This Week in Science

Science  05 Mar 2004:
Vol. 303, Issue 5663, pp. 1433
  1. Taking a Bite Out of Early Hominid Genera

    HAILE-SELASSIE ET AL.

    The last common ancestor of chimps and humans is thought to have lived about 6 million years ago; several recent fossil finds (ascribed to three genera) are starting to resolve the early evolution of hominids immediately after this split. Haile-Selassie et al. (p. 1503; see the Perspective by Begun) describe six new early hominid teeth, including a diagnostic canine, from deposits in Ethiopia that date to 5.2 to 5.8 million years ago. Clear differences in wear are evident versus comparable teeth of apes and ape ancestors. Comparison to other, admittedly sparse material from the few other early hominids implies that available hominid finds may represent less than three genera.

  2. Quantum Criticality from Within

    The traditional description of classical phase transitions may be insufficient to describe some of the subtleties now being observed experimentally in systems exhibiting quantum phase transitions. In contrast to the traditional methods that describe the “order parameter” of the bulk phases, and then home in on the quantum critical point (QCP), Senthil et al. (p. 1490; see the Perspective by Laughlin) approach the problem from within. They look at the theoretical description of the QCP itself and how it evolves as the parameters are varied. By using theoretical tools involving deconfined excitations and “fractional” particles, they describe the phases of a square-lattice antiferromagnet.

  3. Stress and Drink

    Corticotropin-releasing factor (CRF) is strongly linked to the behavioral changes associated with stress and alterations in the hypothalamic-pituitary-adrenal stress axis. Stress-induced drinking of alcohol and relapse behavior have a significant genetic component. The basic mechanisms underlying the interaction between stress, brain CRF, and alcohol are not fully understood. Nie et al. (p. 1512) found that CRF receptor knockout mice lacked the enhancing effect of CRF and ethanol on GABAergic neurotransmission in the central amygdala, a brain region prominently involved in alcohol dependence and reinforcement. CRF1 antagonists blocked both CRF and ethanol effects in wild-type animals, suggesting a direct role for CRF receptor-mediated processes in the acute effects of ethanol.

  4. Magnetic Metamaterials

    The magnetic response of materials found in nature generally tend to be limited to the lower frequency gigahertz bands of the electromagnetic spectrum. Yen et al. (p. 1494) have fabricated artificial materials, or metamaterials, that consist of arrays of split-ring resonators with tunable magnetic responses in the higher frequency terahertz range. The components themselves have no permanent magnetic moments. The ability to tune the magnetic response simply by varying the dimensions of the individual components opens the possibility to extend the effect into the optical regime.

  5. Wnts in Development

    During embryogenesis, cells may acquire new identities concomitantly with their migration to new locations. Morphogenetic changes are often induced by extracellular ligands and their receptors. What signaling pathways coordinate changes in gene expression with dynamic changes in cell adhesion and migration? Nelson and Nusse (p. 1483) review evidence of possible interrelationships between Wnt and other growth factor signaling and cadherin-mediated cell adhesion.

  6. Pathogens Caught in Neutrophil NET

    Neutrophils are cells of the immune system that exude a fibrous matrix when activated by a range of bacterial pathogens. Brinkmann et al. (p. 1532; see the cover and the Perspective by Lee and Grinstein) have found that the matrix consists of DNA, which provides a skeleton for a network of enzymes, including elastase, cathepsin G, myeloperoxidase, lactoferrin, and gelatinase. These neutrophil extracellular traps (NETs) appear to be a type of innate immune response that ensnares pathogens and disarms their virulence factors.

  7. The Genetics of Mosquito Biting

    Throughout the world, mosquitoes of the ubiquitous Culex pipiens species complex are important vectors for several infections, and currently are most notorious for transmission of West Nile Virus. This complex constitutes a bewildering variety of mosquito types showing different behavioral traits that, until now, could not be distinguished genetically. Fonseca et al. (p. 1535; see the news story by Couzin) investigated the genetics of these mosquitoes in relation to biting preferences and hence their capacity to transmit zoonotic viruses. All New World C. pipiens populations tested showed evidence of hybridization with the human-feeding Culex quinquefasciatus, which confers biting characteristics likely to permit West Nile Virus transmission.

  8. Reconstructing European Climate

    CREDIT: LUTERBACHER ET AL.

    Reconstructions of climate for the past 1000 years provide insufficient regional and seasonal detail to allow an accurate picture of climate variability. Luterbacher et al. (p. 1499) present a high-resolution reconstruction of temperature patterns for European land areas back to 1500 A.D. in a multi-proxy approach that includes early instrumental data series and proxy records. The authors determine monthly or seasonal mean temperatures, temporal variability, and the spatial patterns of trends and extremes. They conclude that summer temperatures of the past decade (1994 to 2003) were the hottest in more than 500 years and the 30-year averages of the winter and annual mean temperatures between 1973 and 2002 were the highest for more than half a millennium. Although the European “Little Ice Age” winter and annual temperatures were generally reduced, summer temperatures did not experience systematic century-scale cooling.

  9. A Motoring Microtubule Modulator?

    The kinesin family of proteins include molecular motors that promote the movement of cargo along microtubules and microtubule regulators that promote microtubule disassembly but do not move along microtubule tracks. Bringmann et al. (p. 1519) now show that the mitotic kinesin Xklp1 acts both as a potent inhibitor of microtubule dynamic instability and as a fast kinesin with unusual kinetic properties.

  10. Pathogen Protection via Toll-like Receptors

    Mammalian Toll-like receptor proteins (TLR) have evolved to detect a range of molecular cues displayed by pathogens, such as components of bacterial cell walls and viral nucleic acids (see the Perspective by O'Neill). Zhang et al. (p. 1522) present evidence for a new member of the mammalian TLR family, TLR11, which plays a role in protecting the urogenital tract from bacterial pathogens. TLR7 and TLR8 have yet to be assigned specific pathogen-derived ligands. Diebold et al. (p. 1529) observed recognition of single-stranded influenza viral RNA (ssRNA) by TLR7 in mice and found that stimulation of this receptor pathway within the endosome of the dendritic cell induced antiviral cytokine expression. Heil et al. (p. 1526) also observed guanosine (G)- and uridine (U)-rich ssRNA sequence detection by TLR7 in mouse dendritic cells. However, in human cells, TLR8 rather than TLR7 detected GU-rich ssRNA sequences of human immunodeficiency virus type-1, highlighting a level of divergence in TLR-mediated viral RNA detection between species.

  11. Neuronal Death and Prion Proteins

    CREDIT: SOLFOROSI ET AL.

    Very little is understood about the molecular events that drive prion-associated pathologies, including extensive neuronal death. Scrapie-associated prion protein (PrP-Sc) induces neurotoxicity that is fully dependent upon the expression of normal cellular prion protein (PrP-c). Antibody binding to PrP-c can trigger signal transduction in cultured neuronal cells. To test whether signaling by cross-linked PrP-c could trigger neuronal cell death in vivo, Solforosi et al. (p. 1514) stereotaxically injected various PrP-c-specific monoclonal antibodies into the mouse hippocampus. Certain intact PrP-c-specific monoclonal antibodies triggered widespread neuronal death via apoptosis. No damage was detected when Fab fragments of the PrP-c-specific antibodies were injected, or when antibody was delivered to the brains of knockout mice that do not express PrP-c. These findings will be important when considering whether anti-PrP antibodies should be used in prion-disease therapies.

  12. Going Forth to Multiply

    Self-incompatibility, which assures cross-fertilization in plants, has many similarities to other eukaryotic self-nonself recognition systems. Molecular components involved in the self-incompatibility response in Brassica have been identified on the surface of both pollen and receptive stigma. Murase et al. (p. 1516; see the Perspective by Goring and Walker) have now identified another key component in the pathway, the membrane-anchored kinase MLPK, that functions early in the responsive signal transduction cascade after pollen encounters a stigma epidermis cell.

  13. Meteoritic Stardust

    Astronomers have found spectral signatures of silicate grains in many stellar environments, but geochemists have had a difficult time finding silicate grains from other stars in meteorites. Nguyen and Zinner (p. 1496) have detected nine presolar silicate grains in the carbonaceous chondrite Acfer 094. The Mg and O isotopic abundances of these grains provide information about the type of stars and the processes in the stars that created these grains. In particular, the anomalous isotopic ratios in one grain suggest deep mixing of stellar layers in a low mass, thermally pulsing asymptotic giant branch star during cool bottom processing before the star transitioned to a carbon star.

  14. When Time Flies...or Not

    The human perception of time changes when we are actively trying to attend to its passing. What brain regions are involved in the explicit modulation of time estimation when attention is being paid to its passage? In an event-related functional magnetic resonance imaging study, Coull et al. (p. 1506) biased processing from color onto the temporal domain by an attentional instruction. This approach provides a purer paradigm for examining timing, uncontaminated by such processes as motor preparation. A cortico-striatal loop, including the presupplementary motor area, was selectively activated.

  15. Bind and Release

    The transmembrane AMPA receptor regulatory proteins (TARPs) regulate membrane insertion and appropriate synaptic targeting of AMPA receptors. Tomita et al. (p. 1508) examined the interaction and dissociation mechanisms of AMPA receptors with TARP proteins. Stimulation with glutamate or AMPA decreased the association of AMPA receptors with TARPs and lead to AMPA receptor endocytosis without disturbing the TARPs on the neuronal surface. Thus, agonist-induced allosteric changes in AMPA-receptor conformation, even without ion channel activation, may be enough to induce the dissociation of AMPA receptors from their TARPs.

  16. Understanding Networks

    Networks of interacting elements are being found in highly diverse systems. As they can differ widely in size, structure, and discipline, comparisons among them have not been straightforward. Milo et al. (p. 1538) have built on previous studies of motifs to derive statistical significance profiles that could be used to compare biological, social, and technological networks to generate superfamilies of networks. In one example, power grids and protein secondary structure networks belonged to one superfamily.

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