This Week in Science

Science  05 Oct 2012:
Vol. 338, Issue 6103, pp. 11
  1. Plant Anti-Insect Armaments


    Because individual plants are unable to relocate, they are subject to extreme selection by the insects feeding upon them. One means by which plants suppress herbivory is to produce toxic compounds to deter feeding (see the Perspective by Hare). Agrawal et al. (p. 113) compared pesticide–treated or untreated evening primroses. Over 5 years of pesticide treatment, the production of defensive chemicals in the fruit reduced and flowering times shifted, and the primrose's competitive ability against dandelions improved. Züst et al. (p. 116) examined large-scale geographic patterns in a polymorphic chemical defense locus in the model plant Arabidopsis thaliana and found that it is matched by changes in the relative abundance of two specialist aphids. Thus, herbivory has strong and immediate effects on the local genotypic composition of plants and traits associated with herbivore resistance.

  2. Grinding Out Earthquake Physics

    Simulating earthquakes in the lab produces events that are often orders of magnitude lower in energy than large, damaging earthquakes; thus, it is unclear how well the behavior along these simulated faults extrapolates to the physics of large earthquakes. Chang et al. (p. 101; see the Perspective by Shimamoto and Togo) used a rotary apparatus that spins in tandem at high speeds with a disc-shaped rock sample, producing energies comparable to earthquakes of magnitudes 4 to 8. Experiments using both granite and dolomite samples suggest that the weakening of slip along faults during large earthquakes is a product of intense accelerations associated with the rupture event.

  3. Homogeneous Melting


    The nucleation and melting of crystals are primarily driven by surfaces and defects, which can lower the thermodynamic barrier to a phase transition. A harder problem to study is when the transition occurs uniformly. Wang et al. (p. 87; see the Perspective by Weeks) imaged the homogeneous melting of superheated colloidal crystals using a laser to initiate the melting at the interior of the crystal. The authors were then able to track nucleation precursors and nucleus evolution and to find where defects and instabilities limited the homogeneous melting process.

  4. Watching Supercoiled DNA

    The DNA double helix can undergo additional twisting, or supercoiling, that plays a role in transciption and protein binding, in part by bringing distant DNA locations together. The process forms intertwined loops, called plectonemes, and van Loenhout et al. (p. 94, published online 13 September; see the Perspective by Sheinin and Wang) visualized plectoneme dynamics of fluorescently labeled, 21-kilobase tethered DNA molecules using magnetic tweezers to apply twisting forces. Plectonemes could diffuse along the DNA, but move more rapidly if they “hopped”—nucleating a plectoneme at a new position.

  5. Theory Drives Understanding

    The role of theory and simulation in neuroscience has been hotly debated over the past few years, in particular in the context of the recent launch of several big projects aimed at creating artificial or virtual brains. Gerstner et al. (p. 60) review how theory and simulations have interacted over the years and how they have contributed to our present view of how the brain works.

  6. Reversing Autism in Mice

    Autism comprises a heterogeneous group of neurodevelopmental disorders characterized by defects in communication and social inter action. A group of nonsyndromic forms of autism is associated with mutations in the neuroligin genes, which encode postsynaptic adhesion molecules. Using a reversible knockout approach, Baudouin et al. (p. 128, published online 13 September) investigated the in vivo functions of neuroligin-3 in the mouse cerebellum. Mutant mice showed a major defect in metabotropic glutamate receptor–dependent, long-term potentiation; disrupted heterosynaptic competition; and ectopic synapse formation in vivo. These synaptic defects could be rescued by reactivation of the neuroligin gene in the adult.

  7. Lending a Hand to CO2 Reduction

    Although plants and microbes have been reducing CO2 with ease for millennia, people still find it extremely challenging. A cost-effective synthetic scheme for transforming CO2 into fuels and commodity chemicals would be a double boon, lowering atmospheric concentration of the greenhouse gas while supplementing (and perhaps ultimately replacing) dwindling petroleum feedstocks. Toward this end, Costentin et al. (p. 90) show that an iron catalyst for the electrochemical reduction of CO2 to CO gets an efficiency boost from phenol substituents appended to the ligand framework.

  8. A Toothy Problem

    Large mammalian herbivores such as horses and bison are well known to possess a complex, grinding dentition that facilitates processing of their tough, cellulose-rich plant diet. Hadrosaurid, or duck-billed, dinosaurs also possessed complex teeth, but how this was achieved has been unknown because reptiles typically possess simple teeth. Erickson et al. (p. 98) show how Hadrosaurs evolved teeth composed of six tissues, which allowed for the development of tooth complexity rivaling, or exceeding, that of modern herbivorous mammals.

  9. Puzzling Through Gravity

    Much of the excitement of scientific discovery seems to get lost when science is taught as facts by lectures. Granger et al. (p. 105) present a large study of outcomes comparing inquiry-based teaching with more traditional teaching methods. Over 2000 students were involved, in 125 classrooms of 4th- and 5th-graders. The classes studied space-science with a curriculum that uses models and evidence to entice students into improving their own understanding of the science. Students who were encouraged to use evidence to support their models seemed to develop improved knowledge of content.

  10. Of Microbes and Cancer

    Inflammation is a well-established driver of tumorigenesis. For example, patients with inflammatory bowel disease have an elevated risk of developing colorectal cancer (CRC). Whether the gut microbiota also contributes to the development of CRC is less well understood. Arthur et al. (p. 120, published online 16 August; see the Perspective by Schwabe and Wang) now show that the microbiota does indeed promote tumorigenesis in an inflammation-driven model of CRC in mice. Although germ-free mice were protected against developing cancer, colonization of mice with Escherichia coli was sufficient to drive tumorigenesis.

  11. Regulating Opioid Responses

    Different drugs of abuse are thought to highjack similar reward systems in the brain using common mechanisms. However, Koo et al. (p. 124) now observe that some of the neural mechanisms that regulate opiate reward can be both different and even opposite to those that regulate reward by stimulant drugs. While knockdown of brain-derived neurotrophic factor (BDNF) in the ventral tegmental area in mice antagonized the response to cocaine, the same manipulation strengthened the potential of opiates to increase dopamine neuron excitability. Optogenetic stimulation of dopaminergic terminals in the nucleus accumbens could counteract the effects of BDNF on morphine reward blockade.

  12. Gut, Heal Thyself


    Foods, drugs, and pathogens all represent possible threats to our guts on a daily basis. Fortunately, the gut is quite good at repairing itself—but how? Working in mice, Miyoshi et al. (p. 108, published online 6 September; see the Perspective by Barrett) selectively injured intestinal crypts containing intestinal stem cells and observed therepair process. The noncanonical Wnt ligand, Wnt5a, was required for crypt regeneration. Wnt5a inhibited intestinal stem cell proliferation, which paradoxically promoted regeneration of crypt tissue.

  13. Salience, Values, and Decisions

    How does the brain make value-based decisions? There are two major competing models: the goodsbased model and the action-based model of value. Leathers and Olson (p. 132) designed a critical experiment to decide between these two views. In the monkey brain, lateral intraparietal neurons responded strongly to stimuli predicting both large rewards and large penalties, encoding the salience of the stimulus rather than reward value, which refutes both models.

  14. Changing Your Belief

    The ability to display behavioral flexibility depends on an internal representation of the environment—a framework of beliefs that can be adjusted on the basis of experience. Recording from multiple electrodes in the rat medial prefrontal cortex, Karlsson et al. (p. 135) investigated how ensembles of neurons changed their activity during the performance of a task in which the animal had to update its knowledge of reward contingencies. The results suggest that changes in perceived action-outcome contingencies were associated with abrupt switches in neuronal representations in the rat medial prefrontal cortex.

  15. Close to a Black Hole

    At the center of our Galaxy, there is a black hole that is 4 million times as massive as the Sun. Using data from the Keck Observatory, Meyer et al. (p. 84) detected a star orbiting this black hole with a period of 11.5 years, the shortest period among the stars orbiting it. The star is the second well-sampled star with an orbital period under 20 years. Having detailed knowledge about two stars with short periods and full orbit coverage will be crucial in testing Einstein's theory of general relativity in the gravitational field close to a massive black hole.

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