This Week in Science

Science  14 Jun 2013:
Vol. 340, Issue 6138, pp. 1264
  1. Holding Your Breath


    Hemoglobin and myoglobin are widely responsible for oxygen transport and storage (see the Perspective by Rezende). The ability of diving mammals to obtain enough oxygen to support extended dives and foraging is largely dependent on muscle myoglobin (Mb) content. Mirceta et al. (p. 1234192) found that in mammalian lineages with an aquatic or semiaquatic lifestyle, Mb net charge increases, which may represent an adaptation to inhibit self-association of Mb at high intracellular concentrations. Epistasis results from nonadditive genetic interactions and can affect phenotypic evolution. Natarajan et al. (p. 1324) found that epistatic interactions were able to explain the increased hemoglobin oxygen-binding affinity observed in deer mice populations at high altitude. In mammals, the offloading of oxygen from hemoglobin is facilitated by a reduction in the blood's pH, driven by metabolically produced CO2. However, in fish, a reduction in blood pH reduces oxygen carrying capacity of hemoglobin. Rummer et al. (p. 1327) implanted fiber optic oxygen sensors within the muscles of rainbow trout and found that elevated CO2 levels in the water led to acidosis and elevated oxygen tensions.

  2. The Brain Speaks

    The human brain, although overall bilaterally symmetric, shows asymmetry in certain functions such as speech. Bishop (p. 1302) reviews what is known about lateralization of the brain and acquisition of language, focusing on specific language and literacy impairments. Noninvasive imaging techniques have advanced our knowledge of how the brain develops during childhood and suggest that brain lateralization may not be as stable or as determinative as previously thought.

  3. Fermionic Quantum Magnetism


    Optical lattices loaded with cold atoms have been used successfully as quantum simulators of condensed matter systems; however, in the case of fermionic quantum magnetism, achieving low enough temperatures has been a major obstacle. Greif et al. (p. 1307, published online 23 May; see the Perspective by Porto) selectively tuned the exchange interactions in an optical lattice of fermions, forcing a redistribution of entropy such that in the low-entropy subsystem the effective temperature was sufficiently low enough to lead to magnetic correlations.

  4. Redox Recycling

    Plate tectonics drive the continuous exchange of material between Earth's crust and mantle. Subduction adds crustal materials to the mantle, which influence the composition of erupted lavas at mid-ocean ridges. Because chemical and physical processes in the mantle change over time as a response to the availability of oxygen, the redox state of mid-ocean ridge basalts may trace the history of recycling between crust and mantle. Cottrell and Kelley (p. 1314, published online 2 May) analyzed the relation between the oxidation state of iron in a global suite of mid-ocean ridge basalts and tracers for mantle source composition. Over tectonic time scales, the recycling of reduced carbon in ancient crustal sediments may result in the preservation of more reduced zones in the mantle.

  5. Dusty Origins

    The formation of cirrus clouds begins with the production of ice nuclei, on which water vapor then condenses. Cziczo et al. (p. 1320, published online 9 May) determined the kinds of particles on which cirrus ice crystals form by sublimating samples collected by research aircraft and analyzing the chemical and physical properties of the residual seeds. Most of the seed particles were either mineral dust or metallic.

  6. Common Water

    The Moon has been traditionally considered bone-dry, but in recent years a number of studies have shown that during mantle melting, the lunar mantle had as much water as Earth's upper mantle. Saal et al. (p. 1317, published online 9 May; see the cover) measured the isotopic composition of hydrogen dissolved in volcanic glass and olivine-hosted melt inclusions recovered from the Moon by the Apollo 15 and 17 missions. Lunar magmatic water was indistinguishable from the bulk water in carbonaceous chondrites and similar to terrestrial water, implying a common origin for the water contained in the interiors of Earth and the Moon.

  7. Methylation and Methuselah?

    Hutchinson-Gilford progeria syndrome (HGPS) and other prelamin A–associated progeroid disorders arise when farnesylated and methylated forms of prelamin A accumulate at the nuclear envelope. Ibrahim et al. (p. 1330, published online 16 May; see the Perspective by Johnson) show that reducing the activity of the isoprenylcysteine carboxyl methyltransferase (ICMT) mislocalizes prelamin A, triggers prelamin A–dependent AKT-mTOR signaling, and eliminates disease phenotypes in 30-week-old progeria model mice. Reduced ICMT expression increased the proliferation and delayed the premature senescence of progeria model mouse fibroblasts and cells from children with HGPS.

  8. A Sense of Place

    Hippocampal place cells are believed to be mainly governed by visual and self-motion cues. However, the contribution of sensory cues such as smells, sounds, and textures, etc., is difficult to eliminate. In virtual reality, these cues will not provide any information about the animals' position. Ravassard et al. (p. 1342, published online 2 May) developed a virtual-reality system as immersive and close to the real world as possible and compared place cells in rats running in this apparatus and in the real world. Twice as many neurons were active in a real-world situation compared to virtual reality. While place cells in the real world encoded position, place cells in a virtual world encoded distance.

  9. Choosing Water

    Aquaporins are proteins that facilitate transport of water across biological membranes. They must be selective for water, without binding it so tightly as to impede transport, and they must prevent proton transfer by rapid exchange between hydrogen-bonded water molecules. Kosinska Eriksson et al. (p. 1346; see the Perspective by Abramson and Vartanian) describe the subangstrom resolution structure of yeast aquaporin, which allows assignment of side-chain conformations and shows that the H-bond geometry of water molecules prevents proton conductance without compromising water transport.

  10. Atomic Layer Heterostructures—More Is More

    The isolation of stable layers of various materials, only an atom or several atoms thick, has provided the opportunity to fabricate devices with novel functionality and to probe fundamental physics. Britnell et al. (p. 1311, published online 2 May; see the Perspective by Hamm and Hess) sandwiched a single layer of the transition metal dichalcogenide WS2 between two sheets of graphene. The photocurrent response of the heterostructure device was enhanced, compared to that of the bare layer of WS2. The prospect of combining single or several-atom-thick layers into heterostructures should help to develop materials with a wide range of properties.

  11. Converting Polarization


    The conversion of a light signal from one polarization direction to another plays an important role in communication and metrology. The components that are presently used for polarization conversion, however, tend to be relatively large, which is an issue that can make it difficult to integrate with chip-scale optoelectronic circuits. Grady et al. (p. 1304, published online 16 May) used a metasurfaces approach involving a designed array of cut wires to manipulate the polarization state of the propagating terahertz signals. Proper design of the device structure allowed for the control of the polarization conversion state for both reflected and transmitted light over a broad frequency range.

  12. Too Much or Too Little

    An important task of the nervous system is to distribute information appropriately throughout the brain. The olfactory and gustatory systems of Drosophila provide good models for understanding these processes and the underlying mechanisms (see the Perspective by Su and Carlson). Lin et al. (p. 1338) mapped out the circuit that detects carbon dioxide (CO2), an important environmental and communication signal for fruit flies. Two distinct classes of projection neurons mediate avoidance of high and low concentrations of CO2, while a third class, comprising inhibitory neurons, shuts down the low-concentration pathway at high concentrations. In contrast to other basic taste qualities, salt is innately attractive at low concentrations, but aversive at high concentrations. The mechanisms underlying salt detection are poorly understood in any species mainly because of a lack of specific molecular tools. Zhang et al. (p. 1334) discovered that Drosophila uses two types of gustatory receptor neurons to distinguish between high and low concentrations of salt. One type is activated maximally by low salt and induces attractive feeding behavior. The other class of receptors is activated primarily by high salt and leads to avoidance behavior.