This month's sponsor
AIDS 2006: XVI International AIDS Conference, Toronto, Canada , 13-18 August 2006
Time to Deliver - Passons aux actes. Join us in Toronto for the world's premier gathering of scientists and other stakeholders involved in the global response to HIV/AIDS. With a record 12,000-plus abstracts submitted, AIDS 2006 will offer unparalleled research findings. Late breaker abstract submission 29 May -12 June. Continuing Education Credits Available. For more information, visit http://www.aids2006.org/
Cancer Treatment Gets Personal
Advances in understanding the genetic basis of cancer have led to promising new therapies, which in turn have fueled discussions about a future model of cancer care in which treatment decisions are guided by molecular attributes of the individual patient. In a special collection of articles published with the 26 May 2006 issue, Science and its online Knowledge Environments examined this model and other emerging themes in cancer research. News and Perspective articles in Science explored what it will take to make personalized cancer treatment a reality, the role of biomarkers and molecular imaging in cancer diagnosis and treatment, the promising effects of antiangiogenic drugs and other targeted therapies, and mechanisms of tumor growth and development. The Signal Transduction Knowledge Environment (STKE) looked at the role of hypoxia-inducible factor signaling in cancer progression and a splice variant of the c-H- ras oncogene with potential tumor-suppressor activity; and the Science of Aging Knowledge Environment (SAGE KE) explored the relationship between stem cell aging and cancer, cancer cell self-consumption, and gender differences in melanoma risk. In addition, an interactive poster ( http://www.sciencemag.org/sciext/cancerposter/) illustrated the conceptual framework of the new patient-centered model of cancer care and offered a collection of links to related papers and Web resources, and a special podcast ( http://www.sciencemag.org/about/podcast.dtl) featured discussions with experts on cancer biomarkers, tumor bioenergetics, and more.
The Pain of Dread
People generally prefer to get unpleasant things over with quickly -- anyone who has waited to get a shot at the doctor's office can attest to that. Theoretical models of decision-making have assumed that this mentality occurs because there is a cost to waiting, which we call dread. But does dread have a neurobiological basis? In a Report in the 5 May 2006 Science , Berns et al. ( http://www.sciencemag.org/cgi/content/short/312/5774/754) investigated this question by monitoring the brains of study participants confronted with the prospect of an impending electrical shock. Some individuals dreaded the shock so much that, when given the choice, they preferred to receive a stronger jolt rather than wait. The researchers found that these "extreme dreaders" showed increased neural activity in the pain matrix -- a cluster of brain regions that are activated during the experience of pain --and that this activation intensified as the shock became more imminent. These results suggest that dread derives, in part, from the attention devoted to the expected physical response and not simply from fear or anxiety. An accompanying Perspective by G. Lowenstein ( http://www.sciencemag.org/cgi/content/short/312/5774/704) highlighted the findings and the implication that information serves not only as an input into decision-making, but as a source of pleasure and pain in its own right.
Planning for the future is a fundamental human survival strategy, but whether this skill is a uniquely human adaptation remains controversial. Now, new results suggest that other animals can anticipate future needs and that this ability has roots more ancient than previously thought. In a Report in the 19 May 2006 Science , Mulcahy and Call ( http://www.sciencemag.org/cgi/content/short/312/5776/1038) described a series of experiments designed to investigate future planning in bonobos and orangutans, our closest and most distant great ape relatives, respectively. The team found that both species can select a suitably useful object, keep it with them overnight, and bring it back for use the next day as a tool for retrieving a food reward. These findings suggest that the precursor skills for planning for the future evolved in great apes before 14 million years ago, when they shared a common ancestor. In a related study published online 18 May on Science Express, Dally et al. ( http://www.sciencemag.org/cgi/content/abstract/1126539v1) reported that scrub-jays hide food caches for future consumption, keep track of which birds watched them during particular caching events, and relocate their food accordingly to minimize the chance that it will be stolen by others. However, these actions may be driven by behavioral predispositions, specific learning algorithms, or both, rather than by reasoning about past and future. As noted in an accompanying Perspective by T. Suddendorf ( http://www.sciencemag.org/cgi/content/short/312/5776/1006), more clever experimentation will be required to determine the limits of animal foresight.
Paradigms in the Virosphere
Except for when they affect our health, we rarely concern ourselves with the vast world of viruses; nevertheless, the "virosphere" is ubiquitously influential in our everyday lives. Viruses play an important role in regulating microbial nutrient cycling in the ocean, they endow bacteria with new genes and phenotypes by way of horizontal gene transfer, and they have been instrumental in the development of modern molecular biological techniques. In conjunction with the 12 May 2006 issue, Science and it online companion the Signal Transduction Knowledge Environment ( STKE; http://stke.sciencemag.org/) teamed up to explore these and other attributes of viruses that are distinct from their ability to cause human disease. In Science , News, Review, and Perspective articles examined the role of viruses in the evolution of life, their utility in nanotechnology applications, and mechanisms of viral survival. STKE looked more closely at how viruses exploit signaling pathways in host cells to ensure their own replication and persistence. And a related podcast ( http://www.sciencemag.org/about/podcast.dtl) offered discussions about viruses as a platform for nanotech and the worldwide campaign to eradicate the polio virus.
Controlling Auxin Flow
The plant hormone auxin regulates a variety of growth and developmental responses and must be transported within the plant in an organized fashion. Three studies reported in Science this month offered molecular insights into how auxin flow is controlled. In the 12 May 2006 issue, Petrášek et al. ( published online 6 April; http://www.sciencemag.org/cgi/content/short/312/5775/914) showed that a family of plant-specific proteins called PINs are responsible for the direction in which auxin flows out of the cell and that these proteins operate independently of a known family of auxin pumps called PGPs. Further emphasizing the importance of PINs, Wisniewska et al. ( also published online 6 April; http://www.sciencemag.org/cgi/content/short/312/5775/883) reported that PIN orientation in the cell determines the direction of auxin flow. Directional transport is crucial for processes like root development during which auxin flows across epidermal cells from the root tip, which perceives gravity, to the elongation zone where growth takes place. In a related Report in the 26 May issue (published online 11 May), Dharmasiri et al. ( http://www.sciencemag.org/cgi/content/short/312/5777/1218) identified a protein required for the localization of AUX1, a protein that mediates cellular influx of auxin. A Perspective by T. Sieberer and O. Leyser ( http://www.sciencemag.org/cgi/content/short/312/5775/858) in the 12 May issue highlighted the findings.
Sea Squirt Blueprint
The path from an egg to an adult requires a complex dance of genes, transcription factors, signaling pathways, and other regulatory components. Remarkable progress has been made in identifying the genes and pathways responsible for tissue and organ development in model organisms like worm, fruit flies, and frogs, but less is known about the regulatory networks that drive body plan development. In a Report in the 26 May 2006 Science , Imai et al. ( http://www.sciencemag.org/cgi/content/short/312/5777/1183) offered new insights into chordate development by systematically analyzing gene expression in the developing embryo of the sea squirt, a primitive chordate whose tadpole larvae share a common body plan with vertebrates. By tracking the cell-by-cell expression of 76 regulatory genes that control sea squirt embryogenesis, and then mapping the interactions of these genes, the researchers were able to deduce circuit diagrams for the specification and initial differentiation of several tissues in the sea squirt tadpole, including the gut, tail muscles, notochord, heart, nerve cord, and brain. These diagrams offer a glimpse of the genetic and cellular interactions that might have operated in the earliest ancestors of the vertebrates, and provide a foundation for understanding the evolutionary origins of the chordate body plan. An accompanying Perspective by P. Lemaire ( http://www.sciencemag.org/cgi/content/short/312/5777/1145) highlighted the study.
Special Speciation on Madagascar
Relative to land area, Madagascar has more native (endemic) species than any other place in the world. The long isolation of Madagascar from Africa (more than 150 million years) and India (less than 90 million years) partially explains this extraordinary level of biodiversity. Even more intriguing is that many of the plants and animals have very small distributions on the island, a phenomenon known as microendemism. In a Report in the 19 May 2006 Science Wilmé et al. ( http://www.sciencemag.org/cgi/content/short/312/5776/1063) proposed a new hypothesis to explain the process of explosive speciation on Madagascar . Using an analysis of the island's watersheds and land vertebrate records in the context of paleoclimatic shifts, the researchers theorize that river catchments with sources at relatively low elevations experienced more-pronounced arid conditions during periods of climate change, which in turn created small zones of isolation -- particularly for forest-dwelling species -- and gave rise to speciation on a local scale. In contrast, more hospitable higher-elevation habitats served as zones of animal retreat and dispersion and hence contain proportionately lower levels of microendemism. In addition to explaining the evolutionary history of regional speciation on Madagascar , the new analysis provides a basis for prioritizing conservation efforts in the remaining natural forest habitats on the island.
From spaceships that vanish in Star Trek movies to Harry Potter's inherited invisibility cloak, making objects disappear has been a mainstay of science fiction and fantasy. Now, two Reports published online 25 May 2005 in Science Express offered mathematical recipes for theoretical "metamaterials" that could make invisibility a reality. Metamaterials are a unique class of manmade electromagnetic materials whose properties can be tuned by tinkering with the material's nano-structure rather than its chemistry. According to Pendry et al. ( http://www.sciencemag.org/cgi/content/abstract/1125907) and Leonhardt ( http://www.sciencemag.org/cgi/content/abstract/1126493), the key to an effective cloaking device would be a metamaterial that can bend light around an object, without producing a reflection or a shadow. The researchers explain how the speed of light would have to vary from point to point within a spherical or cylindrical shell to achieve invisibility, but leave it to others to design materials that can meet the necessary specifications. Future applications might include protecting structures from vibrations and sound, improving wireless communications, seeing through obstructions; and hiding objects. An accompanying News story by A. Cho ( http://www.sciencemag.org/cgi/content/short/312/5777/1120a) highlighted the tantalizing prospects of the new work.
Extensive dunes, like those seen in the Namib and Sahara deserts in Africa , have also been spotted on Mars and Venus. In a Report in the 5 May 2006 Science , Lorenz et al. ( http://www.sciencemag.org/cgi/content/short/312/5774/724) analyzed high-resolution radar images taken from the Cassini spacecraft, which show that large regions of Saturn's moon Titan are dominated by similar dunes. The dunes are up to 150 meters high and hundreds of kilometers long, and span thousands of kilometers of Titan's equatorial surface. Their east-west alignment and other flow features suggest that they are formed by a combination of easterly winds that prevail in the upper atmosphere and a variable north-south tidal wind. More broadly, the existence of dunes on Titan is indicative of geological processes that create sand-sized particles (such as fluvial activity and atmospheric deposition), and a lack of persistent surface liquids to act as sand traps. As noted in an accompanying Perspective by N. Lancaster ( http://www.sciencemag.org/cgi/content/short/312/5774/702), their discovery thus "provides further evidence of the variety of processes on planetary surfaces and the wonders of our solar system."
Earth's Magnetic History
The strength of Earth's magnetic field has steadily weakened by about 5% each century since accurate measurements began in 1840. This trend has led to speculation that the field will disappear or reverse within this millennium. But what about variations in the field before the start of this decline in strength? In a study reported in the 12 May 2006 Science , Gubbins et al. ( http://www.sciencemag.org/cgi/content/short/312/5775/900) combed ships' logbooks to extract early directional measurements of Earth's magnetic field (which predate those of intensity by more than 250 years). They combined these data with paleomagnetic intensity measurements from rock samples and archaeological remains to show that magnetic field strength was nearly constant between 1590 and 1840. Their analysis suggests that most of the recent decline in field strength comes from growing and migrating patches of reverse magnetic flux in the Southern Hemisphere. A related Perspective by M. Kono ( http://www.sciencemag.org/cgi/content/short/312/5775/865) highlighted the Report.
Polymerization by Shuttling
The plastics industry depends on catalysts to produce millions of tons of polyolefins each year. These polymers of hydrocarbon molecules are the building blocks of many plastics. Advances in catalyst design have enabled the production of new classes of block copolymers (consisting of sequences of one unit followed by long sequences of another) with useful combinations of physical properties. However, the "living" polymerization processes required to make these materials are uneconomical because they produce only one polymer chain per catalyst molecule and must be made in batches. The low reaction temperatures these systems require also limits the types of polymer blocks that can be synthesized. In a Report in the 5 May 2006 Science , Arriola et al. ( http://www.sciencemag.org/cgi/content/short/312/5774/714) presented a new strategy for building polymers in which a molecular shuttle transfers growing polymer chains back and forth between two catalysts with differing selectivities. The result is a polymer that contains block segments with the microstructural signature of each catalyst. In addition, the shuttling technique tolerates high temperatures (to maintain polymer solubility) and is amenable to economically efficient continuous flow conditions. As noted in an accompanying Perspective by V. C. Gibson ( http://www.sciencemag.org/cgi/content/short/312/5774/703), the technology "provides the long-sought platform for producing microblock polyolefin materials on a commercial scale."
Carbon Nanotube Membranes
Separation of gases and liquids into their constituents is crucial for many industrial processes, including water purification and desalination. Many of the current tecnniques involving polymeric membranes are costly in both money and energy, and suffer trade-offs between flux and selectivity. In a Report in the 19 May 2006 Science , Holt et al. ( http://www.sciencemag.org/cgi/content/short/312/5776/1034) reported the development of a new kind of membrane made of carbon nanotubes and silicon that could overcome these fundamental hurdles and lead to more efficient filters. The membrane consists of a silicon matrix dotted with carbon nanotube pores that are about 1 to 2 nanometers in diameter. Surprisingly, gas and water flows 100 to 10,000 times faster through these membranes than classical models predict. This is likely because the walls of nanotubes are much smoother (on atomic scales) than other materials. Future work will need to focus on whether these membranes can show high selectivity in what they can filter. An accompanying Perspective by D. S. Sholl and J. K. Johnson ( http://www.sciencemag.org/cgi/content/short/312/5776/1003) noted that the next big challenge from an application perspective will then be to scale up fabrication techniques to economically produce nanotube membranes with large surface areas.
This month's sponsor
AIDS 2006: XVI International AIDS Conference, Toronto, Canada , 13-18 August 2006
Time to Deliver - Passons aux actes. Join us in Toronto for the world's premier gathering of scientists and other stakeholders involved in the global response to HIV/AIDS. With a record 12,000-plus abstracts submitted, AIDS 2006 will offer unparalleled research findings. Late breaker abstract submission 29 May-12 June. Continuing Education Credits Available. For more information, visit http://www.aids2006.org/.