Volume 441 Number 7092 pp383-548 25 May 2006 封面故事：抑制癌变干细胞而保护造血干细胞的药物能引发和维持癌症的干细胞非常像正常细胞，以至于难以设计专门针对癌症的药物来。这是一个严重的问题，因为举例来说，在白血病治疗期间受损的血液干细胞能造成造血机能丧失，甚至导致患者死亡。现在，对肿瘤抑制因子PTEN（在白血病和其他癌症中经常是没有活性的）所做的一项研究，发现了正常干细胞与癌变干细胞在自我更新上的一大差别。PTEN正常情况下抑制磷脂酰肌醇-3-OH激酶信号通道，限制细胞增殖和存活。在没有PTEN时，白血病干细胞能够增殖，但正常干细胞被耗尽。这说明，能够模仿PTEN的药物也许能够抑制白血病，而不会伤害血液干细胞。事实上，在缺失Pten的小鼠身上，雷帕霉素（Rapamycin）能杀死白血病干细胞，但却能保护血液干细胞的功能。另一项研究证实了PTEN在调控血液干细胞中所起的作用。（Article p.475; Letter p.518; News and Views）本期封面图片为在组织培养中由一个缺失Pten的造血干细胞形成的一组血液细胞。
GRB在银河系中比较少见在其死亡的阵痛中，巨型恒星经常产生超新星，偶尔还会产生持续时间很长的伽马射线暴（GRB）。这说明，GRB和超新星应能在类似环境中找到，但以“哈勃太空望远镜”1000小时以上的观测结果为依据所做的研究表明，这种期待是错误的。大多数持续时间很长的GRB存在于很小的、暗淡的、不规则的星系中。超新星在螺旋星系和不规则星系之间似乎是等分的。GRB集中在它们主星系中最亮的部分，在那里超新星在其整个主星系中都出现。该发现一个让人高兴的结论是，GRB在银河系中相对较少见，如果它们在我们附近爆炸的话会在地球上造成灾难。
动物也有副突变现象副突变（Paramutation）首次于上个世纪50年代在玉米中被发现，后在其他植物和真菌中被发现，它是一种不符合法则的遗传形式。大多数情况下，孟德尔的遗传定律（该定律认为基因对中的等位基因独立遗传）都是对的。但副突变是具有同一位点的两个等位基因之间的相互作用，它导致其中一个等位基因发生一个可遗传的变化。现在，这种类型的非孟德尔遗传已在一种动物中被发现。在对小鼠的Kit基因进行研究的过程中，研究人员发现，在与无效突变体杂交之后，野生型表现型没有得到充分表达。Kit+/Kit+基因型事实上是按预料中的频率生成的，但由于副突变，它们中大多数仍然有白点突变体表现型。这种外成（独立于DNA的）遗传的机制涉及配子与合子之间的RNA转移。RNA是这方面的一个关键成分，它参与了植物的各种不同类型的外成遗传，作为遗传信息的存储地点，或作为起调控作用的“微RNA”（microRNA）。
研究磁现象的新技术目前已经是一种功能强大的研究仪器的电子显微镜，随着“磁园二色性”（MCD）被发现能够用传统透射电子显微镜探测到，它的功能还可能变得更强大。如果在施加一个磁场的情况下左、右圆偏振光的吸收有所不同，材料就会显示“磁园二色性”。利用同步加速器X-射线光子产生的这种效应的应用，是研究磁现象的一个强大工具。名为EMCD（energy loss magnetic chiral dichroism）的新技术利用X-射线吸收与无弹性电子散射之间的相似性来实现昂贵的同步加速器通常才具有的TEM功能。EMCD在包括自旋电子学和纳米磁学在内的很多领域都可能有用。
有望成为高性能FET的新型锗/硅纳米线以半导体纳米线为基础的场效应晶体管（FET）有一天可能会取代微型电路中标准的硅MOSFET（金属氧化物半导体场效应晶体管)。 MOSFET是用于高速切换和电脑集成电路中的一种普及型的晶体管。一种专门设计的、具有锗外壳和硅内核的纳米线，有希望成为一种纳米尺度的场效应晶体管：它有一个近乎完美的导电通道。现在，在半导体配置中，这种锗/硅纳米线表现出了包括电导高和切换时间延迟短在内的性能，这些性能优于最新硅MOSFET材料。
海洋中水下火山喷发的直接观测地球火山活动的四分之三在海洋底下。我们很少知道火山在什么时候和什么地方喷发，大多数观测结果都是间接的，是由表面船只获得的，或是在喷发之后获得的。现在，Embley等人报告了对位于关岛东北的北马里亚纳群岛中的一个水下弧形火山的一次正在进行中的喷发所做的直接观测和取样研究结果。遥控的潜水装置首次被用来在540米的深度处、在一个最近被测绘出的水下火山的最高峰附近识别一个由喷发形成的热液柱。之后，研究人员又在2004年3/4月和2005年10月对火山活动进行了监测。长期喷发活动形成了一个不寻常的化学环境和一个也许是活的弧形和热点火山所特有的生态系统。
与人为善于己方便演化，尤其是合作行为的维持，需要做一些解释。合作群体会被自私地利用共同资源的“骗子”所葬送，大量理论预测，骗子通常会取代合作者。但对为什么欺骗并不总能大行其道所做的一个可能的解释，来自酵母菌种之间的竞争实验。实验所用的酵母菌种既表现为合作者，也表现为欺骗者，相互之间竞争葡萄糖，并有效地或自私地利用它。实验结果表明，两个策略能够共存，因为两个策略都与代价和利益相联系。进行欺骗是有代价的，在该实验中这种代价就是欺骗者所产生的后代少于对手。（Letter p. 498）Ohtsuki等人在对由一个曲线上的点构成的有层次的“虚拟”种群的演化动态所做的一项研究中，用图形方式显示了自然选择会支持合作。如果无私行为的利益被代价所除的结果超过邻居的平均数量的话，合作就会受到支持。所以，即使在没有声誉效应或策略复杂性的情况下，合作也能作为这种“社会凝聚性”的一个结果而演化和发展。
Wolbachia的寄生环境Wolbachia是非常成功的细胞内寄生虫。它们存在于多数节肢动物体内，也因有可能成为控制疟疾的工具而成为新闻，它们的转基因变种有可能阻止疟原虫在蚊子中成熟。同线粒体一样，这些细菌也是由母亲传播的。它们还在物种之间横向传播，但对其中所涉及的细胞机制我们却知之甚少。现在Frydman等人报告，Wolbachia能跨过组织障碍到达生殖细胞。在新发生的或遗传的感染中，它们喜欢寄居在果蝇卵巢的体干细胞中。这种干细胞环境似乎是感染生殖细胞的细菌的一个聚居地。
shRNA在活体中有很强毒性虽然尚处在初期阶段，但RNA干涉（RNAi）已经被看作是一种用来沉寂基因的具有潜在重要性的治疗方法。在活体中输送“短干涉RNA”（siRNA）的一种办法是，将siRNA序列作为“短发夹”克隆进一种腺病毒载体中。当送入动物体内时，该发夹序列被表达出来，形成一个“双链RNA”（shRNA），并被RNAi通道处理。然而，对成年小鼠肝脏中shRNA的表达的长期效应所做的一项研究为我们敲响了警钟。该研究结果表明，很多shRNA在小鼠中表达时是有毒的。这种经常是致命的毒性似乎是由shRNA与内生微RNA之间为与Exportin-5结合所展开的竞争造成的。Exportin-5是一个参与将分子输送出细胞核的因子。人们对开发基于shRNA的疗法非常感兴趣，而此前几乎没有证据表明shRNA在活体中有很强毒性。
ContentsEditorials
Policing ourselves p383
Biologists should push forward with an effort that began in California last weekend to wrestle with the implications of synthetic biology.
doi:10.1038/441383a
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Coping with complexity p383
A more detailed understanding of scientific concepts does not lead to simplicity.
doi:10.1038/441383b
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Carbon omissions p384
The European Union's greenhouse-gas trading system needs reinforcement.
doi:10.1038/441384a
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Research Highlights
Research highlights p386
doi:10.1038/441386a
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News
Synthetic biologists try to calm fears p388
Conference discusses voluntary code of conduct.
Erika Check
doi:10.1038/441388a
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Mars explorers seek spot for touchdown p389
Planetary scientists debate where to land next.
Tony Reichhardt
doi:10.1038/441389a
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Teenager waits 40 years for recognition p390
Fossil is finally hailed as new Asian plesiosaur.
Ichiko Fuyuno
doi:10.1038/441390a
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Election fever inflames the US stem-cell debate p391
Senators tackle research policy in race for seats.
Erika Check
doi:10.1038/441391a
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Named and shamed p392
As accusations of scientific misconduct in China become rife, some fear persecution reminiscent of that used in the Cultural Revolution.
David Cyranoski
doi:10.1038/441392a
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Sidelines p394
doi:10.1038/441394a
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Physicists plead to make final tweak to fusion experiment p394
Is there time to make the ITER reactor a little fuzzy?
Geoff Brumfiel
doi:10.1038/441394b
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News in brief p396
doi:10.1038/441396a
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News Features
Genetics: What is a gene? p398
The idea of genes as beads on a DNA string is fast fading. Protein-coding sequences have no clear beginning or end and RNA is a key part of the information package, reports Helen Pearson.
doi:10.1038/441398a
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The dark side of the Sun p402
The Sun occasionally hurls streams of particles towards Earth, where they can wreak havoc with satellites. Predicting these solar storms is hard, but some physicists believe we're about to face the biggest bout of solar flares in years. Stuart Clark reports.
doi:10.1038/441402a
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Business
Carbon market survives gas leaks p405
Searing volatility has led some to dismiss Europe's nascent emissions market as a farce — but it is still hanging in there. Quirin Schiermeier reports on the project's teething troubles.
doi:10.1038/441405a
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Correspondence
Climate: open review may ease acceptance of report p406
Michael MacCracken
doi:10.1038/441406a
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Climate: US has always made IPCC drafts available p406
Harlan L. Watson
doi:10.1038/441406b
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HIV denialists ignore large gap in the study they cite p406
Nathan Geffen, Nicoli Nattrass and Glenda Gray
doi:10.1038/441406c
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Books and Arts
Building on failure p407
Working out why something doesn't work is a good starting point for improving the design.
J. M. Ottino reviews Success Through Failure: The Paradox of Design by Henry Petroski
doi:10.1038/441407a
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A mammoth murder mystery p408
Alan B. Shabel reviews Twilight of the Mammoths: Ice Age Extinctions and the Rewilding of America by Paul S. Martin
doi:10.1038/441408a
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Electrifying book wins Aventis Prize p408
doi:10.1038/441408b
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Everyone hates a know-all p409
David Philip Miller reviews The Last Man Who Knew Everything: Thomas Young, the Anonymous Polymath Who Proved Newton Wrong, Explained How We See, Cured the Sick, and Deciphered the Rosetta Stone, Among Other Feats of Genius by Andrew Robinson
doi:10.1038/441409a
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Life, the Universe and entropy p409
Robert J. McEliece reviews Decoding the Universe: How the New Science of Information is Explaining Everything in the Cosmos, From our Brains to Black Holes by Charles Seife
doi:10.1038/441409b
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Science in culture: Form becomes feeling p410
Siobhan Davies looks to science to shape her dance.
Martin Kemp
doi:10.1038/441410a
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News and Views
Social sciences: A New World of differences p411
For richer, for poorer — the countries of the Americas and those of the Caribbean present stark contrasts in fortune. An explanation of those contrasts invokes branching chains of cause and effect.
Shaun Miller and Jared Diamond
doi:10.1038/441411a
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Genetics: Paramutable possibilities p413
A curious genetic phenomenon allows certain genetic instructions to be passed between generations without the gene variants involved being transmitted. Some spotty mice provide clues to how this might happen.
Paul D. Soloway
doi:10.1038/441413a
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Nanomaterials: Display of flexibility p414
Treated the right way, carbon nanotubes can be moulded into large, flexible electron-emitting sheets. The material is one half of what's needed for an electronic display you could fold up and slip in your pocket.
László Forró
doi:10.1038/441414a
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Immunology: Adaptable innate killers p415
Natural killer cells are versatile white blood cells that act in the innate immune system. Quite how adaptable they can be in the absence of other, more specialized, immune cells comes as a surprise.
Peter Parham
doi:10.1038/441415a
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Meteoritics: How to make a chondrule p416
Chondrules, the stony, seed-like grains in meteorites, were formed when some event melted rock in the solar nebula. The latest analyses narrow the possible 'when', 'where' and 'how' of that process.
Steve Desch
doi:10.1038/441416a
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Ecology: Paradox of the clumps p417
A fresh look at an established model in ecology has generated insights into how species coexist with each other. But it has also raised a vexed question: what constitutes the ecological identity of species?
Sean Nee and Nick Colegrave
doi:10.1038/441417a
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Materials science: Film review p418
Maria Bellantone
doi:10.1038/441418a
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Stem cells: Good, bad and reformable p418
The ability of stem cells to continuously supply vast numbers of cells is magnificent, but it can be devastating if it runs amok, as in some tumours. So what makes a normal stem cell turn bad, and can it be redeemed?
Viktor Janzen and David T. Scadden
doi:10.1038/441418b
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Brief Communications
Ecology: Avoidance of disease by social lobsters p421
These gregarious animals shun lobsters that carry a lethal virus, even when they still seem to be healthy.
Donald C. Behringer, Mark J. Butler and Jeffrey D. Shields
doi:10.1038/441421a
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Brief Communications Arising
Correspondence patterns: Mechanisms and models of human dynamics pE5
Alex Kentsis
doi:10.1038/nature04901
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Correspondence patterns: Mechanisms and models of human dynamics (Reply) pE5
J. G. Oliveira and A.-L. Barabàsi
doi:10.1038/nature04902
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Insight: Signalling in cancer - Produced with support from:
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Insight: Signalling in cancer
Signalling in cancer p423
Alex Eccleston and Ritu Dhand
doi:10.1038/441423a
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Ras, PI(3)K and mTOR signalling controls tumour cell growth p424
Reuben J. Shaw and Lewis C. Cantley
doi:10.1038/nature04869
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Nuclear factor-B in cancer development and progression p431
Michael Karin
doi:10.1038/nature04870
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Hypoxia signalling in cancer and approaches to enforce tumour regression p437
Jacques Pouysségur, Frédéric Dayan and Nathalie M. Mazure
doi:10.1038/nature04871
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New signals from the invasive front p444
Gerhard Christofori
doi:10.1038/nature04872
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Validating cancer drug targets p451
John D. Benson, Ying-Nan P. Chen, Susan A. Cornell-Kennon, Marion Dorsch, Sunkyu Kim, Magdalena Leszczyniecka, William R. Sellers and Christoph Lengauer
doi:10.1038/nature04873
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Mechanisms of drug inhibition of signalling molecules p457
Judith S. Sebolt-Leopold and Jessie M. English
doi:10.1038/nature04874
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Articles
Long -ray bursts and core-collapse supernovae have different environments p463
A. S. Fruchter, A. J. Levan, L. Strolger, P. M. Vreeswijk, S. E. Thorsett, D. Bersier, I. Burud, J. M. Castro Cerón, A. J. Castro-Tirado, C. Conselice, T. Dahlen, H. C. Ferguson, J. P. U. Fynbo, P. M. Garnavich, R. A. Gibbons, J. Gorosabel, T. R. Gull, J. Hjorth, S. T. Holland, C. Kouveliotou, Z. Levay, M. Livio, M. R. Metzger, P. E. Nugent, L. Petro, E. Pian, J. E. Rhoads, A. G. Riess, K. C. Sahu, A. Smette, N. R. Tanvir, R. A. M. J. Wijers and S. E. Woosley
doi:10.1038/nature04787
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RNA-mediated non-mendelian inheritance of an epigenetic change in the mouse p469
Minoo Rassoulzadegan, Valérie Grandjean, Pierre Gounon, Stéphane Vincent, Isabelle Gillot and François Cuzin
doi:10.1038/nature04674
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Pten dependence distinguishes haematopoietic stem cells from leukaemia-initiating cells p475
Ömer H. Yilmaz, Riccardo Valdez, Brian K. Theisen, Wei Guo, David O. Ferguson, Hong Wu and Sean J. Morrison
doi:10.1038/nature04703
Abstract | Full Text | PDF (989K) | Supplementary information
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Letters
Chondrule formation in particle-rich nebular regions at least hundreds of kilometres across p483
Jeffrey N. Cuzzi and Conel M. O'D. Alexander
doi:10.1038/nature04834
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Detection of magnetic circular dichroism using a transmission electron microscope p486
P. Schattschneider, S. Rubino, C. Hébert, J. Rusz, J. Kune, P. Novák, E. Carlino, M. Fabrizioli, G. Panaccione and G. Rossi
doi:10.1038/nature04778
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Ge/Si nanowire heterostructures as high-performance field-effect transistors p489
Jie Xiang, Wei Lu, Yongjie Hu, Yue Wu, Hao Yan and Charles M. Lieber
doi:10.1038/nature04796
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Long-term eruptive activity at a submarine arc volcano p494
Robert W. Embley, William W. Chadwick, Jr, Edward T. Baker, David A. Butterfield, Joseph A. Resing, Cornel E.J. de Ronde, Verena Tunnicliffe, John E. Lupton, S. Kim Juniper, Kenneth H. Rubin, Robert J. Stern, Geoffrey T. Lebon, Ko-ichi Nakamura, Susan G. Merle, James R. Hein, Douglas A. Wiens and Yoshihiko Tamura
doi:10.1038/nature04762
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Resource competition and social conflict in experimental populations of yeast p498
R. Craig MacLean and Ivana Gudelj
doi:10.1038/nature04624
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A simple rule for the evolution of cooperation on graphs and social networks p502
Hisashi Ohtsuki, Christoph Hauert, Erez Lieberman and Martin A. Nowak
doi:10.1038/nature04605
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Homology of arthropod anterior appendages revealed by Hox gene expression in a sea spider p506
Muriel Jager, Jérôme Murienne, Céline Clabaut, Jean Deutsch, Hervé Le Guyader and Michaël Manuel
doi:10.1038/nature04591
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Somatic stem cell niche tropism in Wolbachia p509
Horacio M. Frydman, Jennifer M. Li, Drew N. Robson and Eric Wieschaus
doi:10.1038/nature04756
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S-Nitrosylated protein-disulphide isomerase links protein misfolding to neurodegeneration p513
Takashi Uehara, Tomohiro Nakamura, Dongdong Yao, Zhong-Qing Shi, Zezong Gu, Yuliang Ma, Eliezer Masliah, Yasuyuki Nomura and Stuart A. Lipton
doi:10.1038/nature04782
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PTEN maintains haematopoietic stem cells and acts in lineage choice and leukaemia prevention p518
Jiwang Zhang, Justin C. Grindley, Tong Yin, Sachintha Jayasinghe, Xi C. He, Jason T. Ross, Jeffrey S. Haug, Dawn Rupp, Kimberly S. Porter-Westpfahl, Leanne M. Wiedemann, Hong Wu and Linheng Li
doi:10.1038/nature04747
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Identification of a tumour suppressor network opposing nuclear Akt function p523
Lloyd C. Trotman, Andrea Alimonti, Pier Paolo Scaglioni, Jason A. Koutcher, Carlos Cordon-Cardo and Pier Paolo Pandolfi
doi:10.1038/nature04809
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GTP-dependent twisting of dynamin implicates constriction and tension in membrane fission p528
Aurélien Roux, Katherine Uyhazi, Adam Frost and Pietro De Camilli
doi:10.1038/nature04718
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Rec8 phosphorylation and recombination promote the step-wise loss of cohesins in meiosis p532
Gloria A. Brar, Brendan M. Kiburz, Yi Zhang, Ji-Eun Kim, Forest White and Angelika Amon
doi:10.1038/nature04794
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Fatality in mice due to oversaturation of cellular microRNA/short hairpin RNA pathways p537
Dirk Grimm, Konrad L. Streetz, Catherine L. Jopling, Theresa A. Storm, Kusum Pandey, Corrine R. Davis, Patricia Marion, Felix Salazar and Mark A. Kay
doi:10.1038/nature04791
First paragraph | Full Text | PDF (549K) | Supplementary information
See also: Editor's summary
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Naturejobs
Prospect
Prospect p543
Fledgling UK postdoc association can learn from other efforts.
Paul Smaglik
doi:10.1038/nj7092-543a
Full Text | PDF (168K)
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Special Report
Animal intelligence p544
Use of animals for testing early in the drug-development process aims to provide vital information to make new drugs safe and effective — and the process is being constantly refined. Hannah Hoag finds out what is involved.
Hannah Hoag
doi:10.1038/nj7092-544a
Full Text | PDF (468K)
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Careers and Recruitment
Jai Nagarkatti, president and chief executive, Sigma-Aldrich, St Louis, Missouri p546
Jai Nagarkatti shows loyalty to his company.
Virginia Gewin
doi:10.1038/nj7092-546a
Full Text | PDF (113K)
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Britain's postdocs unite p546
UK postdocs form association.
John Bothwell
doi:10.1038/nj7092-546b
Full Text | PDF (113K)
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Clocking out p546
The shifting passage of time in graduate school.
Milan de Vries
doi:10.1038/nj7092-546c
Full Text | PDF (113K)
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Futures
Paratext p548
Step into another world.
Scarlett Thomas
doi:10.1038/441548a
Full Text | PDF (233K)
