This Week in Science

Science  09 Oct 2009:
Vol. 326, Issue 5950, pp. 201
  1. Protoplanet 2 Pallas


    With a diameter of 265 kilometers, 2 Pallas is one of the largest bodies in the main asteroid belt. Now Schmidt et al. (p. 275) have characterized its surface and shape using images from the Hubble Space Telescope. Color variations and topography were revealed that are possibly linked to the asteroid's thermal evolution and to the formation of its orbital family—the population of asteroids that share the same properties as 2 Pallas and are thought to be the fragments of a collision. In particular, a large-impact crater was observed that could represent the source of the Pallas family. 2 Pallas represents the third intact protoplanet in the main asteroid belt, joining asteroids 1 Ceres and 4 Vesta.

  2. Monsoon Cave Recordings

    Rocky deposits in caves in central China record the changes over time in the Asian Monsoon through the oxygen isotopic composition of the minerals from which they are formed. These deposits can be precisely dated and provide an absolute time line for climate system changes. Cheng et al. (p. 248; see the Perspective by Severinghaus) present oxygen isotope data from speleothems collected from Sanbao Cave, China, for the three glacial terminations that occurred between 120,000 and 350,000 years ago. The data reveal variations in the amount of precipitation delivered by the Asian Monsoon over time. Comparison of the timing of these changes with corresponding changes in ice core and marine sedimentary records provides mechanistic insights into how variations in insolation affect ice sheets and ice age terminations.

  3. Metabolite Arrays

    Methods suitable for the biochemical analysis of multiple metabolic pathways in mixed samples are in short supply. Beloqui et al. (p. 252) report a method to sample the global metabolic state of an organism or mixture of organisms using an array of more than 1500 metabolites linked to a glass slide. The substrates are linked to the plate so that the reaction of an enzyme with one of the metabolites releases a fluorescent dye, which allows sensitive detection of the enzymatic activity. From a sample with small numbers of a mixture of bacteria, the authors were able to collect DNA, amplify it in a host bacterium, and measure its encoded metabolic activity with the array. Furthermore, by coating the substrates on nanoparticles with a specially designed linker, the authors could trap and purify enzymes that reacted with the immobilized substrate. The metabolite array may be useful in the characterization of environmental samples, in diagnostic procedures, and in enzyme discovery.

  4. Extending Quantum Memory

    Quantum information processing and communication relies on the ability to store, retrieve, and manipulate information stored in quantum memories. In most practical instances, however, the stored quantum information is fragile and susceptible to loss during readout. Jiang et al. (p. 267, published online 10 September) used a combination of quantum logic operations on the electronic spin of a nitrogen vacancy center in diamond to control its interactions with a nearby set of proximal nuclear spins of the carbon network. In this setup, the quantum memory of the electron spin could be made more robust. Extending the lifetime and allowing multiple readouts of the quantum memory should prove a useful technique for quantum information processing.

  5. Ear, Ear

    One defining feature of mammals, distinguishing them from other animals, is the separation of the middle ear from the jaw, which improves hearing sensitivity. Ji et al. (p. 278; see the Perspective by Martin and Ruf) describe an adult Mesozoic fossil mammal, in a lineage that led to both marsupials and placentals, in which the middle ear is still ossified to the jaw. Recent developmental studies have shown that the release of the ear is tied to multiple genes and signaling pathways during development. Together, these data suggest how gene patterning may have led to the early evolution of the mammalian ear.

  6. Peeking at Pathogen Response Networks


    Networks controlling gene expression serve as key decision-making circuits in cells, but the regulatory networks that control dynamic and specific gene expression responses to stimuli are often not well understood. This is particularly true for immune dendritic cells (DCs), which respond to pathogens by mounting elaborate transcriptional responses, and are centrally involved in infectious diseases, autoimmunity, and vaccines. Amit et al. (p. 257, published online 3 September) explored the transcriptional response of dendritic cells to specific classes of pathogens. The transcriptional subnetworks responsible for mammalian dendritic cell responses to different pathogens were identified, and the function of 100 regulators clarified.

  7. Quiet Clock

    Many physiological processes have circadian rhythms driven by a biological clock in the suprachiasmatic nuclei (SCN) of the brain. Within the SCN, some neurons express the molecular components of the clock and others do not. Exactly how the clock mechanism is coupled to neuronal activity is not precisely understood. Investigation of the electrophysiological properties of SCN neurons by Belle et al. (p. 281) found that, contrary to the conventionally expected rapid firing rate of the cells during the day, clock-containing cells tended not to fire, despite being in an electrically excited state. Modeling and experimental characterization of changes in channel activity revealed unexpected electrophysiological properties of the SCN cells requiring a reassessment of how the circadian clock regulates activity of SCN neurons.

  8. Anti-HIV Antibodies

    One of the top priorities for an HIV vaccine is the ability to elicit a broadly neutralizing antibody response, which should provide the best protection against infection. In the 25 years since the discovery of HIV, very few broadly neutralizing antibodies have been identified, and those that do exist were discovered nearly two decades ago. Using a high-throughput culture system, Walker et al. (p. 285; published online 3 September) now identify two additional broadly neutralizing antibodies isolated from a clade A HIV-infected African donor. These antibodies exhibit great potency and, in contrast to other known broadly neutralizing antibodies, are able to neutralize a wide range of viruses from many different clades. The antibodies recognize a motif in the trimerized viral envelope protein that is found in conserved regions of the variable loops of the gp120 subunit. Identification of this motif provides an intriguing new target for vaccine development.

  9. Normally Persistent


    In superconductors, currents are expected to flow persistently without dissipation. Quantum mechanics predicts that such persistent currents should also exist in normal mesoscopic metal rings. However, the predicted effect is small, which has made the detection of these currents difficult. Bleszynski-Jayich et al. (p. 272; see the Perspective by Birge) have developed a sensitive technique based on a nanomechanical resonator. An array of aluminum rings on the end of a resonator was fabricated to monitor the shift in frequency of the resonator as the rings were threaded with quanta of magnetic-field flux, setting up currents in the rings. In agreement with a theoretical scenario put forward over a decade ago, the results could be described with a model based on non-interacting electrons.

  10. Chromosomal Mapping

    The conformation of the genome in the nucleus and contacts between both proximal and distal loci influence gene expression. In order to map genomic contacts, Lieberman-Aiden et al. (p. 289, see the cover) developed a technique to allow the detection of all interactions between genomic loci in the eukaryotic nucleus followed by deep sequencing. This technology was used to map the organization of the human genome and to examine the spatial proximity of chromosomal loci at one megabase resolution. The map suggests that the genome is partitioned into two spatial compartments that are related to local chromatin state and whose remodeling correlates with changes in the chromatin state.

  11. Making Split Decisions

    Development of the vertebrate vasculature has been thought to involve just two mechanisms of blood vessel formation. Herbert et al. (p. 294; see the Perspective by Benedito and Adams) identified a third mechanism in zebrafish in which two distinct, unconnected vessels can be derived from a single precursor vessel. Several vascular endothelial growth factors and signaling pathways, including ephrin and notch signaling, coordinated the sorting and segregation of a mixture of arterial and venous-fated precursor cells into distinct arterial and venous vessels. These findings provide a mechanistic framework for how mixed populations of cells can coordinate their behavior to segregate and form distinct blood vessels.

  12. Containing Neuronal Exuberance

    In rats and mice, around the time of birth, neurons of the central nervous system switch from a growth mode and lose their ability to regenerate. Studying retinal ganglion cells of the rat, Moore et al. (p. 298; see the Perspective by Subang and Richardson) identified a gene, Krüppel-like factor-4 (KLF4), that seems to contribute to the switch. The KLF4 gene belongs to a family of related transcription factors that possess repressive or enhancing effects on axon growth. The combinatorial effect of this family of transcription factors before and after birth may fine-tune the ability of the neurons to extend axons.

  13. Phasing-In Emission

    In keeping with quantum mechanics, the dynamics that ensue when molecules absorb light depend not only on the light's frequency but also its phase, which can manipulate excited state trajectories through interference. Recently, an impressive degree of control has been achieved over complex light absorbers, including proteins, by iteratively adapting the phase of a laser excitation pulse. However, the optimal pulses used are often too complicated to reveal straightforward insights into the systems being manipulated. Kuroda et al. (p. 263; see the Perspective by Batista) applied iterative phase manipulation toward optimizing the photoemission efficiency of a macromolecular donor-acceptor system, followed by statistical analysis to isolate a fairly simple phase function underlying much of the control mechanism. Careful follow-up experiments revealed an intuitive picture of the excited state behavior.