This Week in Science

Science  23 Jan 2009:
Vol. 323, Issue 5913, pp. 433
  1. Active Sites on Aluminum Clusters


    The reactivity of electros of metal clusters formed in the gas phase can be dominated by shell-filling rules that arise from quantum confinement of the valence electrons and that mirror the shell-filling rules of atoms. For aluminum clusters, these rules can account for their reactivity with O2. Roachet al. (p. 492) show that reactions of these clusters with water represent a different case and that its propensity for dissociative chemisorption on Al16, Al17, and Al18 clusters depends more on the presence of particular geometric sites than on filling electronic shells.

  2. Teleporting Quantum Matter

    Quantum teleportation is the faithful transfer of the quantum state of one system onto another, and is at the heart of quantum information processing. While photons are ideal for teleportation over long distances, there is also the requirement to store the information locally in quantum memories. Here, trapped ions are ideal candidates because of their long memory times. Olmschenket al. (p. 486; see the Perspective by Kim and Cho) combine the benefits of photons and trapped ions by demonstrating the ability to teleport the quantum state of one trapped ion onto another trapped ion about 1 meter away. The technique may eventually be scalable to larger quantum networks.

  3. Monitoring Human Migrations

    Among the most dramatic of human expansions is the prehistoric colonization of the islands scattered across the Pacific Ocean (see the Perspective by Renfrew). Two competing scenarios attempt to explain this astonishing migration: The pulse-pause scenario posits a Taiwanese origin of the Austronesian language complex between 5000 to 6000 years ago, while the slow boat scenario suggests an origin in Island South/East Asia 13,000 to 17,000 years ago. Gray et al. (p. 479) apply phylogenetic techniques to 210 basic vocabulary words (animals, kinship terms, simple verbs, colors, and numbers) from 400 Austronesian languages to show that the language family has a root in Taiwan, some ∼5000 years ago, followed by languages of the Philippines, Borneo/Sulawesi, Central Malayo-Polynesia, and South Halmahera/West New Guinea, and reflects the origin and path of the migration predicted under the pulse-pause scenario. In a separate approach to migration research, Moodley et al. (p. 527) turned the ubiquitous occurrence of a human pathogen to good use. Helicobacter pylori is a bacterium that specifically colonizes the human stomach, where it occurs in about half the population who do not have access to modern medicines. Because H. pylori is so specific to humans, it has spread around the world and diverged genetically alongside its host since people emerged from Africa. The discovery of the Sahul strain of the bacterium indicates that humans spread from Taiwan in two waves. The first wave spread across the exposed land bridges of what is now the Indonesian Archipelago into New Guinea and Australia. A second wave carrying the Maori strain of the bacterium traveled within humans via the Philippines into Polynesia and New Zealand.

  4. Separating Immune Cell Fate

    The adaptive immune response is mediated in part by CD8+ T cells, which protect against intracellular infection by pathogens and against some tumors. This T cell population fulfills a dual function by providing immediate protection via effector cells and retaining this protective immunity long-term, via memory cells. On infection, naïve T cells carrying pathogen-specific T cell receptors (TCR) differentiate into short-lived effector cells and long-lived memory cells. However, it is unclear how this is regulated, and whether memory cells are formed from the effector cells or differentiate separately (see the Perspective by Feau and Schoenberger). Teixeiro et al. (p. 502) have now shown a direct role for the TCR specifically in CD8+ memory T cell differentiation. Upon bacterial infection of mice harboring defective TCRs, mutant T cells were still able to generate effector T cells and a robust primary immune response, but were specifically impaired in developing memory T cells. Thus, the differentiation of effector and memory CD8+ T cells are separable, and determined by the induction of a distinct set of TCR signals. However, Bannard et al. (p. 505) used a transgenic mouse line to closely map the cell fate of a subset of effector T cells that were generated during the primary response to infection by influenza. These effector cells were found to survive and become memory cells that could replicate and expand during secondary infection.

  5. Cooking and Burning


    A huge plume of air pollution, called the Asian Atmospheric Brown Cloud (ABC), emanates from Southern Asia and persists over much of the Indian continent and the Indian Ocean during the winter. It is so large and dense that its cooling effect may balance, or even surpass, the warming effect of greenhouse gases in the region. In order to know how to mitigate this scourge, its origin must be known. There are two major sources that contribute to the ABC—biomass burning and fossil fuel combustion—whose relative importance is unclear. Gustafsson et al. (p. 495; see the Perspective by Szidat) measured radiocarbon in particles from the cloud, and between one-half and two-thirds of the carbonaceous aerosols were from biomass burning. Thus, controlling biomass combustion, particularly residential cooking and agricultural burning, will be important to mitigate climate effects and to improve air quality in the region.

  6. Bacterial Cytoskeleton Revealed

    The ParMRC DNA-segregation system of bacteria is the simplest known “mitosis-like” DNA partitioning machinery, which uses filament polymerization to move DNA through the cell. Recent studies have demonstrated the similarity of the filaments to actin filaments, uncovered the dynamic properties of the filaments, reconstituted the system in vitro, and determined the structure and function of the filament-polymerizing protein ParR. Salje et al. (p. 509, published online 18 December; see the Perspective by Jensen) observed the ParMRC directly in natively cryoimmobilized cells using a combination of vitreous sectioning and cryoelectron tomography. Small bundles of three to five filaments that may represent the actively segregating filaments were observed close to the surface of the bacterial nucleoid.

  7. Grappling with Membrane Fusion


    The process of membrane fusion is fundamental to cellular organization and has been the focus of a vast literature. Südhof and Rothman (p. 474) review the role of so-called SNARE and SM proteins in membrane fusion and present a hypothesis for how they are regulated by other proteins, termed grapples, exemplified by complexin. Two further papers also shed light on complexin's role in regulating SNARE-mediated membrane fusion. Giraudo et al. (p. 512) show that a structural motif within complexin appears to act as a molecular switch directly interacting with SNAREs during membrane fusion. Maximov et al. (p. 516) confirm that, in neuronal systems, complexin can play a negative or positive role in SNARE-mediated membrane fusion during neurotransmitter release, potentially either clamping SNARES to prevent spontaneous fusion, or promoting fusion when appropriate.

  8. Dying Trees

    Tree mortality rates have more than doubled in recent decades in otherwise undisturbed forests of the western United States, possibly as a consequence of ongoing regional warming. Van Mantgem et al. (p. 521; see the news story by Pennisi) use a long-term set of demographic data to reveal a pervasive increase in background mortality rates for trees in seemingly healthy forest. The increases occur regardless of elevations, tree size, taxon, or fire history and cannot be attributed to processes such as increasing competition or aging of large trees. The increases in mortality are likely to have been driven by environmental changes, with ongoing regional warming and its widespread effects on the western U.S. hydrologic cycle being the most probable contributors. Changes in tree mortality rates can affect future forest structure and composition, which in turn affect ecosystem services such as carbon sequestration, and thereby biological contributions and responses to climatic changes.

  9. Taking a S1P

    Lipid mediators derived from the cell membrane have important signaling functions. Among them, sphingosine-1-phosphate (S1P) activates its cell surface receptor to control immunity, vascular tone, cell migration, and cancer. The amount of extracellular S1P depends upon the conversion of sphingosine to S1P and upon the release mediated by S1P transporters. Kawahara et al. (p. 524, published online 11 December) have identified the S1P transporter, Spns1, by zebrafish forward genetics and show that Spns1 interacts genetically with the S1P receptor-2 (S1P2). S1P released from the yolk syncytial layer by Spns1 activates S1P2 expressed in the mesoderm, thereby regulating heart development.

  10. Let Me Out

    Perforin-like proteins are expressed by many bacterial and protozoan pathogens, but little is known about their mode of action or role in pathogenesis. Kafsack et al. (p. 530, published online 18 December; see the cover) reveal the function of a perforin-like protein, TgPLP1, expressed by the human and animal pathogen Toxoplasma gondii, in the exit of vacuole-enclosed parasites from host cells. TgPLP1 appears to permeabilize the host cell membranes within which the parasite resides and divides and is an essential virulence factor of Toxoplasma in vivo in mice.

  11. Filtering Entanglement

    Devices that are capable of filtering polarization, noise, or wavelength play an important role in information technology. When the information is carried by single photons, then the realm of quantum information is entered. In this regime, interactions between the photons can result in quantum-mechanical entanglement, providing (potentially) a much more powerful method for information processing and computation. Using interferometry, Okamoto et al. (p. 483; see the news story by Cho) construct a device to allow two entangled photons to pass through only when they have the same polarization. Otherwise the photons are filtered out. The demonstrated entanglement filter should find use over a wide range of quantum information processing applications.

  12. Unspun by XANES

    Many transition metal complexes have a dense range of electronic states, spaced closely in energy, that differ primarily in the relative orientation of electron spins. Upon absorbing light, the compounds whir through these states at a pace that makes the ultimate pathway very hard to pinpoint, particularly because the states differ widely in their susceptibility to being probed by standard methods. Bressler et al. (p. 489, published online 11 December) took advantage of a recent breakthrough in short x-ray pulse generation to track subpicosecond spin manifold transitions using x-ray absorption near-edge structure (XANES). Because the electronic transitions in an aqueous tris(bipyridyl) iron complex correlate with metal-ligand bond length shifts underlying XANES spectra, it was possible to map the precise state of trajectory ensuing from the initial excitation.

  13. Genetic Variation and Trait Variation

    The genetic architecture at nucleotide resolution of naturally occurring trait variation is generally unknown. However Gerke et al. (p. 498) now dissect the genetic architecture of differences in sporulation efficiency, a trait controlling entry into the sexual phase of yeast, between oak and vineyard strains. Four nucleotide polymorphisms were observed in three transcription factors that account for (including interactions between them) the majority of the differences in sporulation efficiency between the yeast strains. These findings were confirmed by reciprocal transplants, placing them in an ecological context by population genetic analysis showing that allele frequencies demonstrate population-level variation.