Volume 439 Number 7073 pp117-242封面故事:磁重接的发生范围
磁重接是成对的磁力线进行合并、将磁场能转变成粒子能的一个过程。在合并的磁力线中所形成的缠结结构会产生一种“弹弓效应”，该效应对高速等离子喷射流进行加速，使其远离合并点。这个过程为干扰电网和通信的太阳耀斑和近地宇宙风暴提供能量。空间物理学家早就对磁重接是远距离发生的还是在局部地方随机发生的进行争论了。2002年2月2日，在星际空间相距很远的三艘飞船Cluster、ACE和Wind都在其经过的同一个“太阳磁场切变层”内探测到了类似的等离子喷射流。这是证明存在一个直径为250万公里的重接区域的直接证据，它证实磁重接可以在很长时间内在一个非常大的尺度上发生。本期封面所示为缠结的磁力线加速一对粒子喷射流的情形。
蚂蚁学步而不失其故步
由E. O. Wilson首次描述的前后跑（Tandem running）是在一些蚂蚁物种中所看到的一种行为，即一只蚂蚁领着另一只蚂蚁从蚁穴向食物源跑，它们之间的碰触信号或信息素信号控制速度和路径。对名为Temnothorax albipennis的蚂蚁所做的新的研究工作表明，前后跑的意义还不止我们所看到的那些。它是老师和学生之间通过双向反馈进行教学的一个例子，很可能是这种现象第一次在一种不是人类的动物身上被观察到。
固体行星的形成:坎坷星途路
太阳系的有陆地的行星被认为是从大量小的行星通过合并而不断增长形成的。在数千万年的时间里，数百颗月球至火星大小的行星“胚胎”通过彼此之间以及与木星之间的引力遭遇和共振获得了随机速率。这个过程所产生的跨行星的轨道和碰撞最终产生了现在的四颗有陆地的行星以及月球和小行星。但Asphaug等人现在发现，碰撞的行星并不是简单地合并。在很多情况下，较小的行星会从碰撞过程中逃脱，但严重变形，快速旋转，外层被剥去，有时还会分裂成很多小天体。这些“撞击后就跑掉”的碰撞所留下的残体今天很可能仍然还在，它们以小行星和陨石、也许还有最小的行星的形式存在。
哥斯达黎加青蛙灭绝与全球变暖有关
上个世纪80年代，蒙特维得五彩青蛙和金蝉一起从哥斯达黎加的森林中消失了。为此，它们成为关于全球变暖和生物多样性的辩论中的一个焦点。有些人认为全球变暖是其消失的原因，而另一些人则认为是森林的砍伐破坏了它们的生存环境。一项将属于美洲热带地区本地种的这些物种和很多其他两栖类动物的灭绝与海平面和气温的变化联系起来的新的分析研究的结果，在这一轮辩论中可能会证明是具有结论性的。这项研究还发现了造成这些两栖类动物灭绝的可能的病原体：全球变暖趋势对一种名为Batrachochytrium dendrobatidis的真菌病原体是有利的，这种病原体是“壶菌病”的致病原因，它的增殖使得天平朝着不利于其寄主生存的方向发生了倾斜。
过热的冰已在实验中获得
将一种固体加热到超过其熔点而又不会让其真正熔化，可以通过用作高质量晶体的物质轻易实现。水为什么不能成为这些物质中的一员并没有根本性的原因。但水中将各个分子束缚在一起、使水具有很多独特性质的氢键网络使得我们难以生成无缺陷的水冰。因此，此前过热的冰只存在于理论中。但是现在，在一项实验中，研究人员通过将大块冰的内部在非常短的时间尺度上从零下3摄氏度加热到室温，从而生成了这样的物质。在该实验所持续的250皮秒内，实验用冰仍然保持固体状态，虽说当温度跨度超过大约20摄氏度时冰的确会融化。
一个新的甲烷排放来源
热带森林上面温室气体甲烷的含量出乎意料之高以及最近大气中甲烷浓度增长速度的下降，都不能简单地用已经被人们所接受的全球甲烷预算来解释。现在，一项真正让人吃惊的发现为这些现象提供了一个可能的解释，并且还可能对通过模型研究过去和未来的气候具有参考意义。自然来源的甲烷过去被认为只能在厌氧条件下形成，比如说在沼泽中。事实上，活的植物以及死掉的残枝落叶在好氧条件下也能向大气中排放甲烷。这一额外的甲烷来源有可能占到年甲烷来源量的10%至30%，并且在过去的研究中被忽略了。
义县发现新的哺乳动物化石
中国的义县化石产地在过去十年时间里已经出产了一些最为重要的哺乳动物化石，比如说一系列长羽毛的恐龙化石，并且还在继续出产对关于早期哺乳动物演化的传统观点形成挑战的化石。最新的发现是一个保存完好的名为Spalacotheroid Symmetrodont的动物化石，它是现代兽亚纲哺乳动物（如有袋动物和有胎盘动物）的一个亲缘种。该动物的部分骨架很不像兽亚纲哺乳动物：从胸椎往下到脚踝，该哺乳动物都非常像鸭嘴兽，这也许是功能交汇的结果。从古生物地理角度来看，这一新发现的化石也很有价值：同早白垩纪很多其他哺乳动物一样，这种动物似乎也是最初在欧亚大陆演化、然后向北美扩散的。
混交也有可取之处
混交的雌性能生出父亲为一个以上雄性的后代来。对一种胎生的伪蝎所做的新的研究表明，对那些无法避免与近亲交配的雌性来说，其后代有多个父亲可以是有好处的。在胎生物种中，近亲繁殖不仅增加隐性疾病的风险，而且还能干扰胚胎发育所必要的母亲和胎儿之间的交谈。近亲繁殖导致胎生伪蝎的自然流产率较高。然而，当雌性与一个兄弟和一个非近亲的个体交配时，“外交”产生的胚胎的存在会挽救其“内交”产生的同母异父兄弟姐妹，使得整胎幼仔都能成功发育到要出生的时候。
提取胚胎干细胞而又不破坏胚胎的新方法
确定人类胚胎干细胞系的通常方法是有争议的，因为在这个过程中胚胎被破坏掉了。本期Nature上有两篇研究论文介绍了从小鼠获取这种细胞而又不失去一个克隆出的、有发育潜力的胚胎的不同方法。Meissner 和 Jaenisch描述了一个用小鼠做的原理验证实验，所采用的方法是ANT（改变的核转移），这是一个生成本身不能移植进子宫中的异常胚泡的方法。这个新方法需要阻断Cdx2基因的作用，但由于该基因在采用这些细胞进行的治疗方案中可能需要用到，所以将这种基因剔除做成是可逆的，当胚胎干细胞培养系确定以后，就可以将该基因再打开。ANT是在美国国会就是否能使用NIH（国家卫生研究院）的经费进行涉及干细胞的研究问题举行的听证会上所讨论的可选方法之一。Chung等人介绍了一种提取小鼠胚胎干细胞系的新方法，该方法不会破坏胚胎向子宫内移植并进行发育的能力。这个方法所依靠的是在不育症治疗中使用的“移植前基因诊断”（PGD），即对胚胎可能存在的遗传缺陷进行扫描诊断。如果胚胎是健康的，它们就会被移植进子宫中，让其正常发育。如果能将这种方法转移进已经进行过PGD的人类胚胎，也许就有可能生成人类胚胎干细胞系库，而不会对胚胎本身带来其他风险。
“神经管闭合”缺陷的发病机制
像“脊柱分裂”和“无脑颅症”这样的“神经管闭合”疾病在新生儿中的发病率为1/1000，但这些先天性畸形的内在原因基本上不清楚。用动物模型进行的研究工作曾表明，PCP（planar cell polarity）信号通道在胚胎形成过程中所发生的“神经管闭合”中扮演一个角色。现在Ciruna等人为这一过程中找到了一个新机制，即被称为Van Gogh-like 2的PCP蛋白沿着前/后轴方向极化神经前体。该蛋白是子细胞以层间插入的方式插入在“神经管闭合”前形成的一个被称为神经龙骨的中间结构中所需要的。PCP通道似乎将细胞分裂与形态的形成耦合起来，这个系统中的畸形可能是“神经管闭合”缺陷的一个以前未曾识别出的原因。
Editorials
Ethics and fraud p117
The trajectory of the Hwang scandal highlights the shortness of the path between unethical behaviour and outright misconduct.
doi:10.1038/439117a
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Three cheers for peers p118
Thanks are due to researchers who act as referees, as editors resolve their often contradictory advice.
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Top of pageResearch Highlights
Research highlights p120
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Top of pageNews
Verdict: Hwang's human stem cells were all fakes p122
Korean scientist did not clone a human embryo but did clone a dog.
David Cyranoski
doi:10.1038/439122a
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French research chief quits over reforms p122
Plans for restructured agency prompt resignation.
Declan Butler
doi:10.1038/439122b
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Yes, but will it jump? p124
Experts divided on whether H5N1 bird flu will gain ability to spread between people.
Declan Butler
doi:10.1038/439124a
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Sidelines p126
doi:10.1038/439126a
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DNA tests put death penalty under fire p126
Campaigners hope re-examination of evidence will undermine capital punishment.
Emma Marris
doi:10.1038/439126b
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Bird lovers keep sharp eye on owls p127
Visitors from Europe ruffle conservationists' feathers.
Jim Giles
doi:10.1038/439127a
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Methane finding baffles scientists p128
Plant production of greenhouse gas throws up questions for climate models.
Quirin Schiermeier
doi:10.1038/439128a
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News in brief p129
doi:10.1038/439129a
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Correction p129
doi:10.1038/439129b
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Top of pageNews Features
Origins of DNA: Base invaders p130
Could viruses have invented DNA as a way to sneak into cells? John Whitfield investigates.
doi:10.1038/439130a
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Space exploration: A shot in the dark? p132
Japan's mission to collect a sample from a distant asteroid looks to have ended in failure. Ichiko Fuyuno investigates how the setback will affect Japan's struggling space programme.
doi:10.1038/439132a
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Prion disease: The shape of things to come p134
A number of fatal brain diseases are linked to misfolded proteins, an effect researchers are mimicking in the lab. But as they generate new versions of these malformed molecules, could they be creating a monster? Roxanne Khamsi finds out.
doi:10.1038/439134a
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Top of pageBusiness
All systems go p136
Industrial chemists are borrowing techniques from drug researchers to track down materials with desirable properties. Andrea Chipman reports.
doi:10.1038/439136a
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In brief p137
doi:10.1038/439137a
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Market Watch p137
doi:10.1038/439137b
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Top of pageCorrespondence
Neuroscience gears up for duel on the issue of brain versus deity p138
Kenneth S. Kosik
doi:10.1038/439138a
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Testing is necessary on animals as well as in vitro p138
Andrew Huxley
doi:10.1038/439138b
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Animal-rights extremists lose public support p138
P. Browne
doi:10.1038/439138c
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Why should child care be seen as a women's issue? p138
Maria José Hötzel
doi:10.1038/439138d
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Top of pageBooks and Arts
In the grey zone p139
If behaviour arises from interactions between genes and the environment, in what sense is it hardwired?
Erik Parens reviews Hardwired Behavior: What Neuroscience Reveals about Morality by Laurence R. Tancredi
doi:10.1038/439139a
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The monster that is medicine p140
W. F. Bynum reviews Dr Golem: How to Think about Medicine by Harry Collins and Trevor Pinch
doi:10.1038/439140a
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A little judgement p141
Harry Collins reviews Nano-Hype: The Truth Behind the Nanotechnology Buzz by David M. Berube
doi:10.1038/439141a
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Science in culture: A bigger picture of apes p142
The recent King Kong film highlights how our perceptions of gorillas have changed.
Janet Browne
doi:10.1038/439142a
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Top of pageNews and Views
Extinctions: A message from the frogs p143
The harlequin frogs of tropical America are at the sharp end of climate change. About two-thirds of their species have died out, and altered patterns of infection because of changes in temperature seem to be the cause.
Andrew R. Blaustein and Andy Dobson
doi:10.1038/439143a
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Space Physics: Breaking through the lines p144
Magnetic field lines are known to reorganize themselves in plasmas, converting magnetic to particle energy. Evidence harvested from the solar wind implies that the scale of the effect is larger than was thought.
Götz Paschmann
doi:10.1038/439144a
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Medicine: Politic stem cells p145
Research on embryonic stem cells holds huge promise for understanding and treating disease. Many people oppose such research on religious and ethical grounds, but two new methods may bypass some of these objections.
Irving L. Weissman
doi:10.1038/439145a
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50 & 100 years ago p147
doi:10.1038/439147a
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Global change: A green source of surprise p148
Living terrestrial vegetation emits large amounts of methane into the atmosphere. This unexpected finding, if confirmed, will have an impact on both greenhouse-gas accounting and research into sources of methane.
David C. Lowe
doi:10.1038/439148a
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Behaviour: Smells, brains and hormones p149
Contrary to the traditional view, the main olfactory pathway can mediate responses to pheromones as well as to common odours. Recent studies show that pheromone-activated hormonal systems extend widely within the brain.
Gordon M. Shepherd
doi:10.1038/439149a
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Top of pageObituary
Lawrence C. Katz (1956–2005) p152
Neuroscientist who helped to make sense of sense.
Carla J. Shatz
doi:10.1038/439152a
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Top of pageBrief Communications
Teaching in tandem-running ants p153
Tapping into the dialogue between leader and follower reveals an unexpected social skill.
Nigel R. Franks and Tom Richardson
doi:10.1038/439153a
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Top of pageArticles
Hit-and-run planetary collisions p155
Erik Asphaug, Craig B. Agnor and Quentin Williams
doi:10.1038/nature04311
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Widespread amphibian extinctions from epidemic disease driven by global warming p161
J. Alan Pounds, Martín R. Bustamante, Luis A. Coloma, Jamie A. Consuegra, Michael P. L. Fogden, Pru N. Foster, Enrique La Marca, Karen L. Masters, Andrés Merino-Viteri, Robert Puschendorf, Santiago R. Ron, G. Arturo Sánchez-Azofeifa, Christopher J. Still and Bruce E. Young
doi:10.1038/nature04246
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A quantitative protein interaction network for the ErbB receptors using protein microarrays p168
Richard B. Jones, Andrew Gordus, Jordan A. Krall and Gavin MacBeath
doi:10.1038/nature04177
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Top of pageLetters
A magnetic reconnection X-line extending more than 390 Earth radii in the solar wind p175
T. D. Phan, J. T. Gosling, M. S. Davis, R. M. Skoug, M. Øieroset, R. P. Lin, R. P. Lepping, D. J. McComas, C. W. Smith, H. Reme and A. Balogh
doi:10.1038/nature04393
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A semiconductor source of triggered entangled photon pairs p179
R. M. Stevenson, R. J. Young, P. Atkinson, K. Cooper, D. A. Ritchie and A. J. Shields
doi:10.1038/nature04446
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Ultrafast superheating and melting of bulk ice p183
H. Iglev, M. Schmeisser, K. Simeonidis, A. Thaller and A. Laubereau
doi:10.1038/nature04415
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Methane emissions from terrestrial plants under aerobic conditions p187
Frank Keppler, John T. G. Hamilton, Marc Bra and Thomas Röckmann
doi:10.1038/nature04420
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Stability of hydrous melt at the base of the Earth's upper mantle p192
Tatsuya Sakamaki, Akio Suzuki and Eiji Ohtani
doi:10.1038/nature04352
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A Cretaceous symmetrodont therian with some monotreme-like postcranial features p195
Gang Li and Zhe-Xi Luo
doi:10.1038/nature04168
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Outbred embryos rescue inbred half-siblings in mixed-paternity broods of live-bearing females p201
Jeanne A. Zeh and David W. Zeh
doi:10.1038/nature04260
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Specificity in Toll-like receptor signalling through distinct effector functions of TRAF3 and TRAF6 p204
Hans Häcker, Vanessa Redecke, Blagoy Blagoev, Irina Kratchmarova, Li-Chung Hsu, Gang G. Wang, Mark P. Kamps, Eyal Raz, Hermann Wagner, Georg Häcker, Matthias Mann and Michael Karin
doi:10.1038/nature04369
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Critical role of TRAF3 in the Toll-like receptor-dependent and -independent antiviral response p208
Gagik Oganesyan, Supriya K. Saha, Beichu Guo, Jeannie Q. He, Arash Shahangian, Brian Zarnegar, Andrea Perry and Genhong Cheng
doi:10.1038/nature04374
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Generation of nuclear transfer-derived pluripotent ES cells from cloned Cdx2-deficient blastocysts p212
Alexander Meissner and Rudolf Jaenisch
doi:10.1038/nature04257
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Embryonic and extraembryonic stem cell lines derived from single mouse blastomeres p216
Young Chung, Irina Klimanskaya, Sandy Becker, Joel Marh, Shi-Jiang Lu, Julie Johnson, Lorraine Meisner and Robert Lanza
doi:10.1038/nature04277
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Planar cell polarity signalling couples cell division and morphogenesis during neurulation p220
Brian Ciruna, Andreas Jenny, Diana Lee, Marek Mlodzik and Alexander F. Schier
doi:10.1038/nature04375
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A single amino acid governs enhanced activity of DinB DNA polymerases on damaged templates p225
Daniel F. Jarosz, Veronica G. Godoy, James C. Delaney, John M. Essigmann and Graham C. Walker
doi:10.1038/nature04318
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Palindromic assembly of the giant muscle protein titin in the sarcomeric Z-disk p229
Peijian Zou, Nikos Pinotsis, Stephan Lange, Young-Hwa Song, Alexander Popov, Irene Mavridis, Olga M. Mayans, Mathias Gautel and Matthias Wilmanns
doi:10.1038/nature04343
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Structure of the Sec13/31 COPII coat cage p234
Scott M. Stagg, Cemal Gürkan, Douglas M. Fowler, Paul LaPointe, Ted R. Foss, Clinton S. Potter, Bridget Carragher and William E. Balch
doi:10.1038/nature04339
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Top of pageNaturejobs
Prospect
The best-laid plans p239
Planning should take into account the unexpected.
Paul Smaglik
doi:10.1038/nj7073-239a
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Career Views
Miodrag Stojkovic, deputy director of regenerative medicine, Prince Felipe Research Centre, Valencia, Spain p240
Leading stem-cell biologist heads across Europe.
Siëlle Gramser
doi:10.1038/nj7073-240a
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Mentors & Protégés p240
Physics student praises mentor for good career guidance.
Timothy Stoltzfus-Dueck
doi:10.1038/nj7073-240b
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Alumnus Journal: Writing up p240
Finishing a thesis can be worrisome and wonderful.
Sidney Omelon
doi:10.1038/nj7073-240c
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Top of pageFutures
Printcrime p242
Copy this story.
Cory Doctorow
doi:10.1038/439242a
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