Editors' Choice

Science  14 Jul 2017:
Vol. 357, Issue 6347, pp. 160
  1. Cosmochemistry

    Meteorites formed in two reservoirs

    1. Keith T. Smith

    Jupiter's orbit marks the boundary between the formation reservoirs of two distinct meteorite types.

    CREDIT: NASA

    Meteorites are rocky debris left over from the formation of the solar system, which later fall to Earth. Kruijer et al. measured tungsten and molybdenum isotope ratios for a variety of iron meteorite groups and showed that they separate into two sequences—just like stony meteorites are already known to do. Because iron meteorites require parent bodies that grew massive enough to form metal cores, this dichotomy implies two separate regions in the early solar system where planetesimals formed. The authors speculate that the two reservoirs were respectively within and outside the orbit of Jupiter. If that is correct, the giant planet must have formed rapidly, before the meteorite parent bodies did.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1704461114 (2017).

  2. Neuroscience

    Mechanisms for maintaining mental maps

    1. Peter Stern

    When an animal runs around, some hippocampal neurons are selectively active in specific locations called their place fields. A maplike representation created from many such place fields serves as a navigation mechanism. How such hippocampal maps stabilize is still unknown. Roux et al. investigated a discrete form of high-frequency neuronal oscillations called sharp wave ripples. In a spatial learning task, they focally silenced a subpopulation of hippocampal area CA1 neurons during sharp wave ripple events. The place fields of the silenced neurons were altered, and their spatial information content failed to increase. Control place cells, however, largely kept their spatial correlates and showed increased information after learning. Sharp wave ripple–associated neuronal firing is necessary for stabilizing and refining hippocampal place fields.

    Nat. Neurosci. 20, 845 (2017).

  3. Neurodegeneration

    A microglia type associated with AD

    1. Stella M. Hurtley

    The role of specific subsets of immune cell in the onset and progression of Alzheimer's disease (AD) is poorly understood. Keren-Shaul et al. profiled the entire immune cell population in the brains of wild-type and AD-transgenic (Tg-AD) mice. They identified a microglial cell type (DAM) that is associated with neurodegenerative diseases. The DAM cells contained internalized amyloid-β—presumably promoting its clearance. One key player was the AD-associated risk factor Trem2. Single-cell analysis of DAM in Tg-AD and Trem2−/− Tg-AD mice suggested that activating the DAM program involved two steps. An initial Trem2-independent step involved down-regulation of microglia checkpoints, followed by subsequent activation of a Trem2-dependent program. Activating these disease-associated microglia could possibly help in the future treatment of AD and other neurodegenerative diseases.

    Cell 169, 1276 (2017).

  4. Neurodevelopment

    Late to the party

    1. Pamela J. Hines

    Throughout life, new neurons are added to the brain. Just like people arriving late to a cocktail party, the newbies need to figure out how to integrate with those already embroiled in conversations. The zebrafish brain, already capable of complex visual processing at larval stages, accepts new neurons throughout the fish life span. Boulanger-Weill et al. tracked the location, movement, and functional integration of single newborn neurons in developing zebrafish larvae. Following their own developmental trajectories, newborn neurons began with limited dendritic arbors, no neurotransmitter identity, and spontaneous, but not directed, activity. As each neuron matured, its activity began to parallel that of its more mature neighbors. Spatial tuning curves shifted with further maturation, keeping the overall visual response in balance. Bringing new neurons into the fold seems to require synaptic connection with mature neurons already in place.

    Curr. Biol. 27, 1707 (2017).

  5. Biotechnology

    Bulking up algae for biofuels

    1. Barbara R. Jasny

    Vat of cultured microalgae, such as those used to produce biofuels

    PHOTO: PASCAL GOETGHELUCK/SCIENCE SOURCE

    In theory, algae could be a workhorse for the production of biofuels. When the industrial microalga Nannochloropsis gaditana is starved, it converts carbon to lipid for storage, which can then be extracted and converted to biofuel. However, scientists have been struggling to sustain growth while optimizing lipid production. Now Ajjawi et al. have announced that they can double the lipid content of the algae, without dramatically inhibiting growth. They used CRISPR-Cas9–mediated knockout of transcription factors that could be acting as repressors of lipid production to identify the regulator ZnCys. Rather than knocking out ZnCys completely (which mimicked starvation in its effects on growth), the investigators attenuated its expression. Although this advance is necessary if biofuel production from Nannochloropsis is to become an industrial reality, much more work needs to be done

    Nat. Biotechnol. 10.1038/nbt.3865 (2017).

  6. Nanomaterials

    Growing nanosheets off nanowires

    1. Phil Szuromi

    Junctions between different nanomaterials sometimes display unusual properties that can have applications in optoelectronics and catalysis. Chen et al. used copper sulfide (Cu2−×S) nanowires as templates for growing molybdenum sulfide (MoS2) and selenide (MoSe2) nanosheets, which form at right angles to the nanowire axis. Transmission electron microscopy revealed an epitaxial nanowire/nanosheet interface. After ion exchange with cadmium (Cd2+), the resulting CdS-MoS2 heterostructures were much more active than CdS for the hydrogen evolution reaction with visible light, because MoS2 helped slow electron-hole recombination.

    J. Am. Chem. Soc. 10.1021/jacs.7b03752 (2017).

  7. Conservation

    Bumble bees create a buzz

    1. Julia Fahrenkamp-Uppenbrink

    Foraging bees create characteristic vibrations at frequencies of 120 to 400 Hz. Miller-Struttmann et al. set out to investigate whether the vibrations created by bumble bees can be used to estimate pollination success. They show that physical attributes such as body size and tongue length, which influence pollination success, are correlated with characteristic buzz frequencies. They then used buzz density—that is, the number of buzzes per hour—to estimate pollination services at the landscape scale. Acoustic signatures can thus serve as an inexpensive method to monitor bee populations and assist in their management.

    PLOS ONE 10.1371/journal. pone.0179273 (2017).

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