This Week in Science

Science  09 Mar 2012:
Vol. 335, Issue 6073, pp. 1145
  1. Bee Adventurous

    CREDIT: ZACHARY HUANG/ HTTP://BEETOGRAPHY.COM

    Individuals differ in their behavior, sometimes in consistent ways. For example, some people may seek out new experiences, while others prefer to stick with what they know. This is true in bees as well, where some workers take on the dangerous, novelty-seeking task of scouting more often than others. Liang et al. (p. 1225) found that bees that display such scouting behavior not only tend to scout in multiple contexts (both foraging and searching for nests) but also show differences in gene expression in their brains. Experimental manipulation of gene expression predictably changed scouting behavior. The molecular underpinnings of bee scouting behavior appear to be similar to those associated with novelty-seeking in vertebrate species, including humans.

  2. Mechanics of a Meltdown

    For all the potential hazards presented by nuclear power plants, there have been very few incidents that have caused human or environmental harm. However, those that have happened have often had disastrous consequences, for example, the accidents at Chernobyl in Ukraine and, just last year, at Fukushima Daiichi in Japan. Burns et al. (p. 1184; see the cover) review the state of knowledge on the chemical and physical processes following the nuclear reactor accident and how these results may inform decision-making during future events. Because a large portion of prior research has focused on radionuclide transport following leaks from nuclear waste repositories, and not active reactors, experiments at the more extreme conditions experienced in major nuclear core-melt accidents may have more predictive value.

  3. Lessons from SIV

    HIV infection in humans is a chronic infection and, if left untreated, the majority of infected individuals will succumb to AIDS. Many species of African nonhuman primates are chronically infected with simian immunodeficiency virus (SIV); however, in the majority of these species, the animals remain healthy despite the presence of high viral loads. Chahroudi et al. (p. 1188) review the underlying immune mechanisms that help protect natural hosts from progressing to AIDS and how these responses differ from what is observed in HIV-infected humans and SIV-infected nonhuman primate species that develop AIDS.

  4. Smooth Operator

    CREDIT: KIM ET AL.

    When thin sheets are compressed they can buckle and wrinkle, such as when the edges of a sheet of paper, or two areas of skin, are pushed together. Variations in local thickness and stiffness will alter the buckling patterns, but controlling this in a simple and predictable way is difficult. Kim et al. (p. 1201; see the Perspective by Sharon) used halftone lithography with two photomasks to create highly cross-linked dots embedded in a lightly cross-linked matrix of a swellable polymer. This material could generate “smooth” swelling profiles on thin sheets with arbitrary two-dimensional geometries so that complex three-dimensional structures could be produced.

  5. Making Immune Cells Young Again

    Hematopoiesis, the development of the immune system, occurs in distinct waves. The immune system is first populated by cells that arise from fetal hematopoietic stem cells (HSCs) and then later by cells derived from adult HSCs. Furthermore, fetal HSCs give rise to lymphocytes with innate immunelike properties, whereas adult HSCs give rise to classical T and B cells. Yuan et al. (p. 1195, published online 16 February) now uncover the molecular mechanism behind these distinct waves of hematopoiesis. Expression of the RNA binding proteins Lin28 and Lin28b is enriched in fetal hematopoietic stem/progenitor cells (HSPCs) in mice and humans. Ectopic expression of Lin28 in mouse adult HSPCs was sufficient to induce the differentiation of both classical and innate-like lymphocyte lineages.

  6. A Useful Cover-Up

    Many industrial catalysts that consist of metal nanoparticles adsorbed on metal oxide supports undergo deactivation after prolonged use. Organic reactants can decompose and cover the metal with carbon (“coking”), and other processes can push the size distribution to fewer but larger particles that have less overall surface area available for reaction (“sintering”). Lu et al. (p. 1205) used atomic-layer deposition to apply a uniform overlayer of alumina onto supported palladium nanoparticles. This coating greatly increased the resistance of the nanoparticles to coking and sintering during the oxidative dehydration of ethane to ethylene.

  7. Tuning Hydrogen Adsorption

    Heterogeneous metal catalysts for hydrogenating unsaturated organic compounds need to bind molecular hydrogen strongly enough that it dissociates and forms adsorbed hydrogen atoms, but must not bind these atoms too strongly, or the transfer to the organic molecule will be impeded. Kyriakou et al. (p. 1209) examined surface alloy catalysts created when palladium (Pd) atoms are adsorbed on a copper (Cu) surface using scanning tunneling microscopy and desorption techniques under ultrahigh vacuum conditions. The Pd atoms could bind hydrogen dissociatively—which, under these conditions, the Cu surfaces could not—allowing the Cu surface to take up adsorbed hydrogen atoms. These weakly bound hydrogen atoms were able to selectively hydrogenate styrene and acetylene.

  8. Bringing Magnetic Materials to the Moon

    The Apollo missions to the Moon revealed that portions of the lunar crust are strongly magnetized. Lunar rocks are poor at recording the magnetic field, thus these magnetic anomalies have been difficult to explain. Based on numerical simulations of large-scale impacts, Wieczorek et al. (p. 1212; see the Perspective by Collins) show that the vast majority of lunar magnetic anomalies can be explained by highly magnetic materials that originated outside the Moon and were delivered by the asteroid that hit the Moon and formed the South Pole–Aitken basin, the largest impact basin in the solar system.

  9. A Price of Civilization

    Large expanses of rainforests in parts of Central Africa were abruptly replaced by savannas around 3000 years ago, presumably because of climate change. However, that succession occurred at a time of expansion by Bantu tribes, from near the border of present-day Cameroon and Nigeria to the south and east, in a migration that brought with it agriculture and iron-smelting technologies. Bayon et al. (p. 1219, published online 9 February; see the Perspective by Dupont) analyzed the nearby marine sedimentary record and found that chemical weathering in Central Africa also increased markedly at this time. This increase in weathering could have been caused by forest clearing by the Bantu to create arable land and to fuel their smelters, rather than climate change alone.

  10. Avoiding Infanticide

    In male dominated hierarchies, newly dominant males will sometimes kill resident infants. In lab studies in mice conducted in the 1950s, Hilda Bruce showed that females introduced to an unfamiliar male will terminate their pregnancies, a process subsequently referred to as a Bruce Effect. Roberts et al. (p. 1222, published online 23 February) followed multiple dominance transitions within wild gelada baboons and showed that live birthrate among females previously identified as pregnant within unstable groups was much lower than within stable groups. Furthermore, females that terminated their pregnancies following transitions had a much shorter interbirth interval than those that did not, suggesting a higher overall reproductive success and fitness.

  11. A Time and a Place

    CREDIT: CHRIS HIGGINS/UNC CHAPEL HILL AND LIANG GAO/JANELIA FARM

    The onset of morphogenetic cell shape changes is thought to be triggered by initiation of actomyosin contractions. Roh-Johnson et al. (p. 1232, published online 9 February; see the Perspective by Razzell and Martin) have now discovered in both Caenorhabditis elegans and Drosophila embryos that the actomyosin contractions driving morphogenesis run constitutively, only being engaged to trigger cell shape changes at a specific time during development.

  12. Nucleosome Maps and Mutation

    Understanding the processes governing the accumulation of mutations impacts many facets of evolutionary biology. Combining data from a mutation accumulation experiment in a DNA repair-deficient yeast strain with genome-wide substitution, Chen et al. (p. 1235) demonstrate that C/G to T/A changes are more likely to affect regions that are nucleosome-free. Furthermore, a similar pattern was seen when comparative analyses were performed among yeast species and in lines of Medaka fish and nematodes. The results are consistent with a model in which DNA bound by nucleosomes is protected against mutations caused by DNA damage.

  13. Neurogenesis and Pattern Integration

    The adult hippocampus continuously produces new neurons that integrate into the dentate gyrus network and contribute to information processing. What features of adult-born neurons are important for information processing in the dentate gyrus? Marín-Burgin et al. (p. 1238, published online 26 January; see the Perspective by Kempermann) labeled newborn neurons and used sophisticated electrophysiological and imaging techniques to show that immature neurons integrated a broader variety of synaptic inputs from different origins compared with mature neurons, which were highly input specific. Thus, immature neurons may represent a population of integrators that are broadly tuned during a transient period and may encode most features of incoming information. After maturation, new granule cells display a high activation threshold and input specificity to become good pattern separators.

  14. Flashy Feathers

    Feather colors play key roles in the lives of birds, functioning in everything from camouflage, to thermoregulation, to sexual signaling. Much recent research has revealed that some dinosaurs also had feathers, and examination of feather components in fossil and preserved feathers has begun to reveal how feather color may have played a role in the lives of these dinosaurs. Li et al. (p. 1215) compared the characteristics of the melanosomes of the paravian dinosaur Microraptor to those found in extant birds, which suggest that its feathers were black and iridescent. The existence of this subtle color reflectance, together with morphological aspects of the feathered tail, suggests an important role for signaling in the early evolution of feathers.

  15. A Toxic Barrel

    Many studies have suggested that oligomers are an important toxic species in amyloid diseases such as Alzheimer's disease. In an effort to better define these oligomers, Laganowsky et al. (p. 1228) identified a segment of the fibril-forming protein αB crystalline (ABC) that forms both amyloid fibrils and a relatively stable oligomer. ABC oligomers were toxic in a cell viability assay and were recognized by an amyloid-oligomer–specific antibody. A crystal structure of the oligomers showed that six peptides formed an antiparallel barrel termed a cylindrin. Amyloid oligomers are likely to be structurally polymorphic, but cylindrin-like assemblies offer a model for these elusive structures.