- Imaging Techniques
Probing interfaces with electrons
- Marc S. Lavine
When molecules move on surfaces, they behave differently from when inside a solid. But surface layers give off limited signals, so to probe these systems, scientists need to act fast. Gulde et al. developed an ultrafast low-energy electron diffraction technique and used it to study how a polymer moved and melted on a graphene substrate (see the Perspective by Nibbering). After hitting the sample with a laser pulse, energy transferred across the graphene-polymer interface, the polymer film became less orderly, and an amorphous phase appeared.
Balancing your incomings and outgoings
- Gilbert Chin
Economic theory predicts that when someone receives money should have little effect on their spending patterns. Gelman et al. constructed a data set of 60 million transactions made by 75,000 people to test this theory. People do seem to go on a mini–spending spree after they get their paychecks or pensions. However, closer inspection reveals that that's mostly explained by the convenience of linking regular payments, such as rent and utilities, to regular income. Unsurprisingly, cash-strapped people are more likely to increase their spending in response to receiving income.
Science, this issue p. 212
- Ocean Microbes
Up and down go the cyanobacteria
- Caroline Ash
Plankton move together in strikingly coordinated daily patterns, sinking at night to avoid being eaten and rising to the surface in daylight to photosynthesize. Otteson et al. found similar activity patterns in even the smallest of planktonic organisms, such as photosynthetic bacteria (see the Perspective by Armbrust). Because it's hard to take regular samples in the open ocean, the authors built a robotic sampler and set it adrift for several days in the mid-Pacific. The captured bacteria showed immediate responses to changes in light, temperature, and salinity in ways that could affect the ocean's carbon and nitrogen cycles.
Chloride causes seizures in glioma
- Yevgeniya Nusinovich
Gliomas, a common brain tumor, frequently induce epileptic seizures as they grow, but it is not clear why. Pallud et al. show that the epileptic activity in the brain around gliomas happens because neurons respond anomalously to the neurotransmitter γ-aminobutyric acid (GABA). Usually GABA turns neurons off, but when gliomas are nearby, it turns them on instead. Also seen in temporal lobe epilepsy, this unusual cell behavior happens because the neurons take up too many chloride ions. Glioma tumor cells also take up too much chloride, which helps them spread and invade into normal brain tissue. Perhaps drugs that block chloride uptake could interfere with both glioma-induced seizures and tumor growth, a two-for-one hit.
Sci. Transl. Med. 6, 244ra89 (2014).
- Cancer Therapy
Staying one step ahead of tumors
- Paula A. Kiberstis
Cancer treatments require continual adjustment. A drug that works initially will lose its potency as the tumor acquires new mutations that allow it to bypass the drug's lethal effects. To stay ahead of the tumor, oncologists need a noninvasive way to collect tumor cells from patients over the course of their treatment. Analyzing the mutations in these samples may help them choose the right drugs as the tumors change. In a small study of breast cancer patients, Yu et al. show that rare tumor cells circulating in the blood can be captured in viable form and used for this purpose.
Science, this issue p. 216
Interfering with the signal to relax
- Nancy R. Gough
In people with high blood pressure, tissue perfusion is often reduced. In response to specific stimuli, endothelial cells that line arteries instruct the surrounding smooth muscle cells to relax, increasing blood flow into the tissue. Endothelial cells extend small processes called myoendothelial projections (MEPs) to communicate with smooth muscle cells. Sonkusare et al. found that the calcium-conducting ion channel TRPV4 and the scaffold protein AKAP150 concentrated at MEPs and visualized calcium signals at these sites. In a mouse model of hypertension, AKAP was not concentrated in MEPs, and the endothelial cells failed to tell the smooth muscle to relax, reducing tissue perfusion.
Sci. Signal. 7, ra66 and pe16 (2014).
- Space Weather
How the ionosphere gains influence
- Margaret M. Moerchen
In Earth's upper atmosphere, the reconnection of magnetic field lines converts latent magnetic energy into the thermal and kinetic energy of plasma flows. But reconnection appears to produce faster flows before midnight compared with after. To find out why, Lotko et al. simulated this energy exchange. Challenging common assumptions about our space weather environment, they conclude that the ionosphere plays an active role when coupled to the magnetosphere in driving the behavior of the magnetotail.
Science, this issue p. 184
Optically probed superconductor
- Jelena Stajic
The exotic superconductor UPt3 has two superconducting phases that appear at different temperatures, but their nature remains unclear. Schemm et al. shone circularly polarized light on a crystal of UPt3 and studied its reflection (see the Perspective by van der Marel and Sawatzky). In the low-temperature phase, the pairs of electrons that make the material superconducting have a handedness to them. The finding narrows down the possible descriptions of the electron-pair wave function.
- HIV Latency
For HIV: Location, location, location
- Kristen L. Mueller
HIV-infected cells linger even in the face of therapy, and this persistence, termed the latent reservoir, is a major hurdle for curing HIV. HIV integrates itself into the DNA of its host cells. Could that affect the latent reservoir? To find out, Maldarelli et al. drew blood from five HIV patients on antiretroviral therapy and analyzed sites where HIV had inserted itself into the blood cells' DNA (see the Perspective by Margolis and Bushman). In many cases, these sites were not random; HIV often weaseled its way into genes that help cells grow and proliferate. Where HIV integrates into the host genome may thus determine the size of the latent reservoir.
- HIV Transmission
HIV needs to be fit to transmit
- Kristen L. Mueller
Although you might not think it, it's hard to catch HIV. Less than 1% of unprotected sexual exposures result in infection. What then leads to transmission? Carlson et al. determined the amino acid sequence of viruses infecting 137 Zambian heterosexual couples in which one partner infected the other (see the Perspective by Joseph and Swanstrom). The authors then used statistical modeling and found that transmitted viruses are typically the most evolutionarily fit. That is, compared to other viral variants in the infected person, the transmitted virus most closely matches the most common viral sequence found in the Zambian population.
- Bacteria Cell Wall
Building the cell wall is flipping difficult
- Stella M. Hurtley
The cell wall of bacteria is constructed from a polysaccharide called peptidoglycan (PG). It forms a matrix that surrounds cells and is essential for the integrity of the cytoplasmic membrane. Many of our most successful antibiotics target PG synthesis. The synthetic pathway involves the assembly of sugar building blocks on a lipid carrier at the inner face of the cytoplasmic membrane. The reactions that produce this so-called lipid II precursor and the enzymes that catalyze them have been known for decades. However, the identity of the flippase enzyme that “flips” lipid II in the membrane to expose the sugar building blocks on the cell surface for polymerization has remained highly controversial. Sham et al. now show that the essential protein MurJ is the long sought-after flippase responsible for the translocation of lipid-linked cell wall precursors across the bacterial cytoplasmic membrane (see the Perspective by Young). The work completes the cell wall biogenesis pathway and defines the function of an attractive target for new antibiotics.
Identifying a cuprate look-alike
- Jelena Stajic
Superconductivity in cuprate compounds remains poorly understood. Recreating its features in an unrelated material may provide insight. Kim et al. used a spectroscopic technique to study the electronic states of the material Sr2IrO4 at relatively high temperatures. They observed phenomenology similar to that of cuprates as they varied the surface carrier concentration. The study highlights the essential properties a material needs in order to exhibit cuprate-like features in the normal (nonsuperconducting) state.
Science, this issue p. 187
Assessing calculated DFT properties
- Phil Szuromi
Density functional theory (DFT) is now widely used to calculate molecular and material properties. DFT's reliability is usually assessed by comparison with experimental values and higher-level theoretical methods. Medford et al. used the BEEF-vdW, an exchange-correlation density functional tailored for surface chemistry, and looked at uncertainties with ensembles of functionals. For the specific case of ammonia synthesis catalyzed by transition-metal surfaces, relative rates between different catalysts had lower errors than the absolute rates.
Science, this issue p. 197
- Heme Enzymes
Peroxidase proton placement
- Jake Yeston
Heme enzymes catalyze a variety of biochemical oxidations through the activation of oxygen by iron. Casadei et al. used neutron crystallography to elucidate the mechanism of cytochrome c peroxidase (see the perspective by Groves and Boaz). In the highly reactive intermediate state termed compound I, the iron(IV) oxo, or ferryl, fragment was not protonated, whereas a nearby histidine residue was protonated. The sensitivity of neutron scattering to proton locations revealed these protonation states, where more common techniques, such as x-ray diffraction, have yielded more ambiguous results.
- Earthquake Dynamics
Supershear rupture down below
- Nicholas S. Wigginton
Deep earthquakes occur in complex fault zones more than 70 kilometers below Earth's surface. Although they do not pose much of a hazard, they can still provide valuable insight into how earthquakes rupture. Zhan et al. found that a magnitude 6.7 aftershock of the largest deep earthquake recorded to date—the 2013 magnitude 8.3 Sea of Okhotsk earthquake—ruptured faster than the velocity of its seismic waves. This so-called “supershear” rupture shows that deep earthquakes have diverse rupture mechanisms and have several routes to dissipate energy.
Science, this issue p. 204
- Genetic Oscillations
Observing an embryonic Doppler effect
- Beverly A. Purnell
The sound of an oncoming train changes as it passes you, a phenomenon termed the Doppler effect. Soroldoni et al. propose a similar event during the formation of vertebrate embryo body segments. It is generally thought that the internal timing of a genetic oscillator called the “segmentation clock” sets the rhythm of body segments called somites. However, time-lapse microscopy of the spatial waves of oscillations and the timing of body segment formation showed segments forming faster than spatial genetic oscillations. This “Doppler effect” occurs because the end of the oscillating tissue moves steadily into the oncoming waves. Thus, the rhythm of sequential body segmentation is a function of genetic oscillations, their changing wave pattern, and tissue shortening.
Science, this issue p. 222
- Marine Pollution
Seas are awash with microplastics
- Julia Fahrenkamp-Uppenbrink
Plastics litter beaches and the open ocean. Scientists are increasingly concerned about a less visible form of plastic pollution: microplastics. Microplastics arise from the deterioration of larger plastic items and from microbeads used in cosmetics. In their Perspective, Law and Thompson explain that because marine currents distribute the pollutants in unpredictable ways, trends in microplastic pollution are difficult to measure. Microplastics can contain harmful chemicals and may also release toxic additives used in their manufacture. They are ingested by and can poison many marine organisms. We are currently unable, and may never be able, to remove microplastics from the oceans. We thus need to understand the environmental effects of this major pollutant in the hope of mitigating its worst effects.
Science, this issue p. 144