This Week in Science

Science  04 Mar 2005:
Vol. 307, Issue 5714, pp. 1371
  1. Maser Distance Markers


    It is difficult to determine the distance to nearby galaxies in the Local Group of galaxies, but such data are needed in order to estimate the local distribution of matter and galactic dynamics, as well as to provide a calibration point for other distance scales, such as Cepheid variables. Brunthaler et al. (p. 1440) determined a distance to the Triangulum galaxy (M33) of 730 ± 168 kiloparsecs by observing two water masers with the Very Long Baseline Array (VLBA) of radio telescopes. This value agrees well with previous distance values, and their study also determined M33's angular rotation.

  2. Hot Rocks, Lost City

    Recently, a deep-ocean hydrothermal system was discovered in the Atlantic Ocean. The Lost City hydrothermal field is powered by sea water hydrating rocks in ocean crust to form the mineral serpentine, a process that releases heat. Because this reaction potentially occurs throughout the oceans, this type of system may be widespread. Detailed mapping of the system and chemical and microbial analyses by Kelley et al. (p. 1428; see the Perspective by Boetius) show that primarily archaea inhabit the vents living of methane. The surrounding diversity of marcofauna is high and comparable to that of mid-ocean ridge hydrothermal systems.

  3. Water Shuffle

    Solvation processes likely involve subtle rearrangements of the solvent molecules around the solute that vary only slightly in energy. Clarkson et al. (p. 1443, published online 3 February 2005) explore such processes in a model gas-phase system in which the organic molecule formanilide forms two different types of complexes with a water molecule via hydrogen bonds, either a donor link to the C=O group or an acceptor link to the NH group. A laser excitation scheme (stimulated emission pumping) boosts the vibrational energy of either isomer selectively. When sufficient energy is provided, the water can shift from one binding site to the other. The data support an energy difference of roughly 200 wavenumbers (cm−1) or less between isomers, and lower bounds of 870 ± 120 cm−1 were extracted for the isomerization thresholds under experimental conditions.

  4. Distorted Heliosphere


    Measurements of the direction of neutral hydrogen flow as it enters the inner heliosphere from the Solar and Heliospheric Observatory (SOHO) by Lallement et al. (p. 1447; see the Perspective by Jokipii) show that the heliosphere is distorted. The distortion is probably caused by the interstellar magnetic field, which forces the termination shock to be more elongated with increasing ecliptic latitude. Voyager 1, which is at about 90 astronomical units from Earth, has sent back controversial signals that suggest it may have left the heliosphere. However, if the heliosphere is distorted, as suggested by the SOHO data, then Voyager 1 is still trapped within the elongated region of the heliosphere and has not crossed the termination shock.

  5. Organizing Enamel

    Like bone, tooth enamel is composed of ordered carbonated apatite crystals, but unlike bone, enamel does not include collagen to direct crystallie growth, nor does enamel remodel like bone. At an early stage of development, enamel contains a large fraction of amelogenin proteins. Du et al. (p. 1450; see the Perspective by Veis) used in vitro studies to show that these proteins form nanospheres that subsequently organize into microribbons. These structures may control the subsequent oriented growth of apatite crystals during mineralization.

  6. Doubling Resistance

    Segmental duplications within the genome are fundamental to both human disease and evolution. Because certain duplications span genes involved in immune defense, some differences in the ability to fight infections can be attributable to dosage effects resulting from the number of copies of specific genes. Gonzalez et al. (p. 1434, published online 6 January 2005; see the cover and the Perspective by Nolan et al.) noted differences in segmental duplications spanning the variant of the CCL3 chemokine, CCL3L1, in different ethnic and geographic populations. The CCL3 receptor, CCR5, is an important coreceptor for human immunodeficiency virus-1 (HIV-1) infection. The authors found that increased segmental duplications increased resistance to acquiring HIV-1 and progression to AIDS, and correlated with CCL3L1 expression, levels of CCR5, and reduced CD4+ T cell decline. Similar duplications in chimpanzees suggest that some duplications may be an ancient adaptive response of the immune system to environmental pressures.

  7. High-Pressure Existence

    Despite the deep sea being the largest environment within the biosphere, adaptation to this habitat is still poorly understood. Photobacterium profundum has become a model for ocean depth adaptation, as it grows optimally at high hydrostatic pressure. In genome and expression analysis, Vezzi et al. (p. 1459) find hints of adaptations in metabolism and protein structure to high-pressure life. This bacterium apparently uses alternative carbon sources at these depths because enzymes for chitin, pullulan, and cellulose degradation are activated at 28 megapascals. This bacterium is so finely tuned to high-pressure life that atmospheric pressure triggers a stress response that activates distinct chaperones and DNA repair proteins.

  8. Dangers of an All-Diatom Diet

    In the plankton food chains in the ocean, it has been believed that copepods primarily feed on diatoms. However, laboratory studies have indicated that copepods do not fare well with a pure diatom diet, and it has recently been suggested that diatoms may be toxic to copepods. Jones and Flynn (p. 1457) show that diatoms are not so much toxic to copepods as of poor nutritional value. In a series of feeding experiments, they show that copepods fed a mixed diet of diatoms and flagellates fare better than copepods fed a diet of diatoms alone, and also that the nutritional status of the diatoms themselves is important in determining the copepods' response.

  9. To Kill a Male Drosophila

    Certain cytoplasmically inherited microorganisms disturb the reproduction of their host to increase their own propagation. The mechanism by which host systems are affected are unclear. In particular, “male-killer” bacteria pass from a female insect to her daughters and sons, and selectively kill sons during embryogenesis. Around 20% of insect species may be afflicted in this way, but how do these bacteria kill just males? Veneti et al. (p. 1461) used the male-killer Spiroplasma poulsonii, which infects Drosophila melanogaster, to address this question. When male-killers were placed in flies carrying mutations within the gene dosage compensation system that is involved in male specification, any mutation in the dosage compensation complex increased the survival of male offspring.

  10. Linking Caspase-8 and NF-κB Activation


    The protease caspase-8 functions in signaling from death-inducing receptors on the cell surface, but analysis of humans lacking the enzyme suggests that it must also play a role in signaling from antigen and Fc receptors on cells in the immune system. Su et al. (p. 1465) show that activation of nuclear factor κB (NF-κB, a key player in immune responses) is defective in cells lacking caspase-8. Antigen or Fc receptors stimulate NF-κB through a process mediated by a molecular complex that contains numerous signaling proteins, and caspase-8 physically interacts with adaptor proteins that aid in the formation of these signaling clusters. When it signals cell death, caspase-8 undergoes autoproteolysis that generates a fragment with strong protease activity. After activation of antigen receptors, however, catalytic activity of caspase-8 was still required for signaling, but the enzyme remained intact, perhaps in a conformation with a more moderate proteolytic activity. These results help explain the range of physiological effects seen in patients after loss of this single protein-degrading enzyme.

  11. Skin Feels the Heat

    Unlike other members of the transient receptor potential (TRP) family of ion channels that function as temperature sensors, TRPV3 is expressed in epithelial keratinocytes rather than sensory neurons in the skin. Moqrich et al. (p. 1468) generated a TRPV3 knockout mouse and found that the ion channel is required for animals to detect temperatures in the ambient range. Camphor potentiated the activation of TRPV3 by heat, and mice lacking TRPV3 could not respond to camphor. Once thought to be an exclusive function of neurons, the study extends thermosensation to keratinocytes.

  12. Dopamine, Reward, and Attention

    What is the functional significance of the fast burst firing of midbrain dopaminergic neurons, and what are the normal afferents projecting to these cells that carry the information to which the neurons respond? Dommett et al. (p. 1476) found that the superior colliculus is the major input source of short latency visual responses of dopaminergic neurons. The induction of visual responses in dopaminergic neurons leads to increase in dopamine release in the striatum. However, dopaminergic cells only responded to the novel visual stimuli when the colliculus was pharmacologically disinhibited.

  13. Cooking and Climate

    Large quantities of black carbon emitted from South Asia pollute extensive regions of the atmosphere over the Indian Ocean, but identifying the sources of this pollution is more difficult than merely observing its distribution. Venkataraman et al. (p. 1454) identify biofuels, which are used widely throughout the region for cooking, as the largest source of black carbon emissions in India. Their conclusion is based on measurements of emissions from a comprehensive set of biofuels, such as wood, agricultural waste, and dried animal manure, and estimates of biofuel use. These emissions are thought to have a significant influence on regional climate, so their control is of central importance for climate change mitigation in the South Asian region.

  14. Variation in a Gut Bacterium

    Bacteroides fragilis normally lives in the human colon and is commonly associated with abscess, soft tissue infections, and anaerobic bacteraemia. Cerdeño-Tárraga et al. (p. 1463) sequenced the roughly 5-megabase genome and showed that it contained DNA inversion sites whose presence suggests a more complex system of variation than has been seen in other microorganisms. This genome appears to incorporate machinery that can control expression of many different components, including surface and secreted components, regulatory molecules, and restriction-modification proteins.

  15. Cholesterol Modulates Intracellular Signaling

    Oxysterol binding protein (OSBP) binds oxysterols, but the exact function of this interaction has remained elusive. Disruption of the OSBP gene in mice is embryonic lethal at the four-cell stage. Because cholesterol is required for the assembly of an oligomeric phosphatase complex that has dual specific activity for the inactive phosphorylated kinase pERK, lowering cellular cholesterol levels leads to the hyperactivation of ERK1/2. Wang et al. (p. 1472) identify OSBP as the molecule that holds the phosphatase complex together and show that it uses bound cholesterol as a cofactor during assembly. Surprisingly, oxysterols actually stimulate disassembly of the oligomeric phosphatase. Thus, cholesterol functions outside of the lipid bilayer in regulating the activity levels of a key signaling component, and other lipids might regulate the assembly of other multiprotein signaling complexes in a similar fashion.

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