This Week in Science

Science  18 Jul 2003:
Vol. 301, Issue 5631, pp. 273
  1. Sulfur Puzzles

    In addition to their adverse health effects, sulfate aerosols exert a large influence on cloud formation and therefore on Earth's climate. Models for the formation of sulfate aerosols on a global scale generally underestimate their abundance. Laskin et al. (p. 340) present results from laboratory simulations which show that OH reacts with NaCl, the major component of sea-spray particles, to generate OH in the particles. This process buffers the pH within the particles and causes certain reactions to “self-quench,” and ultimately leads to increased production of sulfate. This mechanism may also clarify a number of other puzzling observations about the chemical composition of sea-salt aerosols.

  2. A Forceful Approach to Biological Assays

    The forces that hold biological macromolecules together (such as DNA stands or muscle protein fibers) are typically in the piconewton range. The measurement of these forces normally requires much time and calibration, but Albrecht et al. (p. 367) describe a differential methodology that rapidly compares relative forces. Short single DNA strands are attached to a surface and to an atomic force microscope tip, and a third longer strand with complementary ends and a fluorescent label is allowed to bind. After the tip is removed, the end with the stronger attachment retains the fluorescent label. The method can be used to detect a single mismatch in a 20-base pair DNA strand. Furthermore, a standardized set of DNAs, coupled to one member of a pair of interacting proteins, makes it possible to vary the range of forces and to assess the relative binding strengths of mouse and human antibodies raised against interleukin-5 for the mouse and human interleukin-5 species.

    CREDIT: ALBRECHT ET AL.
  3. Getting a Charge into Water

    The fundamentals of the interaction of water with ions are the focus of two reports (see the Perspective by Robertson et al.). The addition of large amounts of salt to water can change several of its bulk properties, such as viscosity, and the classical explanation has been that the ions either enhance or disrupt the hydrogen-bonding network. Studies examining such changes at a molecular level have begun to question this model. Omta et al. (p. 347) used ultrafast spectroscopy to measure changes in orientational correlation times of water molecules in pure water versus several molar salt solutions. They find no appreciable changes in the correlation times for water molecules in high salt other than the ones in the first solvation shell of the ions. They argue that the changes in bulk effects are caused instead by rheology of the larger clusters that nucleate around ions. The traditional view of acid-base neutralization in water is that the two species diffuse toward each other until they are close enough to transfer a proton and diffuse away. However, diffusion is slower than the actual proton transfer step, so verifying this model has been difficult. Rini et al. (p. 349) switched on the proton transfer optically by using a molecule that changes its acidity by several pH units after photoexcitation. They then followed the subsequent steps with femtosecond mid-infrared spectroscopy and resolve the difference between a slow transfer step when there are water molecules between the acid and the base and very fast kinetics when the species are already in direct hydrogen-bond contact.

  4. Extracting Metallic Nanotubes

    Single-walled carbon nanotubes are synthesized as a mixture of metallic and semiconducting tubes that hampers device fabrication. Krupke et al. (p. 344; see the 27 June news story by Service) show that they can extract a small fraction of the metallic tubes with about 80% purity after dissolving the nanotubes with a surfactant and then performing an electrophoretic separation. Although the process works with very small volumes, it should lend itself to significant scale-up with the microfluidic dielectrophoretic separation cells commonly used in biology.

  5. Tidal Ocean Mixing

    Turbulence in the interior of the ocean cannot account for the degree of ocean mixing that has been observed, and it has been suggested that tidal motion, especially in regions of rough topography, may provide the missing energy needed for mixing. However, it has proven difficult to connect short-scale tidal mixing to ocean mixing quantitatively. Rudnick et al. (p. 355) present results from a series of modeling and observational studies at the Hawaiian Ridge, in which they synthesize and evaluate observations and numerical models covering spatial scales from thousands of kilometers to centimeters. They suggest that consideration of tidal dissipation over rough ocean floor topography makes it possible to account for almost all of the unexplained mixing that occurs in the sea.

  6. Rocking the Fossil Record

    Fossil records can contain potential biases that hamper the reconstruction of the true tree of life. For example, rocks of different ages are not all equally exposed, and so a greater number and diversity of fossils may have been collected for some past eras than others. Crampton et al. (p. 358; see the Perspective by Smith) have used a complete database on New Zealand fossils and outcrops to examine this bias and its effects. Their analysis shows that outcrop area can be used to normalize diversity patterns through time. However, the exact correction depends on the whether an area or time was more stable or was undergoing tectonic activity.

  7. Ready to Become Animals

    The close phylogenetic relationship of multicellular metazoa and choanoflagellates (a group of unicellular and colonial flagellates) may allow for the identification of the minimal set of genes necessary for animal evolution through comparative genomics. King et al. (p. 361) found that choanoflagellates express members of a wide variety of protein families found in animals for cell interactions, signaling, and adhesion. The presence of these factors indicates that key proteins necessary for animal development evolved before the origin of animals.

  8. Boning Up on Hox Genes

    In vertebrate development, the Hox genes, which establish patterns and encode positional information, are found in groups of paralogs. Mutations in individual mouse Hox genes can perturb skeletal elements, but the variable expressivities and penetrance observed with mutations in paralogous Hox genes make it hard to distinguish whether these genes cause patterning at the global or local level. Wellik and Capecchi (p. 363) now report targeted disruptions of all of the alleles of the Hox10 or Hox11 paralogous family to show that Hox genes act in global patterning of the lumbosacral region of the axial skeleton and are integral in patterning principle elements of the limbs.

  9. Mouse Model for Meningitis

    How the bacterial agent for human meningitis, Neisseria meningitidis, crosses an epithelial barrier in the nasopharynx as well as the blood-brain barrier has not been well understood, but it has been known that its pili recognize human cell-surface receptor CD46. Recently, CD46 was suggested to be a link between innate and acquired immunity. Johansson et al. (p. 373) now show that transgenic mice expressing human CD46 are susceptible to meningococcal disease. Further, CD46 is required for spread of bacteria from the nasopharynx to blood and for subsequent transfer across the blood-brain barrier. This transgenic mouse model offers a novel experimental system for rapid analysis of vaccine candidates and for studies of bacterial meningitis.

    CREDIT: JOHANSSON ET AL.
  10. Catalyzing Diabetes Drug Discovery

    One relatively unexplored drug target for type 2 diabetes is the glucose-sensing enzyme glucokinase (GK); mutations that reduce GK activity cause a rare inherited form of diabetes in humans. Grimsby et al. (p. 370; see the news story by Couzin) have identified a class of small molecules that allosterically activate GK. When orally administered to rodent models of type 2 diabetes, these compounds significantly improved glucose tolerance by enhancing glucose-dependent insulin secretion from the pancreas and by stimulating glucose utilization in the liver.

  11. Asymmetric Localization of Cognitive Function

    The neurophysiological basis underlying hemisphere-specific mechanisms of cognitive control in the brain has not yet been fully clarified. In a combined functional magnetic resonance imaging and psychophysical study, Stephan et al. (p. 384; see the Perspective by McIntosh and Lobaugh) used a statistical method of functional connectivity to discern specific, task-related interactions between left-and right-anterior cingulate cortex and specific regions in the left-and right-hemisphere of the brain that are implicated in letter and visuospatial decisions, respectively. Despite identical stimuli, the activation patterns were different depending on the task that was demanded by subjects. The authors conclude that cognitive control mediated by the anterior cingulate cortex is located in the same hemisphere as the areas involved in task execution.

    CREDIT: STEPHAN ET AL.
  12. Deconstructing the Blues

    Stressful life events such as the loss of a job can lead to depression, but not everyone shows this response. A study of a large group of young adults in New Zealand by Caspi et al. (p. 386; see the news story by Holden) provides evidence that stress is more likely to cause depression in individuals who carry a particular allelic variant of the gene encoding the serotonin transporter, a protein that controls serotonin levels at brain synapses. These results reinforce the emerging view that mental illness and other complex diseases cannot always be explained by genetic or environmental factors alone, but more likely arise from an interaction between the two.

  13. Capturing Protein on the Fly

    One goal for microfluidics would be to develop a way to trap or preconcentrate proteins from solution and then release them on demand. Huber et al. (p. 352) have developed a polymer film that can switch thermally from a hydrophilic to a hydrophobic state in less than 1 second. They show that they can achieve differential trapping responses for proteins that can be either kinetically or thermodynamically controlled.

  14. Assigning Protein Functions in Rice

    Draft genome sequences can be used to predict how genes fit into the genome, but the next step is to look at the actual genes that get transcribed. Kikuchi et al. (p. 376) have analyzed an exhaustive collection of complementary DNA clones from the rice strain japonica. From this collection of 28,000 transcribed units, tentative protein function can be assigned for about 75% of them. Comparisons between sequences of the two rice strains, japonica and indica, and also information from Arabidopsis, give insight into how close gene predictions get to reality.

  15. Prisoners of the Light

    The circadian behavior of mammals is regulated by two transcription factors, CLOCK and NPAS2, that are related in sequence but differ in expression patterns. Dudley et al. (p. 379; see Perspective by Green and Menaker) found that NPAS2-deficient mice have abnormal sleep patterns during the night and, in contrast to wild-type mice, were unable to adapt to changes in feeding schedule. This phenotype suggests that their circadian behavior was dictated primarily by the light-dark cycle. These results are consistent with a model in which CLOCK is used for light-controlled rhythms and NPAS2 for sensory-controlled rhythms such as feeding. This duality may allow mammals to be more adaptable to changing environmental conditions.

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