Cadherin 23 is a component of the tip link in hair-cell stereocilia
Mechanoelectrical transduction, the conversion of mechanical force into electrochemical signals, underlies a range of sensory phenomena, including touch, hearing and balance. Hair cells of the vertebrate inner ear are specialized mechanosensors that transduce mechanical forces arising from sound waves and head movement to provide our senses of hearing and balance; however, the mechanotransduction channel of hair cells and the molecules that regulate channel activity have remained elusive. One molecule that might participate in mechanoelectrical transduction is cadherin 23 (CDH23), as mutations in its gene cause deafness and age-related hearing loss. Furthermore, CDH23 is large enough to be the tip link, the extracellular filament proposed to gate the mechanotransduction channel. Here we show that antibodies against CDH23 label the tip link, and that CDH23 has biochemical properties similar to those of the tip link. Moreover, CDH23 forms a complex with myosin-1c, the only known component of the mechanotransduction apparatus, suggesting that CDH23 and myosin-1c cooperate to regulate the activity of mechanically gated ion channels in hair cells.
专家说美国“干净核武器”计划不可靠 美国国防部“国防科学局”最近的一份报告提出，要制造新一代核武器，这种核武器可以最小的连带损坏和很少或几乎为零的辐射尘埃污染摧毁地下设施。该提议受到很多批评。Michael A. Levi也持批评态度，他在本期Nature的“评论”文章中指出，如果把评估设计新型传统大规模杀伤性武器时所用的同样严格的标准用来评估这些“干净核武器”，那么后者将会通不过评估。
Environment: Whale-call response to masking boat noise
Background noise can interfere with the detection and discrimination of crucial signals among members of a species. Here we investigate the vocal behaviour in the presence and absence of whale-watcher boat traffic of three social groups (pods) of killer whales (Orcinus orca) living in the nearshore waters of Washington state. We find longer call durations in the presence of boats for all three pods, but only in recent recordings made following a period of increasing boat traffic. This result indicates that these whales adjust their behaviour to compensate for anthropogenic noise once it reaches a threshold level.
有机薄膜电子装置的发展 基于有机薄膜材料的电子装置正在迅速成为一种日常技术。基于活性有机薄膜材料的装置，最有名的是几种移动电子装置的显示屏，已经进入了市场。不久，新一代超低成本、轻便灵活的电子装置将会问世，来完成传统上用基于硅等传统半导体材料的非常昂贵的设备来完成的任务。Stephen R. Forrest对这一领域的最新进展进行了评述，重点是有机电子和光子领域的制造方法。
The path to ubiquitous and low-cost organic electronic appliances on plastic
Organic electronics are beginning to make significant inroads into the commercial world, and if the field continues to progress at its current, rapid pace, electronics based on organic thin-film materials will soon become a mainstay of our technological existence. Already products based on active thin-film organic devices are in the market place, most notably the displays of several mobile electronic appliances. Yet the future holds even greater promise for this technology, with an entirely new generation of ultralow-cost, lightweight and even flexible electronic devices in the offing, which will perform functions traditionally accomplished using much more expensive components based on conventional semiconductor materials such as silicon.
研究双脉冲星体系的一个几何模型 去年12月，Nature上的一篇研究报告宣布发现了脉冲星PSR J0737-3039，与看起来像是一颗中子星的恒星成对出现。一个月后，当来自澳大利亚Parkes天文望远镜的数据被重新分析时，研究人员发现该中子星实际上是另一颗脉冲星。所以这是第一个已知的双脉冲星体系，现在的名称是J0737-3039 A and B。预计这两颗绕彼此运行的脉冲星会为了解关于脉冲星发射物理学的更多情况提供极好的机会。但是，研究人员首先需要一个几何模型作为参照点。Jenet 和Ransom提出了这样一个模型。他们的模型基于标准脉冲星发射几何，同时假设当被来自“脉冲星A”的脉冲束照射时，“脉冲星B”的强度有很大增加。该模型提供了大量可检验的预测，这些预测的结果将显示更多关于这一迷人体系的情况。
The geometry of the double-pulsar system J0737–3039 from systematic intensity variations
Two pulsars (PSR J0737–3039A and B) were recently discovered in highly relativistic orbits around one another. The system contains a rapidly rotating pulsar with a spin period of 22.7 ms and a slow companion with a spin period of 2.77 s, referred to here as 'A' and 'B', respectively. A unique property of the system is that the pulsed radio flux from B increases systematically by almost two orders of magnitude during two short portions of its orbit. Here we report a geometrical model of the system that simultaneously explains the intensity variations of B and provides constraints on the spin axis orientation and emission geometry of A. Our model assumes that B's pulsed radio flux increases when illuminated by emission from A. We predict that A's pulse profile will evolve considerably over the next several years owing to geodetic precession until it disappears entirely in 15–20 years.
Primitive chondritic meteorites contain material (presolar grains), at the level of a few parts per million, that predates the formation of our Solar System. Astronomical observations and the chemical composition of the Sun both suggest that silicates must have been the dominant solids in the protoplanetary disk from which the planets of the Solar System formed, but no presolar silicates have been identified in chondrites. Here we report the in situ discovery of presolar silicate grains 0.1–1 µm in size in the matrices of two primitive carbonaceous chondrites. These grains are highly enriched in 17O (17OSMOW > 100–400), but have solar silicon isotopic compositions within analytical uncertainties, suggesting an origin in an oxygen-rich red giant or an asymptotic giant branch star. The estimated abundance of these presolar silicates (3–30 parts per million) is higher than reported for other types of presolar grains in meteorites, consistent with their ubiquity in the early Solar System, but is about two orders of magnitude lower than their abundance in anhydrous interplanetary dust particles. This result is best explained by the destruction of silicates during high-temperature processing in the solar nebula.
The development of manipulation tools that are not too 'fat' or too 'sticky' for atomic scale assembly is an important challenge facing nanotechnology. Impressive nanofabrication capabilities have been demonstrated with scanning probe manipulation of atoms and molecules on clean surfaces. However, as fabrication tools, both scanning tunnelling and atomic force microscopes suffer from a loading deficiency: although they can manipulate atoms already present, they cannot efficiently deliver atoms to the work area. Carbon nanotubes, with their hollow cores and large aspect ratios, have been suggested as possible conduits for nanoscale amounts of material. Already much effort has been devoted to the filling of nanotubes and the application of such techniques. Furthermore, carbon nanotubes have been used as probes in scanning probe microscopy. If the atomic placement and manipulation capability already demonstrated by scanning probe microscopy could be combined with a nanotube delivery system, a formidable nanoassembly tool would result. Here we report the achievement of controllable, reversible atomic scale mass transport along carbon nanotubes, using indium metal as the prototype transport species. This transport process has similarities to conventional electromigration, a phenomenon of critical importance to the semiconductor industry.
Maturation trends indicative of rapid evolution preceded the collapse of northern cod
Northern cod, comprising populations of Atlantic cod (Gadus morhua) off southern Labrador and eastern Newfoundland, supported major fisheries for hundreds of years. But in the late 1980s and early 1990s, northern cod underwent one of the worst collapses in the history of fisheries. The Canadian government closed the directed fishing for northern cod in July 1992, but even after a decade-long offshore moratorium, population sizes remain historically low. Here we show that, up until the moratorium, the life history of northern cod continually shifted towards maturation at earlier ages and smaller sizes. Because confounding effects of mortality changes and growth-mediated phenotypic plasticity are accounted for in our analyses, this finding strongly suggests fisheries-induced evolution of maturation patterns in the direction predicted by theory. We propose that fisheries managers could use the method described here as a tool to provide warning signals about changes in life history before more overt evidence of population decline becomes manifest.
发育很快的“穴居人” 原始人类寿命的延长（通常与牙齿生长速度较慢相关）被认为与死亡率的降低和大脑尺寸的增加是同步发展的。对牙冠生长速度所做的测定表明，现代人类发育速度要比原始人类（Homo antecessor 和 Homo heidelbergensis）慢。但对“穴居人”（Neanderthals）牙齿生长所做的一项新的研究却得出一个让人吃惊的结果。肌肉与我们相似的近亲“穴居人”牙齿生长速度非常快，快于前面提到的所有原始人种。尽管有一个大的脑子，但“穴居人”的发育期相对较短。这使得它们成为一种特点明显的原始人种，适应了当地的自然条件，在那里，高热量饮食和高代谢速度能够保证身体快速生长，还能够支持一个大的脑子。
Surprisingly rapid growth in Neanderthals
Life-history traits correlate closely with dental growth, so differences in dental growth within Homo can enable us to determine how somatic development has evolved and to identify developmental shifts that warrant species-level distinctions. Dental growth can be determined from the speed of enamel formation (or extension rate). We analysed the enamel extension rate in Homo antecessor (8 teeth analysed), Homo heidelbergensis (106), Homo neanderthalensis ('Neanderthals'; 146) and Upper Palaeolithic-Mesolithic Homo sapiens (100). Here we report that Upper Palaeolithic-Mesolithic H. sapiens shared an identical dental development pattern with modern humans, but that H. antecessor and H. heidelbergensis had shorter periods of dental growth. Surprisingly, Neanderthals were characterized by having the shortest period of dental growth. Because dental growth is an excellent indicator of somatic development, our results suggest that Neanderthals developed faster even than their immediate ancestor, H. heidelbergensis. Dental growth became longer and brain size increased from the Plio-Pleistocene in hominid evolution. Neanderthals, despite having a large brain, were characterized by a short period of development. This autapomorphy in growth is an evolutionary reversal, and points strongly to a specific distinction between H. sapiens and H. neanderthalensis.
Mating with more than one male is the norm for females of many species. In addition to generating competition between the ejaculates of different males, multiple mating may allow females to bias sperm use. In Drosophila melanogaster, the last male to inseminate a female sires approximately 80% of subsequent progeny. Both sperm displacement, where resident sperm are removed from storage by the incoming ejaculate of the copulating male, and sperm incapacitation, where incoming seminal fluids supposedly interfere with resident sperm, have been implicated in this pattern of sperm use. But the idea of incapacitation is problematic because there are no known mechanisms by which an individual could damage rival sperm and not their own. Females also influence the process of sperm use, but exactly how is unclear. Here we show that seminal fluids do not kill rival sperm and that any 'incapacitation' is probably due to sperm ageing during sperm storage. We also show that females release stored sperm from the reproductive tract (sperm dumping) after copulation with a second male and that this requires neither incoming sperm nor seminal fluids. Instead, males may cause stored sperm to be dumped or females may differentially eject sperm from the previous mating.
Detecting selection using a single genome sequence of M. tuberculosis and P. falciparum
Selective pressures on proteins are usually measured by comparing nucleotide sequences. Here we introduce a method to detect selection on the basis of a single genome sequence. We catalogue the relative strength of selection on each gene in the entire genomes of Mycobacterium tuberculosis and Plasmodium falciparum. Our analysis confirms that most antigens are under strong selection for amino-acid substitutions, particularly the PE/PPE family of putative surface proteins in M. tuberculosis and the EMP1 family of cytoadhering surface proteins in P. falciparum. We also identify many uncharacterized proteins that are under strong selection in each pathogen. We provide a genome-wide analysis of natural selection acting on different stages of an organism's life cycle: genes expressed in the ring stage of P. falciparum are under stronger positive selection than those expressed in other stages of the parasite's life cycle. Our method of estimating selective pressures requires far fewer data than comparative sequence analysis, and it measures selection across an entire genome; the method can readily be applied to a large range of sequenced organisms.
17OSMOW > 100–400
), but have solar silicon isotopic compositions within analytical uncertainties, suggesting an origin in an oxygen-rich red giant or an asymptotic giant branch star. The estimated abundance of these presolar silicates (3–30 parts per million) is higher than reported for other types of presolar grains in meteorites, consistent with their ubiquity in the early Solar System, but is about two orders of magnitude lower than their abundance in anhydrous interplanetary dust particles. This result is best explained by the destruction of silicates during high-temperature processing in the solar nebula.
