Editors' Choice

Science  06 Jan 2017:
Vol. 355, Issue 6320, pp. 36
  1. Marine Nitrogen Cycle

    The absence of loss

    1. H. Jesse Smith

    Little nitrogen loss occurs in the oxygen minimum zone of the Bay of Bengal.

    PHOTO: RAJARSHI CHOWDHURY/GETTY IMAGES

    Anaerobic microbial processes in oxygen minimum zones cause a disproportionately large fraction of the loss of fixed nitrogen in the open ocean. Interestingly, though, there has been no indication of such nitrogen loss in the oxygen minimum zone of the Bay of Bengal. Bristow et al. quantify the abundance of microbial genes associated with N2 production to help resolve this enigma, finding that the Bay of Bengal supports denitrifier and anammox microbial populations that mediate low but significant N loss while at the same time allowing the trace levels of oxygen to support nitrite oxidation. If this oxygen were removed, nitrogen loss in the Bay of Bengal oxygen minimum zone could accelerate greatly.

    Nat. Geosci. 10.1038/NGEO2847 (2016).

  2. Molecular Evolution

    Beetle ornaments mediated epigenetically

    1. Laura M. Zahn

    Many male beetles exhibit enlarged ornaments and weapons, which are believed to function in sexual selection. However, the size and degree to which these structures can develop in an individual is variable and dependent on nutrition. Ozawa et al. found that the nutritional effect on the size of the mouthparts of the broadhorned flour beetle is mediated by epigenetic modifying factors, such as histone deactylases and Polycomb group proteins. Silencing of one histone deacetylase (HDAC1) in the beetle larvae shrank the mandibles of the ensuing adults, whereas silencing of another (HDAC3) led to exaggerated mouthparts without much affecting other body parts. The results indicate that ornamentation in these beetles is under modular epigenetic control.

    Proc. Natl Acad. Sci. U.S.A. 10.1073/pnas.1615688114 (2016).

  3. Synthetic Biology

    Expanding the genetic code in vertebrates

    1. Valda Vinson

    Unnatural amino acids can be incorporated into target proteins by using a transfer RNA (tRNA)—aminoacyl-tRNA synthetase pair that adds an unnatural amino acid at an amber stop codon. The strategy has been used in prokaryotic and eukaryotic cells and for generating transgenic invertebrates. Chen et al. have succeeded in integrating a construct coding for the unnatural amino acid p-azido-phenylalanine (AzF) into the mouse genome. The artificial gene was transmitted to subsequent generations and caused no obvious physiological defects. Primary cells from adult transgenic mice incorporated AzF into a fluorescent reporter protein containing an amber codon. Similarly, the genetic code of zebrafish was expanded, and in vivo incorporation of AzF into reporter protein was achieved. This opens the potential to investigate the function of target proteins in living animals.

    Cell Res. 10.1038/cr.2016.145 (2016).

  4. Immunology

    B cells safeguard against premature labor

    1. Priscilla Kelly

    B cell failure can cause preterm labor in mice.

    PHOTO: ANYAIVANOVA/ISTOCKPHOTO

    Around one-third of cases of premature labor are caused by infection and inflammatory responses. B cells are specialized immune cells that should protect from pathogens, but their role in pregnancy is poorly defined. Huang et al. have identified a functionally distinct population of B cells in the choriodecidua (a specialized uterine lining that separates the mother from the fetus) that is associated with preterm labor in women. Mice lacking B cells had diminished levels of progesterone-induced blocking factor 1 (PIBF1) and were also more prone to premature labor after inflammation. But when B cell function was compensated by administering PIBF1, inflammation in the uterus and preterm labor were reduced in the B cell—deficient mice. The cytokine interleukin-33, which normally raises the alarm for inflammation, is responsible for stimulating B cell production of PIBF1. These insights provide therapeutic possibilities for maintaining term pregnancy.

    Nat. Med. 10.1038/nm.4244 (2016).

  5. Development

    Crumbs2 gets mesoderm moving

    1. Sarah Harrison

    The protein Crumbs2 is essential for gastrulation.

    PHOTO: RAMKUMAR ET AL., NATURE CELL BIOLOGY 18 (21 NOVEMBER 2016) © NATURE

    The epithelial-to-mesenchymal transition (EMT) is the process by which cells move out of a structured, epithelial tissue and become motile. EMT is implicated in cancer metastasis and is critical during embryonic development. At gastrulation, newly specified mesodermal cells undergo EMT and move inside the embryo, giving it a trilaminar structure. Ramkumar et al. show that in mice, the apical protein Crumbs2 is critical for cells to leave the epithelial epiblast and move inside the embryo to form a new tissue layer. In the absence of this protein, mesoderm formation is disrupted, and cells do not ingress. Instead, a single layer forms, and the embryo fails to properly establish its body plan, leading to embryonic arrest.

    Nat. Cell Biol. 18, 1281 (2016).

  6. Optics

    An all-optical electron gun

    1. Ian S. Osborne

    Short bunches of electrons are used extensively to yield information about the structure of materials and the dynamics of phase transitions. Traditionally associated, perhaps, with “big science,” the availability of accelerator beam time and the timing resolution of the pulses can be limiting factors for experimental studies. Huang et al. have developed a matchbox-sized all-optical electron gun in which a single terahertz pulse is injected into a copper waveguide. Synchronized with a photogenerated pulse of electrons, the terahertz pulse accelerates the electron bunch over high fields and with low energy spread so that they can be used for low-energy electron diffraction studies. Further developments could lead to the generation of ultrashort relativistic electron bunches and the prospect of miniaturized accelerators.

    Optica 3, 1209 (2016).

  7. Materials Science

    A solid approach to improving batteries

    1. Marc S. Lavine

    Many of the limitations of lithium ion batteries arise from the liquid electrolytes because they limit the operating voltage; they are often flammable and can contribute to the decreased capacity of a cell. Solid-state electrolytes could solve these problems, but there have been challenges at the interfaces to reduce the impedance, and when lithium is used as the anode, it can react with most solid-state electrolyte materials. Han et al. show they can solve the interfacial stability and wetting problems between lithium and the garnet-like electrolyte Li7La2.75Ca0.25Zr1.75Nb0.25O12 by depositing a thin layer of aluminum oxide by means of atomic layer deposition. A full cell using a high-voltage Li2FeMn3O8 cathode robustly cycled at voltages above 4 V.

    Nat. Mater. 10.1038/NMAT4821(2016).