This Week in Science

Science  01 Apr 2011:
Vol. 332, Issue 6025, pp. 10
  1. How Much Information Is Out There?

      In the past 20 years, there have been dramatic changes in the world's ability to generate, communicate, and store information. Hilbert and López (p. 60, published online 10 February) conducted a survey of 60 categories of analog and digital technologies during the period from 1986 to 2007 and observed their changing contributions to global informational capacity. The capacity estimates took into account improvements in hardware performance and in software-based compression rates. The revolution in digital technology appears to have sustained an exponential increase in the global capacity to process information.

    1. Genetics of Candidiasis

        Chronic mucocutaneous candidiasis disease (CMCD) is characterized by chronic or recurring infection with Candida albicans and, to a lesser extent, with Staphylococcus aureus. The underlying cause of CMCD is unknown. Puel et al. (p. 65, published online 24 February; see the Perspective by Dominguez-Villar and Hafler) now report two genetic etiologies associated with CMCD. The first is an autosomal recessive mutation in interleukin 17 (IL-17) receptor A, which prevents its expression. The second is an autosomal dominant mutation in the cytokine IL-17F, which partially reduces its activity. Thus, human IL-17–mediated immunity is required for protection against these mucocutaneous infections.

      1. Conservation: Learning from the Past


          The consequences of climate change are now being taken seriously by conservation bodies and governments, just as information from fossil, historical, and present-day studies is providing new insights into how different species have responded, and could respond. Dawson et al. (p. 53) review evidence that points to a need to move beyond predictions based solely on niche models, because these models neglect many biological differences between species. The emerging challenges are to find alternative ways of anticipating and managing the biodiversity consequences of climate change and to build conservation actions around the natural mechanisms that have allowed species to persist through environmental changes in the past.

        1. Cosmic Complications

            Earth is constantly bombarded by cosmic rays—subatomic charged particles (mostly protons and helium nuclei) that are thought to be accelerated in the shock waves produced by stellar explosions. Using data from the satellite-borne PAMELA experiment, Adriani et al. (p. 69, published online 3 March) report spectral differences between protons and helium in cosmic rays. The results do not match predictions from models of cosmic-ray acceleration and their subsequent propagation through our Galaxy, suggesting that more complex processes need to be considered.

          1. Charging Ahead

              Polymerization resembles a chemical reaction run amok; instead of forming a single discrete product, reagents latch on to one of a slew of growing chains, which in turn can latch on to each other. Some semblance of order can be imposed in a so-called living process, in which catalysts or mediators keep all the chains in the system at more or less the same length throughout the growth period. Magenau et al. (p. 81) used electrochemistry to introduce a finer level of control. Varying an applied bias allowed for rapid modulation of the oxidation state of a copper polymerization catalyst through charge transfer. Because the catalyst is only active in one of the oxidation states, this modulation successively triggered and halted polymerization, facilitating precise control of chain structure.

            1. The Melt Also Rises

                The hot liquid rock that seeps out of mid-ocean ridges makes its way through the oceanic crust when the solid mantle below rises and depressurizes. Understanding the initial stages of melt formation and migration, however, has been based on indirect seismic measurements or limited experimental approaches. Zhu et al. (p. 88) collected three-dimensional images of melting mantle rocks using x-ray synchrotron microtomography. The images reveal the formation of an interconnected melt network at the scale of single mineral grains with a continuous increase of flow velocity of melt in partially molten rocks. Melt is thus extracted from the mantle as a function of the properties of the liquid (for example, viscosity and melt fraction) and not because of a shift in the porosity or permeability of the ocean crust.

              1. Stress Relief

                  The reversible phosphorylation of proteins allows cells to adapt to sudden changes in their environment. Tsaytler et al. (p. 91, published online 3 March; see the Perspective by Wiseman and Kelly) describe a specific small-molecule inhibitor of a regulatory subunit of protein phosphatase 1, guanabenz. Guanabenz selectively bound to a regulatory subunit of protein phosphatase 1 and selectively disrupted the stress-induced dephosphorylation of a subunit of translation initiation factor 2, thereby prolonging translation attenuation in stressed cells. This favored protein folding, promoting resistance to protein misfolding in the endoplasmic reticulum.

                1. Down in the Valley

                    CREDIT: JOHNNY SANDERS

                    Breathtaking alpine landscapes illustrate the powerful nature of glacial erosion. The balance of climate-related forces on the topography and height of mountains is generally measured by the rate of erosion relative to the rate of uplift, but uncertainties related to field measurements compared to models have obscured the general mechanisms. Shuster et al. (p. 84) combined these two approaches on the mountains of Fiordland, New Zealand, to tease out these interrelationships. Isotopic dating suggests that erosion due to glacial activity removed most of the landscape that was older than 2.5 million years. Combined with a landscape evolution model, the results suggest that the modern topography of the region formed as the result of successive advances of erosion up valleys.

                  1. Molecular Motor

                      In most eukaryotes, spatial reorganization of the microtubule cytoskeleton during cell division depends crucially on microtubule cross-linking motors of the kinesin-5 family. Roostalu et al. (p. 94, published online 24 February) combined in vitro and in vivo experiments to examine Cin8, a mitotic kinesin-5 from budding yeast. Single fluorescent molecule imaging and microtubule-sliding assays on chemically functionalized surfaces, as well as in vivo imaging revealed that Cin8 is a bidirectional motor, unlike any other kinesins. Surprisingly, the “default directionality” of this motor was opposite to that of other kinesin-5 proteins. However, the motor was able to switch directionality, depending on whether it was working alone on individual microtubules or as a member of a team between antiparallel microtubules, like those found in the mitotic spindle. Cin8 may thus regulate directionality by sensing the motor-microtubule configuration.

                    1. Nanoparticle Doping

                        CREDIT: MOCATTA ET AL.

                        The deliberate introduction of impurities into semiconducting materials is used to control their electrical properties and forms the basis of modern electronics. When considering nanometer-sized particles, the addition of only a few defect atoms can make the particle highly doped. However, forcing the foreign atoms into the nanoparticle is a challenge. Mocatta et al. (p. 77; see the Perspective by Cao) developed a method to add Cu, Ag, or Au impurities into InAs nanocrystals, which will be important in the fabrication of highly efficient, quantum dot–based electronic devices such as photovoltaic cells and light-emitting diodes.

                      1. Plant Ultraviolet Perception

                          Numerous plant photoreceptors act in the visible wavelengths of light. Now, Rizzini et al. (p. 103) report the discovery of a plant ultraviolet (UV)–B photoreceptor with distinctive mechanistic features. The plant UV-B photoreceptor, the Arabidopsis UVR8 protein, used a specifically positioned aromatic amino acid, tryptophan, as its chromophore. The UV-driven monomerization of UVR8 dimers signaled receptor activation. Furthermore, this plant UV perception system could be transplanted into yeast and mammalian cells.

                        1. Real-World Coevolution

                            In test-tube experiments using bacteria and their viruses, “arms races” evolve between hosts and parasites. Gómez and Buckling (p. 106) took genetically tagged bacteria and their respective phage and developed an experimental system in which soil microcosms containing a background microbial community were inoculated with the tagged microbes. Over time and locally in space, bacteria became resistant to coexisting phage. But resistance is more costly in terms of reproductive capacity in soil compared with the lab, and so the bacteria did not maintain resistance to past strains of phage. Similarly, neighboring strains of phage could not infect bacteria in other neighborhoods. Thus, in the wild, bacteria and phage rapidly coevolve.

                          1. It Takes Heart

                              The once-in-a-lifetime migration of sockeye salmon from the sea to their natal spawning grounds subject fish to extremely challenging physical conditions. These conditions are variable—fish that spawn in coastal tributaries have much easier journeys than those who traverse up-river for many weeks. Eliason et al. (p. 109) examined eight salmon populations that experienced a variety of migration conditions within the Fraser River in British Columbia, Canada. The fish with the most challenging journeys possessed the largest hearts and the best-developed cardiorespiratory system. Thus, local selective regimes have driven physiological adaptation to differing migratory conditions.

                            1. Ferroelectric Bent-Core Mesogen

                                Rodlike mesogenic molecules can form liquid crystal phases where the molecules pack with an overall orientation order but without the translational order found in a solid crystal. If you modify the molecule so that it remains stiff, but has a curved shape like a banana or boomerang, the molecules still form liquid crystalline phases but with a more layered structure. Frustration between the curved shape of the molecule and the desire to pack in a way that minimizes energy can lead to more complex ordering. Reddy et al. (p. 72) show that it is possible to achieve a ferroelectric phase using a bent-core mesogen, despite the fluidity of the material. The ferroelectric properties emerge within the layered ordering, rather than between neighboring layers.

                              1. Regulating snRNAs and snoRNAs

                                  Covalent addition of methyl groups regulates the function of a number of proteins, including histones. The carboxy-terminal domain (CTD) of RNA Polymerase II (RNAPII) is made up of 7-mer repeats, and their site-specific phosphorylation results in the recruitment of regulators to the transcription complex. Sims et al. (p. 99) find in mammalian tissue culture cells that one specific arginine residue, Arg 1810, in a nonconsensus CTD repeat, is methylated by coactivator-associated arginine methyltransferase 1. This methylation event occurs before CTD phosphorylation—thus, before transcription initiation—and plays a role in the regulation of the expression of small nuclear RNAs and small nucleolar RNAs. Arg 1810 and the surrounding sequences are highly conserved in mouse, fish, worms, and flies, which suggests that this mode of regulation will be found in other eukaryotes.