Editors' Choice

Science  31 Aug 2018:
Vol. 361, Issue 6405, pp. 889
  1. Paleoecology

    Climate change in a mountain ecosystem

    1. Andrew M. Sugden

    Conifer pollen from Yellowstone lake sediments reveals vegetation shifts over 18,000 years.

    PHOTO: DESIGN PICS/DAVID PONTON/GETTY IMAGES

    Fossil pollen in lake sediments provides valuable records of past vegetation patterns and offers a baseline for assessing how vegetation responds to climate change. To assess how the vegetation composition and distribution of a mountain system has varied with climate change over 18,000 years, Iglesias et al. studied pollen sequences from lakes in the Greater Yellowstone Ecosystem of the United States. They found complex patterns, with long-term stability in some plant communities and rapid change in others. The present-day mixed conifer forest cover, known to be vulnerable to climate warming, is now more compressed in its elevation range than in previous postglacial millennia. These data provide a context for assessing future responses to climate change.

    J. Biogeogr. 45, 1768 (2018).

  2. Neuroscience

    Degrees of stress in neurodegeneration

    1. Lisa D. Chong

    In the neurodegenerative disorder amyotrophic lateral sclerosis (ALS), the nuclear protein called transactive response DNA binding protein of 43 kDa (TDP-43) accumulates in stress granules within the cytoplasm of neurons and glia and is linked to disease pathology. McGurk et al. report that TDP-43 binds to poly(ADP-ribose) (PAR), which triggers phase separation of TDP-43 and its subsequent recruitment to stress granules. Under short-term stress, phosphorylated TDP-43, which is considered a hallmark of disease, is unexpectedly excluded from stress granules. This finding indicates that the granules initially prevent phosphorylated TDP-43 aggregation unless stress is prolonged. This work also points to an approach to ALS treatment by inhibition of PAR polymerase (PARP) to reduce PAR production. For instance, a small-molecule inhibitor of PARP that prevents cancer-cell proliferation also blocks cytoplasmic TDP-43 aggregation.

    Mol. Cell 10.1016/j.molcel.2018.07.002 (2018).

  3. Education

    Disruptive classmates, long-term harm

    1. Brad Wible

    Exposure to disruptive behavior, like bullying, during primary school can have lifelong effects.

    PHOTO: FATCAMERA/GETTY IMAGES

    Children who are behaviorally disruptive during primary school can have harmful impacts on their classmates into adulthood. Carrell et al. use data from Florida, USA, to show that a child who experiences domestic violence at home (a well-recognized proxy for that child demonstrating disruptive behavior such as bullying) can lower their classmates' secondary-school math and reading test scores, lower their likelihood of enrolling in college, and reduce earnings in their mid-20s by 3%. Differential exposure to such classmates accounts for roughly 5% of the rich-poor earnings gap in adulthood.

    Amer. Econ. Rev. www.aeaweb.org/articles?id=10.1257/aer.20160763 (2018).

  4. Reprogramming

    FACTs behind control of cell fate

    1. Beverly A. Purnell

    As animals develop, their cells become progressively less plastic and follow defined functional destinies. Kolundzic et al. used a genetic screen of the worm Caenorhabditis elegans to uncover proteins that prevent cells from straying from their intended fate. They found that the histone chaperone FACT plays a regulatory part in an unexpected way: It is nonrepressive and also promotes gene expression. FACT acts as a barrier to cell reprogramming by stabilizing gene expression and thereby safeguarding cell identity. A germline-specific isoform of FACT ensures that cells with intestinal and germline programming confirm their fate and do not adopt a neuronal role. Furthermore, depletion of FACT in human fibroblasts enhances production of induced pluripotent stem cells, indicating that a conserved mechanism is at work to channel cell fate in animals.

    Dev. Cell 10.1016/j.devcel.2018.07.006 (2018).

  5. Framework Materials

    Transversal zigzag linkers

    1. Phil Szuromi

    The linkers for metal-organic frameworks are usually bidentate molecules (for example, dicarboxylic acids) connected by an organic group to create a linear or, in some cases, a bent geometry like isophthalic acid. Guillerm et al. explored the effect of a “zigzag” linker, trans,trans-muconic acid (tmuc), that forces an offset of inorganic building blocks. Reaction with ZrCl4 formed the metal-organic framework Zr6O4(OH)4(tmuc)8(H2O)8, which had an eight-connected bcu topology, a subset of the 12-connected fcu topology seen with linear linkers. This bcu topology was maintained with linkers of even larger transversal width, such as azobenzene-3,3′-dicarboxylic acid.

    J. Am. Chem. Soc. 140, 10153 (2018).

  6. Microbiology

    Impermanent permafrost

    1. Caroline Ash

    Permafrost constitutes a quarter of Earth's surface and about half the buried ancient carbon. Thaw releases water, and, together with higher temperatures, this promotes microbial respiration. Thus, permafrost melt during global warming represents a threat for escalating greenhouse gas release. Müller et al. extracted 2-meter core samples from Svalbard permafrost in Norway for 16S ribosomal RNA gene analysis. Sampling at 3-centimeter intervals, they noted distinctive strata of microbial communities. On thawing and subsequent incubation, each community showed different metabolic rates and different CO2 fluxes. Within 24 hours, thawing the deepest permafrost layers released most CO2, but over a longer term, most CO2 was produced under shallow aerobic conditions. These Svalbard mineral soils also have high iron availability. Intimate knowledge of the microbial, as well as the physicochemical, conditions prevailing in any specific permafrost area is needed to accurately estimate CO2 emission during anthropogenic climate warming.

    Environ. Microbiol. 10.1111/1462-2920.14348 (2018).

  7. Quantum Computation

    Trapped ions tackle chemistry

    1. Jelena Stajic

    Some of the most likely first applications of future quantum computers may be in quantum chemistry. Even with currently available quantum computers consisting of just a few qubits, it is possible to address certain simple problems, but most of the development has occurred in systems using superconducting qubits. Hempel et al. used up to four qubits encoded by trapped ions to calculate the ground-state energies of two simple molecules, H2 and LiH. They made use of a hybrid classical-quantum method called the variational quantum eigensolver, which relegates parts of the computation such as preprocessing and optimization to a classical computer.

    Phys. Rev. X 8, 031022 (2018).