Editors' Choice

Science  30 Aug 2019:
Vol. 365, Issue 6456, pp. 879
  1. Parasites

    Breaking the species barrier

    1. Caroline Ash

    The ubiquitous protist parasite Toxoplasma gondii infects many species but only develops sexually in cats.

    PHOTO: DPA PICTURE ALLIANCE/ALAMY STOCK PHOTO

    The protozoan parasite Toxoplasma gondii is found in most mammals and is spread by ingestion of contaminated food and water. It is a health risk to humans because it can form brain cysts and cause life-changing complications during pregnancy. Despite this parasite's ability to infect many mammals, it can only complete its life cycle in felids, including domestic cats. Martorelli di Genova et al. sought to understand the basis for the specificity of the sexual stages for the gut epithelium of cats. Using cat gut organoids, they found that the parasite's sexual stages are stimulated to develop by the plant fat linoleic acid. Cats uniquely lack the enzyme needed for linoleic acid digestion, delta-6-desaturase. To test whether intact linoleic acid acts as a parasite signal, mice were given a chemical treatment to inhibit their desaturase, then fed linoleic acid and infected. T. gondii promptly initiated sexual development and the mice shed infectious oocysts in their feces 6 days later.

    PLOS Biol. 17, e3000364 (2019).

  2. Physics

    Twisted multilayer graphene

    1. Jelena Stajic

    Since the recent discovery of superconductivity in twisted bilayer graphene, physicists have been exploring other twisted heterostructures, including those in which two bilayers of graphene are twisted with respect to each other. These experiments have shown signatures of exotic states, inspiring theorists to try to understand their properties. Liu et al. undertook a theoretical study of the general case of two graphene multilayers, each of which could contain an arbitrary number of graphene monolayers, twisted with respect to each other. They found that such heterostructures retained the approximately flat bands characteristic of twisted bilayer graphene at the same “magic” twist angle. Additionally, twisted multilayer graphene showed interesting topological properties that depended on the number and stacking of monolayers in each multilayer.

    Phys. Rev. X 9, 031021 (2019)

  3. Fungal Genetics

    Fairy rings magically prevent mutation

    1. Laura M. Zahn

    The fairy ring–forming fungus Marasmius oreades

    PHOTO: WALLY EBERHART/GETTY IMAGES

    Mutation can often occur as part of the process of cellular division and may have deleterious consequences for multicellular organisms. Through genomic sequencing of Marasmius oreades, a species of fairy ring mushroom, Hiltunen et al. found that in this relatively long-lived species, the accumulation of mutations is an order of magnitude less than previously discovered for any organism. This could not be attributed to purifying selection and indicates that this species has evolved high-fidelity replication and/or repair mechanisms to prevent mutation accumulation. Given that fungi, unlike mammals, do not sequester their reproductive germ cells, this is of interest in understanding how an organism can police its own cell division to maintain a low rate of mutation accumulation.

    Curr. Biol. 29, 2758 (2019).

  4. Biosynthesis

    Building psychoactives with purpose

    1. Michael A. Funk

    Plants are skilled, if unwitting, organic chemists that produce a panoply of natural products that influence human biochemistry and cognition. Farrow et al. identified a suite of enzymes in the iboga plant, Tabernanthe iboga, that produce (−)-ibogaine from a complex precursor alkaloid. The carbon scaffold is rearranged in a series of steps that follow or mirror the synthesis of (+)-catharanthine, an intermediate in the formation of the anticancer drug vinblastine. Knowledge of their biosynthetic pathways may stimulate research into the psychoactive properties of iboga alkaloids, including potential antiaddictive activities.

    J. Am. Chem. Soc. 141, 12979 (2019).

  5. Cell Biology

    Born in the ribosomal tunnel

    1. Stella M. Hurtley

    The correct folding and processing of nascent polypeptides requires ribosome-associated chaperones. One such chaperone, the ribosome-bound nascent polypeptide–associated complex (NAC), cross-links to newly assembled polypeptides. Gamerdinger et al. discovered that NAC is positioned above the ribosomal exit site, from where it antagonizes incorrect endoplasmic reticulum protein targeting. Remarkably, the extended N-terminal tail of the β subunit inserts deeply inside the ribosomal tunnel to facilitate their folding and sorting. As the peptide elongates, it displaces NAC from the ribosomal tunnel. NAC then rearranges on the surface of the ribosome, ready to coordinate further cotranslational activities.

    Mol. Cell 10.1016/j.molcel.2019.06.030 (2019).

  6. Physics

    Controlling exciton lifetimes

    1. Ian S. Osborne

    Excitons are electron-hole pairs optically induced in condensed matter systems which reemit a photon when they recombine. Monolayer transition metal dichalcogenides, e.g., MoSe2, are of particular interest owing to the strong binding energy of the excitons and an ultrafast response time. By sandwiching the monolayers of MoSe2 between layers of hexagonal boron nitride (hBN), Fang et al. show that the lifetime of the excitons can be controlled across an order of magnitude from 1 to 10 picoseconds with the lifetime determined simply by the thickness of the hBN sandwiching layers. Such control of the exciton lifetime and transport properties should be applicable to other two-dimensional materials and could be exploited for use in a variety of ultrafast optoelectronic applications.

    Phys. Rev. Lett. 123, 067401 (2019).

  7. Regenerative Medicine

    Improving heart muscle

    1. Gemma Alderton

    Heart failure is caused by injury to the myocardium, the heart muscle, which results in irreversible loss because this tissue cannot regenerate itself. Bargehr et al. investigated whether regenerative medicine approaches involving human embryonic stem cell (hESC)–derived epicardial cells, which produce stromal cells, smooth muscle cells, and growth factors, can remuscularize injured heart. They showed that hESC-derived epicardial cells improved the structure and function of heart tissue in vitro and improved hESC-derived cardiomyocyte grafts in rats with heart tissue loss. The improvements to heart function in vivo persisted for 3 months, suggesting an approach for improving heart regenerative medicine.

    Nat. Biotech. 37, 895 (2019).

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