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<jats:p>Despite the importance of myelin for the rapid conduction of action potentials, the molecular bases of oligodendrocyte differentiation and central nervous system (CNS) myelination are still incompletely understood. Recent results have greatly advanced this understanding, identifying new transcriptional regulators of myelin gene expression, elucidating vital roles for microRNAs in controlling myelination, and clarifying the extracellular signaling mechanisms that orchestrate the development of myelin. Studies have also demonstrated an unexpected level of plasticity of myelin in the adult CNS. These recent advances provide new insight into how remyelination may be stimulated in demyelinating disorders such as multiple sclerosis.</jats:p>

<jats:p>Microglia are resident brain cells that sense pathological tissue alterations. They can develop into brain macrophages and perform immunological functions. However, expression of immune proteins by microglia is not synonymous with inflammation, because these molecules can have central nervous system (CNS)–specific roles. Through their involvement in pain mechanisms, microglia also respond to external threats. Experimental studies support the idea that microglia have a role in the maintenance of synaptic integrity. Analogous to electricians, they are capable of removing defunct axon terminals, thereby helping neuronal connections to stay intact. Microglia in healthy CNS tissue do not qualify as macrophages, and their specific functions are beginning to be explored.</jats:p>

<jats:p>The atom formed from an electron and positron interacts with molecules almost as if it were a free electron.</jats:p>

<jats:title>Tonic Inhibition</jats:title> <jats:p> Neuronal inhibition has recently drawn much attention; however, the mechanisms involved in tonic release of and the cellular source of the neurotransmitter involved, γ-aminobutyric acid (GABA), have been difficult to pin down. <jats:bold> Lee <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="790" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1184334">790</jats:related-article> , published online 23 September) showed that tonic release of GABA in the cerebellum occurs through the Bestrophin 1 anion channel of cerebellar astrocytes and Bergmann glial cells. These results confirm that glia can serve as a source of GABA for tonic inhibition of neurons and provide more evidence for interactions between neurons and glia cells that have implications for our understanding of brain-signaling mechanisms. </jats:p>

<jats:title>Dissecting Self-Incompatibility</jats:title> <jats:p> Although the pollen may be available for a flower to fertilize itself, molecular determinants on the pollen and the pistil prevent inbreeding in a process termed self-incompatibility. In the <jats:italic>Petunia</jats:italic> self-incompatibility, if male determinants (F-box proteins) on pollen are recognized by a female ribonuclease determinant on the pistil, the pollen tube is killed when its ribosomal RNA is digested. Outcrossed fertilizations can occur because of allelic diversity in the female that fails to recognize its male counterparts; however, the genetic diversity of the ribonuclease gene is greater than that of the known <jats:italic>F-box</jats:italic> gene. <jats:bold> Kubo <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="796" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195243">796</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6005" page="796" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195243"> <jats:bold>Indriolo and Goring</jats:bold> </jats:related-article> ) have discovered that there are several related <jats:italic>F-box</jats:italic> genes in <jats:italic>Petunia</jats:italic> , each of which brings its own allelic diversity to bear—thus, increasing the variety of potential mating partners. </jats:p>

<jats:title>Through a Lens Brightly</jats:title> <jats:p> Astronomical sources detected in the submillimeter range are generally thought to be distant, dusty galaxies undergoing a vigorous burst of star formation. They can be detected because the dust absorbs the light from stars and reemits it at longer wavelengths. Their properties are still difficult to ascertain, however, because the combination of interference from dust and the low spatial resolution of submillimeter telescopes prevents further study at other wavelengths. Using data from the Herschel Space Telescope, <jats:bold> Negrello <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="800" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193420">800</jats:related-article> ) showed that by searching for the brightest sources in a wide enough area in the sky it was possible to detect gravitationally lensed submillimeter galaxies with nearly full efficiency. Gravitational lensing occurs when the light of an astronomical object is deflected by a foreground mass. This phenomenon increases the apparent brightness and angular size of the lensed objects, making it easier to study sources that would be otherwise too faint to probe. </jats:p>

<jats:title>Weakly Interacting Graphene</jats:title> <jats:p> Many unusual properties of graphene are a consequence of the Dirac dispersion of its electrons—a linear relationship between an electron's momentum and energy. Naïvely, this dispersion leads to the conclusion that electrons in graphene are strongly affected by mutual electrostatic interactions; however, there is little experimental evidence for strong interaction. <jats:bold> Reed <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="805" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1190920">805</jats:related-article> ) resolved this discrepancy by using inelastic x-ray scattering spectra of graphite (which consists of loosely bound layers of graphene) to estimate how much the electric field was damped by the presence of mobile charge carriers. In fact, damping was strong at distances in excess of 1 nanometer, suggesting that graphene is more weakly interacting than was assumed. </jats:p>

<jats:title>Bend It, Stretch It</jats:title> <jats:p> Materials (such as those found in some artificial muscle systems) that are used for stimulus-controlled bending or stretching, require long-range ordering so that local chemical triggers will result in long-range bending or flexing motions. <jats:bold> Hosono <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="808" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195302">808</jats:related-article> ) observed that a sandwich of a polymethacrylate between uniaxially stretched Teflon sheets develops three-dimensional ordering. Upon hot pressing, the main chains of the polymer brushes aligned homeotropically to the film plane, whereas the side chains, containing azobenzene groups, oriented horizontally along the drawing direction of the Teflon sheets. With some azobenzene groups, alternate irradiation with ultraviolet and visible light made the composites bend and stretch reversibly. </jats:p>

<jats:title>Broken Symmetries</jats:title> <jats:p> Bilayer graphene samples are expected exhibit quantum Hall states that are ferromagnetic with different types of spin ordering. <jats:bold> Weitz <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="812" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1194988">812</jats:related-article> , published online 14 October) studied the conductance of high-quality suspended bilayer graphene samples. They used an applied perpendicular electric field to induce transitions between the different broken-symmetry states that appear at low carrier densities and deduced their order parameters. These states appeared in both the absence of a magnetic field, as well as in the presence of a symmetry-breaking magnetic field. They also showed that, even in absence of both an applied magnetic or electric field, the bilayer exhibits an energy gap, which indicates that electron-electron interactions contribute to the band structure. </jats:p>

<jats:title>Volatiles Versus Vegetation</jats:title> <jats:p> Plants act as both global sources and sinks of highly reactive volatile organic compounds (VOCs). Models typically treat the uptake and degradation of these compounds as if they are mostly unreactive, like other more commonly studied biogenic gases such as ozone. A study by <jats:bold> Karl <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="816" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1192534">816</jats:related-article> , published online 21 October) suggests that VOCs may be more reactive than expected. By monitoring six field sites representing a range of deciduous ecosystems, several oxidized VOCs were found to have high deposition fluxes. Fumigation experiments in the laboratory confirmed that leaves are capable of oxidizing these compounds, and do so through an enzymatic detoxification or stress-response mechanism. Budgets for VOC flux in the atmosphere suggests that, on a global scale, plants may take up significant levels of VOCs in polluted regions, especially in the tropics. </jats:p>