This Week in Science

Science  05 Jun 2020:
Vol. 368, Issue 6495, pp. 1076
  1. Reproductive Biology

    Local control of sperm maturation

    1. Beverly A. Purnell

    Fluorescence microscopy image revealing localization of the protease ovochymase-2 (purple) within the caput epididimus, which is part of the male reproductive tract in mammals

    CREDIT: KIYOZUMI ET AL.

    Newly produced spermatozoa within the testis do not have fertilizing ability but become fully functional when they mature in the epididymis. The development of the epididymis itself is dependent on testicular factors arriving via luminal flow. Improper signaling between the testis and epididymis is hypothesized to result in male infertility. Kiyozumi et al. identified NELL2 as a testicular luminal protein that binds to its receptor, ROS1, on the luminal epididymis surface and induces epididymal differentiation (see the Perspective by Lord and Oatley). In turn, differentiated epididymis secretes a fertility-essential protease, ovochymase-2, to make spermatozoa fully mature and functional. Thus, testis-epididymis interorgan communication by this “lumicrine” regulation ensures mammalian reproduction.

    Science, this issue p. 1132; see also p. 1053

  2. Wearable Devices

    Improving ionic thermoelectrics

    1. Brent Grocholski

    Using ions as charge carriers in thermoelectric devices usually requires using either thermal diffusion or redox reactions at two electrodes with different temperatures. Han et al. leveraged both of these strategies to develop a gelatin-based ionic thermoelectric device that uses alkali salts and an iron-based redox couple to generate a large thermopower. This device is capable of generating useful amounts of energy from body heat.

    Science, this issue p. 1091

  3. Plastic Pollution

    Not just settling

    1. H. Jesse Smith

    What controls the distribution of microplastics on the deep seafloor? Kane et al. show that the answer to that question is more complicated than particles simply settling from where they are found on the sea surface (see the Perspective by Mohrig). Using data that they collected off the coast of Corsica, the authors show that thermohaline-driven currents can control the distribution of microplastics by creating hotspots of accumulation, analogous to their role in causing focused areas of seafloor sediment deposition. Such currents also supply oxygen and nutrients to deep-sea benthos, so deepsea biodiversity hotspots are also likely to be microplastic hotspots.

    Science, this issue p. 1140; see also p. 1055

  4. Coronavirus

    Smothering fecal-oral coronavirus spread

    1. Ifor Williams

    Diarrhea is a common symptom in patients with coronavirus disease 2019 (COVID-19). Zang et al. used organoid cultures of cells from the epithelial lining of human small and large intestine as an in vitro model system with which to study viral entry and replication in enterocytes. Mature enterocytes expressing the viral receptor were susceptible to productive infection, which was also stimulated by the expression of a protease involved in viral entry. A subset of patients with COVID-19 shed high amounts of viral RNA in feces, but experiments with simulated human colonic fluid suggested that any shed virus would be rapidly inactivated during transit through the colon.

    Sci. Immunol. 5, eabc3582 (2020).

  5. Topological Optics

    Topological insulators in the spotlight

    1. Ian S. Osborne

    In addition to having an insulating interior while at the same time supporting conducting surface states, topological insulators have many other interesting properties. Higher-order topological insulating states, where regions of interest are along edges and at corners, have been difficult to identify unambiguously. Peterson et al. developed a theoretical framework to help identify and characterize these exotic states, including a new topological marker—the fractional charge density—that can be used to detect topological states of matter when the spectroscopic probe of gapless surface states is not accessible. The agreement between experimental work and theory is encouraging for applicability to other topological platforms.

    Science, this issue p. 1114

  6. Cancer

    How cancer cells adapt to stress

    1. Paula A. Kiberstis

    Bacteria adapt to harsh conditions such as antibiotic exposure by acquiring new mutations, a process called stress-induced mutagenesis. Cipponi et al. investigated whether similar programs of mutagenesis play a role in the response of cancer cells to targeted therapies. Using in vitro models of intense drug selection and genome-wide functional screens, the authors found evidence for an analogous process in cancer and showed that it is regulated by the mammalian target of rapamycin (mTOR) signaling pathway. This pathway appears to mediate a stress-related switch to error-prone DNA repair, resulting in the generation of mutations that facilitate the emergence of drug resistance.

    Science, this issue p. 1127

  7. Archaeology

    Timing the rise of maize in Mesoamerica

    1. Mark Aldenderfer

    Maize, a global staple crop seen here growing in a field in El Salvador, rose to dominate diets in Mesoamerica by 4000 years before present.

    PHOTO: DBIMAGES/ALAMY STOCK PHOTO

    Many lines of evidence suggest that maize (Zea mays) became a dietary staple across ancient Mesoamerica. However, there has been little direct evidence of its consumption, and the timing of how it came to dominate the diet of the peoples of the region is unknown. Using stable isotopic evidence from human skeletons excavated from two rock shelter sites in Belize, Kennett et al. show that there is no clear evidence of maize consumption by the sites' inhabitants before 4700 years ago. However, isotopes from more recent individuals show the increasing importance of maize in the diet, such that by 4000 years ago, maize had become a persistent dietary staple.

    Sci. Adv. 10.1126/sciadv.aba3245 (2020).

  8. Analytical Chemistry

    Perfluorocarbons' path into soils

    1. Jake Yeston

    Covering carbon chains with fluorines has produced a variety of useful nonstick coatings. However, growing concern about the toxicity and extraordinary environmental persistence of the underlying compounds is spurring a search for alternatives. The precise structure of these next-generation alternatives often remains a trade secret. Washington et al. sampled soils in New Jersey and then used mass spectrometry to assign plausible structures—incorporating chlorine and ether segments into the CF2 chain—to compounds that appear to have emanated from their manufacture (see the Policy Forum by Gold and Wagner). The data can inform in-depth studies of these compounds' environmental transport and persistence.

    Science, this issue p. 1103; see also p. 1066

  9. Coronavirus

    Applications of antibody testing

    1. Gemma Alderton

    There has been a strong focus on testing to determine whether an individual has an active severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) infection, but how do we find out if someone has been infected in the past? In a Perspective, Krammer and Simon discuss the key applications of serological tests to detect antibodies against SARS-CoV-2. Serological testing could answer key questions about whether neutralizing antibodies form, and if they do, serological studies could assess the duration of immune protection. Such tests could also identify recovered patients with high amounts of antibody who could donate blood serum for therapeutic use. In addition, population serosurveys could inform mitigation practices, which could be especially important during subsequent predicted waves of infection. However, it is important to ensure that tests are accurate and sufficiently reliable first.

    Science, this issue p. 1060

  10. Computer Science

    From bottom to top

    1. Jelena Stajic

    The doubling of the number of transistors on a chip every 2 years, a seemly inevitable trend that has been called Moore's law, has contributed immensely to improvements in computer performance. However, silicon-based transistors cannot get much smaller than they are today, and other approaches should be explored to keep performance growing. Leiserson et al. review recent examples and argue that the most promising place to look is at the top of the computing stack, where improvements in software, algorithms, and hardware architecture can bring the much-needed boost.

    Science, this issue p. eaam9744

  11. Plasmid Evolution

    Agrobacteria virulence writ large

    1. Caroline Ash

    Plasmids are widespread among bacteria and are important because they spread virulence and antibiotic resistance traits, among others. They are horizontally transferred between strains and species, so it is difficult to work out their evolution and epidemiology. Agrobacteria, a diverse grouping of species that infect plants, inject oncogenic Ti and Ri plasmids, which cause crown galls and hairy root diseases, respectively. The upside is that these plasmids have become valuable biotechnological tools. Weisberg et al. combed through an 80-year-old collection of Agrobacterium strains but found a surprisingly low diversity of plasmids. It is puzzling how limited the number of plasmid lineages is despite reported high levels of plasmid recombination, but what is clear is how plant production systems have influenced plasmid spread into various genomic backbones.

    Science, this issue p. eaba5256

  12. Structural Biology

    Architecture of DNA-organizing complex

    1. Steve Mao

    The highly conserved mammalian CTC1-STN1-TEN1 (CST) complex is critical for genome stability and telomere maintenance. Lim et al. solved the structure of the human CST complex using cryo–electron microscopy. CST forms an unprecedented and substantial decameric supercomplex triggered by telomeric single-stranded binding. This decameric form with single-stranded DNA–binding capacity of up to 10 telomeric repeats, suggested the possibility of CST organizing telomere overhangs into compact and restrictive structures in a manner similar to the nucleosome's organization of double-stranded DNA. This work provides a platform for understanding the mechanisms of various CST functions.

    Science, this issue p. 1081

  13. Chemical Physics

    Watching electrons swarm ammonia

    1. Jake Yeston

    Liquid ammonia is unusual in its capacity to host electrons in stable solution, with vivid blue and bronze colors signifying the low- and high-concentration regimes, respectively. Buttersack et al. used photoelectron spectroscopy and accompanying theoretical simulations to track the precise energetic changes that ensued as steadily rising quantities of electrons were introduced by dissolved lithium, sodium, or potassium (see the Perspective by Isborn). The results point to a gradual transition from the dilute electrolyte solution of paired dielectrons to the more delocalized metallic structure at the highest concentrations.

    Science, this issue p. 1086; see also p. 1056

  14. Organic Chemistry

    Hydrogenations that tolerate N–O bonds

    1. Jake Yeston

    Catalysts that add hydrogen to carbon-carbon, carbon-nitrogen, and carbon-oxygen double bonds are among the most widely used in synthetic chemistry. They are particularly adept at delivering just one of two mirror-image products. However, they may also target adjacent bonds in the compound that would be better left intact. Mas-Roselló et al. report that an iridium catalyst paired with a strong acid can hydrogenate C=N bonds without disturbing a weak N–O bond on the same nitrogen center. The reactions proceed at room temperature with high enantioselectivity.

    Science, this issue p. 1098

  15. Neuroscience

    Making blind retinas see again

    1. Peter Stern

    Photoreceptor degeneration is an important cause of blindness. Nelidova et al. used tunable, near-infrared sensors to render diseased photoreceptors light sensitive again (see the Perspective by Franke and Vlasits). Gold nanorods capable of detecting infrared light were coupled with an antibody to temperature-sensitive ion channels. When the nanorods absorbed light and converted it into heat, the coupled ion channels were gated by infrared light. In a mouse model of retinal degeneration, these ion channels were successfully targeted to cone photoreceptors, and responses to near infrared light could be detected. In the primary visual cortex, more cells responded to near-infrared stimuli in mice expressing these ion channels than in controls. By changing the length of the gold nanorods, the system could be tuned to different infrared wavelengths.

    Science, this issue p. 1108; see also p. 1057

  16. Paleoecology

    Mangroves under sea level rise

    1. Andrew M. Sugden

    The rate of sea level rise has doubled from 1.8 millimeters per year over the 20th century to ∼3.4 millimeters per year in recent years. Saintilan et al. investigated the likely effects of this increasing rate of rise on coastal mangrove forest, a tropical ecosystem of key importance for coastal protection (see the Perspective by Lovelock). They reviewed data on mangrove accretion 10,000 to 7000 years before present, when the rate of sea level rise was even higher than today as a result of glacial ice melt. Their analysis suggests an upper threshold of 7 millimeters per year as the maximum rate of sea level rise associated with mangrove vertical development, beyond which the ecosystem fails to keep up with the change. Under projected rates of sea level rise, they predict that a deficit between accretion and sea level rise is likely to commence in the next 30 years.

    Science, this issue p. 1118; see also p. 1050

  17. Immunology

    Innate immune cells remember

    1. Seth Thomas Scanlon

    Immunological memory is a phenomenon by which immune cells can quickly recognize an antigen that the host has previously encountered. Certain cells of the innate immune system exhibit memory-like responses know as trained immunity. Rapid, antigen-specific secondary (anamnestic) responses were long thought to be the domain of B and T cells. However, Dai et al. report that monocytes and macrophages can acquire memory specific for particular major histocompatibility complex I antigens using paired A-type immunoglobulin-like receptors (PIR-As) (see the Perspective by Dominguez-Andrés and Netea). This pathway contributes to recognition and rejection of allograft-transplanted tissue from a donor of the same species. Genetic depletion or blockade of PIR-As in mice diminished the rejection of kidney and heart allografts. This work, which expands immunological memory to include myeloid cells, points to targets that may improve organ transplantation outcomes in the future.

    Science, this issue p. 1122; see also p. 1052

  18. Molecular Biology

    DNA barcodes in small packages

    1. Michael A. Funk

    Under adverse environmental conditions, some microorganisms form spores that provide robust protection for genetic material. Qian et al. developed a system in which DNA barcodes are encapsulated inside nongerminating microbial spores and can be dispersed on objects or in the environment (see the Perspective by Nivala). These barcoded spores provide a durable, specific marker that can be read out quickly with simple equipment. When applied to soil, the spores can be transferred to and from objects around them, enabling tracking at meter-scale resolution. On plant leaves, the spores are not readily transferred, and the authors demonstrate a potential use for tracking agricultural products.

    Science, this issue p. 1135; see also p. 1058

  19. Gene Editing

    Enforced editing

    1. Lindsey Pujanandez

    Various autoimmune diseases could potentially be treated with regulatory T cells (Tregs), but there are many hurdles between this idea and clinical execution. Honaker et al. devised a gene-editing strategy to enforce the expression of FOXP3, the master Treg transcription factor, in CD4+ T cells isolated from human peripheral blood, thereby overcoming the limitations of Treg isolation and expansion. The resulting stable FOXP3 expression enabled a suppressive phenotype in vitro, and the edited cells were also functional in both a xenogeneic graft-versus-host disease model and an experimental autoimmune encephalitis model. This approach has the potential to rapidly translate to clinical use.

    Sci. Transl. Med. 12, eaay6422 (2020).

  20. Pharmacology

    More targeted endothelial protection

    1. Wei Wong

    The bioactive lipid S1P exerts effects in diverse tissues. Unbiased agonists of the S1P receptor S1P1 trigger a reduced lymphocyte count, or lymphopenia, a useful feature when treating autoimmune diseases but an undesirable side effect when activating S1P1 in other cell types. Poirier et al. identified a G protein–biased S1P1 agonist, SAR247799, which maintained endothelial function and reduced tissue damage caused by ischemia-reperfusion injury in two different animal models. The characteristics of SAR247799 show that it is possible to target S1P1 in the endothelium without compromising immune responses.

    Sci. Signal. 12, eaax8050 (2020).

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