Science Roundup

Sponsored by: CTSciNet, Clinical and Translational Science Network

Nuclear Fusion within Reach?
The National Ignition Facility, the world's largest and highest-energy laser, is aiming to produce the first laboratory-controlled nuclear fusion reaction -- the same high-energy reaction that occurs in nuclear explosions and stars. The goal is to reach inertial fusion ignition, a self-sustaining fusion burn that gives off more energy than was put in to create it -- an achievement that would have profound implications for the world's future energy supply, and for understanding astrophysical phenomena. If all goes according to plan, the intense energy of 192 giant laser beams will be focused on a peppercorn-sized capsule filled with the hydrogen isotopes deuterium and tritium, generating enough heat to implode the capsule, thereby fusing the hydrogen atoms' nuclei and releasing a huge store of energy. Now, in a report published online in Science Express on 28 Jan 2010, Glenzer et al. have addressed a major challenge in this process -- getting the most laser power onto the capsule and doing so symmetrically so that it implodes evenly (see the related News story by D. Clery). Instead of shining the laser beams directly onto the capsule, the team put an empty capsule in the center of a small gold cylinder called a hohlraum. They found that shining the beams through holes in the ends of the hohlraum heated the inner surface to 3.3 million Kelvin -- hot enough to emit x-rays, which cause the capsule to implode. The results pave the way for the next big step: igniting a fuel-filled capsule. In a related Science Express Report, Li et al. showed how charged particles can be used to characterize and measure the conditions within the imploding capsule. In addition to demonstrating the feasibility of a fusion process, the high energies and temperature realized can be used to model astrophysical and other extreme energy processes.

Antimalarial Source Decoded

Malaria is a global health problem estimated to cause 300 to 500 million cases and over 1 million deaths each year. Today, the most effective drug for combating malarial infections is artemisinin, a compound that derives from the leaves of the plant Artemisia annua, but producing enough of the drug to meet world demand has been a major challenge. In a Report in the 15 Jan 2010 Science, Graham et al. presented a genetic map of A. annua and identified key loci that could improve agricultural yields, decrease production costs, and help ensure a steady global supply of artemisinin. The team used deep sequencing of the plant transcriptome (all the messenger RNA molecules present in the plant) to identify genes and markers that could facilitate crossing of highly productive plant varieties and followed up this work with initial breeding trials that resulted in hybrid plants that produced increased yields of artemesinin. A related Perspective by W.K. Milhous and P.J. Weina noted that other strategies to produce artemisinin, including chemical synthesis and microbial-based recombinant systems, have had variable success, but that innovative horticultural technologies have produced the most promise so far and will likely provide the most cost-effective product in the near term.

Clues to Tasmanian Devil Tumors

Tasmanian devils are marsupial carnivores that have been plagued by a transmissible and deadly cancer known as devil facial tumor disease (DFTD) for more than a decade. Afflicted animals develop large facial tumors that frequently metastasize to internal organs, and some models predict that the disease could wipe out wild populations in less than 40 years. DFTD is unusual in that appears to be transmitted through cancer cells themselves that are spread from one animal to another through biting. In a study described in the 1 Jan 2010 Science, Murchison et al. performed a large-scale genetic analysis of DFTD, sequencing 25 paired tumor and host samples as well as samples from unaffected animals across Tasmania. DFTD tumors were found to be genetically distinct from their hosts and almost completely genetically identical to one another, supporting the idea of transmission by allograft (transplantation of genetically distinct cells between unrelated individuals). By examining which genes were expressed in normal versus cancerous devil cells, the team found that tumor cells expressed a suite of genes that are typically only expressed by Schwann cells -- cells that insulate nerves outside of the brain and spinal cord by secreting a fatty substance known as myelin. For example, a distinctive Schwann cell protein called periaxin was expressed in all DFTD tumors cells and could therefore be used as a diagnostic marker of the disease (see the related ScienceNOW story by M. Leslie). In a podcast interview, lead author Elizabeth Murchison noted that Tasmanian devils are prone to a variety of cancers, and that the new results might lead to methods for quickly distinguishing animals with DFTD.

Cradles of Evolution

Coral reefs are well-known hot spots for biodiversity, but scientists have debated whether diversity is actually generated within reefs or if reefs rather attract and act as refuges for marine life that has originated elsewhere. In a Report in the 8 Jan 2010 Science, Kiessling et al. addressed this question by examining a large database of fossil benthic marine invertebrates dating back to the Cambrian. The researchers determined the environment where 6615 genera of marine species originated, based on where the fossils first appeared, and found that 1426 of the genera originated in reef environments -- nearly 50% more than in shallow-water environments (see the related ScienceNOW story by P. Berardelli). In addition to supporting the role of reefs as important evolutionary cradles, the team's analyses show that reefs were also prolific at exporting diversity to other environments, which might be a consequence of low-diversity habitats being more susceptible to invasions.

Bacterial Compartmentalization

Although many biological barriers and compartmental boundaries are lipid-based membranes, there is a growing awareness of protein-based compartments that act as isolated environments within the cell. Many bacterial cells contain such microcompartments, which act as simple organelles by sequestering specific metabolic processes that involve volatile or toxic metabolites. In the 1 Jan 2010 Science Tanaka et al. reported the high-resolution crystal structures of the four major protein constituents of a microcompartment that sequesters ethanolamine metabolism in the E. coli bacterium. This compartment prevents the release of acetaldehyde into the rest of the cell, mitigating the potentially toxic effects of excess aldehyde. Although the four proteins have similar three-dimensional folds, they have distinctive structural features that help explain the specific roles they play in the microcompartment, such as gating molecular transport through pores in the protein shell or binding nucleic acids. An accompanying Perspective by S. Kang and T. Douglas discussed other examples of protein-based microcompartments in nature and noted how deeper understanding of their architectures and dynamics could lead to the development of new multifunctional nanomaterials.

Biologically Inspired Network Design

The slime mold Physarum polycephalum is a singled-celled, gelatinous organism that slimes its way through the world in search of food. As it explores, it connects itself to scattered food sources through a network of tubular structures. As the mold continues to grow, the tube network simplifies such that those tubes carrying a high volume of nutrients gradually expand, while those that are little used slowly contract and eventually disappear. Might human engineers have something to learn from this lowly slime? In an intriguing Report in the 22 Jan 2010 Science, Tero et al. reported that when grown on plates representing a map of Japan, with food sources placed in a pattern that mimicked cities around Tokyo, the slime mold created a tubular network remarkably similar to Tokyo's train system. The absence of central control mechanisms that might instruct the organism about the relative position of the food sources or tell it how to connect them inspired the researchers to develop a corresponding computational model capable of adaptive network design. Using a simple and robust algorithm, the model generates in silico networks that closely resemble those formed by the slime mold. An accompanying Perspective by W. Marwan noted that the described algorithm or similar ones may provide general solutions for developing real-world, fault-tolerant technological systems such as mobile communication networks or networks of dynamically connected computational devices.

Understanding Innate Immunity
Special Online Collection

The innate immune system is our first line of defense against invading pathogens, albeit a non-specific one. Cells of the innate immune system are equipped to detect molecular patterns on microbial cells, thus triggering a variety of defense mechanisms from inflammation to activation of T- and B-cell-mediated immune responses. A special section of the 15 Jan 2010 Science explored developments in our understanding of the innate immune system and identified areas where new discoveries are likely to come. A Perspective examined a family of cellular receptors that sense viral invasion and three Review articles discussed the various functions of microbe-sensing NLR proteins, the regulation of adaptive immunity by the innate immune system, and the role of an immune protein complex in type 2 diabetes and gout. In a companion issue of Science Signaling published on 19 Jan, a collection of articles highlighted the effects of pathogen-derived and host-produced factors on the immune response.

Stronger Hurricanes Predicted

One of the most active questions about the effects of global warming is whether, and how, it might affect the frequency and the strength of hurricanes. In a study reported in the 22 Jan 2010 Science, Bender et al. used a state-of-the-art hurricane prediction model to explore the influence of future global warming on hurricane dynamics over the Atlantic Ocean. The model projects a decrease in the overall number of hurricanes, but an increase in the frequency of the strongest storms in the 21st century. In the team's simulation, the frequency of category 4 and 5 storms -- with maximum winds of 216 kilometers per hour and above -- doubled by the end of the century, while the frequency of storms with winds great than 234 km/hour more than tripled (see the related News story by R.A. Kerr). The largest frequency increase of the most intense hurricanes is predicted in the western Atlantic, which suggests that Hispaniola, the Bahamas, and the Southeast coast of the United States could be at greater risk of storm damage than other areas.

Green Catalysis
Two Reports in Science this month described new catalysts that offer promise for improving biofuel refinement and removing carbon dioxide from the atmosphere.
-- Crossley et al. (1 Jan 2010) converted solid nanoparticles that have solubility in both water and oils into catalysts that can operate in both phases. The particles combine hydrophobic nanotubes with hydrophilic oxides, causing them to accumulate at water-hydrocarbon interfaces. Depositing catalytically active palladium on specific portions of the particles' surfaces localizes the metal in one or both phases. The team demonstrated the utility of the catalysts for facilitating reactions important for converting biomass to fuel -- in which the immiscibility and thermal instability of crude products commonly complicates purification procedures. And because the nanoparticles are solids, they are easily recoverable at the end of each reaction. An accompanying Perspective by D.J. Cole-Hamilton considered the possibility of using similar catalysts to streamline the organic synthesis of drug molecules, which traditionally requires several cycles of reaction and separation.
-- Angamuthu et al. (15 Jan 2010) described a new copper-based catalyst that can capture carbon dioxide, convert it to a different form, and then release it with a small fraction of the energy other capture techniques require. The catalyst selectively binds to pairs of carbon dioxide molecules, knitting them together to form a compound called oxalate. Moreover, the team found a way to recycle the catalyst by first adding lithium salt to the mix to strip the oxalate from the copper complex and then applying a very small voltage to the copper complex to restore it to it original form (listen to the podcast interview with senior author Elisabeth Bouwman). A related News story by R.F. Service noted that the reaction works too slowly and is too expensive to be practical on a large scale, but that the team is already working on faster, cheaper alternatives.

Platelets and Inflammatory Arthritis

Platelets are best known for their critical role in blood clot formation during wound repair, but an appreciation for their role in inflammatory processes is growing. In the 29 Jan 2010 Science, Boilard et al. report that platelet-derived microparticles -- submicrometer membrane vesicles released by activated platelets -- may exacerbate the joint inflammation underlying rheumatoid arthritis, a painful autoimmune disease. The team found these microparticles in knee joint fluid from patients with rheumatoid arthritis and other forms of inflammatory arthritis, but not in joint fluid from patients with osteoarthritis. Moreover, they found that depleting platelets in a mouse model of inflammatory arthritis suppressed the development of the disease. Using both pharmacologic and genetic approaches, the team identified the platelet-specific receptor collagen receptor glycoprotein VI as a key trigger for platelet microparticle generation, and thus a potentially useful therapeutic target. In addition, fibroblast-like cells that line the synovial cavity (joint space) seem to trigger microparticle release. The microparticles then enter the joint space and produce the inflammatory mediator interleukin-1, which in turn triggers synovial cells to synthesize other inflammatory molecules (chemokines and cytokines), fanning the fire of inflammation. A Perspective by G.A. Zimmerman and A.S. Weyrich highlighted the study.

Planet Detection Mission

Launched in March 2009, NASA's Kepler mission was specifically designed to survey our region of the Milky Way galaxy to discover Earth-size and smaller planets in or near the habitable zone -- the region where planetary temperatures are suitable for surface water to exist -- and to determine how many of the billions of stars in our galaxy have such planets. In a Report published online in Science Express on 7 Jan 2010, Borucki et al. reported that during the first six weeks of observations, the telescope monitored 156,000 stars and discovered 5 new "exoplanets" beyond our solar system -- named Kepler 4b, 5b, 6b, 7b and 8b -- with orbital periods between 3.2 and 4.9 days (see the related ScienceNOW story published on 4 Jan). The Kepler space telescope looks for the signatures of planets by measuring dips in the brightness of stars. When planets cross in front of, or transit, their stars as seen from Earth, they periodically block the starlight. The size of the planet can be derived from the size of the dip. Kepler-4b appears to be very similar in size, density, and mass to the planet Neptune, whereas the other four exoplanets are about 40% larger than Jupiter, but unexpectedly lightweight for their size. Their densities range from 0.166 to 0.894 grams per cubic centimeter, while Jupiter, with its rocky core, has a density of 1.326 g/cubic cm.

Deep Mantle Properties

Earth's lower mantle extends from 660 to 2890 kilometers below the surface. The extreme temperatures and pressures at depth can cause mantle minerals to undergo phase transformations, influencing the structure and dynamics of Earth's interior. The rocks and minerals of the deep mantle are generally not accessible in nature, but they can be synthesized and examined at high-temperature and high-pressure conditions in the laboratory. In a Report in the 8 Jan 2010 Science (published online 3 Dec 2009), Irifune et al. used a multianvil apparatus combined with synchrotron-based x-ray radiation to study phase and density changes in a synthetic material similar in composition to the lower mantle (pyrolite). It has been thought that an electronic spin transition that occurs at high pressures in the lower mantle leads to the partitioning of various iron mineral phases, but the team found that the spin transition actually occurs at lower pressures, and thus at shallower depth than previously suggested. More specifically, they found that iron partitioning between the two main lower-mantle constituents -- iron-magnesium silicate perovskite and iron–magnesium oxide -- changes under conditions corresponding to depths below 1100 km. An accompanying Perspective by K. Hirose highlighted the study.

In Science Signaling

Focus on the Immune System

The 19 Jan 2010 issue of Science Signaling -- a companion to the 15 Jan Science special issue on innate immunity -- highlighted the effects of viral and bacterial components on host cells, signaling pathways involved in regulating innate immune responses, and factors that modulate the functions of dendritic cells, which are required for effective adaptive immunity (see the Editorial Guide by Foley and Gough). In two new Research Articles, Préhaud et al. explained why some cells infected with rabies virus live and some die, and Arima et al. investigated how the cytokine TSLP alters dendritic cell activity. A Review by Rodríguez-Fernández et al. offered insight into what is happening on the dendritic cell side of the immunological synapse, a transient structure formed between a dendritic cell and a T cell. And in the Database of Cell Signaling, Weber et al. presented two interrelated Connections Maps and associated Overviews describing signaling by the proinflammatory cytokine interleukin-1beta (IL-1beta): the IL-1 Pathway and the Interleukin-1beta (IL-1beta) Processing Pathway.

Also in Science Signaling this month:
-- Adler described research nominated by scientific experts as the most exciting cell signaling findings in 2009 (5 Jan 2010)
-- Corriden and Insel reviewed signaling in response to ATP (12 Jan 2010)
-- Hall offered a Perspective on recent studies of cell cycle-dependent protein modifications by Wang et al. and Olsen et al. (26 Jan 2010)

In Science Translational Medicine

-- Chow et al. showed that in a mouse model of Alzheimer's disease, a combination therapy involving simultaneous reduction of two of the enzymes that create the plaque-forming peptide beta-amyloid ameliorates symptoms better than elimination of either enzyme alone (6 Jan 2010)
-- Cohen et al. reported that the cumulative effects of chronic sleep loss may be overcome at certain times of day, but that the residual effects of sleep deprivation can profoundly degrade performance -- particularly during the circadian "night" (13 Jan 2010)
-- Cao and Lango discussed problems associated with antiangiogenic therapy (blocking new blood vessel growth) for treating cancer, and how this therapy could be optimized to produce better results for patients (20 Jan 2010)
-- Topol discussed the promise of digital medical devices for changing the future of medicine because of their ability to produce exquisitely detailed individual biological and physiological data (27 Jan 2010)

Image credits (in order of appearance): University of York; Tanaka et al., Science 327, 81 (2010); Science cover, 15 January 2010/Chris Bickel; NASA