This Week in Science

Science  08 Jun 2018:
Vol. 360, Issue 6393, pp. 1082
  1. Tetrapod Evolution

    Out of Antarctica

    1. Sacha Vignieri

    Tutusius mlambo, a basal tetrapod from the Late Devonian, found in what was then the Antarctic Circle

    CREDIT: MAGGIE LAMBERT-NEWMAN

    When we think of Devonian tetrapods, the ancestors of all modern vertebrates, we tend to picture amphibian-like creatures emerging from the water into a wet tropical forest or swamp. Indeed, all previously described specimens of this group have been recovered from the tropics. Gess and Ahlberg now describe two fossil tetrapods from Devonian Antarctica. Thus, the distribution of tetrapods may have been global, which encourages us to rethink the environments in which this important group was shaped.

    Science, this issue p. 1120

  2. Planetary Science

    Measuring martian organics and methane

    1. Brent Grocholski,
    2. Keith T. Smith

    The Curiosity rover has been sampling on Mars for the past 5 years (see the Perspective by ten Kate). Eigenbrode et al. used two instruments in the SAM (Sample Analysis at Mars) suite to catch traces of complex organics preserved in 3-billion-year-old sediments. Heating the sediments released an array of organics and volatiles reminiscent of organic-rich sedimentary rock found on Earth. Most methane on Earth is produced by biological sources, but numerous abiotic processes have been proposed to explain martian methane. Webster et al. report atmospheric measurements of methane covering 3 martian years and found that the background level varies with the local seasons. The seasonal variation provides an important clue for determining the origin of martian methane.

    Science, this issue p. 1096, p. 1093; see also p. 1068

  3. Applied Optics

    Making silicon shine bright

    1. Ian S. Osborne

    Silicon is the workhorse of the semiconductor electronics industry, but its lack of optical functionality is a barrier to developing a truly integrated silicon-based optoelectronics platform. Although there are several ways of exploiting nonlinear light-matter interactions to coax silicon into optical functionality, the effects tend to be weak. Otterstrom et al. used a suspended silicon waveguide racetrack structure to stimulate the stronger nonlinear effect of Brillouin scattering and achieve lasing from silicon. The ability to engineer the nonlinearity and tune the optical response through the design of the suspended cavity provides a powerful and flexible route for developing silicon-based optoelectronic circuits and devices.

    Science, this issue p. 1113

  4. Social Science

    Tipping points in social convention

    1. Barbara R. Jasny

    Once a population has converged on a consensus, how can a group with a minority viewpoint overturn it? Theoretical models have emphasized tipping points, whereby a sufficiently large minority can change the societal norm. Centola et al. devised a system to study this in controlled experiments. Groups of people who had achieved a consensus about the name of a person shown in a picture were individually exposed to a confederate who promoted a different name. The only incentive was to coordinate. When the number of confederates was roughly 25% of the group, the opinion of the majority could be tipped to that of the minority.

    Science, this issue p. 1116

  5. Medicine

    Toward more predictable birthdays

    1. Paula A. Kiberstis

    Low-cost methods for monitoring fetal development could improve prenatal care, especially in low-resource settings. By measuring the levels of certain placental RNA transcripts in maternal blood, Ngo et al. developed two noninvasive blood tests that provide a window into the progression of individual pregnancies. In a small proof-of-concept study, the first blood test predicted fetal age and delivery date with an accuracy comparable to that of ultrasound. The second blood test, also examined in a small pilot study, discriminated women at risk of preterm delivery from those who delivered at full term. The next step will be to assess the reliability of the tests in large, blinded clinical trials.

    Science, this issue p. 1133

  6. Plant Genetics

    Sterility in rice via toxin and antidote

    1. Laura M. Zahn

    Hybrid rice varieties produce sterile pollen.

    PHOTO: X. YU ET AL.

    Crossing wild and domestic rice often results in hybrid sterility. Such genetic barriers can prevent the movement of potentially beneficial genes from wild rice into domestic varieties. To understand the barriers preventing gene flow, Yu et al. mapped a quantitative trait locus (QTL) that determines sterility between wild-type and domestic rice. This QTL encodes two open reading frames (ORFs) that are both expressed during gametogenesis. The ORFs encode a toxin, which affects the development of pollen, and an antidote, which is required for pollen viability. Thus, selfish genetic elements can underlie evolutionary strategies that facilitate reproductive isolation.

    Science, this issue p. 1130

  7. Environmental Studies

    Economic rationale for fishing the high seas

    1. Philippa J. Benson

    Economic evaluations of high-seas fishing have been lacking, in part owing to the scarcity of data on the costs and revenues of fleets that fish in these elusive waters. Sala et al. wanted to quantify high-seas fishing efforts globally and assess whether and when high-seas fishing makes economic sense. They used satellite data and machine learning to track the activity of more than 3600 fishing vessels in near real time. Patterns of fishing profitability varied widely between countries, types of fishing, and distance to port. As much as 54% of present high-seas fishing grounds would be unprofitable without large government subsidies, supporting recent calls for subsidy management reforms for the high seas.

    Sci. Adv. 10.1126/sciadv.aat2504 (2018).

  8. DNA Repair

    DNA-bound ubiquitin coordinates repair

    1. Leslie K. Ferrarelli

    Ubiquitylation is a posttranslational modification that reversibly alters various protein properties. Liu et al. discovered that Lys63-linked polyubiquitin chains bound to the free ends of double-stranded DNA, bridged the broken ends of DNA, and recruited repair proteins. Ubiquitins with DNA-binding motif mutations were found in several types of tumors. When expressed in cultured cells, these mutant ubiquitins impaired the cellular response to DNA-damaging agents, suggesting that it might be possible to therapeutically exploit these mutations in some cancer patients.

    Sci. Signal. 11, eaar8133 (2018).

  9. Great Ape Genomics

    A spotlight on great ape genomes

    1. Laura M. Zahn

    Most nonhuman primate genomes generated to date have been “humanized” owing to their many gaps and the reliance on guidance by the reference human genome. To remove this humanizing effect, Kronenberg et al. generated and assembled long-read genomes of a chimpanzee, an orangutan, and two humans and compared them with a previously generated gorilla genome. This analysis recognized genomic structural variation specific to humans and particular ape lineages. Comparisons between human and chimpanzee cerebral organoids showed down-regulation of the expression of specific genes in humans, relative to chimpanzees, related to noncoding variation identified in this analysis.

    Science, this issue p. eaar6343

  10. Immunology

    Finding a role for PNECs in asthma

    1. Seth Thomas Scanlon

    Pulmonary neuroendocrine cells (PNECs) are a rare cell type located in airway and alveolar epithelia and are often in contact with sensory nerve fibers. They have a wide phylogenic distribution and are found even in the relatively primitive lungs of amphibia and reptiles, suggesting a critical function. Sui et al. found that mice lacking PNECs have suppressed type 2 (allergic) immune responses. PNECs were observed in close proximity to group 2 innate lymphoid cells (ILC2s) around airway branch points. The PNECs enhanced ILC2 activity by secreting CGRP (calcitonin gene-related peptide). They also induced goblet-cell hyperplasia via the neurotransmitter GABA (γ-aminobutyric acid). Interestingly, human asthma patients were found to have increased PNEC numbers, suggesting a potential therapeutic target for the treatment of asthma.

    Science, this issue p. eaan8546

  11. Metabolism

    A missing link in cholesterol absorption

    1. Priscilla N. Kelly

    Cholesterol is important for general health, but too much can build up in artery walls and cause cardiovascular disease. Low-density lipoprotein cholesterol (LDL-C) is often referred to as “bad cholesterol”; keeping LDL-C within stringent limits is recommended to reduce the risk of heart attack and stroke. Zhang et al. discovered that some individuals have an inherited frameshift mutation in the LIMA1 gene (also known as EPLIN or SREBP3). The gene has not been linked to lipid metabolism before, but altered LIMA1 was found to maintain low plasma LDL-C by reducing the absorption of cholesterol through the intestine. Pharmacological targeting through the LIMA1 pathway might thus provide a strategy to improve heart health.

    Science, this issue p. 1087

  12. Organic Materials

    Quantum dipoles go liquid

    1. Jelena Stajic

    Quantum spin liquids do not achieve an ordered magnetic state, even at the lowest temperatures. Hassan et al. studied an organic compound that may be both a spin liquid and a dipole liquid (see the Perspective by Powell). In the layered material κ-(BEDT-TTF)2Hg(SCN)2Br, molecules form charged dimers whose sites are arranged on a triangular lattice. The extra charge associated with each dimer can “live” on one of the two molecules in the dimer, resulting in a nonzero electric dipole moment for the dimer. Raman spectroscopy and heat capacity measurements revealed that, like spins in a quantum spin liquid, these dimers remained disordered down to the lowest temperatures.

    Science, this issue p. 1101; see also p. 1073

  13. Photosynthesis

    Antenna switches partners in the shade

    1. Michael A. Funk

    A cloudy day or an overshadowing tree causes fluctuations in light that can throw off the balance of energy flow in plant photosystems I and II (PSI and PSII). Pan et al. solved structures of PSI bound to two light-harvesting complexes (LHCs). One LHC is permanently associated with PSI. The other LHC delivers light energy to PSII under optimal conditions but can switch to a PSI-associated state after phosphorylation by a kinase that senses the redox environment of the chloroplast. The movement of LHCs between the photosystems helps maintain even energy flux. Two chlorophyll-containing subunits are visible in the structure that connect the PSI core to each LHC.

    Science, this issue p. 1109

  14. Applied Optics

    Metasurfaces for molecular detection

    1. Ian S. Osborne

    Although mid-infrared (mid-IR) spectroscopy is a mainstay of molecular fingerprinting, its sensitivity is diminished somewhat when looking at small volumes of sample. Nanophotonics provides a platform to enhance the detection capability. Tittl et al. built a mid-IR nanophotonic sensor based on reflection from an all-dielectric metasurface array of specially designed scattering elements. The scattering elements could be tuned via geometry across a broad range of wavelengths in the mid-IR. The approach successfully detected and differentiated the absorption fingerprints of various molecules. The technique offers the prospect of on-chip molecular fingerprinting without the need for spectrometry, frequency scanning, or moving mechanical parts.

    Science, this issue p. 1105

  15. Climate Change

    Predicting changes in “extreme” precipitation

    1. Julia Fahrenkamp-Uppenbrink

    As temperatures rise, Earth's atmosphere can hold more moisture. This rise in moisture content is expected to lead to a broadly comparable rise in the intensity of the most extreme precipitation events. In a Perspective, Pendergrass explains that whether this expectation is met depends on the definition of extreme precipitation. The intensity of the most extreme events may rise more than expected, as seen for Hurricane Harvey, whereas that of less extreme events may rise less than anticipated. Atmospheric circulation changes will also affect precipitation events in ways that differ from one place to another. Clear definitions of extreme precipitation are key to anticipating and preparing for future changes in extreme events.

    Science, this issue p. 1072

  16. Plant Science

    Defense cargo shuttles in vesicles

    1. Pamela J. Hines

    Plants can use small RNAs (sRNAs) to interfere with virulence factor gene expression in pathogens. Cai et al. show that the small mustard plant Arabidopsis shuttles defensive sRNAs into the necrotrophic fungus Botrytis cinerea via extracellular vesicles (see the Perspective by Thomma and Cook). The vesicles are associated with tetraspanin proteins, which can interact and form membrane microdomains. Several dozen different sRNAs targeting the pathogenic process were transported from Arabidopsis to B. cinerea in a selective manner.

    Science, this issue p. 1126; see also p. 1070

  17. Evolutionary Cognition

    Understanding zero

    1. Sacha Vignieri

    It has been said that the development of an understanding of zero by society initiated a major intellectual advance in humans, and we have been thought to be unique in this understanding. Although recent research has shown that some other vertebrates understand the concept of the “empty set,” Howard et al. now show that an understanding of this concept is present in untrained honey bees (see the Perspective by Nieder). This finding suggests that such an understanding has evolved independently in distantly related species that deal with complexity in their environments, and that it may be more widespread than previously appreciated.

    Science, this issue p. 1124; see also p. 1069

  18. Zika

    Zika leaves a lasting impact on the brain

    1. Mattia Maroso

    Perinatal Zika virus (ZIKV) infection has been associated with brain alterations in newborns. However, whether ZIKV exposure during development has long-term neurological consequences is not completely understood. Nem de Oliveira Souza et al. report that newborn mice infected with ZIKV developed acute brain abnormalities. During adulthood, perinatally infected mice showed persistent viral replication, neuropathological alterations, behavioral impairments, and altered brain excitability. Blocking tumor necrosis factor–α early after infection prevented this hyperexcitability in the mouse brain. Thus, anti-inflammatory treatments might help to prevent the persistent increase in neuronal excitability induced by ZIKV infection in brain tissue.

    Sci. Transl. Med. 10, eaar2749 (2018).

  19. Embryogenesis

    Modeling embryogenesis

    1. Gemma Alderton

    Understanding the molecular and cellular events of early embryogenesis is crucial to improve assisted reproductive technologies and prevent genetic birth defects. Although some clarity on this process in humans has come from comparative studies in mice, differences exist, so there is a need to better model embryogenesis. In a Perspective, Rossant and Tam discuss the possibility of using nonhuman primate embryos and human stem cell–derived models to better study and understand early development.

    Science, this issue p. 1075

  20. HIV

    Taking residence to defend

    1. Anand Balasubramani

    In HIV+ individuals receiving antiretroviral therapy, CD4+ T cells home to lymphoid tissues (LTs) that are a key site of HIV persistence. Studying the immune response to HIV in LTs has been a challenge. Buggert et al. obtained LTs from HIV+ individuals and carried out comprehensive transcriptional and epigenetic analyses on CD8+ T cells found there. The CD8+ T cells had a signature associated with resident memory T cells. The frequency of these HIV-responsive LT-resident CD8+ T cells was considerably increased in so-called elite controllers—people able to restrain their HIV infections.

    Sci. Immunol. 3, eaar4526 (2018).