This Week in Science

Science  12 Oct 2018:
Vol. 362, Issue 6411, pp. 194
  1. Plant Science

    Keeping the doors open for symbiosis

    1. Pamela J. Hines

    Legumes like this Lotus japonicus send microRNAs from shoot to root to promote root nodule synthesis.

    CREDIT: HARUM.KOH/WIKICOMMONS CC-BY-SA-2.0

    Nitrogen fixation by legumes results from a symbiotic partnership between plant and microbes. These together elaborate nodules on the plant roots that house the bacteria. Tsikou et al. identified a microRNA made in the aboveground shoots of Lotus japonicus that translocates to the plant's roots. In the roots, the microRNA posttranscriptionally regulates a key suppressor of symbiosis, thus keeping the uninfected root susceptible to productive infection by symbiotic bacteria.

    Science, this issue p. 233

  2. Materials Science

    Modeling collapse with soaked cereal

    1. Philippa J. Benson

    Naturally brittle and porous media, like ice shelves and rockfill dams, are collapse-prone when they encounter chemically active fluids, or pressure. What happens when these materials are subject to both forces at once is not well understood. Einav and Guillard analyzed a simpler version of a rockfill dam: a vertical cylinder filled with puffed rice. After applying pressure and then injecting liquid into the bottom of the cylinder, they observed “ricequakes.” These abrupt collapses of wetted puffed rice began shortly after liquid injection and were marked by continuous clicking sounds. A model based on these observations could be applied to analyze the effects of geological pressures over long time scales in crustal rocks and ice sheets.

    Sci. Adv. 10.1126/sciadv.aat6961 (2018).

  3. Supernovae

    Explosive origin of a binary neutron star

    1. Keith T. Smith

    Some types of core-collapse supernovae are known to produce a neutron star (NS). A binary NS merger was recently detected from its gravitational wave emission, but it is unclear how such a tight binary system can be formed. De et al. discovered a core-collapse supernova with unusual properties, including the removal of the outer layers of the star before the explosion. They interpret this as the second supernova in an interacting binary system that already contains one NS. Because the explosion probably produced a second NS (rather than a black hole) in a tight orbit, it could be an example of how binary NS systems form.

    Science, this issue p. 201

  4. Molecular Biology

    Cas12 inhibitors join the anti-CRISPR family

    1. Steve Mao

    Bacteria and their phages continually coevolve in a molecular arms race. For example, phages use anti-CRISPR proteins to inhibit the bacterial type I and II CRISPR systems (see the Perspective by Koonin and Makarova). Watters et al. and Marino et al. used bioinformatic and experimental approaches to identify inhibitors of type V CRISPR-Cas12a. Cas12a has been successfully engineered for gene editing and nucleic acid detection. Some of the anti-Cas12a proteins identified in these studies had broad-spectrum inhibitory effects on Cas12a orthologs and could block Cas12a-mediated genome editing in human cells.

    Science, this issue p. 236, p. 240; see also p. 156

  5. Multiple Sclerosis

    Move over myelin

    1. Lindsey Pujanandez

    Although it is well established that autoreactive lymphocytes induce demyelination in multiple sclerosis, the exact antigenic targets that initiate disease are undefined. Planas et al. studied CD4+ T cells from the cerebrospinal fluid of patients with multiple sclerosis. One CD4+ T cell clone was reactive to the human enzyme guanosine diphosphate (GDP)–l-fucose synthase; T cells from other patients were then identified, as well as myelin-reactive cells. Intriguingly, some of the GDP-l-fucose synthase–reactive cells could also be stimulated by a bacterial version of the enzyme. These results identify an autoantigen and suggest that one possible trigger of disease could be cross-reactivity to microbiota-derived peptides.

    Sci. Transl. Med. 10, eaat4301 (2018).

  6. Magnetism

    Magnons propagating in graphene

    1. Jelena Stajic

    Artist's view of magnon absorption by graphene

    CREDIT: SECOND BAY STUDIOS

    At sufficiently low temperatures, a two-dimensional electron system placed in an external magnetic field can exhibit the so-called quantum Hall effect. In this regime, a variety of magnetic phases may occur, depending on the electron density and other factors. Wei et al. studied the properties of these exotic magnetic phases in graphene. They generated magnons—the excitations of an ordered magnetic system—that were then absorbed by the sample, leaving a mark on its electrical conductance. The magnons were able to propagate across long distances through various magnetic phases in the bulk graphene.

    Science, this issue p. 229

  7. Virology

    Pathologizing Staphylococcus, fast

    1. Caroline Ash

    Bacteriophages are the main vehicle for gene swapping in bacteria, notoriously of pathogenicity islands and antibiotic resistance genes. Chen et al. noticed that the Staphylococcus aureus prophages do not excise from their host's genome until very late in their life cycles (see the Perspective by Davidson). Thus, the phage DNA is amplified while embedded in the bacterial chromosome. The resulting concatemers are processively packed into virus capsules while still integrated in the host chromosome. Each virion is only set loose when the capsule has reached physical capacity—a process called “headful” packaging. In situ amplification maximizes viral replication, and the headful mechanism means adjacent bacterial-host DNA also gets grabbed to fill the capsule. This process ensures that host genes are transmitted along with the phage.

    Science, this issue p. 207; see also p. 152

  8. Nanomaterials

    The twisted carbon nanotube story

    1. Marc S. Lavine

    Despite progress in growing single-walled carbon nanotubes of specific size and chirality, the factors that control their growth are still not fully known. Magnin et al. developed a thermodynamic model for the growth of single-walled carbon nanotubes. The model explains the origin of nanotube chirality in terms of the configurational entropy of the nanotube edge. The model should be useful in helping to guide nanotube growth parameters to enhance selectivity.

    Science, this issue p. 212

  9. Cancer Biomarkers

    Mining immunotherapy clinical trials

    1. Priscilla N. Kelly

    Clinical trial data can provide a wealth of information about how drugs work. Yet such information often belongs to pharmaceutical companies and is rarely accessible to the scientific community at large. Cristescu et al. provide exploratory analysis of a cancer genomics dataset, collected from four separate clinical trials of Merck's PD-1 immunotherapy drug, pembrolizumab. This informative public resource examines more than 300 patient samples representing 22 different tumor types. Two widely used signatures that currently predict immunotherapy response are tumor mutational burden and a “hot” T cell–inflamed microenvironment. The study analyzed these two proposed biomarkers in combination to see what predictive clinical utility they may hold.

    Science, this issue p. eaar3593

  10. Protein Homeostasis

    A way to prevent deadly interaction

    1. Steve Mao

    Many metazoan proteins form oligomers, which is often mediated by modular domains such as BTB domains. Mena et al. now describe a quality control pathway they term dimerization quality control (DQC) (see the Perspective by Herhaus and Dikic). DQC monitors and prevents aberrant dimerization of BTB domain–containing proteins. The system relies on FBXL17, an adaptor protein that recruits an E3 ligase that specifically ubiquitylates nonfunctional BTB heterodimers, triggering their degradation. FBXL17 accesses a degradation signal at the BTB dimer interface in nonphysiological, nonfunctional complexes. The loss of DQC from Xenopus laevis embryos leads to lethal neurodevelopmental defects.

    Science, this issue p. eaap8236; see also p. 151

  11. Structural Biology

    From DNA unwrapping to histone exchange

    1. Steve Mao

    The yeast SWR1 complex, a member of the INO80 family of nucleosome remodelers, exchanges the H2A-H2B histone dimer for the Htz1 variant–containing dimer. Unlike all other remodelers, SWR1 does not translocate the nucleosome. Willhoft et al. applied structural and single-molecule analyses to show that the interaction between SWR1 and the nucleosome destabilizes the DNA wrapped around the histone core. This SWR1-catalyzed partial unwrapping of the DNA was regulated by adenosine triphosphate (ATP) binding but did not require ATP hydrolysis.

    Science, this issue p. eaat7716

  12. Neurodevelopment

    Thyroid hormone in color vision development

    1. Pamela J. Hines

    Cone photoreceptors in the eye enable color vision, responding to different wavelengths of light according to what opsin pigments they express. Eldred et al. studied organoids that recapitulate the development of the human retina and found that differentiation of cone cells into their tuned subtypes was regulated by thyroid hormone. Cones expressing short-wavelength (S) opsin developed first, and cones expressing long- and medium-wavelength (L/M) opsin developed later. The switch toward development of L/M cones depended on thyroid hormone signaling through the nuclear thyroid hormone receptor.

    Science, this issue p. eaau6348

  13. Organic Chemistry

    An acid inaccessible to aldol products

    1. Jake Yeston

    The aldol reaction is a venerable and widely applicable method for making carbon-carbon bonds. Ironically, it is most challenged by the simplest substrates. The trouble is that the product looks a lot like one of the reactants, and so it can latch onto the coupling partner instead. Schreyer et al. report that a bulky phosphorus-based acid catalyst alleviates this problem. The acidic site is buried in a pocket that is too small to activate the product for further reaction. The chiral geometry of the catalyst also induces high enantioselectivity.

    Science, this issue p. 216

  14. Polymers

    Simple routes to self-healing

    1. Marc S. Lavine

    Biology provides many routes for self-healing or repair, but this trait is hard to endow into engineering materials. Although self-repair has been demonstrated for some polymers, it usually required specialized monomers. Urban et al. demonstrate that for a very narrow range of compositions, simple vinyl polymers based on methyl methacrylate and n-butyl acrylate show repeatable self-healing properties (see the Perspective by Sumerlin). A key characteristic of this system is that it relies on van der Waals interactions rather than the reformation of hydrogen or covalent bonds for repair.

    Science, this issue p. 220; see also p. 150

  15. Organic Chemistry

    Iodine smooths the way to ketyl radicals

    1. Jake Yeston

    Chemists typically transform carbonyl compounds through polar two-electron reactions. It is also possible to pursue radical coupling strategies by adding just one electron to form a ketyl group. However, the strong reductant supplying that electron often limits the reaction's versatility. Wang et al. report a mild means of forming ketyls by first adding acetyl iodides across the C=O bond (see the Perspective by Blackburn and Roizen). A photoactivated manganese catalyst then temporarily pulls the iodine away, leaving a ketyl to couple with alkynes. The iodine then returns to one of the alkyne's carbons, stabilizing the product but remaining poised for further transformations.

    Science, this issue p. 225; see also p. 157

  16. Immunotherapy

    The next step for cell therapy?

    1. Gemma Alderton

    Considerable advances have been made in engineering T cells for adoptive cell transfer to treat cancer by manipulating the patients' immune system. In a Perspective, Bluestone and Tang discuss the potential for use of regulatory T cells (Tregs) to treat patients with autoimmunity and other diseases that involve pathological inflammation. Preclinical research has provided encouraging results with Treg therapies, and numerous clinical trials have been initiated to test adoptive Treg transfer in patients with, for example, type I diabetes, organ transplant rejection, and amyotrophic lateral sclerosis.

    Science, this issue p. 154

  17. Cytokines

    Stabilizing the IL-17 response

    1. Erin Williams

    The inflammatory cytokine interleukin-17 (IL-17) can stimulate both antifungal host defense and autoimmunity by promoting the stability of target messenger RNAs (mRNAs). Amatya et al. found that IL-17 increased the abundance of the RNA binding protein Arid5a in mouse cells (see the Focus by Puel and Casanova). Arid5a promoted the cellular response to IL-17 by increasing the mRNA stability of a selection of IL-17–stimulated transcripts. For other transcripts, Arid5a interacted with the translation initiation factor eIF4G to augment their translation.

    Sci. Signal. 11, eaat4617, eaau8876 (2018).

  18. Inflammation

    Brushing up on lung inflammation

    1. Ifor Williams

    Inhaled environmental allergens elicit type 2 lung inflammation and lead to an increase in the risk of developing allergies and asthma. Bankova et al. found that one step along this pathway depends on lipid mediator leukotriene E4 signaling. This occurred via a receptor on respiratory epithelial cells that increased the number of brush cells. These brush cells represent a rare population of chemosensory cells in the lung epithelium that express receptors shared by taste bud cells. The brush cells were identified as the major pulmonary source of interleukin-25, a proinflammatory protein increased in diseases associated with type 2 inflammation.

    Sci. Immunol. 3, eaat9453 (2018).

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