Editors' Choice

Science  16 May 2014:
Vol. 344, Issue 6185, pp. 673
  1. Neurodevelopment

    Neural Circuits One Step At a Time

    1. Pamela J. Hines

    How do simple neurons come together to form a complicated circuit? To answer this question, Pecot et al. studied a well-defined circuit in the eye of the fruit fly Drosophila melanogaster, which is composed of two different types of neurons, to learn the intricate steps in the circuit-building dance. The fruit fly's eye is built of repetitive units made up of eight photoreceptor neurons and five lamina neurons each. Each unit perceives light and transmits chemical signals into the fly's brain. But before the unit can work, the circuit needs to form. That happens step by step, as one neuron signals to another. Photoreceptor neurons of type 1 through 6 send a chemical signal to lamina neuron 3. Lamina neuron 3 in turn sends out a homing beacon to guide photoreceptor neuron 8 to its correct destination. Without the correct signals, lamina neuron 3 dies, and without the lamina homing beacon, photoreceptor neuron 8 remains lost in no-man's land.

    Neuron 82, 320 (2014).

  2. Materials Science

    Perpetual Heart Throb

    1. Marc S. Lavine

    Many cardiac conditions require the implantation of a pacemaker or defibrillator to help regulate the contractions of the heart. While these devices are extremely helpful in extending and improving the quality of a person's life, they need to be replaced every few years, primarily because of the limited life span of the batteries. One potential solution may come from energy-harvesting materials that can convert small mechanical motions into electrical energy, and thus could exploit cardiac motion, muscle contractions, and relaxation, or blood circulation as the driving source for power generation. Hwang et al. created a self-powered artificial pacemaker using single, crystalline PMNPT [(1-x) Pb(Mg1/3Nb2/3)O3 − x PbTiO3] placed on a thin plastic substrate. Through low-frequency flexing of the substrate back and forth, a current of more than 100 microamperes at 8 volts was generated, enough to power a string of commercial LED lights or recharge a coin battery. A sample device was implanted into the cardiac muscle of an anesthetized rat and enabled real-time electrical stimulation. The next step for the authors is to test a stack of devices to see if they can harvest energy from the heart of a larger animal such as a pig.

    Adv. Mat. 10.1002/adma.201400562 (2014).

  3. Biomaterials

    Viral Envelopes Built Better

    1. Barbara R. Jasny

    Drawing inspiration from virus structure has the potential to make nanoparticles more stable and better at hiding from the immune system which might help researchers expand the uses of nanoparticles in the clinic. Nanotechnology can enhance drug targeting and improve the engineering of nanoscale medical devices. Perrault and Shih mimicked the strategy viruses use to protect their genetic information. They fabricated a DNA cage structure in the form of a nanooctahedron with a diameter of 50 nm. The structure had “handles” made from single-stranded DNA on the inside and outside of the cage. The inner set of handles was designed to attach to fluorophore-conjugated oligonucleotides, providing a visible marker for the structure. The outer set of handles was designed to attach to lipid-conjugated oligonucleotides, so that the researchers could then assemble a lipid bilayer around the DNA cage. The resulting particles were 76 nm in diameter and resembled enveloped virus structures. The particles were more resistant to nucleases in vitro and caused immune cells isolated from mouse spleens to produce much lower levels of the inflammatory cytokines IL-6 and IL-12. The particles also stayed in the bodies of injected mice for longer times than unencapsulated DNA cages.

    ACS Nano. 10.1021/nn5011914 (2014).

  4. Paleoclimate

    Too Short to Show

    1. H. Jesse Smith

    During the last ice age, the climate of Greenland (and much of the Northern Hemisphere) jumped between cold intervals (called stadials) and warm ones. Records from ice cores show that the concentration of carbon dioxide in the atmosphere rose during the longer stadials, but how it may have changed during the shorter ones was unclear due to a lack of highly time-resolved CO2 measurements. Ahn and Brooks constructed a detailed time series of atmospheric CO2 from an ice core in Antarctica, which shows that CO2 concentrations changed during the longer stadials but not during the shorter ones. The authors therefore suggest that during short Greenlandic stadials, changes in ocean circulation large enough to cause the transfer of large amounts of CO2 from the deep ocean to the atmosphere did not occur, unlike during longer stadials when the effect is clearly apparent. This, in turn, may imply that the climate links between the Antarctic and the high-latitude Northern Hemisphere could have been controlled by shallow oceanic or atmospheric processes, whereas CO2 changes were controlled by deep oceanic and Southern Ocean ones.

    Nat. Commun. 10.1038/ncomms4723 (2014).