Editors' Choice

Science  25 Jun 2010:
Vol. 328, Issue 5986, pp. 1613
  1. Applied Physics

    Low-Energy Light Switches

    1. Ian S. Osborne
    CREDIT: ISTOCKPHOTO.COM

    The backbone of high-speed communications consists of optic fibers that carry information as pulses of light. Light-sensitive bistable optical resonators coupled to the fibers are capable of controlling the transmitted light, allowing access to the higher information transfer rates offered by all-optical switching. However, the relatively high amount of energy (or light intensity) required to switch an optical resonator between its two states (transmission ON, transmission OFF) can be a limiting factor with regard to power requirements. Sandhu et al. use numerical simulations to show that coherent control, or pulse shaping, of the switching light pulses can reduce the input energy requirements for switching the optical resonator. Moreover, because the peak energy input to the resonator is dependent on the phase of the input pulse, switching by phase modulation should be possible, thus offering the potential for even higher bit rates than attainable with intensity modulation–based protocols.

    Appl. Phys. Lett. 96, 231108 (2010).

  2. Astrophysics

    Whence the Solar System?

    1. Maria Cruz

    Primitive materials within meteorites hold evidence for processes that occurred during the earliest stages of the solar system. In particular, the inclusion of the daughter products of now-extinct, short-lived radioisotopes tells us that the parent isotopes were active at the time they were incorporated into the solar system's earliest solids. One such isotope is 60Fe, whose origin is attributed to either a core-collapse supernova (the thermonuclear explosion of a massive star) or an intermediate-mass asymptotic giant branch (AGB) star. Sun-like stars end their lives as AGB stars; in the late stages of their evolution, these stars expel their outer envelopes and shine as planetary nebulae as their hot surfaces are exposed and ionize material around them. The ejecta of AGB stars or supernovae drive shock fronts into the interstellar medium, a process posited to have triggered the collapse of the cloud from which the Sun formed and then injected freshly synthesized radioisotopes into it. Using numerical simulations to test both scenarios (supernova versus AGB), Boss and Keiser show that only supernovae have thin enough shock waves to inject the material necessary to match the abundances of short-lived radioisotopes measured in primitive meteorites.

    Astrophys. J. 717, L1 (2010).

  3. Biochemistry

    Signaling Without G Proteins

    1. L. Bryan Ray

    The angiotensin II receptor is a key regulator of blood pressure and other physiological processes. Binding of its ligand activates an associated heterotrimeric guanine nucleotide–binding protein (G protein). Rakesh et al. describe a different signal emitted by this receptor in the mouse heart when it responds to a mechanical stimulus. Usually, the protein β-arrestin acts to limit signaling by G protein–coupled receptors, but it can also promote signaling cascades that are independent of G proteins. Stretching the mouse heart by inflating a balloon within the left ventricle triggered receptor signaling that was independent of its associated G protein but that required β-arrestin 2 and the protein kinases that stimulate the association of β-arrestin 2 with the receptor. Such β-arrestin–dependent signaling by the angiotensin II receptor may turn on protective mechanisms when the heart is under stress. Indeed, the hearts of mice lacking β-arrestin 2 or the angiotensin II receptor showed reduced signaling and increased cell death in response to mechanical stretch.

    Sci. Signal. 3, ra46 (2010).

  4. Cell Biology

    The Ins and Outs of Import

    1. Helen Pickersgill
    CREDIT: DISHINGER ET AL., NAT. CELL BIOL. 12, 10.1038/NCB2073 (2010)

    There are several different mechanisms available for moving proteins to where they need to be. In eukaryotes, nuclear proteins, which are synthesized in the cytoplasm, are transported into the nucleus by means of nuclear localization signals encoded in their amino acid sequence; these signals are recognized by receptors of the importin/karyopherin family, which directionally ferry their protein cargo from the cytoplasm into the nucleus with the aid of the small GTPase Ran. A gradient of accessory proteins across the nuclear membrane produces a corresponding gradient of the GTP- and GDP-bound forms of Ran. In the cytoplasm, where there are low levels of RanGTP, the import receptors bind their cargoes and carry them across the nuclear envelope. Upon reaching the nucleus, the receptors encounter high levels of RanGTP and release their loads.

    Dishinger et al. find that this mode of conveyance is also used to transport molecules to a distant part of the cell. They identified a sequence within a kinesin motor protein, KIF17 (green), that targets it to the primary cilium (red), which is an organelle protruding from the cell surface. A RanGTP/GDP gradient between the cilia and the cytoplasm was required for the localization of KIF17 to the cilia. Furthermore, a member of the importin family of receptors bound KIF17, and this interaction was sensitive to RanGTP in vitro, thus revealing shared laborers in nuclear and ciliary import.

    Nat. Cell Biol. 12, 10.1038/ncb2073 (2010).