1038/nature08242
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08242.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08242.html
A genetically encoded photoactivatable Rac controls the motility of living cells pp104-108
The precise spatiotemporal dynamics of protein activity remain poorly understood, yet they can be critical in determining cell behaviour. A genetically encoded, photoactivatable version of the protein Rac1, a key GTPase regulating actin cytoskeletal dynamics, has now been produced; this approach enables the manipulation of the activity of Rac1 at precise times and places within a living cell, thus controlling motility.
Yi I. Wu et al.
doi:10.1038/nature08241
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08241.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08241.html
Antioxidant and oncogene rescue of metabolic defects caused by loss of matrix attachment pp109-113
Normal mammary epithelial cells require attachment to the extracellular matrix (ECM) for survival, but in breast cancers tumour cells acquire the ability to survive outside their natural ECM niches. Here it is found that cell detachment induces metabolic defects which can be rescued by both the expression of the oncogene ERBB2 and [mdash] unexpectedly [mdash] by antioxidants, which, in this context, help promote cancer cell survival and proliferation.
Zachary T. Schafer et al.
doi:10.1038/nature08268
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08268.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08268.html
Direct activation of protein kinases by unanchored polyubiquitin chains pp114-119
The ubiquitin ligase TRAF6 is essential for the activation of NF-[kappa]B and MAP kinases in several signalling pathways important for a range of cellular processes including immune function. TRAF6 functions together with a ubiquitin-conjugating enzyme complex to activate the TAK1 kinase complex downstream, which in turn leads to the activation of NF-[kappa]B. Here, by reconstituting TAK1 activation in vitro, free Lys 63 polyubiquitin chains are shown to activate TAK1 directly.
Zong-Ping Xia et al.
doi:10.1038/nature08247
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08247.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08247.html
Structure of a tetrameric MscL in an expanded intermediate state pp120-124
Mechanosensitive channels protect bacteria from osmotic shock by allowing ions to flow across the membrane in response to changes in membrane tension. MscL is one such channel with a large conductance. Although understanding of its closed and open states has been increasing, little is known about the structures of the important intermediate states. Here, the 3.8 A crystal structure of MscL in what is probably a non-conductive, partially expanded intermediate state, is presented.
Zhenfeng Liu, Chris S. Gandhi and Douglas C. Rees
doi:10.1038/nature08277
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08277.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08277.html
Direct observation of the binding state of the kinesin head to the microtubule pp125-128
Kinesin is a dimeric motor protein which is known to move along microtubule filaments by using its twin motor domains (heads) to carry out an asymmetric, 'hand-over-hand' walk. However, the extent of individual head interactions with the microtubule has remained controversial. Here, a single-molecule assay is developed that can directly report head binding and unbinding during kinesin movement.
Nicholas R. Guydosh and Steven M. Block
doi:10.1038/nature08259
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08259.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08259.html
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FUTURES
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Fine-tuning the Universe p134
Touched by the hand of God.
Merrie Haskell
doi:10.1038/461134a
http://www.nature.com/nature/journal/v461/n7260/full/461134a.html
Reptilian heart development and the molecular basis of cardiac chamber evolution
鸟类、哺乳动物和鳄鱼的心脏都有两个分开的心室，分别服务于单独的肺脏和系统循环。两栖类只有一个心室，但多数爬行类情况却不清楚。对一种蜥蜴（绿变色龙）和一种乌龟（滑龟）所做的一项新的胚胎学研究表明，先祖物种单一心室向两个心室的分化与“T-box转录因子”（ Tbx5）的表达有关。在鸟类和哺乳动物胚胎中，Tbx5表达限于左心室的前体。在乌龟和蜥蜴中，Tbx5最初在整个心室表达，但在乌龟（而非蜥蜴）中它后来限于在心室的左边表达。这说明，被改变的Tbx5表达，是推动胚胎心脏成形、为高能量陆地生活提供关键的适应性变化——完全被隔膜隔开的心脏——的一个可能的进化力量。与这一观点相一致的是，Tbx5功能丧失或扩大的小鼠会形成单一心室——既非左心室也非右心室。本期封面所示为乌龟和蜥蜴心脏的三维图像。（Letter p. 95）封面图片提供：Bogac Kaynak和 Benoit Bruneau。
不同系统临界点逼近前有普遍性警示信号（Tip-offs for tipping points）
Early-warning signals for critical transitions
从生态系统到金融市场和气候在内的很多复杂系统，都会有临界点，在这样的点上可能会发生从稳定态向非稳定态的突变。在这样的临界点到达之前对其进行预测极为困难，但是现在，不同科学领域的研究工作表明，存在普遍性的早期警示信号，对一系列不同体系来说，这些信号会指示一个临界点是否正在逼近。Scheffer等人通过对这项工作进行评估做出了乐观的结论：在怀疑存在一个临界点的情况下，警示标志具有普遍特征的事实表明，它们也许能为一个重要事件发生的概率是否在增加提供有价值的信息。（Review p. 53）
tRNA运输因子Xpo-t的结构被确定（Keeping tRNA in its place）
Structures of the tRNA export factor in the nuclear and cytosolic states
在转录和处理之后，转移RNA（tRNA）被从细胞核输出到细胞质中，在那里发生转录。tRNA被一个名为Xpo-t的运输因子携带穿过核膜中的小孔。现在，Xpo-t的结构已被确定。其结构是在单独情况下和与tRNA及运输所需要的另一个因子Ran-GTP结合的情况下分别被确定的。与tRNA的结合诱导大的构形变化，从而使得Xpo-t将tRNA包围起来，并与其5ʹ端和3ʹ端都发生相互作用。这可解释蛋白合成中质量控制的一个重要机制，按照该机制，具有未成熟端的未被处理的tRNA被阻止，而不能从细胞核中被运送出去。（Article p. 60）
“仙女座”星系M31周围的星系结构（Galactic detritus around M31）
The remnants of galaxy formation from a panoramic survey of the region around M31
对距我们最近的星系邻居、著名的“仙女座”星系M31周围区域所做的一项全景式探测，发现了一些恒星和相干结构，它们几乎肯定是被M31的潮汐场破坏掉的矮星系残留下来的。最亮的伴星“三角座”星系（M 33）被一个以前未知的显著的恒星结构所包围，该结构为最近与M31的一次遭遇提供了证据。关于星系结构的这一新观点与层级宇宙模型是一致的，后者认为，星系是通过吸积更小的星系来增长自己的质量的。（Letter p. 66; News & Views）
设计出的DNA晶体结构（Designer DNA crystals）
From molecular to macroscopic via the rational design of a self-assembled 3D DNA crystal
创造一种具有所期望的微观分子结构的宏观物体（如一种晶体）是一种挑战。一个比较有希望的方法是，使用具有坚固三维模体和粘性端部的大分子，这样将它们彼此搭接起来时，它们就会形成一个周期性排列，通过晶体学技术可对这种排列进行研究。Zhang等人将DNA用于这一目的，DNA分子排列成一个被称为“tensegrity triangle”的结构模体，可生长成200微米大小的晶体，在其中原子的位置可以4埃的分辨率被确定。互补DNA链之间高度针对性的相互作用，使得晶体的单元格有可能实现所期望的、所设计的结构。后者还还具有周期性的洞，这些洞有可能被用来在一个三维周期排列中容纳生物分子，从而使得即使在它们自己不能结晶时也有可能确定它们的结构。（Letter p. 74）
造成海洋中固氮丧失的主要因素（Nitrogen lost at sea）
Denitrification as the dominant nitrogen loss process in the Arabian Sea
固氮的供应量是世界一半以上海洋中初级生产的限制因素。最近的报告表明，造成海洋中氧供应受限区域固氮全部或大部丧失的是氨厌氧氧化（anammox），而非产生双氮气体（N2）的传统反硝化作用。Ward等人发现，在阿拉伯海中主导固氮丧失的是反硝化作用，而非氨厌氧氧化。在这一区域，反硝化细菌比氨厌氧氧化细菌更多，即使当氨厌氧氧化速度很显著时也是如此。这项工作解决了我们对全球氮循环和固氮存量的认识中一大不确定性问题，证实反硝化作用是整个海洋氮循环中的一个主要过程。（Letter p. 78）
手斧在亚洲和欧洲出现的时间间隔被显著缩小（Bridging the gap）
The oldest hand-axes in Europe
技术史上一个关键过渡是，从最早的石器时代的古人类所使用的简单的砍刀一样的工具向被称为手斧的较为精致的、双面制品的过渡。从手斧在亚洲出现到它们在欧洲的最早记录之间有一个非常长的时间间隔，大约为100万年，这个时间间隔长期以来使古人类学家迷惑不解。一般来说，手斧首次在欧洲出现一直被认为是在距今大约50万年前。Gary Scott 和Luis Gibert对西班牙南部两个有手斧的旧石器地点的年代测定重新进行了评估，得出名为La Solana del Zamborino的石屋地点和名为Estrecho del Quípar的石屋地点的年代分别为距今76万年前和距今90万年前，从而将亚洲与欧洲之间的时间间隔显著缩小。（Letter p. 82）
用iPS细胞培育出的小鼠（Mice from iPS cells）
iPS cells produce viable mice through tetraploid complementation / Adult mice generated from induced pluripotent stem cells
自诱导多能干细胞（即iPS细胞）于2006年被首次发现以来，它们的特性以其所模仿的真正的胚胎干细胞为基准得到了测定。最近的一批论文（其中两篇发表在本期|Nature上）报告，从iPS 细胞培育出了能存活的成年小鼠。这是一个引人瞩目的技术成就，它表明，就它们生成构成所有组织和所有器官的潜力来说，这些细胞与胚胎细胞的确非常接近。Zhao等人所采用的一种技术被称为“四倍体互补”，利用该技术，他们从注射的多能细胞生成了嵌合的小鼠，而胚胎组织则完全来自注射的细胞。Boland等人培育出了完全从小鼠胚胎成纤维细胞的可诱导基因重新编程产生的iPS细胞衍生出来的具有生育能力的成年小鼠。这些小鼠的培育成功，为用于研究工作和用于细胞替换疗法应用的、由iPS细胞生成的组织的研究都提供了一个新的资源。（Letters pp. 86, 91）
利用光精确操纵细胞内蛋白活动的新技术（A light touch on proteins）
A genetically encoded photoactivatable Rac controls the motility of living cells
细胞功能的很多方面，取决于各种不同蛋白活动什么时候以及在细胞中的什么地方在分子层面上被打开或关闭。一项利用光来在活细胞内的精确时间和地点操纵某种蛋白活动的新技术，有可能使对蛋白功能的这一基础问题的研究具有可行性。该技术所采用的是Rac1的一个由基因编码的、可用光激发的衍生物。Rac1是一种GTP酶，它调控肌动蛋白细胞骨架动态，可因暴露于激光而被激发。这种局部激发产生精确局部化的细胞突起和皱褶，可引导细胞运动。该方法应能扩展到其他蛋白。（Letter p. 104）
抗氧化剂在某些条件下有利于癌细胞存活（Pro-cancer antioxidants）
Antioxidant and oncogene rescue of metabolic defects caused by loss of matrix attachment
来自试管研究和动物研究的实验证据表明，抗氧化剂也许能抑制癌症形成，尽管有关其在临床条件下的效果还几乎没有结论性证据。然而，发现在某些条件下抗氧化剂能帮助促进癌细胞存活和增殖却有点儿出乎意料。正常表皮细胞如果与在结构上具有支持作用的细胞外基质脱离时就会死亡，但在乳腺癌中，引起癌症的基因如erbB2能为脱离的肿瘤发生细胞提供存活信号。Schafer等人发现，细胞脱离还会引起代谢缺陷，这些缺陷被erbB2和被抗氧化剂都可挽救，抗氧化剂似乎是通过经由脂肪酸氧化提升细胞能量水平来发挥作用的。这些发现指出了一些新的机制，它们有可能被癌细胞利用，来增强自己在被改变的基质环境中的存活能力。（Letter p. 109; News & Views）
----------------------
NEWS AND VIEWS
----------------------
Astrophysics: Hidden chaos in cosmic order pp43-44
[ldquo]Galaxies, like elephants, have long memories,[rdquo] says an influential article from the 1980s. Tapping into these memories has revealed some surprising facts about the history of our neighbouring Andromeda galaxy.
Nickolay Y. Gnedin
doi:10.1038/461043a
http://www.nature.com/nature/journal/v461/n7260/full/461043a.html
Cancer: The fat and the furious pp44-45
Evidence linking metabolic alterations to cancer progression is accumulating. It seems that cancer cells must sustain their energy production and remain well fed to survive detachment from their normal habitat.
Eyal Gottlieb
doi:10.1038/461044a
http://www.nature.com/nature/journal/v461/n7260/full/461044a.html
Materials science: Pulsating vesicles pp45-47
During her travels through Wonderland, Alice finds several ways of growing and shrinking in size. A polymeric vesicle plays the same trick in response to pH, in a process that might one day be useful for drug delivery.
Jan C. M. van Hest
doi:10.1038/461045a
http://www.nature.com/nature/journal/v461/n7260/full/461045a.html
Structural biology: A channel with a twist pp47-49
Mechanosensitive channels release tension in cell membranes by opening 'pressure relief' pores. The structure of a partially open channel suggests a gating mechanism and delivers an unexpected architectural twist.
Valeria Vasquez and Eduardo Perozo
doi:10.1038/461047a
http://www.nature.com/nature/journal/v461/n7260/full/461047a.html
50 & 100 years ago p48
doi:10.1038/461048a
http://www.nature.com/nature/journal/v461/n7260/full/461048a.html
Nitrogen cycle: Oceans apart pp49-50
Reactive nitrogen is lost from the oceans as dinitrogen [mdash] N2 [mdash] produced by microbial metabolism. The latest twist in an ongoing story is that different pathways dominate in two of the oceanic regions concerned.
Maren Voss and Joseph P. Montoya
doi:10.1038/461049a
http://www.nature.com/nature/journal/v461/n7260/full/461049a.html
Neuroscience: Persistent feedback pp50-51
How does the brain remember the consequences of our actions? Persistent activity in the prefrontal cortex and basal ganglia may be crucial for learning correct actions through experience.
Hyojung Seo and Daeyeol Lee
doi:10.1038/461050a
http://www.nature.com/nature/journal/v461/n7260/full/461050a.html
Correction p51
doi:10.1038/461051a
http://www.nature.com/nature/journal/v461/n7260/full/461051a.html
----------------------
REVIEW
----------------------
Early-warning signals for critical transitions pp53-59
Marten Scheffer et al.
doi:10.1038/nature08227
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08227.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08227.html
----------------------
LETTERS
----------------------
The remnants of galaxy formation from a panoramic survey of the region around M31 pp66-69
In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound and distant stars surrounding the galaxy. A panoramic survey of the Andromeda galaxy (M31) now reveals stars and coherent structures that are almost certainly remnants of dwarf galaxies destroyed by the tidal field of M31.
Alan W. McConnachie et al.
doi:10.1038/nature08327
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08327.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08327.html
Laser cooling by collisional redistribution of radiation pp70-73
Collisional redistribution of radiation has been proposed as a cooling mechanism for atomic two-level systems. Here, a proof-of-principle demonstration is reported in which a relative cooling of 66 K is achieved in an ultradense vapour of rubidium atoms and argon buffer gas. This technique may facilitate fundamental studies of supercooling and have applications in optical refrigeration.
Ulrich Vogl and Martin Weitz
doi:10.1038/nature08203
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08203.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08203.html
From molecular to macroscopic via the rational design of a self-assembled 3D DNA crystal pp74-77
Although we live in a macroscopic three-dimensional (3D) world, our best description of the structure of matter is at the atomic and molecular scale. Reconciling these two scales with atomic precision requires high spatial control of the 3D structure of matter, with the simplest practical route to achieving this being to form a crystalline arrangement by self-assembly. Here, the crystal structure of a designed, self-assembled 3D crystal based on the DNA tensegrity triangle is reported.
Jianping Zheng et al.
doi:10.1038/nature08274
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08274.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08274.html
Denitrification as the dominant nitrogen loss process in the Arabian Sea pp78-81
Fixed nitrogen availability limits primary production in over half of the world's oceans. Oceanic oxygen minimum zones (OMZs) are responsible for about 35% of oceanic dinitrogen gas (N2) production and up to half of that occurs in the Arabian Sea. It has recently been argued that anaerobic ammonia oxidation (anammox) alone is responsible for fixed nitrogen loss in the OMZs; however, here it is shown that denitrification rather than anammox dominates the N2 loss term in the Arabian Sea.
B. B. Ward et al.
doi:10.1038/nature08276
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08276.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08276.html
The oldest hand-axes in Europe pp82-85
A key development in the history of technology was the transition to hand-axes and bifacial chopping tools during the Early Pleistocene (about 1.5 million years ago) in Africa. Puzzlingly, the earliest records in Europe of hand-axes lag behind this date by a million years, at around 0.5 million years ago. Here, palaeomagnetic analysis of two sites in southeastern Spain where hand-axes have been found yields revised dates of up to 0.9 million years ago, significantly closing the time gap.
Gary R. Scott and Luis Gibert
doi:10.1038/nature08214
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08214.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08214.html
iPS cells produce viable mice through tetraploid complementation
Induced pluripotent stem (iPS) cells were first created by forced expression of four transcription factors in mouse fibroblasts, a technique that has since been widely used to generate embryonic stem (ES)-cell-like pluripotent cells from a variety of cell types in other species. The generation of several iPS cell lines in mice that are capable of generating viable, fertile live-born progeny by tetraploid complementation [mdash] a technique where chimaeric mice are generated using injected pluripotent cells [mdash] is now reported.
Xiao-yang Zhao et al.
doi:10.1038/nature08267
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08267.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08267.html
Adult mice generated from induced pluripotent stem cells
Differentiated cells can be reprogrammed into induced pluripotent stem (iPS) cells through the transient overexpression of a small number of transcription factors. These iPS cells resemble embryonic stem (ES) cells but, until now, they had not passed the most stringent test of pluripotency by generating full-term or adult mice in tetraploid complementation assays. Here, fertile adult mice derived entirely from iPS cells are reported.
Michael J. Boland et al.
doi:10.1038/nature08310
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08310.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08310.html
Reptilian heart development and the molecular basis of cardiac chamber evolution pp95-98
The hearts of birds, mammals and crocodiles have two ventricles serving separate pulmonary and systemic circulations, whereas the hearts of amphibians have only one ventricle. In most reptiles, however, the situation is unclear, which is of interest in the context of the evolution of cardiac septation. Here, gene expression in the developing ventricles of two reptiles is analysed; the results suggest a role for the T-box transcription factor Tbx5.
Kazuko Koshiba-Takeuchi et al.
doi:10.1038/nature08324
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08324.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08324.html
Coordination of Rho GTPase activities during cell protrusion pp99-103
The Rho GTPase family is involved in the control of cytoskeleton dynamics, but the spatiotemporal coordination of each element (Rac1, RhoA and Cdc42) remains unknown. Here, GTPase coordination in mouse embryonic fibroblasts is examined both through simultaneous visualization of two GTPase biosensors and using a computational approach.
Matthias Machacek et al.
doi:10.1038/nature08242
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08242.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08242.html
A genetically encoded photoactivatable Rac controls the motility of living cells pp104-108
The precise spatiotemporal dynamics of protein activity remain poorly understood, yet they can be critical in determining cell behaviour. A genetically encoded, photoactivatable version of the protein Rac1, a key GTPase regulating actin cytoskeletal dynamics, has now been produced; this approach enables the manipulation of the activity of Rac1 at precise times and places within a living cell, thus controlling motility.
Yi I. Wu et al.
doi:10.1038/nature08241
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08241.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08241.html
Antioxidant and oncogene rescue of metabolic defects caused by loss of matrix attachment pp109-113
Normal mammary epithelial cells require attachment to the extracellular matrix (ECM) for survival, but in breast cancers tumour cells acquire the ability to survive outside their natural ECM niches. Here it is found that cell detachment induces metabolic defects which can be rescued by both the expression of the oncogene ERBB2 and [mdash] unexpectedly [mdash] by antioxidants, which, in this context, help promote cancer cell survival and proliferation.
Zachary T. Schafer et al.
doi:10.1038/nature08268
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08268.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08268.html
Direct activation of protein kinases by unanchored polyubiquitin chains pp114-119
The ubiquitin ligase TRAF6 is essential for the activation of NF-[kappa]B and MAP kinases in several signalling pathways important for a range of cellular processes including immune function. TRAF6 functions together with a ubiquitin-conjugating enzyme complex to activate the TAK1 kinase complex downstream, which in turn leads to the activation of NF-[kappa]B. Here, by reconstituting TAK1 activation in vitro, free Lys 63 polyubiquitin chains are shown to activate TAK1 directly.
Zong-Ping Xia et al.
doi:10.1038/nature08247
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08247.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08247.html
Structure of a tetrameric MscL in an expanded intermediate state pp120-124
Mechanosensitive channels protect bacteria from osmotic shock by allowing ions to flow across the membrane in response to changes in membrane tension. MscL is one such channel with a large conductance. Although understanding of its closed and open states has been increasing, little is known about the structures of the important intermediate states. Here, the 3.8 A crystal structure of MscL in what is probably a non-conductive, partially expanded intermediate state, is presented.
Zhenfeng Liu, Chris S. Gandhi and Douglas C. Rees
doi:10.1038/nature08277
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08277.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08277.html
Direct observation of the binding state of the kinesin head to the microtubule pp125-128
Kinesin is a dimeric motor protein which is known to move along microtubule filaments by using its twin motor domains (heads) to carry out an asymmetric, 'hand-over-hand' walk. However, the extent of individual head interactions with the microtubule has remained controversial. Here, a single-molecule assay is developed that can directly report head binding and unbinding during kinesin movement.
Nicholas R. Guydosh and Steven M. Block
doi:10.1038/nature08259
Abstract: http://www.nature.com/nature/journal/v461/n7260/abs/nature08259.html
Article: http://www.nature.com/nature/journal/v461/n7260/full/nature08259.html
----------------------
FUTURES
----------------------
Fine-tuning the Universe p134
Touched by the hand of God.
Merrie Haskell
doi:10.1038/461134a
http://www.nature.com/nature/journal/v461/n7260/full/461134a.html
| 《Nature》目录要览 — 2011-04-28出版 |
| 《Nature》目录要览：2011-01-20出版 |
| 《Nature》目录要览：2010-12-23出版 |
| 《Nature》目录要览：2010-12-16出版 |
| 《Nature》目录要览：2010-12-09出版 |
| 《Nature》目录要览：2010-12-02出版 |
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