Editors' Choice

Science  03 Jan 2020:
Vol. 367, Issue 6473, pp. 37
  1. Snowball Earth

    Beating the freeze

    1. H. Jesse Smith

    Artist's conception of a Snowball Earth almost entirely covered by ice

    PHOTO: CHRIS BUTLER/SCIENCE SOURCE

    Despite multiple episodes during the Cryogenian period in which the planet was mostly covered in ice for millions of years—essentially shutting down air–sea exchange and causing widespread ocean anoxia—marine aerobic eukaryotes somehow survived those Snowball Earth conditions. How did they do it? Lechte et al. show that oxygenated glacial meltwater was supplied to the oceans near ice sheet grounding lines, offering a lifeline to microbial communities there. This process may have created glaciomarine oxygen oases that were critical to the survival and evolution of those organisms during episodes of extreme glaciation.

    Proc. Natl. Acad. Sci. U.S.A. 116, 25478 (2019).

  2. T Cell Signaling

    Checkpoint cross-talk

    1. Priscilla N. Kelly

    Immunotherapy using antibodies that block the programmed cell death (ligand) 1 [PD-(L)1] or cytotoxic T lymphocyte–associated protein 4 (CTLA-4) immune checkpoint pathways has resulted in impressive responses for some cancer patients. Combined inhibition of both pathways has generally delivered better responses than the targeting of either alone, but how they functionally cross-talk is not well defined. Zhao et al. report that PD-L1 (the main ligand of PD-1) and CD80 (shared ligand for CTLA-4 and the central costimulatory receptor CD28), heterodimerize in cis. Using their model system, the authors found the PD-L1:CD80 cis complexes to be defective in binding either PD-1 or CTLA-4, but the ability of CD80 to activate CD28 appeared to be fully preserved. The interaction of checkpoint pathways might allow opportunities to improve therapy.

    Immunity 51, 1059 (2019).

  3. Metals in Biology

    Copper on the half shell

    1. Michael A. Funk

    Oysters have a particularly critical need for the trace element copper during their late pelagic larval stage (pictured).

    PHOTO: STEPHANIE ALEXANDER, UNIVERSITY OF MARYLAND CENTER FOR ENVIRONMENTAL SCIENCE HORN POINT OYSTER HATCHERY

    Oysters, like many marine mollusks, have a complex life cycle that requires changes in their body and biochemistry. Weng et al. examined how the abundance and distribution of copper, a trace element essential for metabolism, changes in larval and juvenile oysters as they develop. Using a combination of imaging techniques, they see copper accumulation in certain organs during developmental transitions, especially in the cells' mitochondria. Both cell proliferation and programmed cell death involve biochemical processes linked to mitochondrial copper concentrations. Understanding metal ion distributions may offer insights valuable for conservation and cultivation.

    Environ. Sci. Technol. 53, 14724 (2019).

  4. Neuroscience

    Filling a blank canvas

    1. Peter Stern

    Natural scenes can be decoded in the brain in the early visual cortex. Decoding is a product of planned output (feedforward) corrected by experience (feedback). Morgan et al. occluded one quadrant of the visual field of human participants and then presented them with images of landscape scenes. Responses in the visual cortex (areas V1 and V2) were measured for each person by functional magnetic resonance imaging. Even in the occluded region, information about the scene was being decoded. To access what the brain had modeled for the occluded region, participants were asked to complete the image by line drawings on an electronic drawing tablet. The drawings were shown to all participants, who scored how well the “averaged” drawing for each scene matched the complete image. Mental models at the first visual cortical stage were predicted by the line drawings. So, faced with a blank canvas, an artist may be using cortical feedback processing until the lines and edges converge on her mental model of a scene, thus providing a window into her visual cortex.

    J. Neurosci. 39, 9410 (2019).

  5. Cell Biology

    Kill, but don't be killed

    1. Stella M. Hurtley

    Cytotoxic T lymphocytes (CTLs) recognize and destroy infected or malignant cells. CTLs secrete the pore-forming protein perforin into the immune synapse, where perforin disrupts the target cell plasma membrane and initiates cell death pathways. Paradoxically, the secreted perforin only damages the target cell, leaving the producer lymphocytes unscathed and able to attack another target cell. What protects the lymphocyte is unclear. Using a variety of approaches, Rudd-Schmidt et al. found that two distinct but coordinated mechanisms were deployed by CTLs to protect themselves. Both mechanisms depended on the dynamic regulation of plasma membrane lipid composition and topology. High membrane lipid order made the CTL presynaptic membrane refractory to perforin binding. Furthermore, phosphatidylserine, exposed on the killer cell membrane, appeared to bind and inactivate perforin.

    Nat. Commun. 10, 5396 (2019).

  6. Microbiota

    Postantibiotic recovery

    1. Caroline Ash

    Antibiotic consumption by humans is ubiquitous. Although they are lifesaving and valuable medicines, antibiotics can harm resident mutualistic microorganisms in unpredictable ways leading to physiological damage. Ng et al. systematically explored the long-term effects of antibiotic treatment on transplanted human microbiota in mice. The alpha-diversity of Bacteroides spp. suffered mass extinction by streptomycin within hours of treatment, whereas Firmicutes were more resilient. Such taxa-specific selection depended on the antibiotic used, influenced the recovered community composition, and affected resilience to subsequent treatments. Diet was an important variable: Without microbiota-accessible fiber in the diet, mucus grazers predominated, which may facilitate the activity of pathogens, such as Acinetobacter muciniphila. Recolonization from untreated cage mates was also vital for healthy reestablishment of the microbiota, especially of Bacteroidetes. It is possible that selective transplantation of extinct taxa could aid a healthy microbiota to recover after antibiotics exposure.

    Cell Host Microbe 26, 650 (2019).

  7. Physics

    Tailoring electronic properties

    1. Jelena Stajic

    The layered material α-RuCl3 has piqued the interest of physicists as a potential platform for the so-called Kitaev model—a type of quantum spin liquid that hosts exotic excitations. However, in addition to the magnetic interactions of the Kitaev model, α-RuCl3 also hosts non-Kitaev interactions. Biswas et al. investigated theoretically whether a heterostructure consisting of a α-RuCl3 monolayer on top of graphene would be a better approximation of the Kitaev model. Using ab initio calculations, the researchers found that the α-RuCl3 layer would experience strain and become doped by graphene electrons. The strain would make the Kitaev interactions more dominant, and the doping may provide a route towards p-wave superconductivity in this system.

    Phys. Rev. Lett. 123, 237201 (2019).

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