This Week in Science

Science  09 Sep 2011:
Vol. 333, Issue 6048, pp. 1357
  1. Hum Along with Me


    During courtship, male hummingbirds make dramatic aerial dives that are accompanied by loud “songs” produced by the birds' tail feathers. These songs differ among species, suggesting that unique feather morphology contributes to song production. Clark et al. (p. 1430) placed tail feathers from 14 hummingbird species in a wind tunnel and used a scanning laser doppler vibrometer to measure aeroelastic flutter, which occurs when aerodynamic energy causes an airfoil to vibrate. Feather shape influences the sounds produced by this flutter. Thus, species-specific aeroelastic flutter has become essential to courtship.

  2. Small Steps

    The transition in human ancestry from Australopithecus, the genus that existed for 2 million years before Homo, has been enigmatic. A key fossil from near the time of this transition is Australopithecus sediba, which is represented by several specimens discovered in a cave in South Africa. Five reports in this issue discuss important features of the A. sediba fossils, including some that are not well-preserved in other similar hominid remains (see the News stories by Gibbons and Balter). Pickering et al. (p. 1421) show that fossils date to just less than 2.0 million years ago. Kibii et al. (p. 1407) argue that pelvis architecture had begun to evolve toward the Homo condition despite its small brain size of A. sediba. Carlson et al. (p. 1402) describe a brain endocast, which exhibits signs of gradual evolution toward modern brains without enlargement. Kivell et al. (p. 1411) and Zipfel et al. (p. 1417) describe the anatomy of the hands, feet, and ankles, which indicate that A. sediba may still have moved within trees.

  3. Trading Protein for Water

    Migrating birds fly for long periods of time without stopping and are fueled largely by the metabolism of fat; however, high levels of activity require more than just energy, and water is essential for prolonged flight. Migrating birds are known to lose both fat and lean mass, and it has been suggested that protein catabolism, which generates fivefold more water than fat metabolism, may provide endogenous water during extended flights. Gerson and Guglielmo (p. 1434) tested this hypothesis in Swainson's thrushes within a flight tunnel and found that birds flying in dry conditions burn more lean mass than those flying in more humid conditions. Even in very dry conditions over extended flights the birds experienced no water stress, suggesting that they were indeed able to endogenously satisfy their water needs. This mechanism helps to explain why reductions in muscle and organ mass, which at first seem maladaptive, are commonly observed in migrating birds.

  4. All in the Pool

    Catalysts for organic coupling reactions are often developed using one or two simple test substrates, and then afterwards probed in more detail to determine their compatibility with more elaborate molecular structures. Robbins and Hartwig (p. 1423; see the Perspective by Montgomery) showcase a different approach, in which they screened an array of metal and ligand combinations on a mixture of over a dozen different substrates that encompass a wide variety of different chemical functional groups. The substrates were restricted to a narrow molecular weight range, which meant that coupled products fell outside the mass range of any individual reactant, and were detected by simple mass spectrometric screens. Preliminary application of this technique uncovered copper-catalyzed hydroamination and nickel-catalyzed hydroarylation reactions of alkynes.

  5. Tug at the Heart Strings

    When the heart fills with blood, the muscle cells relax and stretch. To find out how individual heart muscle cells, or cardiomyocytes, respond to stretching, Prosser et al. (p. 1440; see the Perspective by Hidalgo and Donoso) suspended single rodent cardiomyocytes between glass rods, stretched them just a little, and monitored the release of tiny amounts of calcium through channels known as ryanodine receptors. Loading the cells with fluorescent dyes sensitive to the binding of calcium or reactive oxygen species (ROS) revealed that activation of the enzyme nicotinamide adenine dinucleotide phosphate oxidase 2 triggered ROS generation, which then led to opening of the ryanodine receptor pore. Cells from animals with muscular dystrophy showed excessive calcium release, which may contribute to impaired muscle function.

  6. Ice Streams


    The great majority of the ice on our planet is located on the continent of Antarctica. It is of great interest to know how the Antarctic ice sheet is evolving with time, since the climate is warming so quickly and the melting polar ice sheets have such a large potential effect on sea level. Rignot et al. (p. 1427, published online 18 August; see the Perspective by Cuffey) present a high-resolution digital map of ice motion for the Antarctic continent constructed from satellite data collected from 2007 to 2009. This analysis shows how ice sheet flow predominantly consists of a complex network of tributaries that originate near topographic divides and which slip over the underlying rocky bed within narrow channels.

  7. Packing Chromosomes

    Bacterial chromosomes are known to be confined within submicron-sized nucleoids somehow. Wang et al. (p. 1445) used super-resolution fluorescence microscopy to work out how the major chromosomal organizing elements—the nucleoid-associated proteins (NAPs)—are distributed in live Escherichia coli cells. While four of the NAPs were distributed uniformly throughout the nucleoid, one (H-NS, a global transcriptional silencer) formed two nanometer-scale nucleoprotein clusters on each chromosome together with the genes it regulates.

  8. Breathing Room


    Stomata, which provide pores for gas exchange, are usually evenly distributed across the surface of the plant leaf epidermis. Robinson et al. (p. 1436) present a model that reveals a limited number of cellular parameters that guide the development of stomata in young Arabidopsis leaves. The size of the cell when it initiated division, the symmetry, or lack thereof, shown by the division plane, and the orientation of the new cell wall relative to previous cell walls, are all features that determine the layout of the tissue. These interactions culminate in each stomata being surrounded by cells of the same lineage and having enough room to open and close.

  9. Translation Checking

    The eukaryotic ribosome is assembled from four RNAs and 78 ribosomal proteins, and assembly is facilitated by about 200 assembly factors. Strunk et al. (p. 1449, published online 11 August) have provided insight into the final maturation of the small (40S) ribosomal subunit in the cytoplasm by using electron cryo-microscopy to determine the structure of the assembly intermediate and to determine the positions of seven bound-assembly factors. These assembly factors are positioned to inhibit multiple steps required for the initiation of translation, probably to ensure that incomplete 40S particles do not enter the translation pathway.

  10. Heads, Tails, and Brain Tumors

    Oligodendrogliomas are common adult brain tumors with a poor prognosis. A characteristic chromosomal aberration in these tumors has led to speculation that chromosomes 19q and 1p harbor tumor suppressor genes that, when inactivated, contribute to tumorigenesis. Bettegowda et al. (p. 1453, published online 4 August) applied an exome sequencing strategy to these cancers and found recurrent somatic mutations in the CIC gene on chromosome 19q and the FUBP1 gene on chromosome 1p, indicating that these are the long-sought-after tumor suppressors in oligodendrogliomas. CIC is the homolog of the capicua gene in the fruit fly Drosophila, where it encodes a transcriptional repressor whose inactivation produces embryos that have head and tail structures but no intervening segments. FUBP1 codes for a protein that binds DNA, including the regulatory region of the MYC oncogene.

  11. Mind Blowing

    The mammalian brain develops more neurons and more synapses than it knows what to do with. Early development is characterized by both loss of neurons and pruning of synapses. Paolicelli et al. (p. 1456, published online 21 July; see the Perspective by Ransohoff and Stevens) have identified the type of cell that is responsible for synaptic pruning in mice. Microglia, which are mobile and phagocytic, seem to be responsible for vacuuming up excess synaptic material. Mice with disabled microglia have abnormally large numbers of synapses, changes in synaptic plasticity, and altered susceptibility to seizures.

  12. Reaching for Light

    During the development of Drosophila larvae, a set of neurons in the brain depend on environmental signals transmitted through the light-sensing Bolwig's organ. Yuan et al. (p. 1458) show how the effects of light signaling translated into alterations in the shape of the neurons. Larvae reared in total darkness have target neurons with longer dendrites than those of larvae reared in the light. The differences in shape were confirmed to be a response to light exposure and not to circadian rhythms. Analysis of mutant flies indicated that the signaling pathways involved in transducing the light signal into cell morphological changes were similar to those acting by learning and memory.

  13. Unraveling Neuropathic Pain

    Neuropathic pain results from nerve damage and is evoked by trauma in conditions ranging from shingles and diabetes to cancer chemotherapy, but the mechanisms remain poorly understood. By using gene knockouts in animal models, Emery et al. (p. 1462) found that a member of the HCN ion channel family is important in both inflammatory and neuropathic pain. This discovery opens up the possibility of developing specific antagonists to treat neuropathic pain.

  14. Uncertain Times Illustrated

    The uncertainty of whether or not you get rained on at your wedding or the ball game can be expressed mathematically as probability. Probabilities are notoriously hard to broadcast to a general public possessing a wide range of mathematical understanding. Knowing that pictures can say more than words, Spiegelhalter et al. (p. 1393) review the types of graphic illustrations available for explaining some of the uncertainties of the world we live in and offer a range of examples for illustrating scientific knowledge in a variety of media that can be optimized to promote understanding among different audiences.