Pigs are a step closer to becoming organ donors for people.

Researchers used molecular scissors known as CRISPR/Cas9 to snip embedded viruses out of pig DNA. Removing the viruses — called porcine endogenous retroviruses, or PERVs — creates piglets that can’t pass the viruses on to transplant recipients, geneticist Luhan Yang and colleagues report online August 10 in Science.

Yang, a cofounder of eGenesis in Cambridge, Mass., and colleagues had previously sliced 62 PERVs at a time from pig cells grown in the lab (SN: 11/14/15, p. 6). Many of the embedded viruses are already damaged and can’t make copies of themselves to pass on an infection. So in the new study, the researchers removed just 25 viruses that were still capable of infecting other cells.
The team had to overcome several technical hurdles to make PERV-less pig cells that still had the normal number of chromosomes. In a process similar to the one that created Dolly the Sheep (SN: 3/1/97, p. 132), researchers sucked the DNA-containing nuclei from the virus-cleaned cells and injected them into pig eggs. The technique, called somatic cell nuclear transfer, is better known as cloning. Embryos made from the cloned cells were transplanted to sows to develop into piglets.

The process is still not very efficient. Researchers placed 200 to 300 embryos in each of 17 sows. Only 37 piglets were born, and 15 are still living. The oldest are about 4 months old. Such virus-free swine could be a starting point for further genetic manipulations to make pig organs compatible with humans.

As the moon’s shadow races across North America on August 21, hundreds of radio enthusiasts will turn on their receivers — rain or shine. These observers aren’t after the sun. They’re interested in a shell of electrons hundreds of kilometers overhead, which is responsible for heavenly light shows, GPS navigation and the continued existence of all earthly beings.

This part of the atmosphere, called the ionosphere, absorbs extreme ultraviolet radiation from the sun, protecting life on the ground from its harmful effects. “The ionosphere is the reason life exists on this planet,” says physicist Joshua Semeter of Boston University.
It’s also the stage for brilliant displays like the aurora borealis, which appears when charged material in interplanetary space skims the atmosphere. And the ionosphere is important for the accuracy of GPS signals and radio communication.

This layer of the atmosphere forms when radiation from the sun strips electrons from, or ionizes, atoms and molecules in the atmosphere between about 75 and 1,000 kilometers above Earth’s surface. That leaves a zone full of free-floating negatively charged electrons and positively charged ions, which warps and wefts signals passing through it.
Without direct sunlight, though, the ionosphere stops ionizing. Electrons start to rejoin the atoms and molecules they abandoned, neutralizing the atmosphere’s charge. With fewer free electrons bouncing around, the ionosphere reflects radio waves differently, like a distorted mirror.
We know roughly how this happens, but not precisely. The eclipse will give researchers a chance to examine the charging and uncharging process in almost real time.

“The eclipse lets us look at the change from light to dark to light again very quickly,” says Jill Nelson of George Mason University in Fairfax, Va.

Joseph Huba and Douglas Drob of the U.S. Naval Research Laboratory in Washington, D.C., predicted some of what should happen to the ionosphere in the July 17 Geophysical Research Letters. At higher altitudes, the electrons’ temperature should decrease by 15 percent. Between 150 and 350 kilometers above Earth’s surface, the density of free-floating electrons should drop by a factor of two as they rejoin atoms, the researchers say. This drop in free-floating electrons should create a disturbance that travels along Earth’s magnetic field lines. That echo of the eclipse-induced ripple in the ionosphere may be detectable as far away as the tip of South America.

Previous experiments during eclipses have shown that the degree of ionization doesn’t simply die down and then ramp back up again, as you might expect. The amount of ionization you see seems to depend on how far you are from being directly in the moon’s shadow.

For a project called Eclipse Mob, Nelson and her colleagues will use volunteers around the United States to gather data on how the ionosphere responds when the sun is briefly blocked from the largest land area ever.
About 150 Eclipse Mob participants received a build-it-yourself kit for a small radio receiver that plugs into the headphone jack of a smartphone. Others made their own receivers after the project ran out of kits. On August 21, the volunteers will receive signals from radio transmitters and record the signal’s strength before, during and after the eclipse.
Nelson isn’t sure what to expect in the data, except that it will look different depending on where the receivers are. “We’ll be looking for patterns,” she says. “I don’t know what we’re going to see.”

Semeter and his colleagues will be looking for the eclipse’s effect on GPS signals. They would also like to measure the eclipse’s effects on the ionosphere using smartphones — eventually.

For this year’s solar eclipse, they will observe radio signals using an existing network of GPS receivers in Missouri, and intersperse it with small, cheap GPS receivers that are similar to the kind in most phones. The eclipse will create a big cool spot, setting off waves in the atmosphere that will propagate away from the moon’s shadow. Such waves leave an imprint on the ionosphere that affects GPS signals. The team hopes to combine high-quality data with messier data to lay the groundwork for future experiments to tap into the smartphone crowd.

“The ultimate vision of this project is to leverage all 2 billion smartphones around the planet,” Semeter says. Someday, everyone with a phone could be a node in a global telescope.

If it works, it could be a lifesaver. Similar atmospheric waves were seen radiating from the source of the 2011 earthquake off the coast of Japan (SN Online: 6/16/11). “The earthquake did the sort of thing the eclipse is going to do,” Semeter says. Understanding how these waves form and move could potentially help predict earthquakes in the future.

Carbondale, Ill., is just a few kilometers north of the point where this year’s total solar eclipse will linger longest — the city will get two minutes and 38 seconds of total darkness when the moon blocks out the sun. And it’s the only city in the United States that will also be in the path of totality when the next total solar eclipse crosses North America, in 2024 (SN: 8/5/17, p. 32). The town is calling itself the Eclipse Crossroads of America.
“Having a solar eclipse that goes through the entire continent is rare enough,” says planetary scientist Padma Yanamandra-Fisher of the Space Science Institute’s branch in Rancho Cucamonga, Calif. “Having two in seven years is even more rare. And two going through the same city is rarer still.”

That makes Carbondale the perfect spot to investigate how the sun’s atmosphere, or corona, looks different when solar activity is high versus low.

Every 11 years or so, the sun cycles from periods of high magnetic field activity to low activity and back again. The frequency of easy-to-see features — like sunspots on the sun’s visible surface, solar flares and the larger eruptions of coronal mass ejections — cycles, too. But it has been harder to trace what happens to the corona’s streamers, the long wispy tendrils that give the corona its crownlike appearance and originate from the magnetic field.
The corona is normally invisible from Earth, because the bright solar disk washes it out. Even space telescopes that are trained on the sun can’t see the inner part of the corona — they have to block some of it out for their own safety (SN Online: 8/11/17). So solar eclipses are the only time researchers can get a detailed view of what the inner corona, where the streamers are rooted, is up to.
Right now, the sun is in a period of exceptionally low activity. Even at the most recent peak in 2014, the sun’s number of flares and sunspots was pathetically wimpy (SN: 11/2/13, p. 22). During the Aug. 21 solar eclipse, solar activity will still be on the decline. But seven years from now during the 2024 eclipse, it will be on the upswing again, nearing its next peak.

Yanamandra-Fisher will be in Carbondale for both events. This year, she’s teaming up with a crowdsourced eclipse project called the Citizen Continental-America Telescope Eclipse experiment. Citizen CATE will place 68 identical telescopes along the eclipse’s path from Oregon to South Carolina.

As part of a series of experiments, Yanamandra-Fisher and her colleagues will measure the number, distribution and extent of streamers in the corona. Observations of the corona during eclipses going back as far as 1867 suggest that streamers vary with solar activity. During low activity, they tend to be more squat and concentrated closer to the sun’s equator. During high activity, they can get more stringy and spread out.

Scientists suspect that’s because as the sun ramps up its activity, its strengthening magnetic field lets the streamers stretch farther out into space. The sun’s equatorial magnetic field also splits to straddle the equator rather than encircle it. That allows streamers to spread toward the poles and occupy new space.

Although physicists have been studying the corona’s changes for 150 years, that’s still only a dozen or so solar cycles’ worth of data. There is plenty of room for new observations to help decipher the corona’s mysteries. And Yanamandra-Fisher’s group might be the first to collect data from the same point on Earth.

“This is pure science that can be done only during an eclipse,” Yanamandra-Fisher says. “I want to see how the corona changes.”

Cube-shaped ice is rare, at least at the microscopic level of the ice crystal. Now researchers have coaxed typically hexagonal 3-D ice crystals to form the most cubic ice ever created in the lab.

Cubed ice crystals — which may exist naturally in cold, high-altitude clouds — could help improve scientists’ understanding of clouds and how they interact with Earth’s atmosphere and sunlight, two interactions that influence climate.

Engineer Barbara Wyslouzil of Ohio State University and colleagues made the cubed ice by shooting nitrogen and water vapor through nozzles at supersonic speeds. The gas mixture expanded and cooled, and then the vapor formed nanodroplets. Quickly cooling the droplets further kept them liquid at normally freezing temperatures. Then, at around –48° Celsius, the droplets froze in about one millionth of a second.

The low-temperature quick freeze allowed the cubic ice to form, the team reports in the July 20 Journal of Physical Chemistry Letters. The crystals weren’t perfect cubes but were about 80 percent cubic. That’s better than previous studies, which made ice that was 73 percent cubic.

Neandertals took stick-to-itiveness to a new level. Using just scraps of wood and hot embers, our evolutionary cousins figured out how to make tar, a revolutionary adhesive that they used to make formidable spears, chopping tools and other implements by attaching sharp-edged stones to handles, a new study suggests.

Researchers already knew that tar-coated stones date to at least 200,000 years ago at Neandertal sites in Europe, well before the earliest known evidence of tar production by Homo sapiens, around 70,000 years ago in Africa. Now, archaeologist Paul Kozowyk of Leiden University in the Netherlands and colleagues have re-created the methods that these extinct members of the human genus could have used to produce tar.
Three straightforward techniques could have yielded enough adhesive for Neandertals’ purposes, Kozowyk’s team reports August 31 in Scientific Reports. Previous studies have found that tar lumps found at Neandertal sites derive from birch bark. Neandertal tar makers didn’t need ceramic containers such as kilns and didn’t have to heat the bark to precise temperatures, the scientists conclude.
These findings fuel another burning question about Neandertals: whether they had mastered the art of building and controlling a fire. Some researchers suspect that Neandertals had specialized knowledge of fire control and used it to make adhesives; others contend that Neandertals only exploited the remnants of wildfires. The new study suggests they could have invented low-tech ways to make tar with fires, but it’s not clear whether those fires were intentionally lit.

“This new paper demystifies the prehistoric development of birch-bark tar production, showing that it was not predicated on advanced cognitive or technical skills but on knowledge of familiar, readily available materials,” says archaeologist Daniel Adler of the University of Connecticut in Storrs, who did not participate in the study.
Kozowyk’s group tested each of three tar-making techniques between five and 11 times. The lowest-tech approach consisted of rolling up a piece of birch bark, tying it with wood fiber and covering it in a mound of ashes and embers from a wood fire. Tar formed between bark layers and was scraped off the unrolled surface. The experimenters collected up to about one gram of tar this way.

A second strategy involved igniting a roll of birch bark at one end and placing it in a small pit. In some cases, embers were placed on top of the bark. The researchers either scraped tar off bark layers or collected it as it dripped onto a rock, strip of bark or a piece of bark folded into a cup. The most tar gathered with this method, about 1.8 grams, was in a trial using a birch-bark cup placed beneath a bark roll with its lit side up and covered in embers.

Repeating either the ash-mound or pit-roll techniques once or twice would yield the relatively small quantity of tar found at one Neandertal site in Europe, the researchers say. Between six and 11 repetitions would produce a tar haul equal to that previously unearthed at another European site.

In a third technique, the scientists placed a birch-bark vessel for collecting tar into a small pit. They placed a layer of twigs across the top of the pit and placed pebbles on top, then added a large, loose bark roll covered in a dome-shaped coat of wet soil. A fire was then lit on the earthen structure. This method often failed to produce anything. But after some practice with the technique, one trial resulted in 15.7 grams of tar — enough to make a lump comparable in size to the largest chunks found at Neandertal sites.

An important key to making tar was reaching the right heat level. Temperatures inside bark rolls, vessels, fires and embers varied greatly, but at some point each procedure heated bark rolls to between around 200˚ and 400˚ Celsius, Kozowyk says. In that relatively broad temperature range, tar can be produced from birch bark, he contends.

If they exploited naturally occurring fires, Neandertal tar makers had limited time and probably relied on a simple technique such as ash mounds, Kozowyk proposes. If Neandertals knew how to start and maintain fires, they could have pursued more complex approaches.

Some researchers say that excavations point to sporadic use of fire by Neandertals, probably during warm, humid months when lightning strikes ignited wildfires. But other investigators contend that extinct Homo species, including Neandertals, built campfires (SN: 5/5/12, p. 18).

Whatever the case, Kozowyk says, “Neandertals could have invented tar with only basic knowledge of fire and birch bark.”

Walls can get the best of clumsy TV sitcom characters and bats alike.

New lab tests suggest that smooth, vertical surfaces fool some bats into thinking their flight path is clear, leading to collisions and near misses.

The furry fliers famously use sound to navigate — emitting calls and tracking the echoes to hunt for prey and locate obstacles. But some surfaces can mess with echolocation.

Stefan Greif of the Max Planck Institute for Ornithology in Seewiesen, Germany, and colleagues put bats to the test in a flight tunnel. Nineteen of 21 greater mouse-eared bats (Myotis myotis) crashed into a vertical metal plate at least once, the scientists report in the Sept. 8 Science. In some crashes, bats face-planted without even trying to avoid the plate.
Smooth surfaces act as acoustic mirrors, the team says: Up close, they reflect sound at an angle away from the bat, producing fuzzier, harder-to-read echoes than rough surfaces do. From farther away, smooth surfaces don’t produce any echoes at all.

Infrared camera footage of wild bat colonies showed that vertical plastic plates trick bats in more natural settings, too.

Crash reel
This video shows three experiments into how smooth surfaces affect bat flight. In one lab test, a vertical metal plate gave a bat the illusion of a clear flight path, causing it to crash into the barrier. In a second lab test, a horizontal metal plate created the illusion of water; the bat dips to surface to take a sip. Finally, near a natural bat colony, a bat collides with a vertically hung plastic plate, showing that smooth surfaces could impact bats in the wild, as well.

Saber-toothed kittens were the spitting image of their parents. Even as babies, the cats not only had the oversized canine teeth but also unusually powerful forelimbs, Katherine Long, a graduate student at California State Polytechnic University in Pomona, and colleagues report September 27 in PLOS ONE.

As adults, the ferocious felines used those strong forelimbs to secure wriggling prey before slashing a throat or belly (thereby avoiding breaking off a tooth in the struggle). Paleontologists have puzzled over whether saber-toothed cats such as Smilodon fatalis developed those robust limbs as they grew.

To compare the growth rate of Smilodon with that of similar-sized non‒saber-toothed cats that lived alongside it, Long and her team turned to fossils collected from the La Brea Tar Pits in Los Angeles. The ancient asphalt traps hold a wealth of species and specimens from juveniles to adults, dating to between 37,000 and 9,000 years ago.

The Smilodon bones, they found, did not show any evidence of an unusual growth spurt. Instead, the bones grew longer and slimmer as the kittens grew up, following the same developmental pattern as the other large cats. That suggests that when it comes to their mighty forelimbs, Smilodon kittens were just born that way.

A misfit gang of superconducting materials may be losing their outsider status.

Certain copper-based compounds superconduct, or transmit electricity without resistance, at unusually high temperatures. It was thought that the standard theory of superconductivity, known as Bardeen-Cooper-Schrieffer theory, couldn’t explain these oddballs. But new evidence suggests that the standard theory applies despite the materials’ quirks, researchers report in the Dec. 8 Physical Review Letters.

All known superconductors must be chilled to work. Most must be cooled to temperatures that hover above absolute zero (–273.15° Celsius). But some copper-based superconductors work at temperatures above the boiling point of liquid nitrogen (around –196° C). Finding a superconductor that functions at even higher temperatures — above room temperature — could provide massive energy savings and new technologies (SN: 12/26/15, p. 25). So scientists are intent upon understanding the physics behind known high-temperature superconductors.
When placed in a magnetic field, many superconductors display swirling vortices of electric current — a hallmark of the standard superconductivity theory. But for the copper-based superconductors, known as cuprates, scientists couldn’t find whirls that matched the theory’s predictions, suggesting that a different theory was needed to explain how the materials superconduct. “This was one of the remaining mysteries,” says physicist Christoph Renner of the University of Geneva. Now, Renner and colleagues have found vortices that agree with the theory in a high-temperature copper-based superconductor, studying a compound of yttrium, barium, copper and oxygen.

Vortices in superconductors can be probed with a scanning tunneling microscope. As the microscope tip moves over a vortex, the instrument records a change in the electrical current. Renner and colleagues realized that, in their copper compound, there were two contributions to the current that the probe was measuring, one from superconducting electrons and one from nonsuperconducting ones. The nonsuperconducting contribution was present across the entire surface of the material and masked the signature of the vortices.

Subtracting the nonsuperconducting portion revealed the vortices, which behaved in agreement with the standard superconductivity theory. “That, I think, is quite astonishing; it’s quite a feat,” says Mikael Fogelström of Chalmers University of Technology in Gothenburg, Sweden, who was not involved with the research.
The result lifts some of the fog surrounding cuprates, which have so far resisted theoretical explanation. But plenty of questions still surround the materials, Fogelström says. “It leaves many things still open, but it sort of gives a new picture.”

One person infected with strep bacteria might get a painful sore throat; another might face a life-threatening blood infection. Now, scientists are trying to pin down why.

Variation between individuals’ immune systems may not be entirely to blame. Instead, extra genes picked up by some pathogens can cause different strains to have wildly different effects on the immune system, even in the same person, researchers report January 11 in PLOS Pathogens.

The idea that different strains of bacteria can behave differently in the body isn’t new. Take E. coli: Some strains of the bacteria that can cause foodborne illness make people far sicker than other strains­. But bacteria have exceptionally large amounts of genetic variation, even between members of the same species. Scientists are still trying to figure out how that genetic diversity affects the way microbes interact with the immune system.
Any species of bacteria has a core set of genes that all its members share. Then there’s a whole pot of genes that different strains of the species pick and choose to create what’s known as an accessory genome. These genes are custom add-ons that specific strains have acquired over time, from their environment or from other microbes — something like an expansion pack for a card game. Sometimes, that extra genetic material gives bacteria new traits.

Uri Sela and his colleagues at the Rockefeller University in New York City tested the way these extra genes influenced the way two common species of bacteria, Staphylococcus aureus and Streptococcus pyogenes, interacted with the immune system. Staphylococcus bacteria can cause everything from rashes to food poisoning to blood infections. Streptococcus bacteria can cause strep throat, as well as a host of more serious illnesses (SN: 10/4/14, p. 22).

Different strains of the same species provoked wildly different immune responses in blood samples collected from the same patient, the researchers first showed. But the strain-specific responses were consistent across patients. Some strains triggered lots of T cells to be made in every sample, for example; others increased B cell activity. (T cells and B cells are the two main weapons of the adaptive immune response, which enables the body to build long-lasting immunity against a particular pathogen.) In tests of strains missing some of their extra genes, though, the T cells didn’t respond as strongly as they did to a matching strain that contained the extra genes. This finding suggests that the variation in immune response across strains was coming, at least in part, from differences in these supplementary genes.
“Currently when a patient comes to the hospital with an infection, we don’t define the strain of the species” for common infections like strep and staph, says Sela, an immunologist. In the future, he says, information about the strain could help doctors predict how a patient’s illness will unfold and decide on the best treatment.

The new study “adds fuel to an active debate” about the role of accessory genes, says Alan McNally, a microbiologist at the University of Birmingham in England — whether or not the collections of genetic add-ons that bacteria maintain are shaped by natural selection, the process that fuels evolution. This research suggests that for some kinds of bacteria, genetic customization might aid survival of certain strains by enabling them to provoke a tailored immune response.

But more research needs to be done to link the strain-to-strain variation in immune response to the accessory genome, he says, as this study looked at only a few extra genes, not the entire accessory genome.

Volcano-fueled holes in Earth’s ozone layer 252 million years ago may have repeatedly sterilized large swaths of forest, setting the stage for the world’s largest mass extinction event. Such holes would have allowed ultraviolet-B radiation to blast the planet. Even radiation levels below those predicted for the end of the Permian period damage trees’ abilities to make seeds, researchers report February 7 in Science Advances.

Jeffrey Benca, a paleobotanist at the University of California, Berkeley, and his colleagues exposed plantings of modern dwarf pine tree (Pinus mugo) to varying levels of UV-B radiation. Those levels ranged from none to up to 93 kilojoules per square meter per day. According to previous simulations, UV-B radiation at the end of the Permian may have increased from a background level of 10 kilojoules (just above current ambient levels) to as much as 100 kilojoules, due to large concentrations of ozone-damaging halogens spewed from volcanoes (SN: 1/15/11, p. 12).

Exposure to higher UV-B levels led to more malformed pollen, the researchers found, with up to 13 percent of the pollen grains deformed under the highest conditions. And although the trees survived the heightened irradiation, the trees’ ovulate cones — cones that, when fertilized by pollen, become seeds — did not. But the trees weren’t permanently sterilized: Once removed from extra UV-B exposure, the trees could reproduce again.

The finding supports previous research suggesting that colossal volcanic eruptions in what’s now Siberia, about 300,000 years before the onset of the extinction event, probably triggered the die-off of nearly all marine species and two-thirds of species living on land (SN: 9/19/15, p. 10). Repeated pulses of volcanism at the end of the Permian may have led to several periods of irradiation that sterilized the forests, causing a catastrophic breakdown of food webs, the researchers say — an indirect but effective way to kill.