This Week in Science

Science  08 Mar 2002:
Vol. 295, Issue 5561, pp. 1789
  1. In Brevia

    A statistical analysis by Brookmeyer and Blades (p. 1861) of the 2001 anthrax outbreak in the United States indicates that the use of prophylactic antimicrobials likely halved the number of resulting infections.

  2. But Not a Drop to Drink

    Although most of the Earth's surface is covered by oceans, much more water is bound up in mineral phases, and many hydrated minerals have been identified in the crust and upper mantle. Murukami et al. (p. 1885) have now synthesized hydrated lower mantle minerals under high-pressure and high-temperature conditions. Perovskite and magnesiowustite in the lower mantle can hold as much as five times more water than the oceans.

  3. Tritium via Sonoluminescence

    Subjecting a liquid to an oscillating acoustic field can result in the observation of a flash of light. This sonoluminescence comes from a bubble that forms in the liquids, expands as the acoustic pressure decreases, and then dramatically collapses. Spectral analysis of the emitted light has shown that the bubbles are hot and effectively emit black body radiation. Recent experiments indicate that the smaller the starting bubble, the hotter it will get upon collapse. However, spontaneous bubble formation is typically restricted to a narrow regime of bubbles some tens of micrometers in diameter. Using a pulse of neutrons, Taleyarkhan et al. (p. 1868; see the Editorial, the news story by Seife, and the Perspective by Becchetti) can nucleate bubbles in deuterated acetone with diameters of only tens of nanometers that produce tritium during their collapse along with characteristic neutron emission. Tritium was not produced when normal acetone was used. Shock-code simulations indicate that the temperature inside the bubble is high enough (~10 million Kelvin) to induce production of tritium.

  4. Energy from Rotating Black Holes

    A rapidly rotating black hole, called a Kerr black hole, has been derived theoretically from general relativity, but has not yet been observed. Van Putten and Levinson (p. 1874; see the cover) have calculated the energy emitted from a black hole rotating within a magnetized torus of plasma. Some of the rotational energy is released in baryon-poor outflows that may be associated with gamma-ray bursts. Another fraction of the energy is released as gravitational radiation from the torus, and this radiation might be detectable by the new gravitational wave observatories. Thus, it may become possible to see Kerr black holes and to understand the physics behind energetic events like gamma-ray bursts.

  5. Shaking Surprises

    If you shake a can of mixed nuts, the much larger Brazil nuts migrate toward the top. Such size-dependent segregation through vibration arises from either the diffusion of the smaller nuts through the voids created between the larger ones, or through granular convection. Burtally et al. (p. 1877; see the Perspective by Mullin) now show that vibration can separate particles of the same size but different density if there is sufficient air pressure to drive the segregation. At low vibration rates, bronze particles formed a surface layer above the similarly sized lighter glass particles, with a sharp interface between them. At higher vibration frequencies, the bronze particles formed a middle layer surrounded by the glass beads.

  6. Hydrides Nudge Their Way into Oxides

    At first glance, the incorporation of hydrogen atoms directly into a transition metal oxide framework might appear to be a difficult route for synthesizing water. Hayward et al. (p. 1882; see the Perspective by Poeppelmeier) show that hydride (H-), obtained from disproportionation of CaH2 at elevated temperature, could replace oxide species in LaSrCoO4 to form LaSrCoO3H0.7. The presence of hydride is revealed in the compound's unusual magnetic properties and neutron diffraction structure as well as by water evolution under more oxidizing conditions. This approach appears to be a general route to oxyhydrides.

  7. How to Charge a Battery

    Many microorganisms live under anaerobic conditions and must use other oxidizing agents, usually by coupling the reduction of one metabolite to the oxidation of another. In Escherichia coli, one such redox loop involves nitrate reductase, which reduces nitrate to nitrite, and formate dehydrogenase, which oxidizes formate to carbon dioxide. The flow of electrons is itself used to pump protons across the plasma membrane and creates an electrochemical gradient that is essentially equivalent to a battery. Jormakka et al. (p. 1863; see the Perspective by Richardson and Sawers) present the crystal structure of the membrane protein formate dehydrogenase at 1.6 angstroms and describe how the electrons travel along a 90-angstrom chain of carriers from one side of the membrane to the other.

  8. Flipping Earth's Field

    Earth's magnetic field can be approximated as a dipole, and every so often some process connected with the geodynamo somehow causes the dipole to reverse its polarity so that the field flips direction. Li et al. (p. 1887) have conducted a long-time scale, three-dimensional magnetohydrodynamic simulation of a reversing dipole in an idealized spherical dynamo. The field flipped only when the convection pattern became nonsymmetric, when the dynamo was in a high-energy state, and when the quadrupole mode was increasing.

    CREDIT: LI ET AL.
  9. The Nemesis Within Nematodes

    Filarial nematodes can invade our bodies and cause river blindness, which targets the skin and eyes, or elephantiasis, which targets the lymphatic system. When the nematodes die, the host immune response may lead to inflammation, cell infiltration, and loss of vision or blockage of lymph vessels. Saint André et al. (p. 1892; see the news story by Pennisi), have discovered that symbiotic Wolbachia bacteria living within the nematodes, which possess immune reactive lipopolysaccharides, provoke the blinding inflammatory response in rodents, rather than the nematodes themselves. As the Wolbachia are critical for the development of the nematode worms and are also killed by antibiotics, this discovery may lead to new strategies for combating these diseases.

  10. A Sense of Cell

    The transcription factor CtBP associates with transcriptional repressors for the regulation of genes involved in development, cell cycle regulation, and transformation. Zhang et al. (p. 1895) show that the corepressor activity of CtBP can be regulated by the redox state of the cell. Mammalian CtBP is regulated by physiological concentrations of nuclear nicotinamide adenine dinucleotides (NADs). When the nuclear concentration of free NAD and NADH increases, CtBP increases its affinity to viral and cellular repressors and represses transcription. This regulatory mechanism suggests how protein interactions respond to metabolic balances for the regulation of transcription.

  11. Krill Under Ice

    The reported feeding behavior of certain whale species suggests that Antarctic krill, Euphausia superba, are concentrated under the ice, at least at the ice pack margin. Using an autonomous subsurface vehicle traveling 15 to 20 kilometers under the sea ice, Brierley et al. (p. 1890) have found that krill abundance peaks within 1 to 13 kilometers of the ice margin. Here, the krill are safe from predators and have access to phytoplankton released from the undersurface of the ice.

    CREDIT: BRIERLEY ET AL.
  12. Sugarcoated Dispatches

    The signals for clearing circulating glycoproteins from the bloodstream are likely their carbohydrate tags, and it has long been proposed that membrane lectins perform this task. Lee et al. (p. 1898) examined the role of the mannose receptor (MR) in this process. A proteomic analysis of blood from mice that genetically lacked MR revealed elevated levels of proteins tagged with mannose and N-acetylglucosamine. All of these proteins are involved in the inflammatory response, which correlates with the down-regulation of MR in the early stages of inflammation.

  13. Doing Transcription Backward

    It is usually assumed that gene transcription in eukaryotes is initiated when sequence-specific activators bind their targets in DNA and recruit proteins that modify chromatin. The chromatin modifiers convert the normally repressive chromatin to a form that permits the assembly of the RNA polymerase II preinitiation complex. Soutoglou and Talianidis (p. 1901; see the Perspective by Fry and Peterson) now show that, for the differentiation-induced α1-antitrypsin gene promoter, a complete preinitiation complex is assembled prior to chromatin modification and long before transcription is initiated. Instead, it is the reconfiguration of the chromatin to the permissive state by the chromatin modifier proteins that is the defining step in transcription initiation.

  14. Location and Synapse Strength

    When synaptic inputs occur far out in the dendritic tree, are they simply attenuated by the filtering effect of the neuronal membrane or are there compensatory mechanisms at work? Williams and Stuart (p. 1907; see the Perspective by Mel) used simultaneous triple patch-clamp recordings to explore the strength of spontaneous and artificially elicited excitatory postsynaptic potentials (EPSPs) along the length of dendrites in neocortical pyramidal neurons. Although they reconfirmed earlier findings that EPSP amplitude increases with distance from the soma, they also found that the somatic EPSP impact still decreases with distance. Thus, a single input has fairly little influence on somatic potential, but coincident inputs could still generate dendritic spikes and subsequent action potentials in the postsynaptic neuron.

  15. Stable Singlet Diradicals

    Singlet diradical species can form as intermediates when a chemical bond is cleaved within a molecule. Much effort has been directed at preparing stable organic molecules containing two nearby antiparallel spins, but even careful choices of substituent groups on the atoms bearing the unpaired spins leads to lifetimes that are still only fractions of a second. Scheschkewitz et al. (p. 1880; see the Perspective by Wentrup) have found that they can use noncarbon atoms (heteroatoms) to create a singlet diradical that is stable in both solution and the solid state. Alkyl-bearing boron atoms carrying the unpaired spins are bridged by diphosphine groups; electrostatic repulsions within the ring help prevent the formation of a bond between the boron atoms.

  16. Tracking Down Cerebellar Defects

    Studies of the cerebellum and neuronal development have been greatly facilitated by the discovery years ago of a variety of mutations that affect mouse behavior. Mice with mutations in the Purkinje cell degeneration (pcd) gene develop ataxia in early adulthood when the Purkinje cells in their cerebellum degenerate. Male infertility is also often part of the syndrome. Fernandez-Gonzalez et al. (p. 1904) now identify the genetic locus of the pcd mutation. The affected gene encodes for a protein that is already known for its activation in response to axonal regeneration.

  17. Dose-Dependent Responses to Calcium

    Dynamic changes in signaling mechanisms may encode specific information critical to cellular regulation. Deciphering these messages requires sophisticated measurements of key signaling molecules in living cells. Teruel and Meyer (p. 1910) present a method that allows them to measure calcium-dependent translocation of fluorescently tagged protein kinase Cγ (PKCγ) to the cell membrane in many single, living rat basophilic leukemia cells grown on glass microscope slides. The enzyme showed two distinct modes of response. When calcium was released from internal stores, there was transient movement of PKCγ to the cell surface for only a few seconds. However, signals that caused entry of extracellular calcium caused a persistent translocation of the enzyme to the cell surface that lasted for more than half a minute. Cells showed primarily the former response to low doses of platelet activation factor, and the latter response to larger doses. The results help explain how a common messenger like calcium can control discrete cellular responses.

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