This Week in Science

Science  02 Mar 2007:
Vol. 315, Issue 5816, pp. 1189
  1. Bring Some Order to an Explosion


    The Lophotrochozoa, which comprise mollusks, worms, brachiopods, bryazoans, and several other animals, played a large role in the Cambrian explosion. Their origins and early relations are uncertain, but bear on the pace and magnitude of Cambrian evolution, and a key issue has been the origin of several enigmatic lophotrochozoans from the Burgess Shale, principally the halkieriids and wiwaxiids. Conway Morris and Caron (p. 1255) describe several examples of a new fossil species from the Burgess Shale that seems to unite these two groups and implies an early evolution of mollusks.

  2. Insights into Hurricane Intensity

    Predicting how a hurricane's intensity will change duing its lifetime is challenging, in part because of difficulties in forecasting how the internal structure of the storm will evolve. Houze et al. (p. 1235; see the Perspective by Willoughby) examine a key component of that process, “eyewall replacement.” They document in great detail the eyewall-replacement cycle in Hurricane Rita using high-resolution airborne radar observations of wind speed as well as temperature, humidity, and pressure data, and develop a conceptual model for this process. They also suggest how obtaining specific data on small-scale structure of hurricanes could improve forecasting of intensity changes.

  3. Water from the Ground Up

    The simple structure of the water molecule belies the extreme complexity of the interactions responsible for the properties of the bulk liquid. In general, theoretical analysis of liquid water relies on potential energy functions derived at least in part from experimentally measured parameters. Bukowski et al. (p. 1249; see the Perspective by Stone) present a water potential function derived purely from quantum-mechanical interaction forces, with no experimental inputs. Using this function, they calculate the absorption spectrum of the water dimer to high accuracy, and also reproduce the radial distribution functions and thermodynamic properties of the bulk liquid relatively well.

  4. Electrons in Sharper Focus


    The fabrication of metamaterials that give rise to negative refractive index for electromagnetic radiation has been used to image objects smaller than the conventional diffraction limit, and such materials hold the promise of creating the “perfect lens” that could achieve extremely fine focusing. Cheianov et al. (p. 1252; see the Perspective by Pendry) carry over the principle of the perfect lens and negative refraction to electron flow. They show theoretically that a graphene sheet, which makes electrical contacts such that one side is p-type and the other n-type, should be able to focus the flow of electrons as they pass through the pn-junction. They argue that such an effect could lead to novel applications in electron optics such as electron-beam splitters and lenses.

  5. Towers to Track the Sun

    Both archaeological sites and written and spoken records document that the Incas were making careful solar observations about 500 years ago, but evidence for earlier observational activity has been difficult to obtain. Ghezzi and Ruggles (p. 1239; see the news story by Mann) now describe a series of 13 stone towers that date to 2400 years ago that are arrayed north-south along a hill in the center of a temple complex in coastal Peru, and show that these towers marked the annual rising and setting arcs of the Sun and served as a calendar accurate to a few days. Thus, these towers and the surrounding temple evidently served as an early solar observatory.

  6. Organic Aerosol Evolution

    The abundance and chemical nature of most urban organic aerosols have been thought to be primary in nature—that is, determined at their sources—and essentially static. Robinson et al. (p. 1259) combine observations and models to show that the life histories of organic aerosols are much more complex, and that large numbers of those particles have gone through a cycle of evaporation, photooxidation, and recondensation. Thus, existing theories of organic aerosol distributions, while in many cases match observations fairly well, may often be getting the right answers fortuitously. This improved understanding of organic aerosol behavior could lead to important changes in the ways that they are measured and emissions are regulated.

  7. Rejuvenating the Human Sense of Smell

    Active neurogenesis from neural progenitors continues throughout life in discrete regions of the central nervous system of most mammals. However, human adult neurogenesis is still a contentious issue. Signs of adult neurogenesis have been reported in the hippocampus, but a second neurogenic niche described in rodents has not been found in recent human studies. Now, however, using multiple techniques, Curtis et al. (p. 1243, published online 15 February; see the cover) not only describe this missing rostral migratory stream in great detail but also show that it is organized around a tubular extension of the lateral ventricle that reaches into the olfactory bulb.

  8. Prokaryotic DNA Segregation

    The prokaryotic actin-like protein ParM is dynamically unstable and is thought to play a role in DNA segregation. Garner et al. (p. 1270) describe the complete reconstitution of DNA segregation in vitro using purified components. ParM, together with DNA and a DNA-binding protein, generate a bipolar spindle that can promote the directional movement of DNA and can explain in vivo DNA movements. Thus, a dynamic filament protein can mediate DNA movement in prokaryotes.

  9. Drugs, Dopamine, and Disposition


    Individual differences in drug abuse reflect distinct behavioral and physiological traits. Dalley et al. (p. 1267) found that, compared to controls, spontaneously impulsive rats had decreased dopamine D2/3 receptors in the nucleus accumbens even before exposure to cocaine. Trait impulsivity in rats was predictive of subsequent high rates of intravenous cocaine self-administration. Impulsivity is thus an important mediator of drug abuse vulnerability and not a consequence of chronic drug exposure.

  10. The Heart of Metabolic Syndrome?

    Patients with coronary artery disease (CAD) often have accompanying hypertension, diabetes, and aberrant levels of cholesterol and triglycerides. This diverse group of risk factors is collectively known as “metabolic syndrome,” but the underlying molecular mechanisms that link these disorders are still poorly understood. Mani et al. (p. 1278), have now identified the causative mutation in a family afflicted with a rare, inherited form of early-onset CAD that cosegregates with many features of metabolic syndrome. The culprit gene encodes low-density lipoprotein receptor-related protein 6 (LRP6), a co-receptor in the Wnt cellular signaling pathway.

  11. Reconstituting Transport Proteins

    The few available crystal structures of membrane-transport proteins generally reveal internal symmetry, either about an axis perpendicular to the membrane or, somewhat more surprisingly, about an axis within the plane of the membrane. Transporters in the first class contain two structurally similar domains that exhibit the same membrane topology, which yields an even (2n) number of membrane-spanning helices, whereas those in the second class have oppositely oriented domains and an odd (2n+1) number of helices. By making stepwise modifications to the bacterial drug efflux pump EmrE, Rapp et al. (p. 1282, published online 25 January; see the Perspective by Poolman et al.) show how a functional dimer might evolve from a monomer (containing n helices) that can have either membrane topology.

  12. Local Affects on Virulence

    For public health purposes, controlling infectious diseases requires a clear idea of the processes that select parasite infectivity and virulence. One key assumption is that parasites that are circulating locally in slowly mixing populations will evolve to be less infective and virulent. The converse is that as the host-parasite world becomes more connected and populations more mixed, more dangerous parasite strains will be selected. Boots and Mealor (p. 1284; see the Perspective by Buckling) test the first assumption in an easily manipulated system using a virus that infects caterpillars and verify that the host populations least able to move harbor the least infective strains of virus.

  13. Variation on Synaptic Potentiation

    Synaptic changes linked to associative learning are well known. Lamsa et al. (p. 1262) examined long-term synaptic plasticity in different types of interneurons in rat hippocampal slices. They discovered an induction rule for long-term potentiation (LTP) that shows unusual characteristics. In contrast to known forms of plasticity, pairing synaptic input with hyperpolarization resulted in LTP, whereas pairing it with depolarization prevented it.

  14. Interfering with Interferon

    The early host response to viral infection is regulated by the type I interferons (IFNα/β), which are induced after detection of virus-specific products. The subsequent transcriptional response is mediated via the Janus kinase-signal transducers and activators of transcription (JAK/STAT) pathway, which controls transcription of a range of interferon-stimulated genes (ISGs). The IKK-related kinases TBK (TANK-binding kinase) and IKKϵ (an inhibitor of nuclear factor κB kinase) are also integral components of the IFNβ pathway. However, tenOever et al. (p. 1274) reveal that although mice deficient in IKKϵ are susceptible to viral infection, this susceptibility is not because of a loss of IFNβ expression. Rather, the deficiency resulted from an unanticipated downstream effect in which IKKϵ prevents homodimerization of STAT-1 by its phosphorylation. Instead, STAT-1 was incorporated into a heterotrimeric complex transcribing a distinct set of ISGs.