This Week in Science

Science  25 May 2012:
Vol. 336, Issue 6084, pp. 956
  1. Spring Into Flower


    In spring, plants respond to increasing day length and shifts in the spectrum of solar irradiance by releasing the flowering induction pathway, which includes expression of the FLOWERING LOCUS T (FT) protein. Song et al. (p. 1045) have now identified a trio of controls brought to bear on FT gene expression by the FKF1 (FLAVIN-BINDING, KELCH REPEAT, F-BOX 1) protein. FKF1 removes a repressor and also stabilizes the activating CONSTANS (CO) protein in the afternoons through a binding interaction enhanced by blue light—an increasing component of solar irradiation during spring. Then FKF1 itself helps to activate transcription of the CO gene. Thus, by removing the repressor and shoring up the activator, FKF1 sets flowering on its way.

  2. Pull Me-No!-Push You

    The Drosophila dorsal-ventral (DV) axis is polarized by the movement of the nucleus from the posterior end of the oocyte to its anterior margin. It has long been assumed that the nucleus is pulled to the anterior end by the molecular motor dynein along the polarized microtubule cytoskeleton that defines the anterior-posterior (AP) axis. Using live imaging, Zhao et al. (p. 999, published online 12 April; see the Perspective by Bowerman and O'Rourke) now demonstrate that the nucleus is pushed toward the anterior by the force exerted by growing microtubules hitting its posterior side. DV polarity thus depends on the posterior positioning of the microtubule organizing center rather than on AP axis formation.

  3. Subterranean Eruption Clues

    Volcano monitoring relies upon detecting changing physical conditions around an active source, such as increased seismicity or ground deformation; however, relating these behaviors to magmatic processes below ground remains challenging. The geochemical signatures of erupted magmatic crystals, including chemically distinct zones formed during growth and cooling, provide clues as to the conditions of the magma chamber prior to the eruption. Through a combination of chemical analysis of orthopyroxene crystals and chronometry based on diffusion, Saunders et al. (p. 1023) were able to link the magmatic processes and seismic events leading up to and during the 1980–1986 series of eruptions at Mount St. Helens, USA. The seismic events corresponded to earthquakes caused by magma degassing and ground movement—events of which are routinely detected with geophysical instruments.

  4. Tiny Tinny Bumps


    One challenge in moving to three-dimensional integrated circuit architectures is the need for aligned interconnects to join neighboring layers. Hsiao et al. (p. 1007) applied rapid stirring to the direct current electroplating of copper to produce films with oriented copper grains that have a high density of nanotwin defects. The resulting material was an excellent platform for the growth of copper-tin intermetallic compounds in the form of arrays of microbumps potentially suitable for the soldering of electronic components.

  5. Majoranas Arrive

    When a negatively charged electron meets a positron—its positively charged antiparticle—they annihilate each other in a flash of gamma rays. A Majorana fermion, on the other hand, is a neutral particle, which is its own antiparticle. No sightings of a Majorana have been reported in the elementary particle world, but recently they have been proposed to exist in solid-state systems and suggested to be of interest as a quantum computing platform. Mourik et al. (p. 1003, published online 12 April; see the cover; see the Perspective by Brouwer) set up a semiconductor nanowire contacted on each end by a normal and a superconducting electrode that revealed evidence of Majorana fermions.

  6. Growing in Liquid

    The ability to control the growth of materials at the nanometer scale is key to nanotechnology. Materials grown in liquids, however, are difficult to track on a particle-by-particle basis during growth. Two studies used an in situ liquid cell to follow the formation of larger nanoparticles or nanorods grown in solvents using high-resolution transmission electron microscopes. Liao et al. (p. 1011) watched platinum iron nanorods form from kinked chains of connected nanoparticles that gradually reoriented and straightened to form rigid rods. Li et al. (p. 1014) observed the coalescence of iron oxyhydroxide nanoparticles through an oriented attachment mechanism, whereby two similar particles rotated until their corresponding crystal lattices aligned.

  7. Maximizing Molecular Pore Diameters

    Amorphous materials, such as activated carbon, can have pore diameters of several nanometers, but the synthesis of ordered structures with very large pore diameters is often thwarted by the creation of interpenetrating networks or difficulties in removing guest molecules. Deng et al. (p. 1018) avoided these problems in the synthesis of metal-organic frameworks (MOFs) with very large diameters (some exceeding 3 nanometers) by using a combination of short and very long linking groups. The compounds formed channels almost 10 nanometers in diameter that could be visualized by electron microscopy and that were large enough to accommodate protein molecules.

  8. New Digs

    Many studies predict range alterations among species in response to climate change. Species, however, cannot be thought of as truly independent entities, because they all exist as a part of an interacting community. Most discussions of such interactions have focused on the potential restrictions they might place on range expansion; however, Pateman et al. (p. 1028) show that climate change has the potential to increase the number of species that can interact and thus facilitate expansion. British data collected by the general public on sightings of the Brown Argus butterfly and its host plants revealed an increased affiliation between the butterflies and a previously little-used group of plants. As summers warmed, populations associated with the new host were more productive than those associated with the more “traditional” host, which facilitated expansion of the butterflies into novel regions.

  9. Finessing Crystal Analysis


    Protein crystallography has revolutionized our understanding of a whole variety of biological processes (see the Perspective by Evans). In crystallography, the measure of agreement between the data and the calculated model is not on the same scale as the measure of data quality, making it challenging to choose an optimal high resolution limit beyond which the data should be discarded. Now, Karplus and Diederichs (p. 1030) introduce a statistical model that assesses agreement of model and data accuracy on the same scale. Determining the structures of biological macromolecules by x-ray crystallography requires solving the phase problem. The two techniques that dominate phase evaluation (multi- and single-wavelength anomalous diffraction) rely on element-specific scattering from incorporated heavy atoms. Liu et al. (p. 1033) present procedures for routine structure determination of native proteins with no heavy atom incorporation. The technique, which relies on combining data from multiple crystals, was used to determine the structures of four native proteins, including a 1200-residue complex.

  10. More Glycine, Please

    To better characterize metabolic properties of cancer cells, Jain et al. (p. 1040; see the Perspective by Tomita and Kami) measured systematically the concentrations of hundreds of metabolites in cell culture medium in which 60 different cancer cell lines were growing. The fastest growing cancer cells tended to consume glycine, whereas more slowly growing cells excreted some glycine. The rapidly growing cancer cells appeared to need glycine for synthesis of purine nucleotides required for continued synthesis of DNA. Interfering with glycine metabolism slowed growth of the rapidly proliferating cancer cells. Thus, an increased dependence on glycine by rapidly growing cancer cells could potentially provide a target for therapeutic intervention.

  11. Who's Who

    Different languages rely on distinct sets of terminology to classify relatives, such as maternal grandfather in English, and precision in language usage is a key component for successful communication (see the Perspective by Levinson). Kemp and Regier (p. 1049) propose an organizing framework whereby kinship classification systems can all be seen to optimize or nearly optimize both simplicity and precision. The labels applied to kin are constructed from simple units and are precise enough to reduce confusion and ambiguity when used in communication. Frank and Goodman (p. 998) show that simplicity and precision also explain how listeners correctly infer the meaning of speech in the context of referential communication.

  12. Magnetic Sense

    Many species orient and navigate using aspects of Earth's magnetic field. Magnetic receptors have been found in the eyes, ears, and bills of birds, but there has been no clear evidence of the neural mechanism by which magnetic signals are translated into direction. Recording from the brainstem within conscious pigeons, Wu and Dickman (p. 1054, published online 26 April; see the Perspective by Winklhofer) reveal the presence of neurons in the pigeon's brain that encode the inclination angle and intensity of the geomagnetic field. Thus, pigeons—and perhaps other species—can develop an internal model of geopositional latitude to facilitate spatial orientation and navigation based on magnetoreception.

  13. Human Argonaute Revealed

    RNA interference (RNAi) is mediated by Argonaute (Ago) proteins, which bind small regulatory RNAs that have sequence complementarity to target RNAs destined to be silenced. The structure of bacterial homologs of the Ago proteins, and fragments of eukaryotic Ago proteins, have provided initial insights into Ago function. Now, Schirle and MacRae (p. 1037, published online 26 April; see the Perspective by Kaya and Doudna) have determined the structure of the full-length human Ago protein bound to a single-stranded (ss) guide RNA. Within the bilobed structure, eight nucleotides of the ssRNA are visibly positioned in the RNA-guide, strand-binding site. The “seed” region of the ssRNA has its Watson-and-Crick base edges exposed to solvent, likely aiding target recognition. The location of two free tryptophans in the Piwi domain suggests a possible recruitment site for Ago-interacting proteins.

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