英国《Nature》目录要览：2010-04-08出版

封面故事：鸟群中的尊卑顺序
Hierarchical group dynamics in pigeon flocks
俗话说“物以类聚，人以群分”，但一大群动物到底是怎样协调一致地运动的却没有得到完全解释。它们是跟着一个领头的跑，还是遵守一套简单的行为规则？此前，这个问题在很大程度上一直是通过数值模拟来研究的，但随着重量仅16克的微型背包式GPS记录仪的问世，现在有可能对一群鸟中的每一只进行跟踪，并根据直接测量结果来验证相关模型。利用一群最多达10只的信鸽所做实验显示，一只鸟在飞翔中的位置取决于它在一个明确定义的社会等级中的位置——这种等级体系就相当于空中的“啄序”，即长幼强弱次序。有趣的是，鸟对其主要用左眼看到的“队友”能更快地做出反应，这进一步证明它们具有取决于其在鸟群中位置的具体角色。本期封面的组合图片所示为鸟的实际飞行轨迹，是根据它们在鸟群中的领导地位的排列顺序着色的：在谱图红色端附近者居等级体系顶端；在紫色端附近者居等级体系末端。（Letter p. 890）封面图片：Mate Nagy/images: Simon Walker


量子自旋液体存在的条件（Quantum spin: liquid assets）
Quantum spin liquid emerging in two-dimensional correlated Dirac fermions
量子自旋液体是一个假设的自旋体系（这里所说的自旋如同电子的自旋一样），在其中自旋的取向即使在绝对零度也继续波动。关于这样的状态存在的证据仍然不确定。孟子阳（音译）及其同事建立了一个关于排列在蜂巢晶格（比如说像石墨烯中的那样）上的相关电子的显微模型，并且确定了一种量子自旋液体在这样一个体系中实现所需的条件。这种出乎意料的物质状态是一个共振价键状态，类似于人们所提出的高温超导体的状态，这便提出了通过掺杂产生非传统超导性的可能性。（Article p. 847）


癌细胞恶化所需的微环境（The cancer cell niche）
Bone progenitor dysfunction induces myelodysplasia and secondary leukaemia
虽然单独一个细胞中的一系列遗传事件和后生（非遗传）事件可能是肿瘤发生所必需的，但也有人提出，要使肿瘤的恶性充分发育，也需要一个适当的微环境或小生境。对这一观点的支持来自一个新的小鼠模型，在该模型中，造血细胞的恶性癌变由血细胞微环境中的遗传变化引起。骨先祖细胞中Dicer1（一个参与微RNA处理的基因）的删除导致一种与骨髓增生异常综合症相似的表现型，这种状态可以继续发展成白血病。这些先祖细胞中Sbds（在“Schwachman–Bodian–Diamond综合症”中发生突变的基因）水平下降，这是会导致白血病的一种骨髓衰竭现象。（Article p. 852）


Zscan4蛋白与基因组稳定性（Genomic stability）
Zscan4 regulates telomere elongation and genomic stability in ES cells
小鼠胚胎干细胞（ES细胞）在培养细胞中以基因组稳定性知名，能够在不失去其正常染色体组型（核型）的条件下长期保持存活。现在，Zscan4蛋白被发现有助于维持这些细胞中的端粒和基因组稳定性。ES细胞只有5%在任何时候都表达Zscan4，但几乎所有ES细胞在九次通过中都至少激发Zscan4一次。瞬间的Zscan4-阳性状态与由端粒重组和减数分裂特异性同源重组基因的上调所引起的快速端粒延伸相联系。这个发现提出一个可能性：促进Zscan4表达也许可提高干细胞或癌细胞等其他细胞类型中的基因组稳定性。（Article p. 858）


遥远天体日蚀现象观测（A distant eclipse glimpsed）
Infrared images of the transiting disk in the ϵ Aurigae system
每27.1年，明亮的双星ε Aurigae便会变暗，因为它要经历一次持续约18个月的日蚀。此前，穿越ε Aur体系盘面的天体一直无法探测到，也一直存在很多猜测。人们比较愿意接受的解释是，看不见的伴星是由一颗隐藏的恒星周围的不透明物质所构成的一个倾斜的盘。最近的研究工作显示，该体系可能由一颗可见的F-星与被一个温度约为500K的盘所遮蔽的一颗B5V星配对组成。现在，在2009年11月和12月利用由6个望远镜组成的CHARA望远镜阵列所做的干涉测量观测工作，在红外波段产生了发生日蚀天体的图像，显示它是一个不透明的盘，其椭圆形形状表明，它在如所预测的那样发生倾斜。（Letter p. 870; News & Views）


记忆电阻器可以进行逻辑运算（A memory for logic）
‘Memristive’ switches enable ‘stateful’ logic operations via material implication
将一个记忆元件和一个电阻器的电学性质结合起来（比如说在一个记忆电阻器或记忆电阻装置中）的可能性是Leon Chua在1971年提出来的。直到两年前、在双极电压激发开关被发现是记忆电阻器的物理实现之前，它仍属于理论范畴。这个发现重新激发了人们对记忆电阻装置的兴趣；而现在，Julien Borghetti 及其同事又发现，记忆电阻器还可进行一类基础逻辑运算，这些运算要求各装置同时作为逻辑元件和记忆元件来发挥作用。看来，人们在这方面的兴趣还将持续下去。（Letter p. 873）


放牧会降低一氧化二氮排放（Grazing cuts N₂O emission）
Grazing-induced reduction of natural nitrous oxide release from continental steppe
温室气体一氧化二氮的水平自前工业化时代以来有所增加，这主要是由于农业活动。在这些变化中，有报道指出，放牧会大大增加温带草地的一氧化二氮排放。从中国内蒙古干草原上十个地点全年监测工作获得的新数据对这一观点提出了挑战，因为这些数据突显出了一个以前被忽略的相互作用。利用“自动监控室系统”所做的测量表明，一氧化二氮的释放受春天化冻期间的脉冲支配，在未被牲畜牧食的干草原上最高，随载畜量的增加下降。所以出乎意料的是，放牧会降低而不是增加一氧化二氮排放，因为它会改变土壤水平衡和微生物活动。（Letter p. 881; News & Views）

 
晚更新世猿人古线粒体DNA被测序（Then there were three）
The complete mitochondrial DNA genome of an unknown hominin from southern Siberia
来自距今48,000 和30,000年前、居住在西伯利亚南部阿尔泰山区的一个猿人的古线粒体DNA已被测序（关于该新闻，请访问go.nature.com/sokd1F）。比较基因组研究表明，这一线粒体DNA来自一次“走出非洲”的迁徙事件，但这一事件与产生了“尼安德特人”和现代人的迁徙事件截然不同。该研究中所用的线粒体DNA是从一块骨头中提取的，这块骨头是小拇指（第五个指头）的一部分，是2008年从名叫“Denisova Cave”的洞穴发掘出来的。这个洞穴的地层学研究表明，该猿人居住地点在地理上与“尼安德特人”和现代人相近，而且生活时代也相同。考虑到距今大约17,000 年前“弗洛勒斯人”在印尼的存在，这一发现表明，晚更新世有多个猿人分支长期共存于欧亚大陆。（Letter p. 894; News & Views）


狗可能起源于中东或欧洲（Dog breeds, old and new）
Genome-wide SNP and haplotype analyses reveal a rich history underlying dog domestication
家狗的出现是随人类文明的扩展而迅速发生的形态和功能的急速辐射的一个非常吸引人的例子。对家狗及其野生祖先（灰狼）的超过48,000个单核苷酸多态型所做的一个广泛的、全基因组范围的普查工作，显示了一个引人注目的遗传细分模式。研究人员发现了两个明显分化的类群：一个是古代品种，另一个是19世纪产生的现代品种。对“单倍体型”共享所做的一项分析显示，狗主要起源于中东或欧洲（这与最近的考古发现是一致的），而不是像以前线粒体DNA数据所表明的那样起源于东亚。（Letter p. 898）


通过寿司发生的基因转移（The sushi factor）
Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota
人肠道微生物群落所起的有用作用之一是，提供人类基因组中所缺的消化酶。例如，来自在整个演化过程中一直是人类饮食构成部分的陆地植物的多糖，就是在肠道中被碳水化合物活性酶（CAZymes）分解的，它们当中很多都是来自类杆菌的具有高度特异性的酶。然而，人们对帮助消化可食性海藻如紫菜、海白菜和裙带菜（常见于日本菜）的肠道酶却知之甚少。现在，能够消化来自紫菜类红海藻的硫酸多糖的碳水化合物活性酶已在海洋类杆菌分离菌种中被发现。出乎意料的是，基因组数据挖掘显示，这种酶存在于日本人的肠道细菌中，但在美国人的肠道细菌中却没有。这表明，最近（这里说的“最近”是从演化意义上来讲的）发生了从一种来自海洋环境的类杆菌向日本人肠道细菌“Bacteroides plebeius”的基因转移。紫菜传统上用于寿司中，这表明，接触未灭菌的食物，在带有不同碳水化合物活性酶的肠道细菌在体内积累中是一个普遍因素。（Letter p. 908; News & Views）


VEGF-B在血管功能中所起作用（Lipids on the move）
Vascular endothelial growth factor B controls endothelial fatty acid uptake
VEGF-B是一种“血管内皮生长因子”，在心脏、骨骼肌和褐色脂肪组织中都有高度表达。该因子被发现在将类脂向周围组织定向中起一个出人意料的作用。“血管内皮生长因子”（VEGFs）作为主要血管生成调控因子为人们所熟知，但VEGF-B在血管功能中的详细作用过去一直不清楚。缺失VEGF-B的小鼠在肌肉、心脏和褐色脂肪组织中所积累的类脂较少，而是将它们“推给”白色脂肪组织。VEGF-B在重新分配类脂中所起作用，提出了在糖尿病、肥胖症和心血管疾病中对致病性类脂积累进行调控的可能的新策略。（Letter p. 917）







----------------------
NEWS AND VIEWS
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Microbiology: Genetic pot luck pp837-838
Without the trillions of microbes that inhabit our gut, we can't fully
benefit from the components of our diet. But cultural differences in
diet may, in part, dictate what food our gut microbiota can digest.
Justin L. Sonnenburg
doi:10.1038/464837a
http://www.nature.com/nature/journal/v464/n7290/full/464837a.html

Human evolution: Stranger from Siberia pp838-839
The sequencing of ancient DNA is generating dramatic results. The
sequence from a bone fragment has revealed the existence of an unknown
type of extinct human ancestor that lived in Asia 40,000 years ago.
Terence A. Brown
doi:10.1038/464838a
http://www.nature.com/nature/journal/v464/n7290/full/464838a.html

Microfluidics: Exploiting elephants in the room pp839-840
Microfluidic devices have many applications in chemistry and biology,
but practical hitches associated with their use are often overlooked.
One such device that optimizes catalysts tackles these issues head-on.
Robert C. R. Wootton and Andrew J. deMello
doi:10.1038/464839a
http://www.nature.com/nature/journal/v464/n7290/full/464839a.html

Evolutionary biology: A flourishing of fish forms pp840-842
According to an innovative exercise in 'morphospace analysis', modern
fish owe their stunning diversity in part to an ecological cleaning of
the slate by the mass extinction at the end of the Cretaceous.
Michael Alfaro and Francesco Santini
doi:10.1038/464840a
http://www.nature.com/nature/journal/v464/n7290/full/464840a.html

Stellar astrophysics: Shrouded in a dusty disk pp842-843
For more than a century, the binary star system [epsi] Aurigae has
been a riddle, wrapped in a mystery, inside an enigma. But no more -
the system's previously inferred but unseen disk of dust has been detected.
Edward Guinan
doi:10.1038/464842a
http://www.nature.com/nature/journal/v464/n7290/full/464842a.html

Climate change: Grazing and nitrous oxide pp843-844
Most emissions of nitrous oxide from semi-arid, temperate grasslands
usually occur during the spring thaw. The effects that grazing has on
plant litter and snow cover dramatically reduce these seasonal emissions.
Stephen J. Del Grosso
doi:10.1038/464843a
http://www.nature.com/nature/journal/v464/n7290/full/464843a.html

Cancer: Drug-tolerant insurgents pp844-845
Some cancer cells that become tolerant to a drug remain resistant even
after its withdrawal, yet these cells eventually become sensitive to the
drug again. The underlying molecular mechanism is unusual.
Paul Workman and Jon Travers
doi:10.1038/464844a
http://www.nature.com/nature/journal/v464/n7290/full/464844a.html

----------------------
ARTICLES
----------------------
Quantum spin liquid emerging in two-dimensional correlated Dirac fermions
pp847-851
A quantum spin liquid is a hypothetical system of spins (such as those
carried by electrons), the orientations of which continue to fluctuate
even at absolute zero. Theoretical and experimental evidence for the
existence of such states at the microscopic level is elusive, but these
authors have modelled correlated electrons arranged on a honeycomb lattice
(such as in graphene), and identified the conditions under which a
microscopic quantum spin liquid would be realized in two dimensions.
Z. Y. Meng et al.
doi:10.1038/nature08942
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08942.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08942.html

Bone progenitor dysfunction induces myelodysplasia and secondary leukaemia
pp852-857
A new mouse model is developed in which haematopoietic malignancies are
caused by genetic changes in the microenvironment of blood cells. Deletion
in bone progenitor cells of Dicer1, a gene involved in microRNA processing,
leads to a myelodysplastic syndrome-like phenotype which can progress to
leukaemia. Deregulation of Sbds, which is mutated in human Schwachman-
Bodian-Diamond syndrome, may be involved in this process.
Marc H. G. P. Raaijmakers et al.
doi:10.1038/nature08851
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08851.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08851.html

Zscan4 regulates telomere elongation and genomic stability in ES cells
pp858-863
Zscan4 is shown to be involved in maintaining telomeres in embryonic stem
(ES) cells. Only 5% of ES cells express Zscan4 at a given time, but nearly
all ES cells activate Zscan4 at least once within nine passages. The transient
Zscan4-positive state is associated with rapid telomere extension by
telomere recombination and upregulation of meiosis-specific homologous
recombination genes. Knocking down Zscan4 shortens telomeres, increases
karyotype abnormalities and spontaneous sister chromatid exchange, and
slows down cell proliferation until reaching crisis by eight passages.
Michal Zalzman et al.
doi:10.1038/nature08882
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08882.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08882.html

Molecular mechanism of multivesicular body biogenesis by ESCRT complexes
pp864-869
Here, multivesicular body (MVB) biogenesis is reconstituted using giant
unilamellar vesicles and all of the ESCRT complexes. ESCRT-0 is required
for clustering of cargo proteins, whereas ESCRT-I and -II in combination
deform the membrane into buds, in which cargo is confined. ESCRT-III
subunits localize to the bud neck and are required for scission of the
membrane to form intraluminal vesicles. These results explain how ESCRT
complexes sequester cargo proteins into MVBs.
Thomas Wollert and James H. Hurley
doi:10.1038/nature08849
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08849.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08849.html

----------------------
LETTERS
----------------------
Infrared images of the transiting disk in the [epsi] Aurigae system pp870-872
[epsi] Aurigae is a bright, eclipsing binary star system but the cause of each
18-month-long eclipse has been unknown for nearly 190 years, because the
companion was, until recently, undetectable. The preferred explanation has
been a tilted disk of opaque material and here the authors report interferometric
images that do indeed show an opaque disk of very low mass, tilted as expected,
crossing the disk of the F star.
Brian Kloppenborg et al.
doi:10.1038/nature08968
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08968.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08968.html

'Memristive' switches enable 'stateful' logic operations via material
implication pp873-876
A challenge in the semiconductor industry is to create integrated circuits
that use new physical state variables - other than charge or voltage - to
offer memory and logic functions. Memristive devices, which combine the
electrical properties of a memory element and a resistor, use resistance
instead, and here such 'memristors' are shown to perform logic operations as well.
Julien Borghetti et al.
doi:10.1038/nature08940
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08940.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08940.html

Dislocation nucleation governed softening and maximum strength in nano-twinned
metals pp877-880
The strength of conventional metals is determined by the interaction of
dislocations with obstacles such as grain boundaries. Molecular dynamics
simulations reveal that the strength of ultrafine-grained copper containing
twin boundaries can be controlled by a dislocation nucleation mechanism
activated below a critical twin thickness. Below this thickness the material
becomes softer. The smaller the grains, the smaller the critical twin boundary
spacing, and the higher the metal's maximum strength.
Xiaoyan Li et al.
doi:10.1038/nature08929
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08929.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08929.html

Grazing-induced reduction of natural nitrous oxide release from continental
steppe pp881-884
To examine the effect of increased livestock numbers on nitrous oxide emissions
the authors report year-round nitrous oxide flux measurements at ten steppe
grassland sites in Inner Mongolia. They find that nitrous oxide emission is
much higher during spring thaw and is highest in ungrazed steppe, decreasing
with increasing stocking rate, which suggests that grazing decreases rather
than increases nitrous oxide emissions.
Benjamin Wolf et al.
doi:10.1038/nature08931
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08931.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08931.html

Seismic evidence for widespread western-US deep-crustal deformation caused
by extension pp885-889
Here a method of seismic wave imaging known as 'ambient noise' tomography
is used to generate high-resolution images of seismic wave speeds in the
crust and uppermost mantle. The observations reveal strong and uniform
anisotropy - where waves travel through rock at different speeds depending
on direction - in the deep crust in areas of the western United States that
have undergone significant extension during the past 65 million years.
M. P. Moschetti, M. H. Ritzwoller, F. Lin and Y. Yang
doi:10.1038/nature08951
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08951.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08951.html

Hierarchical group dynamics in pigeon flocks pp890-893
How large groups of animals move in a coordinated way has defied complete
explanation. Inability to track each member of a flock has hampered understanding
of the behavioural rules governing flocks of birds. This, however, has been
achieved for a small group of homing pigeons fitted with lightweight GPS
loggers. A well-defined hierarchy is revealed - the average position of a
pigeon within the flock strongly correlates with is position in the social
hierarchy (a kind of airborne pecking order).
Mate Nagy, Zsuzsa Akos, Dora Biro and Tamas Vicsek
doi:10.1038/nature08891
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08891.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08891.html

The complete mitochondrial DNA genome of an unknown hominin from southern
Siberia pp894-897
Ancient mitochondrial DNA from a hominin individual who lived in the mountains
of Central Asia between 48,000-30,000 years ago has been sequenced. Comparative
genomics suggest that this mitochondrial DNA derives from an out-of-Africa
migration distinct from the ones that gave rise to Neanderthals and modern
humans. It also seems that this hominin lived in close spatio-temporal
proximity to Neanderthals and modern humans.
Johannes Krause et al.
doi:10.1038/nature08976
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08976.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08976.html

Genome-wide SNP and haplotype analyses reveal a rich history underlying dog
domestication pp898-902
An extensive genome-wide survey of over 48,000 single nucleotide polymorphisms
in dogs and their wild progenitor, the grey wolf, was conducted to shed light
on the process of dog diversification. The results reveal that much of genome
diversity came from Middle Eastern progenitors, combined with interbreeding
with local wolf populations, and that recent evolution involved limited
genetic variation to create the phenotypic diversity of modern dogs.
Bridgett M. vonHoldt et al.
doi:10.1038/nature08837
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08837.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08837.html

Human memory strength is predicted by theta-frequency phase-locking of single
neurons pp903-907
Although explored in the rodent, the relationship between single neuron
activity, oscillations and behavioural learning is unknown in humans. Here,
successful memory formation in humans was predicted by the coordination of
spike timing relative to the local theta oscillation. These data provide a
direct connection between the behavioural modulation of oscillations and
plasticity within specific circuits.
Ueli Rutishauser, Ian B. Ross, Adam N. Mamelak and Erin M. Schuman
doi:10.1038/nature08860
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08860.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08860.html

Transfer of carbohydrate-active enzymes from marine bacteria to Japanese
gut microbiota pp908-912
One of the roles of the human gut microbiota is to break down nutrients
using bacterial enzymes that are lacking from the human genome. It is now
shown that the gut microbiota of Japanese, but not American, individuals
contains porphyranases, enzymes that digest sulphated polysaccharides which
are present in the marine environment only. These findings indicate that
diet can select for gene content of the human microbiota.
Jan-Hendrik Hehemann et al.
doi:10.1038/nature08937
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08937.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08937.html

MONOPTEROS controls embryonic root initiation by regulating a mobile
transcription factor pp913-916
During Arabidopsis embryogenesis, a single cell is specified to become the
founder cell of the root meristem - the hypophysis - in response to signals
from adjacent cells. Hypophysis specification requires an auxin-responsive
transcription factor, MONOPTEROS (MP), which promotes transport of auxin
from the embryo to the hypophysis precursor. Here, MP target genes are
identified and the means by which they mediate root formation is shown.
Alexandra Schlereth et al.
doi:10.1038/nature08836
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08836.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08836.html

Vascular endothelial growth factor B controls endothelial fatty acid uptake
pp917-921
VEGF-B is shown to have an unexpected role in targeting lipids to peripheral
tissues. VEGF-B controls endothelial uptake of fatty acids via transcriptional
regulation of vascular fatty acid transport proteins. Bioinformatic analyses
suggest that the uptake of these lipids is tightly coupled with lipid use by
mitochondria. Mice that do not have VEGF-B accumulate less lipids in muscle,
heart and brown adipose tissue, and instead shunt them to white adipose tissue.
Carolina E. Hagberg et al.
doi:10.1038/nature08945
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08945.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08945.html

Chromatin signature of embryonic pluripotency is established during genome
activation pp922-926
To study the changes in chromatin structure that accompany zygotic genome
activation and pluripotency during the maternal-zygotic transition (MZT),
the genomic locations of histone H3 modifications and RNA polymerase II
have been mapped during this transition in zebrafish embryos. H3 lysine 27
trimethylation and H3 lysine 4 trimethylation are only detected after MZT;
evidence is provided that the bivalent chromatin domains found in cultured
embryonic stem cells also exist in embryos.
Nadine L. Vastenhouw et al.
doi:10.1038/nature08866
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08866.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08866.html

Proviral silencing in embryonic stem cells requires the histone methyltransferase
ESET pp927-931
Endogenous retroviruses (ERVs) are widely dispersed in mammalian genomes,
and are silenced in somatic cells by DNA methylation. Here, an ERV silencing
pathway independent of DNA methylation is shown to operate in embryonic stem
cells. The pathway involves the histone H3K9 methyltransferase ESET and
might be important for ERV silencing during the stages in embryogenesis
when DNA methylation is reprogrammed.
Toshiyuki Matsui et al.
doi:10.1038/nature08858
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08858.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08858.html

The kinetics of two-dimensional TCR and pMHC interactions determine T-cell
responsiveness pp932-936
Quantification of the interaction of T-cell receptors with their peptide-MHC
ligands in two-dimensional membranes is shown to yield larger dissociation
rate constants than previous assays where one of the interacting partners
was in solution.
Jun Huang et al.
doi:10.1038/nature08944
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08944.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08944.html

Double Holliday junctions are intermediates of DNA break repair pp937-941
In meiotic cells paired homologues are joined by a set of crossovers known
as a double Holliday junction (DHJ). Whether DHJs form during mitotic
recombination has been unclear, as mitotic cells possess alternative repair
pathways that would not require DHJ formation. Here it is demonstrated that
mitotic and meiotic cells form similar DHJs, but that the levels in mitotic
cells are approximately 10-fold lower, and show a preference for joints
between sister chromatids rather than homologues. Consequently, in mitotic
cells non-crossover outcomes are favoured.
Malgorzata Bzymek et al.
doi:10.1038/nature08868
Abstract: http://www.nature.com/nature/journal/v464/n7290/abs/nature08868.html
Article: http://www.nature.com/nature/journal/v464/n7290/full/nature08868.html

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