Editors' Choice

Science  17 Nov 2017:
Vol. 358, Issue 6365, pp. 883
  1. Nanomaterials

    Etching silicon nanotubes

    1. Phil Szuromi

    Silicon nanotowers made using multiple-patterning nanosphere lithography

    PHOTO: X. XU ET AL., ACS NANO 11, 10384 (2017)

    Arrays of silicon nanotubes have many potential applications, including for solar-energy harvesting, photonics, and biological processes such as drug delivery. Xu et al. show how rounds of etching with polystryrene (PS) nanosphere templates can create periodic arrays of silicon nanotubes with controlled pitch, height, and inner and outer diameters. Close-packed arrays of PS nanospheres were oxygen-plasma–etched to create the initial template for deep reactive-ion etching to make silicon nanorods. The PS nanospheres were then further etched to create templates for depositing nickel rings at the top of the nanorods. After removal of the PS nanospheres, the rings guided the final interior etching to form nanotubes.

    ACS Nano 10.1021/acsnano.7b05472 (2017).

  2. Molecular Biology

    What brings PRC2 to chromatin?

    1. Steve Mao

    Polycomb repressive complex 2 (PRC2), an essential epigenetic regulator, silences gene expression by methylating histone H3. DNA, protein, and RNA have all been previously proposed to recruit PRC2 to chromatin. Using biochemistry and single-molecule imaging, respectively, Wang et al. and Choi et al. show that protein-free DNA predominantly contributes to PRC2's affinity with chromatin in test tubes. Choi et al. also identify a DNA-binding domain in PRC2 and a protein cofactor that increases this binding. Wang et al. further show that RNA sequesters PRC2 away from chromatin by competing with DNA. These results help explain contradictory published observations and provide a framework to test PRC2 recruitment to chromatin in cells.

    Nat. Struct. Mol. Biol. 10.1038/nsmb.3488, 10.1038/nsmb.3487 (2017).

  3. Social Signals

    Be honest

    1. Sacha Vignieri

    Fake signals of aggression are policed and punished among fish.

    PHOTO: BLICKWINKEL/ALAMY STOCK PHOTO

    Signals of quality and intent are common among animals, but there is much debate about how the honesty of these signals is maintained. Generally, it has been concluded that honesty in the signaling of quality is inherent—for example, the production of color can be costly, so bright colors must honestly signal a healthy and high-quality individual. Signals of intent, however, are more easily bluffed. Bachman et al. used manipulation experiments to test the honesty of facial signaling in Princess of Burundi cichlids and whether it was enforced. A single, dynamically controlled black color bar on the face of both males and females honestly signaled aggressive intent in these fish. However, when the stripe was manipulated by experimenters, “dishonest” fish were punished with a greater number of attacks than were control fish. Thus, social policing maintained the honesty of signaling, even though the signal itself is dynamic and easily changed. Such social maintenance of honesty may act as a selective force on dynamic signals.

    Evol. Lett. 10.1002/evl3.24 (2017).

  4. Immunometabolism

    Unusual macrophages contribute to obesity

    1. Seth Thomas Scanlon

    The role of macrophages in the regulation of norepinephrine (NE)–mediated thermogenesis has been a topic of much recent debate. Pirzgalska et al. report a specialized subset of CX3CR1+ sympathetic nerve–associated macrophages (SAMs) in adipose tissue. SAMs display dynamic dendritiform processes but are closer to macrophages than microglia in their gene expression profile. However, SAMs uniquely possess the machinery for NE transport (SLC6A2) and degradation (MAOA) and are recruited and activated in mouse models of obesity. The lineage-specific deletion of Slc6a2 in SAMs results in increased NE levels, thermogenesis, browning of white fat, and weight loss. Given that human sympathetic ganglia are also infiltrated with NE-degrading SAMs, this work suggests an intriguing new target for managing the global obesity epidemic.

    Nat. Med. 10.1038/nm.4422 (2017).

  5. Cell Biology

    Mitochondria help in dead cell clearance

    1. Stella M. Hurtley

    When cells in our body die, it is important that they are cleared from the system so that they do not cause inflammation or further death among neighboring cells. Dead cells are cleaned up by phagocytic cells such as macrophages. Wang et al. studied the mechanisms involved as macrophages take up and degrade multiple cell corpses from the circulation. Interestingly, they found that the macrophages needed to have an intact mitochondrial fission system in place if they were to be able to take up more than one cell corpse. Mitochondrial fission was important to ensure that cytosolic calcium levels remained high enough to drive further rounds of phagocytosis. In its absence, mice exhibited compromised clearance of dead cells, which exacerbated pathology in mouse models of atherosclerosis.

    Cell 10.1016/j.cell.2017.08.041 (2017).

  6. Antimicrobials

    Brush with care

    1. Julia Fahrenkamp-Uppenbrink

    Many commercial toothpastes contain the antimicrobial compound triclosan, which helps to reduce plaque and gum bleeding. Han et al. show that the nylon brushes and elastomer plastic of the toothbrush head absorb triclosan from the toothpaste during brushing and release it again during brushing with triclosan-free toothpaste. Similar effects were seen for other chemicals in the toothpastes. Given concern over release of triclosan and other antimicrobial compounds into the environment, more studies of their unintended release from consumer plastics are warranted.

    Environ. Sci. Technol. 10.1021/acs.est.7b02839 (2017).

  7. Geophysics

    Bombardment-driven early tectonics

    1. Brent Grocholski

    Earth's early history 4 billion years ago was dominated by impact cratering. The impacts delivered energy to Earth, but now O'Neill et al. suggest that they may also have driven surface tectonics. Simulations show that large impacts produced enough heat to induce the mantle to upwell, driving local crustal subduction. This may help explain why there is an abundance of the mineral zircon found in Earth's oldest rocks. It may also help solve the puzzle of why these minerals appear to have recorded a very early magnetic field.

    Nat. Geosci. 10.1038/NGEO3029 (2017).