This Week in Science

Science  13 Oct 2017:
Vol. 358, Issue 6360, pp. 183
  1. Milky Way Galaxy

    Measuring the far side of the Galaxy

    1. Keith T. Smith

    Nearly a complete rotation of a Milky Way spiral arm has been traced.

    ILLUSTRATION: NASA JPL

    Direct measurements of distances to astronomical sources rely on parallax, which can usually only be measured for relatively nearby objects. The far side of the Milky Way has been impossible to measure accurately, because the parallax is very small and interstellar dust blocks optical light from those regions. Sanna et al. used radio interferometry to directly determine the parallax distance to a star-forming region on the far side of the Galaxy. They also used a method of inferring distances from transverse motions, which produced the same answer. This allowed them to trace one of the Milky Way's spiral arms through almost an entire rotation.

    Science, this issue p. 227

  2. Single-Cell Analysis

    3D gene expression blueprint of the fly

    1. Beverly A. Purnell

    When looking at populations of cells, features such as cell heterogeneity and localization are masked. However, single-cell sequencing reveals cellular heterogeneity and rare cell types. At the onset of gastrulation, the fly embryo consists of about 6000 cells with distinct gene expression profiles. Karaiskos et al. developed an algorithm to generate an interactive three-dimensional (3D) “virtual embryo,” with the expression of more than 8000 genes per cell measured for most cells (see the Perspective by Stadler and Eisen). The virtual embryo offers insights into developmental mechanisms—from local expression of regulators such as transcription factors and long noncoding RNAs to spatial modulation of signaling pathways.

    Science, this issue p. 194; see also p. 172

  3. Quantum Systems

    Mechanical systems at the quantum level

    1. Ian S. Osborne

    A number of platforms are being pursued for developing technologies that exploit the enhanced sensing and measurement capabilities of quantum mechanics. Hybrid systems offer the flexibility of combining and optimizing different platforms. Hong et al. combined optomechanical control of motion and single-phonon counting techniques to probabilistically generate a single-phonon Fock state within a nanomechanical resonator. Chu et al. used electromechanical coupling to address a bulk piezoelectric resonator with a superconducting quantum circuit. Both approaches hold promise for developing hybrid quantum technologies.

    Science, this issue p. 203, p. 199

  4. Programmed Materials

    3D texture morphing for camouflage

    1. Marc S. Lavine

    Some animals, such as cephalopods, use soft tissue to change shape reversibly for camouflage and object manipulation. Pikul et al. used fixed-length fiber mesh embedded in a silicone elastomer to transform a flat object into a 3D structure by inflating membranes (see the Perspective by Laschi). Painted models of rocks and plants were also created that could be morphed to fully blend into their surroundings.

    Science, this issue p. 210; see also p. 169

  5. Cancer

    A signature event for organoids

    1. Paula A. Kiberstis

    Human cancer genomes harbor cryptic mutational signatures that represent the cumulative effects of DNA damage and defects in DNA repair processes. Knowledge of how specific signatures originate could have a major impact on cancer diagnosis and prevention. One approach to address this question is to reproduce the signatures in experimental systems by genetic engineering and then match the signatures to those found in naturally occurring cancers. Drost et al. used CRISPR-Cas9 to delete certain DNA repair enzymes from human colon organoids. In a proof-of-concept study, they show that deficiency in base excision repair is responsible for a mutational signature previously identified in cancer genome sequencing projects.

    Science, this issue p. 234

  6. Carbon Cycle

    Forests out of balance

    1. H. Jesse Smith

    Twelve years of data show that tropical forests are a net carbon source.

    PHOTO: MVALIGURSKY/ISTOCKPHOTO

    Are tropical forests a net source or net sink of atmospheric carbon dioxide? As fundamental a question as that is, there still is no agreement about the answer, with different studies suggesting that it is anything from a sizable sink to a modest source. Baccini et al. used 12 years of MODIS satellite data to determine how the aboveground carbon density of woody, live vegetation has changed throughout the entire tropics on an annual basis. They find that the tropics are a net carbon source, with losses owing to deforestation and reductions in carbon density within standing forests being double that of gains resulting from forest growth.

    Science, this issue p. 230

  7. Reproductive Biology

    Fevers, TRPV channels, and birth defects

    1. Wei Wong

    Cardiac and craniofacial birth defects are common, but many cannot be attributed to specific mutations. An environmental trigger associated with these birth defects is maternal fever during the first trimester. Using chick and zebrafish embryos, Hutson et al. found that hyperthermia activated temperature-sensitive TRPV1 and TRPV4 ion channels in neural crest cells, which give rise to the tissues affected by the birth defects. Transiently activating either of these channels in neural crest cells in chick embryos resulted in cardiac and craniofacial birth defects similar to those induced by fever.

    Sci. Signal. 10, eaal4055 (2017).

  8. Brain Imaging

    Newborn brain imaging made easier

    1. Mattia Maroso

    Electroencephalography (EEG) and functional neuroimaging can be used to elucidate brain functions and reveal abnormalities. However, it is challenging to use these technologies at the bedside, owing to their size, lack of portability, and cost. Demene et al. developed a portable, customized, and noninvasive system called fUSI (functional ultrasound imaging) that is capable of continuous video-EEG recording and fast ultrasound imaging of the brain microvasculature of newborn babies. They demonstrated the value of fUSI for bedside monitoring by applying it to observe brain activity and neurovascular changes in two neonates with abnormal cortical development.

    Sci. Transl. Med. 9, eaah6756 (2017).

  9. Immunology

    Light- and dark-zone death dynamics

    1. Seth Thomas Scanlon

    Germinal centers (GCs) are areas within lymphoid organs where mature B cells expand and differentiate during normal immune responses. GCs are separated into two anatomic compartments: the dark zone, where B cells divide and undergo somatic hypermutation, and the light zone, where they are selected for affinity-enhancing mutations after interacting with T follicular helper cells. Mayer et al. studied apoptosis reporter mice and found that both GC zones experience very high rates of apoptosis (see the Perspective by Bryant and Hodgkin). However, the underlying mechanisms were distinct and microanatomically segregated. Light-zone B cells underwent apoptosis by default unless they were rescued by positive selection. In contrast, apoptotic dark-zone B cells were highly enriched among cells with genes damaged by random antibody-gene mutations.

    Science, this issue p. eaao2602; see also p. 171

  10. Catalysis

    A radical route from methane to methanol

    1. Phil Szuromi

    The conversion of methane into chemicals usually proceeds through high-temperature routes that first form more reactive carbon monoxide and hydrogen. Agarwal et al. report a low-temperature (50°C) route in aqueous hydrogen peroxide (H2O2) for oxidizing methane to methanol in high yield (92%). They used colloidal gold-palladium nanoparticles as a catalyst. The primary oxidant was O2; isotopic labeling showed that H2O2 activated methane to methyl radicals, which subsequently incorporated O2.

    Science, this issue p. 223

  11. Surface Chemistry

    Visualizing halogen bonding

    1. Phil Szuromi

    Even though halogen atoms are highly electronegative, a noncovalent bond can form between an electron donor and a halogen atom in a covalent bond. Such interactions are facilitated by the formation of electron-depleted regions in the halogen's covalent bond, a situation least likely for fluorine atoms. Han et al. used noncontact scanning tunneling microscopy with submolecular resolution to explore how the size and polarizability of halogens affect complex formation by halogenated benzene molecules adsorbed on a silver surface (see the Perspective by Neaton). With the help of density functional theory, they show how several weak interactions, including van der Waals forces, electrostatic repulsions, and halogen bonds, affect structure.

    Science, this issue p. 206; see also p. 167

  12. Organic Synthesis

    A gram-scale route to bryostatin

    1. Jake Yeston

    Scientists once accumulated 14 tons of the red, bushy, tufted sea creature Bugula neritina to extract 18 grams of bryostatin 1. The macrocyclic organic compound is under study for treatment of HIV, cancer, and Alzheimer's disease but has proven frustratingly scarce. Wender et al. report a 29-step chemical synthesis of bryostatin 1 that proceeds in 4.8% overall yield and provides gram quantities of the compound (see the Perspective by Lanman). Intermediates along the pathway can be straightforwardly modified to produce analogs, two of which were prepared en route and studied in vitro.

    Science, this issue p. 218; see also p. 166

  13. Biocatalysis

    Teaching an enzyme to switch sites

    1. Jake Yeston

    There has been a recent flurry of activity in modifying enzymes to conduct unnatural chemical reactions more cleanly or selectively than synthetic chemical catalysts. Hammer et al. now report application of a cytochrome P450 variant to an oxidation that has largely eluded efficient catalysis. They used directed evolution to mutate the enzyme so that it placed oxygen at the less substituted carbon of the C=C double bond in styrenes, forming aldehyde products. They thereby attained opposite site selectivity to that of the widely used palladium-catalyzed Wacker-Tsuji oxidation.

    Science, this issue p. 215

  14. Disordered Proteins

    An expanded view of disordered proteins

    1. Valda Vinson

    Disordered proteins sample an ensemble of conformations, but it has remained unclear how compact these conformations are in water. Polymer physics relates the radius of gyration (Rg) to solvent quality, with more chain collapse occurring in poorer solvents. Riback et al. developed an analysis scheme that allows them to extract solvent quality and Rg from a single small-angle x-ray scattering measurement. Applying this method, they found that even disordered proteins with low net charge and high hydrophobicity remain expanded in water.

    Science, this issue p. 238

  15. Fungal Infection

    Type III interferons prime neutrophils

    1. Anand Balasubramani

    Type I interferons (IFNs) have a well-established role in antiviral immunity. Espinosa et al. found that type III IFNs (IFN-λs) play an essential role in driving antifungal responses. They studied immune responses to Aspergillus fumigatus in mice lacking receptors for type I or type III IFNs. Monocyte-derived type I IFNs were key drivers of IFN-λ production. Although the authors could not pin down the sources of IFN-λs, they identified neutrophils as the functional target of IFN-λs. Selective deletion of IFN-λ receptor in neutrophils caused mice to succumb to Aspergillus fumigatus infection.

    Sci. Immunol. 2, eaan5357 (2017).

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