 This month in Science Roundup:
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  Spotlight on HIV/AIDSSpecial Online Collection Eastern Europe is home to an estimated 1.5 million HIV-infected people, and the rate of spread remains dauntingly high. In a special section in the 9 Jul 2010 issue, Science correspondent Jon Cohen looked at the state of the HIV/AIDS epidemic in Russia and Ukraine, which account for more than 90% of HIV infections in the region (a related photo essay featuring the work of photographer Malcolm Linton, with commentary by Jon Cohen, and a podcast segment, highlighted efforts to combat HIV/AIDS in Eastern Europe.). A Review article examined the biology underlying HIV persistence and potential interventions that may lead to a cure; two Policy Forums discussed challenges to achieving universal access to HIV prevention and treatment programs; and two research papers published online in ScienceExpress reported the identification of human antibodies that broadly neutralize HIV-1. Finally, Science Translational Medicine offered a Perspective and podcast on progress in the last 25 years of antiretroviral therapy, and Science Careers profiled a Russian epidemiologist studying HIV transmission in St. Petersburg. Also on the HIV front, in a Research Article published online in ScienceExpress on 19 Jul 2010, Abdool Karim et al. reported on the effectiveness and safety of a vaginal gel containing an antiretroviral microbicide for the prevention of HIV infection. A News story by J. Cohen and podcast feature highlighted the study, which involved nearly 900 South African women in a placebo-controlled trial. Private Profit, Public Good In the corporate world, maximizing profit and social responsibility often seem at odds. However, in the 16 Jul 2010 Science, Gneezy et al. reported that a strategy they termed "shared social responsibility" not only makes these corporate goals compatible, but also highly successful. In a field experiment, customers were either given a fixed price or allowed to choose their own price for a souvenir photo taken at an amusement park. About half of the customers in each group were told that 50% of the sale revenue would go to charity. At a fixed price, the charity component only slightly increased demand and profit. However, customers who could pay what they wanted paid significantly more per photo when half of the revenues went to charity, thus increasing the souvenir company's profit margin and charitable contributions. The researchers suggest that the shared responsibility model may work in part because it allows customers to determine their own contribution to a social cause, thereby minimizing suspicion about a company's intentions. An accompanying Perspective, by S. DellaVigna discussed the complicated role of social preferences in consumer markets, and a podcast segment featured commentary from both DellaVigna and the study's lead author, Ayelet Gneezy.  Gobies to the RescueIn the late 1960s, overfishing coupled with unfavorable environmental conditions led to the collapse of a thriving sardine fishery off the coast of Namibia in southwest Africa. Loss of the filter-feeding sardine changed the structure and function of the ecosystem, which became oxygen-depleted owing to unchecked plankton growth and decay, and dominated by jellyfish and predatory horse mackerel and hake. In a Report in the 16 Jul 2010 Science, Utne-Palm et al. described how the unusual lifestyle of a small fish called the bearded goby has enabled it to thrive as well, and to help sustain the ecosystem overall (see the related News story by E. Pennisi). During the day, the gobies swim along the low-oxygen, hydrogen sulfide -- rich muddy sea floor, which is inhospitable to its predators. At night, the fish ascend to where oxygen levels are higher and spend time amongst jellyfish and other species. And when the researchers examined the stomach contents of gobies, they found that jellyfish represent up to 60% of the fish's diet. Gobies also consume unusual food sources from the sea bed, including diatoms, polychaete worms, and sulfur-containing bacterial mats. In essence, the gobies are bringing "dead-end" products back into the food chain, making the ecosystem more productive than it would be otherwise. Seeing the Light Retinitis pigmentosa refers to a group of genetic eye diseases that lead to blindness, affecting two million people worldwide. The disorder affects retinal photoreceptor cells, which are responsible for sensing light and translating it into visual information in the brain. Over the course of the disease, rod photoreceptors -- which provide sensitivity to dim light -- degenerate first, causing loss of night vision. This is followed by progressive damage to cone photoreceptors, which are responsible for color and daytime vision. In a Research Article in the 23 Jul 2010 Science (published online 24 Jun), Busskamp et al. described a gene therapy approach in a mouse model of retinitis pigmentosa. The researchers showed that inducing expression of a microbial light-activated ion pump, halorhodopsin, in damaged cone photoreceptors restored light sensitivity to these cells, as well as the retinal and neuronal circuit functions required for vision. Treated mice were able to distinguish light from dark and to detect the direction of motion. These results provide promising evidence that cone photoreceptor function can be therapeutically restored, even after damage and loss of vision. An accompanying Perspective by C. Cepko discussed the possibility of using this gene therapy approach to help restore sight in human patients.  Hydrogen in the Early UniverseOne of the tantalizing questions in modern cosmology concerns how the first stars formed at the end of the cosmic dark ages, a few hundred million years after the Big Bang. In a Report in the 2 Jul 2010 Science, Kreckel et al. presented a combination of laboratory and numerical astrophysics to provide an improved value for the production rate of molecular hydrogen, one of the key physical processes that governed the formation of the first stars in the early universe. The first stars began as hot clouds of primordial hydrogen and helium gas that then cooled and condensed. Formation of molecular hydrogen, through electron-expelling collisions of H atoms and negative H ions, is regarded as an important step in this cooling process, but there has been considerable uncertainty about the rate of this process. Using a specially constructed apparatus to carefully tune the relative velocity of merged atom and ion beams, the researchers were able to precisely measure the rate of molecular H formation at different energies. Their results agree with the most recent theoretically calculated rates, which were then used in cosmological simulations, improving the constraints on the predicted masses of the first stars. An accompanying Perspective by V. Bromm highlighted the study. Rupture Dynamics Large earthquakes occur at the margins of two colliding plates, where one plate subducts beneath the other. Two reports in the 9 Jul 2010 Science looked at how the structural evolution of subduction fault zones influences the severity and location of earthquakes (see the related Perspective by K. Wang). Dean et al. compared the rupture zones of the 2004 Sumatra earthquake in Indonesia, which generated a huge tsunami that killed over 240,000 people, and the less severe 2005 earthquake that occurred in the same region. The team observed an expansive structure in the sea-floor sediment in the southern part of the 2004 rupture zone that is absent along the 2005 rupture zone, suggesting that sediment properties may influence the magnitude of earthquakes ruptures and their subsequent tsunamis. Kimura et al. turned their attention to the subduction zone beneath central Japan and found that repeating low-intensity microearthquakes occur where the Philippine Sea plate is scraping under the continental plate, leaving chunks of crust behind. The researchers propose that the evolution of the fault-zone structure with increasing depth as a result of this place fracturing process causes progressive changes in seismogenic behavior. Guardian of T Cell Fate The human hematopoietic system gives rise to all blood cell types. The generation of lymphocytes -- T cells, B cells, and natural killer cells -- is orchestrated at the early developmental stages, when progenitor cells selectively block alternative developmental pathways. The molecular regulation of this process, however, is not fully understood. Now, in the 2 Jul 2010 Science, P. Li et al., L. Li et al., and Ikawa et al. have reported the identification of the transcription factor Bcl11b as a key player in the development of the T cell lineage. T cells arise from progenitor cells that migrate from the bone marrow to the thymus, where they proliferate as thymocytes. Tissue-specific signals then direct their developmental fates. The new studies show that T cell progenitors deficient in Bcl11b fail to up-regulate genes associated with committed T cells and maintain stem cell-like gene expression. Moreover, loss of Bcl11b expression at different stages of T cell development enables "reprogramming" of T cells into cells that closely resemble a different cell lineage called natural killer cells. Thus, Bcl11b is a critical transcription factor that extinguishes the proliferative, stem cell-like characteristics of early progenitors, and focuses T cell commitment by suppressing alternative cell fates. An accompanying Perspective by J.P. Di Santo highlighted the studies.  Spore PropulsionSphagnum moss forms thick mats covering approximately 1% of Earth's land area and is important in the global carbon cycle, potentially storing more carbon than any other plant genus. To reproduce, this ground-hugging moss must launch its spores high enough to be picked up by wind and carried long distances. In a Brevium in the 23 Jul 2010 Science, Whitaker and Edwards explain that the spores are able to reach heights that cannot be explained simply by the force that initially blasts them out of their millimeter-sized pressurized capsules. Ultrahigh-speed videos reveal that the generation of turbulent "vortex rings" by the exploding capsules provides the additional boost needed to propel spores in a continued upward trajectory. The same sort of spiraling structures also help propel jellyfish and squid through the water. An accompanying Perspective by J.L. van Leeuwen offered additional details about the fluid dynamics involved in this spore propulsion mechanism, and lead author Dwight Whitaker discussed the findings in a related podcast interview. Carbonates on Mars Decades of speculation about a warmer, wetter Mars climate in the planet's first billion years postulate a denser carbon dioxide-rich atmosphere than at present. Such an atmosphere should have led to the formation of large deposits of carbonate minerals, for which evidence has been sparse -- until now. In the 23 July 2010 Science (published online 3 Jun), Morris et al. reported the identification of carbonate-rich outcrops in the Columbia Hills of Gusev Crater by the Mars Exploration Rover, Spirit. Measurements from two spectrometers indicate that the carbonate is a major outcrop component, rather than a surface coating. The mineral is rich in magnesium and iron may have formed in the Noachian era (~4 billion years ago) by precipitation from hydrothermal solutions that passed through buried carbonate deposits. Thus, it is likely that extensive aqueous activity under neutral pH conditions did occur on Mars. An accompanying Perspective by R.P. Harvey explained how the new findings strengthen arguments that carbon dioxide played a major role in the early martian climate system.  MESSENGER's Third Mercury FlybyLaunched by NASA in 2004, the Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft -- known as MESSENGER -- is destined for an eventual orbit around the planet Mercury in 2011. Three Reports published online in ScienceExpress on 15 Jul 2010 detailed new information about Mercury's atmosphere and evolution gleaned from MESSENGER's third flyby of the planet, which was completed in September 2009. Slavin et al. reported measurements of the magnetic field in the Mercury's magnetotail, which suggest that the planet's magnetospheric substorms -- space-weather disturbances powered by the rapid release of magnetic energy stored in the lobes of planetary magnetic tails -- are more intense than those on Earth and occur on shorter time scales. Prockter et al. presented imaging data of a large impact basin filled with smooth plains whose geological characteristics, reflectance, and color properties indicate that volcanism on Mercury has extended to much more recent times than previously thought, perhaps well into the second half of solar system history. Finally, Vervack et al. analyzed data from the Mercury Atmospheric and Surface Composition Spectrometer onboard MESSENGER to make measurements of the planet's thin atmosphere, or exosphere. Differences in the altitude profiles of magnesium, calcium, and sodium over the north and south poles of Mercury indicate that multiple processes are at play to create and maintain the exosphere. Prostate Cancer's Cellular Origins The cancer stem cell hypothesis, which proposes that only a small fraction of cells in a tumor are capable of initiating tumor growth, has fueled interest in identifying the specific cell type(s) that give rise to common epithelial cancers. In principle, a single, well-defined cell of origin could lead to more effective targeted therapies. Luminal secretory cells within the prostate epithelium are believed to be the cell of origin in prostate cancer, but this is largely based on histological evidence and/or studies of mouse tumors. Now, in the 30 Jul 2010 Science, Goldstein et al. report results from a new experimental model that challenge this notion. Starting with benign human prostate cells, the researchers introduced various genetic alterations that are commonly found in human prostate cancer, and then injected the transformed cells into mice. They found that a different cell type -- basal cells -- can give rise to prostate tumors that closely resemble human prostate tumors. These results suggest that the cellular origin of prostate cancer may be more complex than previously thought. Cold Atoms in Transition Although it is evident that strong interactions between particles can lead to the formation of quantum-mechanical phases such as high-temperature superconductivity, there are many gaps in our understanding of the underlying physics. Cold atoms trapped in optical lattices, patterned energy landscapes created by laser beams, have emerged as an ideal model system for understanding the creation of these phases because the strength of the particle interactions can be smoothly tuned and complicating factors in solids such as disorder can be controlled. In a Report in the 30 Jul 2010 Science (published online 17 Jun), Bakr et al. used a quantum gas microscope to image the dynamics of individual cold rubidium-87 atoms transforming from a superfluid to an insulating phase. To achieve this transition, the intensity of the laser beams in the lattice is increased such that atoms switch from a state in which they can move freely within the lattice to one in which the number of atoms in each lattice site becomes fixed. By varying the time over which they increased the lattice laser intensity, the team revealed that the phase transition occurs at surprisingly fast time scales. This atomic-scale imaging system may prove useful for studying other quantum phenomena including experiments involving quantum magnetism. An accompanying Perspective by B. DeMarco highlighted the study. In Science Signaling
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