This Week in Science

Science  10 Jan 2003:
Vol. 299, Issue 5604, pp. 161
  1. Pushy Nanoparticles

    Colloidal particles can be strongly held at the fluid interfaces formed between immiscible liquids. Lin et al. (p. 226) show that for particle diameters below 10 nanometers (nm), thermal and interfacial energies become comparable, and interfaces can be exploited for self-assembly. Larger particles (4.6 nm) displaced smaller ones (2.8 nm) at the interface formed by a water droplet in toluene, thus providing a route to size-dependent segregation. Once assembled at the interface, the initially toluene-soluble particles were made water soluble through a photoinduced transformation.

    CREDIT: LIN ET AL.
  2. Cesium Condensation

    Cesium has played a special role in metrology, from its use as a primary frequency standard in atomic clocks to the determination of the fine-structure constant. The formation of a cesium Bose-Einstein condensate (BEC) would be advantageous because all of the atoms would be in the same quantum state, which would minimize signals arising from atom scattering. However, it has proven difficult to cool cesium atoms evaporatively with optical traps alone. To overcome the specific problems encountered in cesium, Weber et al. (p. 232) used a combination of optical trapping and magnetic tuning techniques to cool the cesium atoms into a BEC. The scattering length of cesium atoms could also be tuned, which allowed the exploration of various regimes of the BEC with positive, negative, or null interaction energy.

  3. Greenhouse Guesses

    The method of choice for determining oceanic CO2 uptake is based on the O2/N2 ratio of air, but embedded within this method are certain assumptions and limitations that introduce large uncertainties. McNeil et al. (p. 235) present a global oceanic anthropogenic CO2 uptake estimate from 1980 to 1999 based solely on oceanic observations of chlorofluorocarbons (CFCs), a technique that is independent of the confounding assumptions in the O2/N2 method about terrestrial and oceanic effects. They validate their CFC method with direct observations of anthropogenic CO2 accumulation in the ocean and estimate its uncertainties using a general ocean circulation model.

  4. Ocean Currents Seen from Space

    Seawater is an electrically conducting medium, so as ocean currents move through Earth's magnetic field, they induce electrical currents. These electrical currents generate secondary magnetic fields that now can be measured remotely from space by satellites. Tyler et al. (p. 239) report remote detection of the M2 tide (the main lunar semidiurnal component of ocean tides) made with the CHAMP satellite. These observations open the door to more extensive remote monitoring of ocean flow from space.

  5. How a Forest Grows

    It is currently not known whether the floristic composition in Amazonian forests is homogeneous (dominated by successful species), randomly fluctuating (driven by neutral processes such as dispersal), or patchy (as suggested by niche-based models). Previous inventories represented too few sites to provide conclusive tests, but now Tuomisto et al. (p. 241) present an analysis of a data set that is unprecedented in both its extent and internal consistency. Data from 163 sites from western Amazonia concentrate on ferns and the angiosperm family Melastomataceae. Forests are not floristically homogeneous even within the structurally uniform areas, and a high proportion of the floristic variation can be explained and understood in terms of environmental determinism and, to a lesser extent, neutral processes such as dispersal.

  6. A Small Activator of Apoptosis

    The mitochondrial caspase activation pathway regulates caspase-9, a protease that is required for programmed cell death. Various apoptotic stimuli can release cytochrome c from mitchondria and activate caspase-9 through the formation of a proapoptotic protein complex called the apoptosome. Jiang et al. (p. 223, see the Perspective by Nicholson and Thornberry) discovered a proapoptotic compound through a high throughput chemical screen and then, using a combination of biochemical fractionation and biological tests, identified the molecules responsible for the drug's effect. An oncoprotein called prothymosin-a and a tumor suppressor protein called PHAP (for putative HLA-DR-associated proteins) inhibited or accelerated the apoptosome-caspase-9 pathway, respectively. The study points to the apoptosome as a potential target for drug development.

  7. Assembling Outer Membrane Proteins

    The outer membrane proteins (OMPs) of Gram-negative bacteria assemble after their trek from the cytosol through the inner membrane into the periplasm. The molecular mechanisms involved in this assembly have not been well understood. Voulhoux et al.(p. 262) describe the role of a protein termed Omp85 in OMP assembly. Cells lacking Omp85 were not viable and accumulated unassembled forms of a variety of OMPs. Omp85 is related to a component of the chloroplast protein import machinery.

  8. Instructing the Pupils

    The retinal pigment melanopsin is found in ganglion cells, which are downstream of the classic rods and cone photoreceptors of the visual system. By making knockout mice lacking melanopsin, Lucas et al. (p. 245, see the Perspective by Menaker) show that this pigment likely responds directly to light in order to contribute to non-image-forming functions of the visual system, in particular, the contraction of pupils to a sudden bright light.

    CREDIT: LUCAS ET AL.
  9. Faulty Connections Between Circulatory Paths

    The parallel circulatory systems of blood and lymph separate during development through the differentiation of blood vessel endothelium. Abtahian et al. (p. 247, see the Perspective by Jain and Padera) now show that this separation depends on specific intracellular signaling proteins—SLP-76 and Syk—known to be required for correct lymphocyte and platelet function. Abnormal connections between blood and lymphatic vessels occurred in mice lacking either protein and led to severe circulatory defects and hemorrhage. Surprisingly, expression of SLP-76 was not detected on endothelial cells, and abnormal connections occurred in wild-type mice that had been irradiated and received SLP-76-deficient bone marrow. These results suggest that cells of a hematopoietic lineage are required to help coordinate separation of the two vascular systems.

  10. Lord of the DNA Rings

    The bacterium Deinococcus radiodurans can tolerate extraordinary levels of ionizing irradiation, yet this bacterium encodes a normal battery of DNA repair enzymes. Levin-Zaidman et al. (p. 254) now suggest that the key to radioresistance may be the unusual way the bacterial genome is packaged. The D. radiodurans genome adopts a tightly packed, ring-like morphology that may restrict diffusion and therefore physically facilitate the accurate rejoining of DNA fragments produced by irradiation.

    CREDIT: LEVIN-ZAIDMAN ET AL.
  11. Out of Rhythm

    Atrial fibrillation (AF), a common rhythm disturbance in the heart, is increasing in prevalence as the population ages, yet little is known about its molecular pathogenesis. Chen et al. (p. 251) studied a large family in China with hereditary AF and identified the culprit gene as KCNQ1 on chromosome 11p15.5. KCNQ1 encodes a potassium channel subunit that has been previously linked to the pathogenesis of familial ventricular fibrillation and long QT syndrome. Importantly, the KCNQ1 mutations in the latter disorders lead to loss of channel function, whereas the mutation in the AF family produces a gain of function. Thus, alterations in a single ion channel can evoke distinct heart arrhythmias, a finding that may have important implications for the pharmacologic treatment of these disorders.

  12. Health Through Ribosomal RNA Modification

    Dyskeratosis congenita (DC) is an inherited disorder associated with bone marrow failure, skin defects, and a heightened susceptibility to cancer. Human genetic studies have implicated two genes: DKC1, which encodes a putative pseudouridine synthase that modifies ribosomal RNA (rRNA), and TERC, which encodes the RNA component of telomerase. Studying a mouse mutant expressing a defective allele of DKC1, Ruggero et al. (p. 259) show that the clinical features of DC, including tumor formation, are caused by defects in rRNA modification and can be temporally dissociated from the defects in telomere function, which occur much later. Thus, DC is likely initiated by aberrant production of ribosomes; telomere defects modify or exacerbate the disease.

  13. Double-Strand Breaks and Bloom Syndrome

    Patients with Bloom Syndrome (BS) display genomic instability and a predisposition to cancer. In the fruit fly Drosophila, Blm mutants show similar genomic instability and may provide a good model for understanding the cellular role of Blm, a RecQ helicase. In Drosophila, most DNA double-strand breaks are repaired by a homologous recombination pathway termed synthesis-dependent strand annealing (SDSA). Adams et al. (p. 265) show that the absence of Drosophila Blm leads to repair by pathways that are more error prone and that can result in large deletions

  14. Quantum-Mechanical Salts

    Quantum phase transitions, in which a material can be made to undergo a transition from one phase to another at zero temperature under the stimulus of an external parameter, are actively studied because they may provide better insight into other highly correlated systems. Much of the search is concentrated in the effort of designing, fabricating, and characterizing new test systems. Horiuchi et al. (p. 229) present results on expanded lattice charge-transfer salts and show that pressure and temperature dependence reveal the ability to tune the quantum critical point with external pressure. They provide evidence showing that the system exhibits a neutral-ionic quantum phase transition in which the covalently bonded molecules in the neutral phase can be transformed into an ionic system with the charge and spin reside on the donor and acceptor molecules of the salt complex.

  15. Oxidative Stress and Early-Onset Parkinson's Disease

    In Parkinson's disease, motor abnormalities develop as dopaminergic neurons of the nigrostriatal pathway in the brain die. Bonifati et al. (p. 256) identify mutations in a gene called DJ-1 in an Italian and a Dutch family with an early-onset autosomal recessive form of Parkinson's disease. Although the function of DJ-1, a ubiquitously expressed and highly conserved protein, is unknown, there is indirect evidence that it is involved in the cell's response to oxidative stress.

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