This Week in Science

Science  11 Apr 1997:
Vol. 276, Issue 5310, pp. 173
  1. Breaking HIV-1 entry into cells

    Infection of human cells with the human immunodeficiency virus-type 1 (HIV-1) is facilitated by the chemokine receptors CXCR4 (Fusin) and CCR5. Two reports focus on the blocking of CCR5 function to achieve resistance to the virus that may also prove useful therapeutically. Resistance to macrophage-trophic HIV-1, which makes use of the CCR5 cofactor, can be induced by activating CD4+ T cells with immobilized antibodies to CD3 and CD28. Carroll et al. (p. 273) show that such activation upregulates CXCR5/Fusin transcription but that transcripts for CCR5 could not be detected. The chemokine RANTES can interact with CCR5 to block infection but not efficiently. Simmons et al. (p. 276) show that an aminooxypentane derivative of RANTES is effective in vitro in blocking HIV-1 infection of macrophage and lymphocytes at nanomolar concentrations.

  2. Out of oxygen

    The extinction at the end of the Permian (250 million years ago) is the largest in the fossil record. Anoxia in the deep oceans has been suggested as a likely cause, but most of the exposed rocks that provide a record of this time were deposited at shallow depths. Isozaki (p. 235) describes two sections of deep-ocean deposits, one in Japan, the other in British Columbia, which indicate that at least the large paleo-Pacific Ocean was anoxic at depth and thus was stratified for up to 20 million years around the time of the extinction.

  3. Trapping wet melts

    Adding water to a silicate melt affects its physical and chemical properties (such as its density and the sequence of minerals that crystallize as the melt cools). It has been difficult to study these properties experimentally in water-rich melts at high pressure (equivalent to hydrous partial melts in Earth's upper mantle). Kawamoto and Holloway (p. 240) were able to trap melts in a multi-anvil apparatus and study a hydrous mantle peridotite to a pressure of 11 gigapascals. Their results provide some of the basic phase equilibria needed to understand the role of water in mantle magma dynamics and the origin of rarer, mafic-rich rocks that are presumed to be derived from great depths in Earth's mantle, in part through the effects of hydration.

  4. Three are crowded

    A triple junction is where three tectonic plates meet, and the evolution and changes in triple junctions mark key transitions in the geometry of plate tectonics. Ligi et al. (p. 243) used a variety of geophysical data to catch such a transition in progress in the South Atlantic Ocean. In this region, the Antarctic plate is increasing its size at the expense of the Mid-Atlantic Ridge.

  5. Building blocks

    In order to understand the origin of life, it is important to identify reactions and conditions that could have allowed the fixing of carbon into larger molecules. In several experiments, Huber and Wächtershäuser (p. 245; see the Perspective by Crabtree, p. 222) show that the presence of iron-nickel sulfides catalyzes carbon-carbon bond-forming reactions of carbon monoxide (CO). When these sulfides were doped with selenium, CO reacted with hydrogen sulfide to form acetic acid under conditions typical of low-temperature hydrothermal systems.

  6. Ferroelectric memories

    Ferroelectric field effect transistors (FETs) offer the possibility of active devices that retain their memory state even when switched off. Such devices were conceived in the 1950s, but materials issues have limited their practical use. Mathews et al. (p. 238) show that device performance can be improved by using rare-earth manganates, which recently have been shown to have large magnetoresistive effects, as the semiconducting channel component of ferroelectric FETs.

  7. Neurons sans dopamine

    Parkinson's disease results from degeneration of dopamine neurons in the midbrain. Zetterström et al. (p. 248) show that very early in development, before dopamine expression is apparent, these neurons are dependent on expression of the orphan nuclear receptor Nurr1. The ligand for Nurr1 remains unknown, but it may prove to be significant in the development and maintenance of these critical neurons.

  8. Regulating lipid A

    Expression of bacterial virulence genes is regulated to respond to the host environment. In Salmonella typhymurium, the PhoP-PhoQ proteins regulate more than 40 genes, some of which help defend it against antimicrobial host peptides. Guo et al. (p. 250) used mass spectrometry to show that the PhoP-PhoQ proteins also regulate structural modifications to lipid A, a component of lipopolysaccharide (LPS). The modified form altered the cytokine expression that LPS stimulates in cultured host cells

  9. Bone disposal

    Bones are dynamic structures that are continuously being formed and resorbed. Two reports present microscopy studies that reveal how osteoclasts, large multinucleated cells, process degraded bone (see the Perspective by Mostov and Werb, p. 219). Osteoclasts attached to bone form a sealed zone that contains the ruffled border membrane, which secretes acid and digestive enzymes. Nesbitt and Horton (p. 266) and Salo et al. (p. 270) labeled bone proteins and show that products such as degraded collagen are endocytosed into vesicles at the ruffled border membrane and transported across the cell, where they are then released to the extracellular space. Such vesicular traffic may also regulate the resorption process.

  10. Self-assembly on a grand scale

    By extending the principles of molecular self-assembly, that is, spontaneous self-association of molecules to mesoscale objects in the millimeter-size range, Bowden et al. have achieved controlled self-assembly of complex patterns in two dimensions. Wettability of different surfaces and capillary forces were utilized to form patterns at a liquid-liquid interface. These principles may be used in microfabrication to construct photonic band-gap materials, optical memories, and related structures.

  11. Phylogenetics and biology

    An article and two reports focus on phylogenetic studies that are impacting modern biology (see the Perspective by Hillis). Comparisons of genomic sequences among great varieties of organisms have in recent years been used to formulate hypotheses about which organism evolved from which. This sort of analysis has been applied to a wide range of questions, from forensic use to demonstrate relatedness of human immunodeficiency virus-type 1 strains in different patients to investigating the most ancient question of all, where did eukaryotes come from. Huelsenbeck and Rannala review the conceptual basis for these analyses, the statistical tests by which the hypotheses are tested, and the variety of applications currently being found for phylogenetic analysis. The comparison of genomic DNA sequences between organisms has been applied to evolutionary questions for some time now in order to determine the course taken through evolution to generate groups of related organisms. Pierce and Crawford have instead applied phylogenetic analysis to a study of metabolic pathways. In the evolution of the glycolytic pathway in fish, concentrations of some of the enzymes may vary without offering adaptive value. However, the covariance of certain sets of enzymes indicates that glycolytic throughput may be regulated by the aggregate value of the enzymes, rather than by a single, rate-limiting enzyme. A central question regarding the coevolution of insect-plant associations is the extent to which insect speciation is influenced by the allelochemical makeup of the host plants. Becerra addressed the question of using an ancient and diverse beetle-plant system by comparing the molecular phylogeny of the insects against both the molecular phylogeny of the plants and the host plant chemistry, which was assessed by chromatographic analysis of terpenes. The analysis revealed that plant chemistry has played a significant role in the evolution of host shifts by phytophagous insects, a role that is greater than that contributed by phylogenetic inertia.

  12. Recyling synaptic vesicles

    Release of neurotransmitters from neurons is accomplished by fusion of synaptic vesicles, which contain the neurotransmitters, with the plasma membrane. The vesicle membrane is then recovered by endocytosis to be replenished with neurotransmitter and used again. Shupliakov et al. (see the cover) explored the mechanism by which the protein dynamin promotes such endocytosis. A proline-rich region of dynamin that specifically binds to a sequence (known as Src homology 3, or SH3 domains) in certain other proteins is required for recycling of synaptic vesicles. Their results indicate that endocytosis through clathrin-coated vesicles is necessary for proper recovery of the vesicle membrane and subsequent release of neurotransmitters.

  13. Memory location

    Functional imaging of the brain in normal humans has enabled cognitive neuroscientists to explore the basis for psychological concepts of cognition, such as memory in its various forms. Past studies of the anatomical localization of the retrieval of familiar items and the encoding of novel items yielded conflicting results, at times, because of different experimental paradigms. Gabrieli et al. examined regions within the hippocampal formation, which previously has been implicated as important for memory. Retrieval is associated with activation of the subiculum, while encoding is associated with activation of the parahippocampal gyrus.

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