This Week in Science

Science  27 Mar 2015:
Vol. 347, Issue 6229, pp. 1432
  1. Supernovae

    A place where stars are more predictable

    1. Margaret M. Moerchen

    Composite image of the SN 1006 supernova remnant

    PHOTO: RADIO: NRAO/AUI/NSF/GBT/VLA/DYER, MADDALENA & CORNWELL; OPTICAL: MIDDLEBURY COLLEGE/F.WINKLER, NOAO/AURA/NSF/CTIO SCHMIDT & DSS

    Astrophysicists use reference objects of known brightness to determine distances. For example, type Ia supernova (SN Ia) always reach nearly the same peak brightness. This is because they explode when the progenitor white dwarf exceeds its supportable mass threshold. Kelly et al. find that a particular subset of SN Ia—those in environments with high ultraviolet surface brightness and star-formation density—can calibrate distances even more tightly. It seems that only one or two intrinsic parameters may drive the apparent relationship between luminosity, color, and fading with time.

    Science, this issue p. 1459

  2. Social Science

    Abuse from generation to generation?

    1. Barbara R. Jasny

    Parents who were abused as children are thought more likely to abuse their own children. Widom et al. compared reports from parents, from children, and from child protective service agency records gathered on the same families and on matched controls. They observed different findings depending on which information they used. Increases in sexual abuse and neglect relative to controls were reported by children of abuse victims. However, much of the believed transmission of abuse and neglect between generations could be ascribed to surveillance or detection bias targeted at parents with childhood histories of abuse or neglect.

    Science, this issue p. 1480

  3. Parasitology

    Trypanosomes reveal tricky tricks in vivo

    1. Caroline Ash

    Blood smear containing trypanosomes

    PHOTO: BIOPHOTO ASSOCIATES/SCIENCE SOURCE

    The sleeping sickness parasite, Trypanosoma brucei, is covered with variant surface glyco proteins (VSGs) recognized by the host's immune system. The parasite uses a repertoire of 2000 VSG genes to switch between different surface variants, continually evading the host's defensive responses. Classic experiments showed that one variant succeeded another, causing waves of infection; however, infection in animals shows different behavior. Mugnier et al. discovered that several VSGs are expressed simultaneously and that the repertoire for variation is amplified even more by recombination between the genes to make mosaic VSGs.

    Science, this issue p. 1470

  4. ALS Genes

    New players in Lou Gehrig's disease

    1. Stella M. Hurtley

    Amyotrophic lateral sclerosis (ALS), often referred to as “Lou Gehrig's disease,” is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. Cirulli et al. sequenced the expressed genes of nearly 3000 ALS patients and compared them with those of more than 6000 controls (see the Perspective by Singleton and Traynor). They identified several proteins that were linked to disease in patients. One such protein, TBK1, is implicated in innate immunity and autophagy and may represent a therapeutic target.

    Science, this issue p. 1436; see also p. 1422

  5. DNA Origami

    Reconfigurable DNA structures

    1. Phil Szuromi

    DNA origami—nanostructures created by programming the assembly of single-stranded DNA through base pairing—can create intricate structures. However, such structures lack the flexible and reversible interactions more typical of biomolecular recognition. Gerling et al. created three-dimensional DNA nanostructures that assemble though nucleotide base-stacking interactions (see the Perspective by Shih). These structures cycled from open to closed states with changes in salt concentration or temperature.

    Science, this issue p. 1446; see also p. 1417

  6. Nuclear Physics

    Weighing the neutron against the proton

    1. Jelena Stajic

    Elementary science textbooks often state that protons have the same mass as neutrons. This is not far from the truth—the neutron is about 0.14% heavier (and less stable) than the proton. The precise value is important, because if the mass difference were bigger or smaller, the world as we know it would likely not exist. Borsanyi et al. calculated the mass difference to high precision using a sophisticated approach that took into account the various forces that exist within a nucleon. The calculations reveal how finely tuned our universe needs to be.

    Science, this issue p. 1452

  7. Bone Biology

    Rebuilding bone in osteoporosis

    1. Leslie K. Ferrarelli

    The skeleton undergoes continuous turnover because osteoblast cells build bone and osteoclasts break it down. Too much turnover can cause osteoporosis. The receptor tyrosine kinase DDR2 tilts the balance in favor of bone formation. Zhang et al. found that DDR2 both enhanced the development of osteoblasts and prevented osteoclasts from fully developing and breaking down bone. Viral delivery of DDR2 increased bone density in a mouse model of osteoporosis. Thus, increasing DDR2 levels in both types of bone cells may benefit osteoporosis patients.

    Sci. Signal. 8, ra31 (2015).

  8. Neurodevelopment

    Build the builders before the brain

    1. Pamela J. Hines

    Humans are much smarter than mice—key to this is the relative thickness of the human brain's neocortex. Florio et al. combed through genes expressed in the progenitor cells that build the neocortex and zeroed in on one gene found in humans but not in mice. The gene, which seems to differentiate humans from chimpanzees, drives proliferation of the key progenitor cells. Mice expressing this human gene during development built more elaborate brains.

    Science, this issue p. 1465

  9. Snare Proteins

    An explosive way to fuse membranes

    1. Stella M. Hurtley

    The molecular machine that promotes membrane fusion during intracellular transport involves a number of so-called SNARE proteins. Ryu et al. describe the molecular mechanism by which two proteins—NSF and α-SNAP—disassemble SNARE complexes. A combination of single-molecule techniques resolved intermediate steps of the reaction. Surprisingly, unlike previously assumed, NSF did not unwind SNARE complexes processively. Instead, built-up tension was released in a single burst to “tear” the SNARE complex apart in a one-step global unfolding reaction.

    Science, this issue p. 1485

  10. 1D Nanostructures

    Crafting organic-inorganic shish-kebabs

    1. Zakya H. Kafafi

    Functionalized inorganic nanocrystals can be assembled on polymeric chains like shish-kebabs. Xu et al. developed a clever and unconventional route for the synthesis of one-dimensional (1D) nanostructures. They capitalized on rationally designed amphiphilic wormlike precursors as nanoreactors. The approach opens the door for the design of intriguing hybrid materials with yet to be discovered properties.

    Science Advances 10.1126/sciadv.1500025 (2015).

  11. Pollination

    Conserving pollinator services for crops

    1. Caroline Ash

    If pollination fails, ecosystems are eroded and we will lose reliable sources of many critical foodstuffs. Focusing on the pollination services provided by bees, Goulson et al. review the stresses bees are experiencing from climate change, infectious diseases, and insecticides. We can mitigate some of the stress on bees by improving floral resources and adopting quarantine measures, and by surveillance of bee populations. Crucially, we need to resolve the controversy surrounding prophylactic use of pesticides.

    Science, this issue 10.1126/science.1255957

  12. Molecular Motors

    Making a molecular motor fit for purpose

    1. Stella M. Hurtley

    Dynactin is an essential cofactor of the microtubule motor, cytoplasmic dynein. Dynactin contains 23 subunits built around a short filament of an actin-related protein (Arp1). How dynactin is assembled, how it functions with dynein, and why it is built around an actin-like filament is unclear. Urnavicius et al. combined cryo–electron microscopy structural studies and a crystal structure to determine the three-dimensional architecture of dynactin and how it interacts with dynein.

    Science, this issue p. 1441

  13. Infectious Disease

    Improving treatment options for fungal infections

    1. Julia Fahrenkamp-Uppenbrink

    Fungal diseases are common around the world. Many respond readily to treatment. However, infections such as invasive aspergillosis can be very difficult to treat, leading to high mortality. Drug resistance in fungal pathogens is also a growing problem. In a Perspective, Denning and Bromley explain the challenges encountered in developing new antifungal treatments. Although few antifungal drugs are currently coming to market, there are some reasons for hope: For example, some compounds in clinical or preclinical development are active against novel targets, and much improved diagnostics are making the early stages of drug development more straightforward.

    Science, this issue p. 1414

  14. Geomicrobiology

    Building a biogeochemical battery

    1. Nicholas S. Wigginton

    Iron acts as both a source and sink of electrons for microorganisms in the environment. Some anaerobic bacteria use oxidized Fe(III) as an electron acceptor, whereas phototrophic bacteria can use reduced Fe(II) as an electron donor. Byrne et al. show that the iron-bearing mineral magnetite, which contains both Fe(II) and Fe(III), can serve as both an electron acceptor and donor. Cocultures of iron-reducing and iron-oxidizing bacteria exposed to simulated day/night cycles or changes in organic matter altered the ratio of Fe(II) to Fe(III) in magnetite particles.

    Science, this issue p. 1473

  15. Dark Matter

    Uncloaking the influence of the invisible actor

    1. Margaret M. Moerchen

    The idea of dark matter enjoys popular support, but two major concerns persist: the so-called Standard Model excludes it, and it cannot be directly detected by any telescope. For now, astronomers can only observe dark matter's influence indirectly, such as when watching unseen creatures perturb the surface of a pond. Harvey et al. observed 72 galaxy collisions to compare the resulting centers of mass for the gas and stars (from direct observations) and for the dark matter (by inference). Based on these offsets, dark matter is clearly present.

    Science, this issue p. 1462

  16. Neurotechniques

    Exciting nerve cells deep inside the brain

    1. Peter Stern

    Current techniques to stimulate regions inside the brain need a permanently implanted wire or an optical fiber. Working in mice, Chen et al. developed a method to overcome this problem (see the Perspective by Temel and Jahanshahi). They introduced heat-sensitive capsaicin receptors into nerve cells and then injected magnetic nanoparticles into specific brain regions. The nanoparticles could be heated by external alternating magnetic fields, which activated the ion channel–expressing neurons. Thus, cellular signaling deep inside the brain can be controlled remotely without permanent implants.

    Science, this issue p. 1477; see also p. 1418

  17. Quantum Gases

    Atoms behaving in an orderly manner

    1. Jelena Stajic

    In physics, interactions between components of a system can cause it to become more orderly in an attempt to minimize energy. Such ordered phases appear, for example, in magnetic systems. Schauss et al. simulated these phenomena using a collection of neutral atoms at low temperatures. By shining laser light on the atoms, the authors brought some of them into a high-energy state called the Rydberg state. By carefully varying the experimental parameters, they coaxed these Rydberg atoms into patterns reminiscent of crystal lattices in rod- and disk-shaped atomic samples.

    Science, this issue p. 1455

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