This Week in Science

Science  15 Jun 2018:
Vol. 360, Issue 6394, pp. 1198
  1. Human Impacts

    Nocturnal refuge

    1. Sacha Vignieri

    Human activities are driving many animals, including coyotes (Canis latrans) like this one, to become more nocturnal.

    CREDIT: CYRIL RUOSO/MINDEN PICTURES/GETTY IMAGES

    As the human population grows, there are fewer places for animals to live out their lives independently of our influence. Given our mostly diurnal tendencies, one domain that remains less affected by humans is the night. Gaynor et al. found that across the globe and across mammalian species—from deer to coyotes and from tigers to wild boar—animals are becoming more nocturnal (see the Perspective by Benítez-López). Human activities of all kinds, including nonlethal pastimes such as hiking, seem to drive animals to make use of hours when we are not around. Such changes may provide some relief, but they may also have ecosystem-level consequences.

    Science, this issue p. 1232; see also p. 1185

  2. Machine Learning

    A scene-internalizing computer program

    1. Jelena Stajic

    To train a computer to “recognize” elements of a scene supplied by its visual sensors, computer scientists typically use millions of images painstakingly labeled by humans. Eslami et al. developed an artificial vision system, dubbed the Generative Query Network (GQN), that has no need for such labeled data. Instead, the GQN first uses images taken from different viewpoints and creates an abstract description of the scene, learning its essentials. Next, on the basis of this representation, the network predicts what the scene would look like from a new, arbitrary viewpoint.

    Science, this issue p. 1204

  3. Magnetism

    An intrinsic magnetic tunnel junction

    1. Jelena Stajic

    An electrical current running through two stacked magnetic layers is larger if their magnetizations point in the same direction than if they point in opposite directions. These so-called magnetic tunnel junctions, used in electronics, must be carefully engineered. Two groups now show that high magnetoresistance intrinsically occurs in samples of the layered material CrI3 sandwiched between graphite contacts. By varying the number of layers in the samples, Klein et al. and Song et al. found that the electrical current running perpendicular to the layers was largest in high magnetic fields and smallest near zero field. This observation is consistent with adjacent layers naturally having opposite magnetizations, which align parallel to each other in high magnetic fields.

    Science, this issue p. 1218, p. 1214

  4. Photosynthesis

    Lower-energy photons do the work, too

    1. Michael A. Funk

    Plants and cyanobacteria use chlorophyll-rich photosystem complexes to convert light energy into chemical energy. Some organisms have developed adaptations to take advantage of longer-wavelength photons. Nürnberg et al. studied photosystem complexes from cyanobacteria grown in the presence of far-red light. The authors identified the primary donor chlorophyll as one of a few chlorophyll molecules in the far-red light–adapted enzymes that were chemically altered to shift their absorption spectrum. Kinetic measurements demonstrated that far-red light is capable of directly driving water oxidation, despite having less energy than the red light used by most photosynthetic organisms.

    Science, this issue p. 1210

  5. Cytometry

    Seeing ghosts

    1. Valda Vinson

    In fluorescence-activated cell sorting, characteristic target features are labeled with a specific fluorophore, and cells displaying different fluorophores are sorted. Ota et al. describe a technique called ghost cytometry that allows cell sorting based on the morphology of the cytoplasm, labeled with a single-color fluorophore. The motion of cells relative to a patterned optical structure provides spatial information that is compressed into temporal signals, which are sequentially measured by a single-pixel detector. Images can be reconstructed from this spatial and temporal information, but this is computationally costly. Instead, using machine learning, cells are classified directly from the compressed signals, without reconstructing an image. The method was able to separate morphologically similar cell types in an ultrahigh-speed fluorescence imaging–activated cell sorter.

    Science, this issue p. 1246

  6. Anthropology

    Mesoamerican turquoise locally sourced

    1. Philippa J. Benson

    Isotope analysis indicates a Central American source for Aztec turquoise.

    PHOTO: NATIONAL GEOGRAPHIC CREATIVE/ALAMY STOCK PHOTO

    Scholars have long assumed that Aztec and Mixtec turquoise artifacts uncovered in Mesoamerica were imported from the American Southwest, which is home to abundant turquoise deposits. Thibodeau et al. analyzed the lead and strontium isotopic ratios in 38 Mesoamerican turquoise mosaic tiles (tesserae) from the Sacred Precinct of Tenochtitlan and in five tesserae from Mixtec turquoise mosaics. The isotopic compositions of most of the samples matched copper deposits and crustal rocks of Mesoamerica, suggesting at least one Mesoamerican region as the source of this turquoise.

    Sci. Adv. 10.1126/sciadv.aas9370 (2018).

  7. Neuroscience

    Disentangling specific memories

    1. Peter Stern

    Each memory is stored in a distinct memory trace in the brain, in a specific population of neurons called engram cells. How does the brain store and define the identity of a specific memory when two memories interact and are encoded in a shared engram? Abdou et al. used optogenetic reactivation coupled with manipulations of long-term potentiation to analyze engrams that share neurons in the lateral amygdala (see the Perspective by Ramirez). Synapse-specific plasticity guaranteed the storage and the identity of individual memories in a shared engram. Moreover, synaptic plasticity between specific engram assemblies was necessary and sufficient for memory engram formation.

    Science, this issue p. 1227; see also p. 1182

  8. Infectious Disease

    Designer bugs as drugs

    1. Lindsey Pujanandez

    The endemic persistence and outbreaks of Vibrio cholerae indicate a need for new methods of control. Mao et al. discovered that lactic acid production by the probiotic Lactococcus lactis rendered the infant mouse gut hostile to V. cholerae and engineered L. lactis to detect breakthrough infection. Hubbard et al. extensively modified a contemporary V. cholerae strain for a live oral vaccine, which resulted in an attenuated strain that could protect infant rabbits from V. cholerae challenge within 24 hours of vaccine administration.

    Sci. Transl. Med. 10, eaao2586, eaap8423 (2018).

  9. Immunology

    Modeling memory differentiation in T cells

    1. Seth Thomas Scanlon

    The balance between effector and central memory T cells shifts toward the latter as the number of T cells participating in immune responses increases. Polonsky et al. determined the mechanisms by which T cell quorum sensing affects memory differentiation by using live-cell imaging to track cell proliferation and differentiation. They found that the rate of memory CD4+ T cell differentiation is determined by cell number. This rate substantially increases above a threshold number of locally interacting cells. Mathematical modeling suggests that the number of initially seeded cells and the number of cell divisions are not critical. Instead, the instantaneous number of interacting cells continuously modulates the differentiation rate. This is partly fueled by increased sensitivity to the cytokines interleukin-2 (IL-2) and IL-6, independent of any effects on cell proliferation.

    Science, this issue p. eaaj1853

  10. Cancer

    Chronic stress as a survival tactic

    1. Paula A. Kiberstis

    Most patients with pancreatic ductal adenocarcinoma (PDA) develop liver metastases after surgical removal of their primary tumor. These metastases are thought to potentially arise from quiescent disseminated cancer cells, likely present at the time of surgery, which evade elimination by the immune system. Pommier et al. explored how these quiescent cells survive by analyzing mouse models and tissue samples from patients with PDA. They found that disseminated cancer cells do not express a cell surface molecule that triggers killing by T cells. This phenotypic feature is linked to their inability to resolve endoplasmic reticulum stress. When this stress is resolved, the disseminated cells begin proliferating and form metastases.

    Science, this issue p. eaao4908

  11. Nanotechnology

    Reconsidering resonator sensing

    1. Phil Szuromi

    Changes in the frequency of a nanoscale mechanical resonator can be used for many sensing applications, provided that there is an adequate signal-to-noise ratio. Normally, this ratio is improved by creating resonators with higher quality factors that “ring” for longer times. Taking a cue from the approaches used in atomic force microscopy, Roy et al. show that if the thermomechanical noise of the resonator is well defined, the signal-to-noise ratio of the frequency shift can improve by lowering the quality factor. They used this approach to demonstrate temperature sensing with a double-clamped silicon beam resonator, which performed better at ambient pressures than in a vacuum.

    Science, this issue p. eaar5220

  12. Plant Science

    How to make bioactive alkaloids

    1. Pamela J. Hines

    Vinblastine and vincristine are important, expensive anticancer agents that are produced by dimerization of the plant-derived alkaloids catharanthine and vindoline. The enzymes that transform tabersonine into vindoline are known; however, the mechanism by which the scaffolds of catharanthine and tabersonine are generated has been a mystery. Caputi et al. now describe the biosynthetic genes and corresponding enzymes responsible. This resolves a long-standing question of how plant alkaloid scaffolds are synthesized, which is important not only for vinblastine and vincristine biosynthesis, but also for understanding the many other biologically active alkaloids found throughout nature.

    Science, this issue p. 1235

  13. Neuroscience

    The mechanisms of fear attenuation

    1. Peter Stern

    Surprisingly little is known about how remote fearful memories are stored and attenuated. Khalaf et al. used independent fear memory attenuation paradigms, engram-based tagging techniques, and chemogenetic tools to alter neuronal activity (see the Perspective by Frankland and Josselyn). They found that a discrete subset of neurons within an ensemble is engaged during recall after memory attenuation, which correlated with fear reduction. Memory updating and extinction mechanisms thus likely coexist to make this happen. These findings support the notion that effective memory attenuation is mediated by a rewriting of the original memory trace of fear toward one of safety.

    Science, this issue p. 1239; see also p. 1186

  14. Structural Biology

    Tackling microtubule-tau interactions

    1. Stella M. Hurtley

    Alzheimer's disease is a major cause of death in the elderly. Disease progression is associated with the accumulation of neurofibrillary tangles composed of tau, a protein important for neuronal development and function. Tangle formation is preceded by phosphorylation events that cause tau to dissociate from its native binding partner, microtubules. Microtubule-tau interactions have been mysterious. Kellogg et al. used cryo–electron microscopy and molecular modeling to show how tau interacts with the outer surface of the microtubule, stapling together tubulin subunits and thus stabilizing the polymer. A key tau amino acid within the tightly bound segment between tubulin subunits corresponds to a clinically relevant site of tau phosphorylation, explaining the competition between microtubule interaction and tau aggregation.

    Science, this issue p. 1242

  15. Neuroscience

    Shifts in brain regions with brain size

    1. Pamela J. Hines

    Brain size among normal humans varies as much as twofold. Reardon et al. surveyed the cortical and subcortical structure of more than 3000 human brains by noninvasive imaging (see the Perspective by Van Essen). They found that the scaling of different regions across the range of brain sizes is not consistent: Some brain regions are metabolically costly and are favored in larger brains. This shifts the balance between associative and sensorimotor brain systems in a brain size–dependent way.

    Science, this issue p. 1222; see also p. 1184

  16. Oceans

    Environmental DNA tracks rare species

    1. Julia Fahrenkamp-Uppenbrink

    Marine animals are often elusive, making it difficult to establish their presence in a region or to estimate population sizes. Many of these animals are also rare, making them even more difficult to study. In a Perspective, Pikitch highlights the advantages of environmental DNA studies for detecting rare marine animals, particularly to aid conservation efforts. The method is noninvasive and highly sensitive, allowing detection of the recent presence of animals such as killer whales. However, challenges remain, particularly for estimating population sizes, where the approach should prove useful in combination with more established methods.

    Science, this issue p. 1180

  17. Immunology

    Letting thymocytes go

    1. John F. Foley

    During the process of T cell development, thymocytes must travel from the cortex of the thymus to the medulla, where potentially autoreactive cells are removed by negative selection. Duke-Cohan et al. found that mouse thymocytes lacking the guanosine triphosphatase–activating protein Tagap failed to detach from the cortex. Given that in humans, single-nucleotide polymorphisms in the gene encoding TAGAP are associated with autoimmune disorders, the data suggest that this protein facilitates the trafficking required for the efficient negative selection of autoreactive cells.

    Sci. Signal. 11, eaan8799 (2018).

  18. HIV

    Spontaneous HIV controllers

    1. Anand Balasubramani

    A small number of HIV-infected individuals (<1%) can spontaneously control HIV in the absence of antiretroviral therapy. Because CD4+ and CD8+ T cell responses are thought to contribute to protection, HIV-responsive T cell receptors (TCRs) from these individuals are of considerable interest. Galperin et al. examined how three class II–restricted TCRs observed in spontaneous controllers are capable of binding a Gag peptide in the context of multiple HLA-DR molecules (HLA, human leukocyte antigen). The authors solved the structures of several TCR–peptide–HLA-DR complexes. The findings suggest that the ability of these TCRs to recognize the Gag peptide in the context of multiple HLA-DR allomorphs is shaped by extensive contacts between the TCRs and the peptide itself.

    Sci. Immunol. 3, eaat0687 (2018).