- Latitudinal Gradients
Risky in the tropics
- Sacha Vignieri
It is well known that diversity increases toward the tropics. Whether this increase translates into differences in interaction rates among species, however, remains unclear. To simplify the problem, Roslin et al. tested for predation rates by using a single approach involving model caterpillars across six continents. Predator attack rates were higher toward the equator, but only for arthropod predators.
Science, this issue p. 742
ATP boosts protein solubility
- L. Bryan Ray
Adenosine triphosphate (ATP) has well-characterized roles in providing energy for biochemical reactions within cells. Patel et al. find that ATP may also enhance protein solubility, which could help explain why such high concentrations of ATP are maintained in cells (see the Perspective by Rice and Rosen). Protein concentrations in cells can exceed 100 mg/ml. The authors found that ATP at concentrations found in cells could act as a hydrotrope to help solubilize hydrophobic proteins. The results raise the possibility that ATP concentrations could influence processes such as protein aggregation that occur in disease or liquid-liquid phase separations that occur within cells.
- Molecular Sorption
Drying natural gas efficiently
- Phil Szuromi
Natural gas must be purified before it can be transported. The preparation process also includes a drying step to remove water. Microporous adsorbents such as zeolites are used for this purpose, but they often need to be heated to temperatures up to 250°C to remove the water so that they can be reused. Cadiau et al. describe a fluorinated metal-organic framework containing nickel metal centers that can remove water from gas streams but that can be regenerated by heating to only 105°C.
Science, this issue p. 731
- Planetary Topography
River systems reveal planetary tectonics
- Keith T. Smith
Earth, Mars, and Titan have all hosted rivers at some point in their histories. Rivers erode the landscape, leaving behind signatures that depend on whether the surface topography was in place before, during, or after the period of liquid flow. Black et al. developed two metrics to measure how well river channels align with the surrounding large-scale topography (see the Perspective by Burr). Earth's plate tectonics introduce features such as mountain ranges that cause rivers to divert, processes that clearly differ from those found on Mars and Titan.
- Cell Fate
Blocking somatic genes to make sperm
- Beverly A. Purnell
To generate cells with a specific identity, only a subset of genes is used. Most studies focus on factors that turn on cell type–specific gene expression. However, mechanisms are also needed to block expression of genes that specify other cell lineages. Kim et al. identified such a mechanism in the Drosophila male germ line. A multiple–zinc finger protein and a chromatin remodeler were found to act together to block transcription from cryptic promoters. These factors prevented aberrant gene expression and enabled proper differentiation in the adult sperm stem cell lineage.
Science, this issue p. 717
- Nitrogen Cycle
From air to shining sea
- H. Jesse Smith
Nitrogen is an essential nutrient for phytoplankton growth. Nitrogen is primarily supplied to the surface ocean by mixing from below. However, as fertilizer use and combustion of fossil fuels rise, the atmosphere is expected to become an increasingly important source. Ren et al. measured nitrogen isotopes in organic matter from a South China Sea coral (see the Perspective by Boyle). Their findings suggest that atmospheric deposition of anthropogenic nitrogen began right at the end of the 20th century. This pathway now supplies nearly one quarter of the annual nitrogen input to the surface ocean in this region.
A brain region for social cognition
- Peter Stern
Monkeys recognize social interactions and their meanings quickly and effortlessly. Little is known about the neural circuitry that underlies this understanding. Sliwa and Freiwald scanned monkey brains as the monkeys watched static or moving stimuli. A subset of brain areas was exclusively active during monkey-monkey interactions, as opposed to physical interactions between two objects. This network shares some of its components with the monkey mirror neuron system mapped previously by others and with a possible homolog of the human network involved in the theory of mind.
Science, this issue p. 745
- Reproductive Biology
Why antioxidants do not prevent preeclampsia
- Wei Wong
Preeclampsia impairs fetal growth and can damage maternal organs. Reactive oxygen species (ROS) have been proposed to increase the risk of preeclampsia by blocking blood vessel formation (angiogenesis) in the placenta. However, using a mouse model of preeclampsia, Nezu et al. found that decreasing ROS levels led to reduced placental angiogenesis, fetal growth, and maternal survival. In contrast, increased ROS levels resulted in greater placental angiogenesis and improved fetal and maternal outcomes. These results help to explain why antioxidants have been ineffective at preventing preeclampsia in clinical trials.
Sci. Signal. 10, eaam5711 (2017).
Taking HIV to the gut
- Anand Balasubramani
Antiretroviral therapy (ART) effectively limits HIV replication. Nevertheless, HIV+ individuals need to be medicated for life because ART withdrawal results in rebound of persistent virus. One emerging approach to target HIV is an antibody against integrin α4β7. Integrin α4β7 is a receptor that facilitates homing of CD4+ T cells to the gut, a key site for HIV persistence. Guzzo et al. found that integrin α4β7 is incorporated into the HIV envelope, suggesting that antibody treatment may directly interfere with the ability of HIV to home to intestinal tissues. Their results change our perception of the role of integrin α4β7, a promising therapeutic target in HIV pathogenesis.
Sci. Immunol. 2, eaam7341 (2017).
Glial calcium dynamics in space and time
- Peter Stern
Astrocytes use calcium signals to process information received from neighboring brain cells and thus generate modulatory responses at the local or network level. Previous studies have relied on calcium imaging in line scans or in a single focal plane mostly focusing on the cell bodies of astrocytes. Bindocci et al. used more powerful scanners that can rapidly scan many focal planes. They combined this technique with advanced genetic tools for monitoring calcium gradients with high sensitivity, which allowed three-dimensional calcium imaging of a whole astrocyte. Most of the basal calcium activity occurred in the astrocyte processes, some in the endfeet, and only a small fraction actually in the cell bodies of astrocytes.
Science, this issue p. eaai8185
- Germinal Centers
Guiding immune cells to the center
- Stella M. Hurtley,
- Kristen L. Mueller
Germinal centers (GCs) are the site of antibody affinity maturation. The GC response fundamentally depends on contact-dependent signal exchange between antigen-specific T and B lymphocytes. Lu et al. uncovered a repulsive guidance system that inhibits GC recruitment and retention of T follicular helper (TFH) cells while simultaneously promoting their helper activities locally (see the Perspective by Moschovakis and Forster). This system comprises the GC-specific transmembrane ephrin B1 (EFNB1) molecule and two EFNB1 receptors—EPHB4 and EPHB6—expressed by activated T cells, including TFH cells. In the absence of EFNB1 on GC B cells or when EPHB6 was suppressed on T cells, inappropriately large numbers of T cells were recruited to and retained in the GC as a result of relaxed repulsion of TFH cells.
- Materials Science
Watching defects in heated thin films
- Brent Grocholski
The response of materials to external conditions depends on small-scale features such as defects and grain boundaries. Yau et al. heated gold thin films and used coherent x-ray diffractive imaging to track how these microstructures developed during grain growth (see the Perspective by Suter). The technique allowed nondestructive visualization of the features in three dimensions. The method should help link external stimuli to material response through changes in microstructure, thereby allowing development of novel materials through microstructural engineering.
Graphene takes light to a higher level
- Ian S. Osborne
High harmonic generation is a useful nonlinear effect in which the light-matter interaction within a material results in the conversion of one wavelength to a shorter one. Typically performed in atomic gases, there is now interest in extending such a process to the solid state. Yoshikawa et al. pumped single-layer graphene with intense polarized pulses of infrared light to generate ultraviolet light, up to the ninth harmonic. Theoretical analysis of the process suggests that the effect could be transferred to other solid-state systems, providing a possible route to develop coherent light sources across the spectrum.
Science, this issue p. 736
- Developmental Biology
Embryo viability relies on placental repression
- Beverly A. Purnell
The insulin-like growth factor (IGF) signaling pathway controls maternal supply of and fetal demands for nutrients. Yang et al. report that the essential KRAB–zinc finger protein ZFP568 specifically and directly represses a placental-specific IGF2 transcript during early mouse development. Elimination of ZFP568 in vivo leads to the inappropriate early activation of transcription, which results in embryonic death owing to overexpression of IGF2 peptide. Thus, the specific, targeted preimplantation repression of a promoter is essential for viability.
Science, this issue p. 757
No quick fix for climate solutions
- Julia Fahrenkamp-Uppenbrink
Policy scenarios for limiting climate change mostly assume that technologies for removing carbon dioxide from the atmosphere will be able to compensate for ongoing carbon emissions. In a Perspective, Field and Mach caution that most of these technologies are in their infancy and that relying on their future large-scale use is risky. Techniques such as bioenergy with carbon capture and storage, reforestation, and afforestation to remove carbon dioxide would require vast amounts of land and water and thus endanger food security and biodiversity. Furthermore, allowing temperatures to peak as emissions continue and then decline as carbon dioxide is removed risks further instability in the Earth system and human society.
Science, this issue p. 706
- Heart Failure
A brainy treatment for heart failure
- Yevgeniya Nusinovich
Respiratory difficulty and diaphragm weakness are known symptoms of heart failure, but they are usually attributed to pulmonary edema damaging the diaphragm through physical stress. Foster et al. found that this is not the only contributing factor. In mouse models, diaphragm weakness developed even in heart failure without pulmonary edema. The authors linked this observation to changes in angiotensin II and β-adrenergic signaling, which result in centrally controlled ventilatory overdrive. Drugs targeting β-adrenergic signaling were effective in preventing ventilatory overdrive and subsequent diaphragmatic injury, but only if they penetrated the blood-brain barrier.
Sci. Transl. Med. 9, eaag1303 (2017).
Neural crest rules the gut
- Pamela J. Hines
The neurons and glial cells that regulate gut function derive from neural crest cells that emerge from the developing neural tube. Lasrado et al. used single-cell transcriptomics and mosaic mutagenesis to follow how the enteric nervous system is built in mice. Overlapping expression of regulatory programs supports dynamic determination of cell fates, with the developing neurons organized by clonal lineages. The clonal build model may explain how gut motility is coordinated in sequential segments and gut secretion is coordinated with motility.
Science, this issue p. 722