This Week in Science

Science  25 Jan 2013:
Vol. 339, Issue 6118, pp. 371
  1. Hunger and Memory

    During starvation, are all brain functions slowed down, or are specific functions disabled to save energy? Plaçais and Preat (p. 440) investigated how the brain of Drosophila deals with severe resource limitation. The brain cut selected expenses to reduce the threat to survival and switched off the formation of aversive long-term memory that depends on costly protein synthesis. However, Hirano et al. (p. 443) focused on mild food-deprivation, which actually enhanced long-term memory formation. Presumably, improved memory should enhance survival when competing for limited food. After longer food deprivation, enhancement of aversive long-term memory decreased, while that of appetitive long-term memory remained high: Presumably, as starvation nears, it becomes more important to pursue food at all costs, and so appetitive memory takes precedence over aversive memories.

  2. Axonal Actin


    How actin is organized in the axons and dendrites of neurons is largely unknown. Xu et al. (p. 452, published online 13 December) imaged actin in axons and dendrites using stochastic optical reconstruction microscopy. Surprisingly, while actin in dendrites formed long filaments, the actin in axons was organized into evenly spaced ringlike structures at the axon circumference. Spectrin, which is known to interact with actin to form a membrane cytoskeleton in erythrocytes, formed periodic structures that alternated with those of actin. This actin-spectrin cytoskeletal structure might give mechanical support to axons and could also organize other membrane proteins.

  3. Proton Still Too Small

    Despite a proton's tiny size, it is possible to measure its radius based on its charge or magnetization distributions. Traditional measurements of proton radius were based on the scattering between protons and electrons. Recently, a precision measurement of a line in the spectrum of muonic hydrogen—an atom consisting of a proton and a muon, instead of an electron—revealed a radius inconsistent with that deduced from scattering studies. Antognini et al. (p. 417; see the Perspective by Margolis) examined a different spectral line of muonic hydrogen, with results less dependent on theoretical analyses, yet still inconsistent with the scattering result; in fact, the discrepancy increased.

  4. Environmentally Friendly Ferroelectrics

    Ferroelectrics—which are widely used as piezo elements, sensors, and actuators—maintain charge polarization even in the absence of an external electric field. The best ferroelectric properties are found in perovskites such as barium titanate (BTO) and lead zirconate titanate; however, environmentally friendly, lead-free alternatives are highly desirable. Fu et al. (p. 425; see the Perspective by Bonnell) find that the organic molecular crystal diisopropylammonium bromide has ferroelectric properties comparable to those of BTO and may represent a viable alternative to perovskites.

  5. Radically Organic

    Metals such as manganese are relatively stable over a wide range of oxidation states. In contrast, purely organic compounds are rarely susceptible to incremental addition or removal of electrons without accompanying fragmentation or coupling reactions. Barnes et al. (p. 429; see the Perspective by Benniston) report a catenane (a compound comprising interlocked rings) in which the topological structure stabilizes six different states that successively differ by the presence or absence of one or two electrons in the framework. The hepta-oxidized state proved remarkably resilient to oxygen exposure.

  6. Bat Genomes

    Bats are of great interest because of their ability to fly and as hosts for infectious disease. Zhang et al. (p. 456, published online 20 December) sequenced the genomes of two distantly related bat species, David's Myotis and Black flying fox. Analysis of the two genomes revealed likely changes that accompanied the evolution of bats, including selection for increased expression of genes involved in the oxidative phosphorylation pathway needed to generate the energy required for flight. Furthermore, while some immune genes have been lost, others are under positive selection, which may potentially explain bats' status as viral reservoirs.

  7. When Stars Get Too Close


    Stellar outbursts used to come in two classes: supernovae and novae, the complete explosions and the thermonuclear runaways on the surface of evolved stars, respectively. Over the past two decades a class of stellar outbursts emerged with luminosities between those of novae and supernovae—intermediate-luminosity red transients (ILRTs). Ivanova et al. (p. 433) propose that these ILRTs are the signature of common envelope events in which a lower-mass star in a close binary system is engulfed by matter transferred from its more massive and more evolved companion star.

  8. Masterminding Mitochondrial Fission

    Mitochondria are highly dynamic and undergo fusion and fission and they move in cells. Defects in mitochondrial dynamics are implicated in many neurodegenerative diseases. Recent findings have suggested that mitochondrial fission occurs preferentially at endoplasmic reticulum (ER) contact sites, with ER circumscribing mitochondria and possibly promoting the constriction of mitochondria during fission. Korobova et al. (p. 464) now suggest that an ER-localized formin, INF2, is required for mitochondrial fission and that INF2-mediated actin polymerization facilitates mitochondrial constriction.

  9. Completing the Catalog

    Despite the widely held belief that the number of taxonomists is decreasing, there is evidence that increasing numbers of authors are describing species new to science. In parallel, several statistically sophisticated attempts have been made to better quantify the number of species that may exist on Earth, including the oceans. Estimates of recent extinction rates have also been re-examined to question whether we are in, or heading toward, an anthropogenic mass extinction event. Costello et al. (p. 413) review these findings, provide hope that science will describe most species within this century, and suggest how this complete description can be facilitated.

  10. Reconstituting Synaptic Vesicle Fusion

    Membrane fusion reactions have been reconstituted in vitro, but often the reconstituted reactions have not directly mirrored the requirements for synaptic vesicle fusion in vivo. Previous work generally used only N-ethylmaleimide–sensitive factor (NSF) attachment protein SNAP receptors (SNAREs) and one or two additional components and could not explain why deletion of Munc18-1 or Munc13 abolishes neurotransmitter release completely, yielding the severe disruptions of synaptic vesicle release in knockout mouse. Ma et al. (p. 421, published online 20 December; see the Perspective by Hughson) now present a faithful reconstitution of synaptic vesicle fusion. Membrane fusion required Munc18-1 and Munc13 when the reconstitution experiments included all eight key components (three SNAREs, Munc18-1, Munc13, synaptotagmin-1, NSF, and α-SNAP).

  11. Pondering Pulsars

    Pulsars are rapidly rotating, magnetized neutron stars that are powered by the loss of rotational energy. Because their emission is beamed, their light appears to pulse on and off at regular intervals. Changes in radio emission behavior have been observed for a number of pulsars, manifesting themselves as switches between ordered and disordered variations in intensity and pulse shapes, but these changes have not been seen at other wavelengths. Based on simultaneous radio and x-ray observations of pulsar PSR B0943+10, Hermsen et al. (p. 436) show that changes in emission state identified in radio measurements show counterpart fluctuations in the strength and temporal behavior of x-rays. Some of these changes were unexpected in their character and physical properties, challenging pulsar emission theories.

  12. Mobilizing Transposable Elements

    Transposable elements are parasitic DNA elements that can jump around the genome. They make up large portions of eukaryotic genomes (up to 50% of the human genome). In the short term, transposable elements can generate mutations and cause large-scale damage; but, in the long term, they can drive evolution. Majumdar et al. (p. 446) show that the human THAP9 gene (hTh9), which contains a THAP DNA binding domain also found in the Drosophila P-element transposase, is capable of mobilizing P-elements in Drosophila cells. The hTH9 gene also caused the excision of plasmid-borne Drosophila P-elements in human cells. Furthermore, hTh9 is able to nick P-element DNA and direct its transposition into the human genome.

  13. Epigenetic Controls

    Germ cells in mammals give rise to sperm and eggs. During their development, germ cells undergo extensive epigenetic reprogramming, including global DNA demethylation, which is vital for the totipotency of the developing embryo. Hackett et al. (p. 448) show that the enzymes Tet1 and Tet2 are involved in the demethylation of individual genes and in imprinted gametic differentially methylated regions. The enzymes were also responsible for the global conversion of CpG methylation to 5-hydroxymethylcytosine, which then progressively declines. The findings suggest that demethylation can occur by replication-coupled dilution, although active mechanisms cannot be excluded. A small number of loci escape demethylation, providing a possible mechanistic basis for transgenerational inheritance.

  14. Transcription Factor as Computer

    Cellular signaling pathways can serve to process information so that cells respond appropriately to various environmental stimuli. Hao et al. (p. 460) show that a single yeast transcription factor that is activated in response to stress—Msn2—can act as a signal processor. In an experimental setup in which the amplitude and duration of signaling in the cells could be tightly controlled, sites of phosphorylation on Msn2 that determine its transport into or out of the nucleus allowed it to have different dynamic responses depending upon the amplitude of the signal detected. The transcription factor could either track with the incoming signal, filter (ignore) it, or integrate it. Understanding such properties may be useful in designing behavior of biological control systems.

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