This Week in Science

Science  02 Dec 2016:
Vol. 354, Issue 6316, pp. 1114
  1. Atmospheric Science

    How new particles form

    1. H. Jesse Smith

    The CLOUD chamber at CERN, Switzerland

    PHOTO: MAXIMILIEN BRICE, CERN

    New particle formation in the atmosphere produces around half of the cloud condensation nuclei that seed cloud droplets. Such particles have a pivotal role in determining the properties of clouds and the global radiation balance. Dunne et al. used the CLOUD (Cosmics Leaving Outdoor Droplets) chamber at CERN to construct a model of aerosol formation based on laboratory-measured nucleation rates. They found that nearly all nucleation involves either ammonia or biogenic organic compounds. Furthermore, in the present-day atmosphere, cosmic ray intensity cannot meaningfully affect climate via nucleation.

    Science, this issue p. 1119

    Correction (5 December 2016): Science used an incorrect photograph for the summary of Dunne et al. The photograph should have shown the CERN CLOUD chamber but in fact showed a different facility. The PDF and HTML versions have been corrected with a photograph of the CERN CLOUD chamber.

  2. Galaxy Formation

    A massive galaxy forming from molecular gas

    1. Keith T. Smith

    The most massive galaxies gather their stars by merging with smaller galaxies and by accreting gas, which is then consumed during star formation. Emonts et al. investigated the Spiderweb Galaxy, a massive galaxy in the process of forming in the early universe, seen now as it was over 10 billion years ago (see the Perspective by Hatch). Radio observations of carbon monoxide revealed large quantities of molecular gas around the galaxy. The gas is not associated with the merger process but may have been recycled from earlier phases of galaxy formation.

    Science, this issue p. 1128; see also p. 1102

  3. Cancer

    Running interference

    1. Yevgeniya Nusinovich

    Interleukin 2 (IL-2) binds to receptors on different types of T cells. CD8+ T cells, which can kill tumor cells, have IL-2 receptors with two subunits. When IL-2 binds to these, it promotes T cell activation. In contrast, T regulatory cells dampen the antitumor immune response. These cells express a different type of IL-2 receptor, which contains CD25 in addition to the other two subunits. CD25 binds IL-2 tightly but does not activate a T cell response. Arenas-Ramirez et al. developed an antibody that can block CD25. Delivering this antibody together with IL-2 allowed IL-2 to bind specifically to the activating receptors and promote an antitumor immune response without interference from T regulatory cells.

    Sci. Transl. Med. 8, 367ra166 (2016).

  4. Topological Matter

    Shining light on a peculiar coupling

    1. Jelena Stajic

    One of the long-standing predictions regarding topological insulators is the magnetoelectric effect, a coupling between a material's magnetic and electric properties. Thanks to this coupling, Maxwell's equations inside topological insulators are modified, resulting in so-called axion electrodynamics. Wu et al. used time-domain terahertz (THz) spectroscopy to observe signatures of these unusual electrodynamics in a thin film of Be2Se3. They detected tiny changes to the polarization of THz light after it passed through the thin film, confirming the expected quantization of the magnetoelectric coupling.

    Science, this issue p. 1124

  5. Pain Research

    Glial cells contribute to pain

    1. Peter Stern

    Pain hypersensitivity can spread to unaffected body regions immediately surrounding the initial insult. Sometimes it can even spread to the opposite site of the body or to large body areas and cause widespread pain. Kronschläger et al. discovered a form of synaptic plasticity in the spinal cord that may explain the spread of pain hypersensitivity. This plasticity was induced by the activation of glial cells. The spread was mediated by gliotransmitters that diffuse widely, even reaching the cerebrospinal fluid at biologically relevant concentrations.

    Science, this issue p. 1144

  6. Structural Biology

    Zika virus is fit to be tied

    1. Kristen L. Mueller

    Zika virus (ZIKV) has been associated with fetal microcephaly and Guillain-Barre syndrome. Other mosquito-born flaviviruses, such as dengue virus, encode noncoding subgenomic flavivirus RNAs (sfRNAs) in their 3′ untranslated region that accumulate during infection and cause pathology. Akiyama et al. now report that ZIKV also produces sfRNAs that resist degradation by host exonucleases in infected cells. The authors solved the structure of one of ZIKV's sfRNAs by x-ray crystallography and found that the multi-pseudoknot structure that it adopts underlies its exonuclease resistance.

    Science, this issue p. 1148

  7. Hematopoiesis

    How to maintain hematopoietic stem cells

    1. Beverly A. Purnell

    Hematopoietic stem cell

    PHOTO: SPL / SCIENCE SOURCE

    Hematopoiesis provides the body with a continuous supply of blood cells (see the Perspective by Sommerkamp and Trumpp). Taya et al. report that amino acid content is important for hematopoietic stem cell (HSC) maintenance in vitro and in vivo. Dietary valine restriction seems to “empty” the mouse bone marrow niche. Ito et al. used single-cell approaches and cell transplantation to identify a subset of HSCs at the top of the HSC hierarchy. Self-renewal relied on the induction of mitophagy, a quality-control process linked to a cell's metabolic state. Both studies may be helpful in improving clinical bone marrow transplantation.

    Science, this issue p. 1103, p. 1152; see also p. 1156

  8. Vaccination

    Protecting by changing the code

    1. Kristen L. Mueller

    Live attenuated vaccines can be very potent, but their potential to revert to their pathogenic form limits their use. In an attempt to get around this, Si et al. expanded the genetic code of influenza A viruses. They propagated viruses that were mutated to encode premature termination codons (PTCs) in a cell line engineered to be able to express these flu proteins. Despite not being able to replicate in conventional cells, PTC-containing viruses were highly immunogenic and protected mice, guinea pigs, and ferrets against influenza challenge.

    Science, this issue p. 1170

  9. Oxidative Stress

    Overactive antiviral responses in lupus

    1. John F. Foley

    Detection of viral RNAs causes oligomerization of mitochondrial antiviral signaling (MAVS) protein, which leads to the production of type I interferons (IFNs). Buskiewicz et al. found that MAVS oligomerization in the absence of virus may contribute to lupus disease severity. Mitochondrial reactive oxygen species (ROS) induced MAVS oligomerization and type I IFN production in uninfected cells. The MAVS C79F variant, which is associated with decreased lupus severity, did not oligomerize in response to ROS, and cells expressing this variant produced less type I IFN.

    Sci. Signal. 9, ra115 (2016).

  10. Innate Immunity

    Shared logic in diverse immune systems

    1. Pamela J. Hines

    The innate immune systems of both plants and animals depend on the ability to recognize pathogen-derived molecules and stimulate a defense response. Jones et al. review how that common function is achieved in such diverse kingdoms by similar molecules. The recognition system is built for hair-trigger sensitivity and constructed in a modular manner. Understanding such features could be useful in building new pathways through synthetic biology, whether for broadening disease defenses or constructing new signal-response circuits.

    Science, this issue p. 10.1126/science.aaf6395

  11. RNA Splicing

    Tie me up, cut me down

    1. Pamela J. Hines

    Group II in trons are mobile genetic elements found in all domains of life. They are large ribozymes that can excise themselves from host RNA. Costa et al. determined the structure of an excised group II intron in its branched conformation. This conformation is comparable to the branched “lariat” seen during the splicing of nuclear RNA transcripts. The lariat conformation helps assemble the group II active site for the reverse splicing reaction. The lariat in spliceosomal splicing may also have a similar role in the second step of messenger RNA intron removal.

    Science, this issue p. 10.1126/science.aaf9258

  12. Water Chemistry

    Frame-by-frame view of acidic transport

    1. Jake Yeston

    Protons in acidic solution constantly hop from one water molecule to the next. In between the hopping, controversy lingers over the extent to which the proton either sticks largely to one water molecule in an Eigen motif or bridges two of them in a Zundel motif. It has been hard to probe this question directly because the distinguishing vibrational bands in bulk aqueous acid spectra are so broad. Wolke et al. studied deuterated prototypical Eigen clusters, D+(D2O)4, bound to an increasingly basic series of hydrogen bond acceptors (see the Perspective by Xantheas). These clusters displayed sharp bands in their vibrational spectra, highlighting a steadily evolving distortion toward a Zundel-like motif and pointing the way toward further investigations.

    Science, this issue p. 1131; see also p. 1101

  13. Neuroscience

    Attention changes local brain activity

    1. Peter Stern

    There is a well-known correlation between arousal and neuronal activity in the brain. However, it is unclear how these general effects are reflected on a local scale. Engel et al. recorded from higher visual areas in behaving monkeys and discovered a new principle of cortical state fluctuations. A special type of electrodes revealed that the state changes affected neuronal excitability across all layers of the neocortex. When the animals attended to a stimulus, the vigorous spiking states became longer and the faint spiking states became shorter. These states correlated with fluctuations in the local field potential. A sophisticated computational model of the state changes fitted a two-state model of neuronal responsiveness.

    Science, this issue p. 1140

  14. Working Memory

    How to reactivate forgotten memories

    1. Peter Stern

    Sophisticated techniques can decode stimulus representations for items held in a person's working memory. However, when subjects shift their attention toward something else, the neural representation of the now unattended item drops to baseline, as though the item has been forgotten. Rose et al. used single-pulse transcranial magnetic stimulation (TMS) to briefly reactivate the representation of an unattended item. A short pulse of TMS enhanced recognition of “forgotten” stimuli, bringing an unattended item back into focal attention.

    Science, this issue p. 1136

  15. T Cell Exhaustion

    The epigenetics of exhaustion

    1. Kristen L. Mueller

    During cancer or chronic infection, T cells become dysfunctional, eventually acquiring an “exhausted” phenotype. Immunotherapies aim to reverse this state. Using a mouse model of chronic infection, two studies now show that the epigenetic profile of exhausted T cells differs substantially from those of effector and memory T cells, suggesting that exhausted T cells are a distinct lineage (see the Perspective by Turner and Russ). Sen et al. defined specific functional modules of enhancers that are also conserved in exhausted human T cells. Pauken et al. examined the epigenetic profile of exhausted T cells after immunotherapy. Although there was transcriptional rewiring, the cells never acquired a memory T cell phenotype. Thus, epigenetic regulation may limit the success of immunotherapies.

    Science, this issue p. 1104, p. 1165; see also p. 1160

  16. Epidemiology

    How bats spread viruses

    1. Julia Fahrenkamp-Uppenbrink

    Bats carry numerous viruses, such as rabies and Ebola, which they can transmit to humans. In a Perspective, Hayman highlights recent genetic studies showing that male vampire bats are key to rabies dispersal and transmission in Peru. Rabies is more often transmitted between related species than between unrelated ones. For many other bat-virus systems, little is known about how the virus is transmitted within and between species. Although challenging, further such studies of this and other bat-virus systems are needed to inform public health efforts.

    Science, this issue p. 1099

  17. Atherosclerosis

    Letting SLE-Ping plaques lie

    1. Angela Colmone

    Patients with the autoimmune disease systemic lupus erythematosis (SLE) are more likely to develop atherosclerosis than healthy individuals. Smith et al. hypothesized that invariant natural killer T (iNKT) cells contribute to this process because of their connection to both immune responses and lipids. The authors found that iNKT cells from SLE patients with asymptomatic plaque (SLE-P) produced more of the Th2 cytokine interleukin-4 than those from SLE patients with no plaques. These SLE-P iNKT cells were associated with changes in lipid composition and monocyte skewing to the M2 phenotype. Thus, SLE-P iNKT cells may connect changes in lipids and the immune response, contributing to the development of cardiovascular disease in SLE patients.

    Sci. Immunol. 1, eaah4081 (2016).