Breakthroughs and Insights
Special Online Collection
In the 17 Dec 2010 issue, the editors and news team at Science named their annual breakthrough of the year. This year, the honor went to the first quantum machine -- a microscopic cantilever ingeniously lowered to its lowest possible energy, the quantum ground state. The result may lead to ultrasensitive force detectors and to ways of controlling an object's mechanical vibrations as deftly as we now control electricity and light. Other impressive achievements honored with runners-up commendations included the first cell with a synthetic genome, the genome sequence of the Neandertal, and a microbicidal gel that reduces a woman's risk of being infected with HIV. The news staff also took a break from their regular reporting to look back at the past 10 years and highlight 10 great scientific "insights of the decade" and the technologies that made them possible. Cryoelectron tomography, for example, brought into focus the cell's components, allowing scientists to get atomic-level detail of whole-cell organization. And ever more powerful computers have enabled high-throughput genome sequencing methods, calculations needed to model protein folding on the time scale of milliseconds, and digital surveys of the cosmos. Features on Science Online included a video highlighting the year's top breakthrough and a Science Careers profile of a graduate student who contributed to the achievement; a special edition of the podcast featuring some big ideas from the past decade; and a roundup of readers' picks for this year's crowning scientific advance.
Thought for Food
Researchers have found that repeated exposure to a particular food -- as in taking bite after bite of a steak or spoonful after spoonful of an ice cream sundae -- decreases the desire to consume more. This process, which psychologists call habituation, dampens appetite independently of physiological signals like rising blood sugar levels or an expanding stomach. In a Report described in the 10 Dec 2010 Science, Morewedge et al. investigated whether merely imagining oneself eating could have the same dampening effect. The team described five experiments showing that people who repeatedly imagined eating a food (such as cheese) many times, subsequently consumed less of the imagined food than did people who repeatedly imaged eating that food fewer times, imagined eating a different food (such as candy), or did not imagine eating a food. They did so because they desired to eat it less, not because they considered it less palatable ( see the related ScienceNOW story by G. Miller). In a related podcast interview lead author Carey Morewedge noted that these results run counter to many diets that urge people to suppress thoughts of foods they crave, and may have implications for ways to control one's appetite.
Positive Feedback
One of the major uncertainties about global climate change is the effect of clouds, which cool the climate by reflecting incoming solar radiation back to space, but also warm the climate by trapping heat that might otherwise escape. So as the planet warms, will clouds change in ways that counter warming by greenhouse gases (a negative cloud feedback), or further amplify it (a positive cloud feedback)? In a Report in the 10 Dec 2010 Science, Dessler estimated the cloud feedback based on 10 years of satellite data on the flux of radiation through the top of the atmosphere. After subtracting feedbacks due to other factors, such as changing water vapor, the analysis indicates a small positive feedback overall ( listen to the related podcast interview). Although the data only cover the past decade, and therefore represent short-term climate fluctuations, they do corroborate several leading global climate models that yield a similar feedback and an increase in global temperature of several degrees Celsius for a doubling of atmospheric carbon dioxide. A related News story by R. A. Kerr highlighted the study.
Analyzing Culture through Books
Books are an important part of our cultural heritage and the information that we pass on from generation to generation. Imagine just how much information could be gleaned from reading every book ever published. That feat would be impossible for any human, but the digitization of millions of books by Google has enabled a new way to mine written words. In a Research Article published online in Science Express on 16 Dec 2010, Michel et al. presented a quantitative analysis of culture using millions of digitized books. The researchers began by constructing a corpus of 5,195,769 digitized books containing ~4% of all books ever published. Focusing on the English language between 1800 and 2000, they revealed 500,000 English words missing from dictionaries, tracked the rise and fall of ideologies and famous people, and even identified possible cases of political suppression that may have escaped the attention of historians (see the related News story by J. Bohannon). The team suggests that "culturomics" -- which they define as the application of high-throughput data collection and analysis to the study of human culture -- can be used to investigate countless other phenomena including trends in disease, civil war, battles of the sexes, diet, and science and religion.
From Genome to Regulatory Networks
How do animal embryos successfully transform the two-dimensional code of their genome into multidimensional functional organisms? Complete genome sequences provide a view of the full instruction set of an organism, but understanding the functional content of a genome requires more than just the DNA sequence. Two Research Articles in the 24 Dec 2010 Science (published online 22 Dec), reported results from the modENCODE project (model organism Encyclopedia of DNA Elements) -- an effort to systematically annotate the functional genomic elements of the nematode Caenorhabditis elegans (see Gerstein et al.) and the fruit fly Drosophila melanogaster (see The modENCODE Consortium et al.). The studies provide insights into the organization, structure, and function of the two genomes, summarizing full transcriptome analyses over various developmental stages of the worm and fly, genome-wide identification of transcription factor binding sites, and high-resolution maps of chromatin organization (see the related Perspective by M. Blaxter). Both teams identified many new genes and parts of genes, found a similar complexity of patterns of chromatin modifications and their correlations with gene expression, and discovered a curious class of short DNA elements bound by an unusually large number of transcription factors. The findings will help guide future focused and genome-wide studies in these organisms, and, as noted in an accompanying Editorial by B. Alberts, add to our molecular understanding of how cells and organisms work: information that is vital to translational medicine endeavors.
Plant Pathogen Genomics
A variety of microbial pathogens afflict important crop plants, both driving loss of yield and incurring expensive control measures. Four comparative-genomics Reports in the 10 Dec 2010 Science analyzed microbial genomes to better understand how plant pathogens function (see the Perspective by P.N. Dodds). Raffaele et al. described how the genome of the potato blight pathogen accommodates transfer to diverse host plant species. Spanu et al. analyzed the genomes of fungal powdery mildews, offering insight into the molecular basis of their parasitic lifestyle, which is entirely dependent on living plant cells. Schirawski et al. examined the genomes of two species of smut fungi, both of which infect maize, to identify virulence determinants. And Baxter et al. reported the genome sequence of a natural pathogen of the model plant Arabidopsis thaliana -- another pathogen that extracts nutrients from living plant tissue and cannot survive apart from its host. These studies highlight how comparative genomics can assist in identifying important virulence genes with host-specific functions, which may eventually be useful for improving agricultural crop management and breeding.
Rubber from Nanotubes
Materials with the slow-flowing behavior of a thick liquid (like honey), but also the recoverable stretchiness of elastic, are said to be viscoelastic (think foam ear plugs and shoe soles). These materials typically break down when they get too hot and become brittle when they get too cold, but in a Report in the 3 Dec 2010 Science, Xu et al. reported on a new material -- comprised of a random network of long, interconnected and entangled carbon nanotubes -- that remains viscoelastic from -196 to 1000 degrees Celsius: a working range three times greater than that of silicone rubber. The researchers suggest that unlike polymers, in which temperature-dependent molecular rearrangement governs viscoelasticity, thermal stability in their material stems from energy dissipation through the zipping and unzipping of carbon nanotubes upon contact. An accompanying Perspective by Y. Gogotsi noted that with further developments, such entangled nanotube materials could be used in extremely cold interstellar space or inside extremely hot vacuum furnaces, as well as in down-to-earth applications such as wrinkle-free textiles or shoe insoles that reduce mechanical shock.
Rhea's Atmosphere
The presence of water ice on most of the large satellites of the outer planets was established many years ago through near-infrared observations with ground-based telescopes. Frozen carbon dioxide, sulfur dioxide, methane, nitrogen, and other molecular ices are also found in various combinations on inner planets such as Mars to bodies far beyond Pluto. Now, in a Report in the 24 Dec 2010 Science (published online 25 Nov), Teolis et al. report flyby measurements from the Cassini spacecraft that reveal a very tenuous oxygen and carbon dioxide atmosphere around Saturn's icy moon Rhea. Approximately one in five trillionth of Earth's atmospheric pressure at sea level, the atmosphere appears to be maintained by ongoing chemical decomposition of the moon's surface water ice by irradiation from Saturn's magnetosphere. Detection of this oxidizing atmosphere is consistent with remote observations of other icy bodies, such as Jupiter's moons Europa and Ganymede, and suggestive of a reservoir of oxygen still locked within Rhea's ice. An accompanying Perspective by D.P. Cruikshank highlighted the findings.
Spin Control
Controlling and manipulating the spin of an electron is a central requirement for applications in spintronics -- a branch of electronics that aims to use electron spin in addition to its charge to transport and store information. Some of the challenges researchers are facing include efficient creation of spin currents, minimization of Joule heating, and extending the lifetime of electron spins. Three Reports in the 17 Dec 2010 Science describe advances that directly address these issues. Costache and Valenzuela designed and constructed a simple, efficient single-electron transistor that uses superconduction to produce a spin current with controlled flow. The transistor consists of a superconducting island with different metal contacts on either side. In the presence of a magnetic field, this asymmetry leads to a ratchet effect (or diode-like behavior), allowing the separation of "up" and "down" spins. Jonietz et al. used electric currents five orders of magnitude smaller than those used previously in nanostructures to manipulate magnetization in manganese silicon, pointing the way toward decreased Joule heating in spintronic devices. And McCamey et al. found a way to extend the short lifetime of an electron spin in phosphorous doped silicon, a widely used semiconductor, by mapping it onto the much longer lived nuclear spin of the atom. This mapping enables production of a spin memory with a storage time exceeding 100 seconds, after which the spin can be mapped back onto an electron, to be "read out" electrically by conventional methods.
Spotlight on Metabolism
Special Online Collection
For a generation of biologists, metabolism was an area of biochemistry to be mastered and then put aside. Metabolism was always there in the background, providing the cell with the energy and resources to do what was required, but was rarely recognized to determinedly influence, and be influenced by, the physiological state of the cell. In a special section of the 3 Dec 2010 issue, Scienc celebrated a resurgence of interest in metabolism and its central role in disparate areas of cell biology, physiology, medicine, and synthetic biology. An opening Perspective offered a broad look at the field, while four Review articles examined the links between metabolism and cancer, autophagy, circadian clocks, and molecular engineering. Complementing the special section, the 7 Dec 2010 issue of Science Signaling highlighted signaling pathways with roles in metabolism and a Review in Science Translational Medicine published on 1 Dec discussed a possible therapeutic target for metabolic disease.
In Science Signaling
Building Bone
The loss of bone density that afflicts individuals with osteoporosis makes them more vulnerable to bone fractures. One way to counteract decreases in bone density is through exercise, which mechanically stimulates bone tissue and initiates proliferation of bone-forming cells (osteoblasts). Alternatively, the signaling pathways that mediate this proliferative response could be therapeutically activated to mimic the effects of mechanical stimulation. In the 21 Dec 2010 issue of Science Signaling, Rangaswami et al. delineated a pathway in mechanically stimulated osteoblasts whereby activation of protein kinase G (PKG) signaling ultimately leads to a proliferative response. This suggests that PKG-activating drugs could be used to mimic the anabolic effects of mechanical stimulation on bone in the treatment of osteoporosis. An accompanying Perspective by Bidwell and Pavalko described other examples of signaling pathways that mediate mechanotransduction in bone cells.
Also in Science Signaling this month:
-- Schieder et al. described a method for recording ionic currents from lysosomes (7 Dec 2010)
-- Otsuji et al. developed a model of the feedback loops that regulate pseudopod formation and cell migration during chemotaxis (14 Dec 2010)
-- Zhang et al. determined how human leukocyte antigen I may contribute to transplant rejection; senior author E. Reed discussed the findings in a related podcast (23 Nov 2010)
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Bodenmiller et al. performed a system-wide analysis of protein phosphorylation in yeast and discussed their findings in a podcast (21 Dec 2010)
In Science Translational Medicine
-- Forssman et al. developed a virus entry inhibitor that prevents HIV-1 from anchoring to and infecting host cells and showed that it can lower viral load up to an order of magnitude in HIV-infected patients (22 Dec 2010)
-- Weiss et al. found that amplification of the FGFR1 gene -- which encodes fibroblast growth factor receptor 1 -- is a major oncogenic aberration in smoking-related lung cancer, suggesting that FGFR inhibitors may be a viable therapeutic option (see the related Perspective by Turner and Seckl) (15 Dec 2010)
-- Lo et al. demonstrated that sequencing plasma DNA from a pregnant woman permits genome-wide scanning for the mutational status of the fetus prenatally and noninvasively (8 Dec 2010)
-- Broadhurst et al. provided insight into the physiological effects of helminth infection on ulcerative colitis, based on a case study in which ingestion of the Trichuris trichiura worm decreased a patient's disease-associated inflammation (1 Dec 2010)
Image credits (in order of appearance):Science cover, 17 December 2010/Yael Fitzpatrick and Matthew Twombly; Image Science & Analysis Laboratory, NASA Johnson Space Center; Wikimedia; Teolis et al., Science 330, 1813 (2010); Science cover, 3 December 2010/painting by David S. Goodsell, scientific design by Zhou Du and Daniel J. Klionsky
