This Week in Science

Science  15 Jan 2016:
Vol. 351, Issue 6270, pp. 236
  1. Traumatic Brain Injury

    The very vulnerable cerebellum

    1. Orla M. Smith

    Soldiers exposed to blasts often experience traumatic brain injuries

    PHOTO: © ERIN TRIEB/CORBIS

    Mild traumatic brain injuries—the signature injury of the wars in Iraq and Afghanistan—can result from explosion-related shock waves. Currently, we have limited understanding of how such blasts cause persistent brain injuries in animals or humans. Meabon et al. now report that the cerebellum, a brain structure important for integrating sensory information and movement, is preferentially injured in blast-exposed mice. This damage is concentrated in regions corresponding to areas of the cerebellum that are also abnormal in brain images from blast-exposed combat veterans.

    Sci. Transl. Med. 8, 321ra6 (2016).

  2. RNA Biochemisty

    Chemical modification of RNA for function

    1. Guy Riddihough

    Chemical modifications play an important role in modifying and regulating the function of DNA and RNA. Delatte et al. show that, in the fruit fly, many messenger RNAs (mRNAs) contain the modified base 5-hydroxymethylcytosine (5hmC). The chemical mark is added by the same enzyme that adds 5hmC to DNA. Because many mRNAs involved in neuronal development contain 5hmC, blocking the enzyme causes brain defects and is lethal. In vivo, RNA hydroxymethylation promotes mRNA translation.

    Science, this issue p. 282

  3. Organic Chemistry

    Opening one ring to tack on another

    1. Jake Yeston

    Curious chemists have long sought to learn just how tightly carbon atoms can be bound together. For instance, it's possible to form a bond between two opposite corners of an already strained four-membered ring to make an edge-sharing pair of triangles. Gianatassio et al. have now devised a general use for these and related molecular curiosities. They show that appropriately modified nitrogen centers can pop open the most highly strained bond, leaving the more modestly strained ring motif intact. In this way, small rings can emerge as a convenient diversifying element in compounds, including new pharmaceutical candidates.

    Science, this issue p. 241

  4. Applied Optics

    Tunable lasers

    1. Ian S. Osborne

    Lasers emit coherent light at wavelengths that are well defined. These wavelengths are usually fixed once the device has been fabricated. Now, Chakraborty et al. have combined an atomically thin graphene sheet with terahertz quantum cascade lasers to realize a terahertz laser that can be tuned via the carrier doping level of the graphene layer (see the Perspective by Polini). The demonstration opens up the possibility of reversible control over the laser emission through the integration of graphene waveguides.

    Science, this issue p. 246; see also p. 229

  5. Neuroscience

    Connected astrocytes coordinate seizures

    1. Wei Wong

    Astrocytes are glial cells in the nervous system that are interconnected by gap junctions formed by connexins. Gap junctions form pores that enable the connected cells to function as a unit by rapidly passing cytosolic signals. By analyzing hippocampal slices from mice that were deficient in astroglial connexins, Chever et al. found that interconnected astrocytes coordinated bursts of neuronal activity over large regions, which contributed to the intensity of induced seizures. Indeed, mice with disconnected astrocytes had more frequent but less severe chemically induced seizures than did normal mice.

    Sci. Signal. 9, ra6 (2016).

  6. Lunar Atmosphere

    The Moon's time-variable exosphere

    1. Keith T. Smith

    Earth's Moon does not have a conventional gaseous atmosphere, but instead an “exosphere” of particles ejected from the surface. Colaprete et al. have used NASA's LADEE orbiter to investigate how the exosphere varies over time, by using the glow from sodium and potassium atoms as a probe (see the Perspective by Dukes and Hurley). The exosphere composition varies by a factor of 2 to 3 over the course of a month, as different parts of the Moon are exposed to sunlight. There are also increases shortly after the Moon passes through streams of meteoroids.

    Science, this issue p. 249; see also p. 230

  7. Paleoanthropology

    Earliest human Arctic occupation

    1. Andrew M. Sugden

    Weapon-inflicted damage on a bone from a frozen mammoth carcass

    PHOTO: ALEKSEI TIKHONOV

    Paleolithic records of humans in the Eurasian Arctic (above 66°N) are scarce, stretching back to 30,000 to 35,000 years ago at most. Pitulko et al. have found evidence of human occupation 45,000 years ago at 72°N, well within the Siberian Arctic. The evidence is in the form of a frozen mammoth carcass bearing many signs of weapon-inflicted injuries, both pre- and postmortem. The remains of a hunted wolf from a widely separate location of similar age indicate that humans may have spread widely across northern Siberia at least 10 millennia earlier than previously thought.

    Science, this issue p. 260

  8. Muscle Physiology

    Another micropeptide flexes its muscle

    1. Paula A. Kiberstis

    Genome annotation is a complex but imperfect art. Attesting to its limitations is the growing evidence that certain transcripts annotated as long noncoding RNAs (lncRNAs) in fact code for small peptides with biologically important functions. One such lncRNA-derived micropeptide in mammals is myoregulin, which reduces muscle performance by inhibiting the activity of a key calcium pump. Nelson et al. describe the opposite activity in a second lncRNA-derived micropeptide in mammalian muscle, called DWORF (see the Perspective by Payre and Desplan). This peptide enhances muscle performance by activating the same calcium pump. DWORF may prove to be useful in improving the cardiac muscle function of mammals with heart disease.

    Science, this issue p. 271; see also p. 226

  9. Gene Regulation

    Reactivating the fetal globin gene

    1. Beverly A. Purnell

    Mutation of adult-type globin genes causes sickle cell disease and thalassemia. Although treating these hemoglobinopathies with gene therapy is possible, there is a pressing need for pharmacologic approaches to treat general patient populations. One promising approach is to reactivate repressed expression of fetal-type hemoglobin (HbF) in adult erythroid cells. Masuda et al. reveal a molecular mechanism governing HbF repression as mediated by the LRF/ZBTB7A transcription factor. The study may encourage the development of new HbF reactivation therapies for hemoglobinopathies.

    Science, this issue p. 285

  10. Viral Immunity

    Microbial villages shape viral infections

    1. Kristen L. Mueller

    Viruses infecting the intestinal tract, such as noroviruses and rotaviruses, are major human pathogens. Despite facing an extreme environment within their hosts, which includes pH gradients, digestive enzymes, and the billions of microbes that inhabit human guts, these viruses somehow manage to survive and often thrive. Pfeiffer and Virgin review the complex microbial encounters that occur between enteric viruses and gut microbiota. Trans-kingdom interactions (that is, between viruses, bacteria, archaea, helminthes, fungi, and phage) are particularly important in shaping the course of a viral infection and the ensuing host immune response.

    Science, this issue p. 10.1126/science.aad5872

  11. Comparative Genetics

    Identifying the IRESs of humans and viruses

    1. Laura M. Zahn

    Most proteins result from the translation of 5′ capped RNA transcripts. In viruses and a subset of human genes, RNA transcripts with internal ribosome entry sites (IRESs) are uncapped. Weingarten-Gabbay et al. systematically surveyed the presence of IRESs in human protein-coding transcripts, as well those of viruses (see the Perspective by Gebauer and Hentze). Large-scale mutagenesis profiling identified two classes of IRESs: those having a functional element localized to one small region of the IRES and those with important elements distributed across the entire region. An unbiased screen across human genes suggests that IRESs are more frequent than previously supposed in 3′ untranslated regions.

    Science, this issue p. 10.1126/science.aad4939; see also p. 228

  12. Organic Chemistry

    Amino acids can lend palladium a hand

    1. Jake Yeston

    Metals such as rhodium and palladium (Pd) are adept at activating otherwise inert carbon-hydrogen bonds toward useful reactivity. To get properly oriented, they often require some help from oxygen or nitrogen groups nearby. Appending and removing these directing groups, however, detracts from the efficiency of chemical synthesis. Zhang et al. show that amino acids can act as temporary directing groups in the Pd-catalyzed coupling of arenes with aldehydes or ketones. By reversibly binding to these latter substrates just long enough for the Pd catalysis to ensue, the amino acids eliminate the need for more laborious directing group manipulations.

    Science, this issue p. 252

  13. Astronomy

    The most luminous supernova to date

    1. Keith T. Smith

    Supernovae are exploding stars at the end of their lives, providing an input of heavy elements and energy into galaxies. Some types have near-identical peak brightness, but in recent years a new class of superluminous supernovae has been found. Dong et al. report the discovery of ASASSN-15lh (SN 2015L), the most luminous supernova yet found by some margin. It appears to originate in a large quiescent galaxy, in contrast to most super-luminous supernovae, which typically come from star-forming dwarf galaxies. The discovery will provide constraints on models of superluminous supernovae and how they affect their host galaxies.

    Science, this issue p. 257

  14. Phytoplankton

    Using solar energy suboptimally

    1. H. Jesse Smith

    How efficient are phytoplankton at converting sunlight into the products of photosynthesis? The two other pathways that that absorbed energy can take are emission back to the environment by fluorescence or conversion to heat. Lin et al. measured phytoplankton fluorescence lifetimes in the laboratory and combined them with satellite measurements of variable chlorophyll fluorescence. Combined, they determined the quantum yields of photochemistry and fluorescence in four ocean basins. Approximately 60% of absorbed solar energy is converted to heat, a figure 50% higher than has been determined for conditions of optimal growth.

    Science, this issue p. 264

  15. Neural Circuits

    Fixation on learned syllables

    1. Pamela J. Hines

    Zebra finches learn their beautiful songs by listening to other zebra finches. Vallentin et al. observed zebra finch brains as learning proceeded, only to find that inhibition of the neuronal circuits was critical to fixating on learned sequences. For song syllables that have been adequately learned, the inhibitory neurons fired coherently. Song syllables not yet learned failed to produce this flag. Thus, it is the learning process that alters the neuronal circuits. The inhibitory neuronal firing, not the age of the bird, locks in the learning.

    Science, this issue p. 267

  16. Metabolism

    How to shape mitochondrial networks

    1. L. Bryan Ray

    Mitochondria undergo fragmentation or fusion in response to changes in cellular metabolism. Toyama et al. report that adenosine monophosphate–activated protein kinase (AMPK) is both necessary and sufficient to control mitochondrial fragmentation. AMPK functions as a sensor to monitor the energy status of the cell by phosphorylating mitochondrial fission factor (MFF), a protein of the mitochondrial outer membrane. MFF then acts to recruit a cytoplasmic guanosine triphosphatase that promotes mitochondrial fission.

    Science, this issue p. 275

  17. Infectious Diseases

    One disease does not a pathogen make

    1. Julia Fahrenkamp-Uppenbrink

    The composition of microbial communities within an infected organism can determine whether that organism develops a disease. For example, the presence of one or more particular bacterial strains may make it more difficult for a pathogen to colonize the host. As Byrd and Segre explain in a Perspective, these findings are important for understanding how diseases develop. A broader approach to understanding disease causation should include sequencing of microbial communities, modeling their interactions, culturing suspected pathogens, and knowledge of the host's genetics and exposure history.

    Science, this issue p. 224