This Week in Science

Science  23 Aug 2019:
Vol. 365, Issue 6455, pp. 769
  1. Asteroids

    Landing on the surface of Ryugu

    1. Keith T. Smith

    Photograph of the surface of (162173) Ryugu, taken at night by the MASCOT camera

    PHOTO: MASCOT/DLR/JAXA

    In October 2018, the Hayabusa2 spacecraft dropped the Mobile Asteroid Surface Scout (MASCOT) lander onto the surface of the asteroid (162173) Ryugu. Jaumann et al. analyzed images taken by the MASCOT camera during its descent and when resting on the surface. Colored light-emitting diodes were used to illuminate the lander's surroundings at night and produce color images. Ryugu's surface is dominated by two types of rock, but there is no evidence for fine-grained dust. Millimeter-sized inclusions in the rocks are similar to those present in carbonaceous chondrite meteorites. MASCOT operated for 17 hours on the surface before its nonrechargeable batteries ran out.

    Science, this issue p. 817

  2. Gene Therapy

    Safe and effective gene delivery

    1. Mattia Maroso

    Niemann-Pick disease type A (NPD-A) is caused by loss-of-function mutations in the gene encoding for acid sphingomyelinase. Gene replacement therapies are effective in other monogenic neurological disorders. Samaranch et al. evaluated the safety and efficacy of adeno-associated viral vector serotype 9 (AAV9)–based gene therapy. AAV9-mediated delivery of human acid sphingomyelinase in the cerebellomedullary cistern allowed for widespread expression of this gene in brain and spinal cord of nonhuman primates without signs of toxicity. The treatment prevented motor and memory impairment and increased survival in a mouse model of NPD-A.

    Sci. Transl. Med. 11, eaat3738 (2019).

  3. Biomaterials

    A CRISPR set of materials

    1. Marc S. Lavine

    CRISPR technology is best known as a gene editing tool. English et al. developed a group of stimuli-responsive hydrogels to respond to the programmable nuclease Cas12a (see the Perspective by Han et al.). The materials undergo molecular to macroscopic changes after Cas12a-dependent cleavage of double- or single-stranded DNA integrated into the gel. The authors show controlled release of particles linked to or imprisoned within the DNA, degradation of a gel with DNA solely forming the cross-links, and permeabilization of a gel with DNA partially forming the cross-links. These tools allow for the production of materials that release encapsulated nanoparticles and cells, act as degradable fuses, and enable remote radio-frequency identification signaling.

    Science, this issue p. 780; see also p. 754

  4. Cancer

    A reverse route into metastasis

    1. Leslie K. Ferrarelli

    Signaling proteins in the semaphorin family guide cell migration. Transmembrane semaphorins can act both as ligands (the so-called “forward” signaling pathway) and as receptors (the “reverse” signaling pathway). Gurrapu et al. found that semaphorin 4C (Sema4C) acted as a receptor to promote metastasis by activating transforming growth factor–β signaling in invasive breast cancer cell lines. Overexpression of Sema4C in breast or prostate cancer cells resulted in increased numbers of metastatic colonies in mice. High levels of Sema4C in primary breast tumors correlated with increased metastasis in patients.

    Sci. Signal. 12, eaav2041 (2019).

  5. Plant Science

    NAD depletion as pathogen response

    1. Pamela J. Hines

    One way that plants respond to pathogen infection is by sacrificing the infected cells. The nucleotide-binding leucine-rich repeat immune receptors responsible for this hypersensitive response carry Toll/interleukin-1 receptor (TIR) domains. In two papers, Horsefield et al. and Wan et al. report that these TIR domains cleave the metabolic cofactor nicotinamide adenine dinucleotide (NAD+) as part of their cell-death signaling in response to pathogens. Similar signaling links mammalian TIR-containing proteins to NAD+ depletion during Wallerian degeneration of neurons.

    Science, this issue p. 793, p. 799

  6. Phase Separation

    Keeping RNA processing contained

    1. Valda Vinson

    Biomolecular condensates that assemble by phase separation are involved in RNA processing. Posttranslational modifications in intrinsically disordered regions of proteins can regulate RNA processing by regulating phase separation. Kim et al. used nuclear magnetic resonance spectroscopy to characterize phase separation in a model system comprising the C-terminal disordered regions of the translational regulators FMRP and CAPRIN1 that repress translation by deadenylating mRNA. Interactions between the proteins involve specific sequences in FMRP and CAPRIN1, and the propensity for mRNA to partition into the condensates depends on the phosphorylation patterns in the disordered regions. This mechanism integrates signaling pathways with the regulation of RNA processing.

    Science, this issue p. 825

  7. Geophysics

    Slow earthquake segmentation

    1. Brent Grocholski

    The Japan Trench is responsible for disastrous megathrust earthquakes like the 2011 Tohoku-Oki quake. Nishikawa et al. used new observations from the S-net ocean-bottom seismic network to map slow earthquakes—disturbances that do not cause ground shaking—along the Japan Trench (see the Perspective by Houston). They found that the area that ruptured during the 2011 quake was bounded by areas that have large numbers of slow earthquakes. A segmentation likely caused the 2011 rupture to cease, an observation that is important for assessing risk from future major earthquakes.

    Seafloor sensors deployed off the Pacific coast of Japan monitor seismic disturbances large and small.

    PHOTO: NATIONAL RESEARCH INSTITUTE FOR EARTH SCIENCE AND DISASTER RESILIENCE

    Science, this issue p. 808; see also p. 750

  8. Neuroscience

    Robust memories through neuron networks

    1. Peter Stern

    How does the brain store information over a long period of time? Gonzalez et al. chronically implanted custom-built high-sensitivity microendoscopes and performed long-term imaging of neuronal activity in freely moving mutant mice. The majority of neurons were active on most days, but their firing rate changed across sessions and tasks. Although the responses of individual neurons changed, the responses of groups of neurons with synchronous activity were very stable across days and weeks. In addition, the network activity in hippocampal area CA1 recovered after an extended period without performing the task or even after abnormal activity induced by local lesions. These findings indicate the presence of attractor-like ensemble dynamics as a mechanism by which the representations of an environment are encoded in the brain.

    Science, this issue p. 821

  9. Soil Ecology

    Microbes' role in soil decomposition

    1. Andrew M. Sugden

    Soils harbor a rich diversity of invertebrate and microbial life, which drives biogeochemical processes from local to global scales. Relating the biodiversity patterns of soil ecological communities to soil biogeochemistry remains an important challenge for ecologists and earth system modelers. Crowther et al. review the state of science relating soil organisms to biogeochemical processes, focusing particularly on the importance of microbial community variation on decomposition and turnover of soil organic matter. Although there is variation in soil communities across the globe, ecologists are beginning to identify general patterns that may contribute to predicting biogeochemical dynamics under future climate change.

    Science, this issue p. eaav0550

  10. Conservation

    Think local when protecting forests

    1. Julia Fahrenkamp-Uppenbrink

    Tropical deforestation, which causes habitat loss, worsens climate change, and affects local communities, is an issue of global importance. In a Perspective, Seymour and Harris explore the drivers that contribute to tropical forest loss in South America, Southeast Asia, and Africa. For example, cattle ranching dominates in the Brazilian Amazon, whereas small-scale clearing is most important in the Congo Basin. The authors caution against a reliance on commitments to remove deforestation from commodity supply chains and argue that to be effective, policies must be adapted to local circumstances.

    Science, this issue p. 756

  11. Molecular Machines

    Innovations in an ATPase/ATP synthase

    1. Michael A. Funk

    Enzymes that couple the chemical energy of adenosine triphosphate (ATP) to movement of ions across a membrane are present in all domains of life. Like their F-type cousins in mitochondria, chloroplasts, and most bacteria, vacuolar/archaeal (V/A-type) ATPases couple synthesis or hydrolysis of ATP to movement of protons across the membrane. To uncover mechanistic differences in energy coupling between F- and V/A-type enzymes, Zhou and Sazanov determined structures of a V/A-type ATP synthase from the bacterium Thermus thermophilus. With structures of multiple substates visible, the domain interfaces are made clear and a role for the elastic peripheral stalks is apparent in coupling rotational energy from Vo into the ATP-synthesizing V1 domain.

    Science, this issue p. eaaw9144

  12. Development

    Seeing the embryo

    1. Gemma Alderton

    Recent advances have allowed visualization of developing mammalian embryos, providing unprecedented cellular detail of the process of embryonic development. In a Perspective, Wallingford discusses the path to seeing and recording images of embryos accurately and explains the remaining challenges and future possibilities.

    Science, this issue p. 758

  13. Malaria

    Mapping the malaria parasite

    1. Caroline Ash

    Several species of the parasite Plasmodium cause human malarial diseases, and, despite determined control efforts, a huge global disease burden remains. Howick et al. present a single-cell analysis of transcription across the malaria parasite life cycle (see the Perspective by Winzeler). Single-cell transcriptomes generated from 10 different life-cycle stages of the rodent-model malaria parasite P. berghei identified 20 “modules” among 5156 core transcriptome genes. These clusters enabled functional assignment of hypothetical and conserved genes, and they hint at further substructure of established life-cycle stages. The atlas also allowed for P. falciparum and P. malariae transcriptomes from patient isolates to be deconvoluted and for classification of parasitemia according to developmental stage.

    Science, this issue p. eaaw2619; see also p. 753

  14. Quantum Simulation

    An interacting topological phase

    1. Jelena Stajic

    Most topologically nontrivial systems discovered to date consist of noninteracting particles. Their properties can therefore be explained within a single-particle picture. De Léséleuc et al. engineered a topological phase of bosonic atoms in which interactions play a crucial role. The atoms, which were in highly excited Rydberg states, were held in an array of optical tweezers. Depending on the spatial arrangement of the tweezers, the dipole-dipole interactions between the atoms gave rise to two configurations with different topological properties.

    Science, this issue p. 775

  15. Genomics

    Manifold destiny

    1. Steve Mao

    Mapping of genetic interactions (GIs) is usually based on cell fitness as the phenotypic readout, which obscures the mechanistic origin of interactions. Norman et al. developed a framework for mapping and understanding GIs. This approach leverages high-dimensional single-cell RNA sequencing data gathered from CRISPR-mediated, pooled perturbation screens. Diverse transcriptomic phenotypes construct a “manifold” representing all possible states of the cell. Each perturbation and GI projects the cell state to a particular position on this manifold, enabling unbiased ordering of genes in pathways and systematic classifications of GIs.

    Science, this issue p. 786

  16. Malaria

    Ebb and flow of parasite populations

    1. Caroline Ash

    The population genetics of the malaria parasite Plasmodium falciparum across Africa is poorly understood but important to know for grasping the risks and dynamics of the spread of drug resistance. Harnessing the power of genomics, Amambua-Ngwa et al. of the Plasmodium Diversity Network Africa found substantial population structure within Africa that is consistent with human and vector population divergence (see the Perspective by Sibley). Specific signatures of selection by antimalarial drugs were detected, along with indications of the effect of colonization and slavery. Furthermore, whole-genome sequencing showed that there is extensive gene flow among the different regions and that Ethiopia has a distinctive population of P. falciparum, which may be indicative of coexistence with another malaria parasite, P. vivax.

    Science, this issue p. 813; see also p. 752

  17. Ceramics

    Joining the laser welding club

    1. Brent Grocholski

    Laser welding is an integral part of modern manufacturing, but it fractures ceramic materials. Penilla et al. developed two methods for welding ceramics using ultrafast lasers. One method tunes the ceramic properties, allowing the laser to transit through the ceramic and weld at the interface between pieces. The other method optimizes a gap between pieces to efficiently deposit energy. Both methods leverage short but energetic pulses to create a melt pool that allows ceramics to be joined, without the high temperature used for traditional ceramic welds.

    Science, this issue p. 803