Single-celled microbes may have taught plants and animals how to pack their genetic baggage.

Archaea, a type of single-celled life-form similar to bacteria, keep their DNA wrapped around proteins much in the same way as more complex organisms, researchers report in the Aug. 11 Science. This finding provides new insight into the evolutionary origins of the DNA-packing process and the secret to archaea’s hardiness, which enables some to live in acid, boiling water or other extreme environments.
All eukaryotes, including plants and animals, store their genetic material in cell compartments called nuclei. Such organisms cram meters of genetic material into the tiny nuclei by wrapping strands of DNA around clusters of proteins called histones (SN: 1/10/15, p. 32). “It doesn’t really matter which eukaryote you look at, whether it’s amoebas or plants or humans or fish or insects or anything,” says coauthor John Reeve, a microbiologist at Ohio State University. “They all have exactly the same structure.”

Unlike bacteria, some archaea also contain histones, but researchers weren’t sure whether these microbes spool DNA around the protein bobbins the way eukaryotes do. So Reeve and colleagues used a method called X-ray crystallography to discern, for the first time, the precise shape of archaea DNA bound to histones.

The researchers saw that archaea DNA coils around the histones, similar to the way it does in eukaryotes. “It’s a big deal actually seeing this,” says Steven Henikoff, a molecular biologist at the Fred Hutchinson Cancer Research Center in Seattle who was not involved in the work. The resemblance between archaea and eukaryote DNA wrapping means that the first organism that used this storage scheme was an ancestor of both modern eukaryotes and archaea, the researchers conclude.

But the way archaea DNA twists around histones isn’t identical to the coils of DNA seen in eukaryotes. In eukaryotes, a strand of DNA loops twice around a cluster of eight histones to create what’s called a nucleosome, and connects many of these nucleosomes like beads on a string. Archaea DNA string together bundles of proteins, too. But while eukaryotes always tether eight-protein clumps, archaea DNA can spiral around stacks of many more histones to create rod-shaped structures of various lengths. “So it’s not as uniform as in eukaryotes,” says coauthor Karolin Luger, a biophysicist and Howard Hughes Medical Institute investigator at the University of Colorado Boulder.

Researchers tested the importance of that rodlike architecture by tampering with the histone-DNA structures of some archaea and then observing how these mutant archaea fared in different conditions. “We tried to mimic some real-life situations that some of these organisms could get into,” Luger says.
For instance, some archaea that live in volcanic vents that emit sulfurous gases sometimes get spewed out and have to survive sans sulfur. Archaea with normal histone-DNA shapes can handle that kind of midlife crisis. But when researchers cut their mutant microbes off sulfur, the microorganisms’ growth was stunted. These microbes may not have been able to adapt to sulfur deprivation as well as their wild counterparts “because they can’t unpackage their DNA as readily if the structure has been changed,” Reeve says.

Henikoff calls it “a pretty cool experiment.” It showed that the archaea’s particular DNA-histone architecture was “biologically relevant, not just a novelty,” he says.

A total solar eclipse shines a light on the sun’s elusive atmosphere. When the moon blocks the sun, it’s finally possible to see how this diffuse cloud of plasma, called the corona, is magnetically sculpted into beautiful loops. The material there is about a trillionth the density of the solar surface. From its delicate and diaphanous appearance, you might expect the corona to be where the sun goes to cool off.

That couldn’t be more wrong. The corona is a mysteriously sizzling inferno where the temperature jumps from a mere few thousand degrees to several million degrees. Why?
“It’s one of the longest unanswered questions in all of solar physics,” says Paul Bryans of the High Altitude Observatory at the National Center for Atmospheric Research in Boulder, Colo. “There are a bunch of different ideas about what’s going on there, but it’s still highly debated.” Data collected during the Aug. 21 solar eclipse may bring scientists closer to settling that debate.

The sun simmers at about 5,500° Celsius at its visible surface, the photosphere. But the gas just above the photosphere is heated to about 10,000° C. Then in the corona, the temperature makes an abrupt jump to several million degrees.

“It’s counterintuitive that as you move away from a heat source, it gets warmer,” Bryans says. The corona’s diffuseness makes its heat even stranger — the most basic ways to heat a material rely on particles crashing into each other, but the corona is too tenuous for that to work.

An eclipse first brought this abnormal arrangement to light. German astronomer Walter Grotrian observed spectral lines — the fingerprints of elements that show up when light is split into its component wavelengths — emitted by the corona during a total solar eclipse in 1869.

Astronomers at first assumed those lines were due to a new element they dubbed coronium. But Grotrian realized that iron atoms stripped of several of their electrons by the heat were responsible. These iron lines in the corona are still used to measure its temperature: The more electrons lost, the hotter the material in the corona (SN Online: 6/16/17).
Such extreme temperatures have something to do with the corona’s magnetic field, which is probably where all that energy is stored. Once the energy is there, the corona has a hard time radiating it away, so it builds up. Most of the ways that materials release energy — stripping electrons from atoms, accelerating those electrons so they release X-rays and ultraviolet particles of light — are already maxed out in the corona.
“We know there’s energy coming in, and it’s hard to get it out unless you get very hot,” says Amir Caspi of the Southwest Research Institute in Boulder, Colo. “What we don’t understand is how that energy gets into the corona in the first place.”

Physicists have several ideas. Maybe loops of magnetic field lines in the corona vibrate like guitar strings, heating things up, sort of like how a microwave oven heats food. Maybe the magnetic anchors of those loops on the sun’s surface braid and twist the magnetic field above them, dumping in energy that is then continually radiated away like the heating element in a toaster.

Or maybe tiny explosions called nanoflares or jets called spicules carry energy away from the photosphere and into the corona. The formation of new coronal loops that connect to existing ones could dump in enough extra energy to heat the plasma up.

During the solar eclipse, dozens of groups of scientists across the country will deploy telescopes equipped with filters to pick out polarized light, infrared light or those electron-deprived iron atoms in search of answers. Bryans and his colleagues will be on a mountaintop near Casper, Wyo., in the path of totality. There, the team will take images at a fast clip in both visual and infrared wavelengths to map how the corona changes as the moon moves across the sun. (I will be in Wyoming with this team on the day of the eclipse and will be sharing more about how the experiments went.)

“We can look at how things change as we move from the surface up into the atmosphere,” Bryans says. “How that changes is tied to understanding how the corona is heated.”

Probably all of those mechanisms scientists have thought up contribute to the corona’s extreme heat. It’s difficult to declare just one the most important. But ultimately, the solar eclipse is the best chance scientists have to test them. It’s the only time the corona is the star of the solar show.

Horses can leap over high hurdles, gallop at speeds of up to 70 kilometers per hour and haul around up to nearly 1,000 kilograms of body weight — and all with just one big toe on each foot. Now, a new study published August 23 in Proceedings of the Royal Society B helps explain why: Streamlined digits improved horses’ strength and speed.

Along with zebras and donkeys, horses are among the few single-toed creatures in the animal kingdom. Scientists have long suspected that horses’ single, hoofed toes helped them run farther and faster over grasslands, letting them flee predators and find fresh forage. But the hypothesis that having one big toe is better than having several, biomechanically speaking, has never been directly tested.
“This study takes an important step” toward resolving why horses shed digits during their early evolution, says Karen Sears, an evolutionary biologist at UCLA.

Ancient horses had a lot of toes to lose. The dog-sized Hyracotherium, which lived about 55 million years ago, had four toes on its front feet, and three on its back feet. Merychippus, which lived about 10 million years ago, resembled a modern horse but had three toes, including one long middle digit with a protective, toenail-like hoof at the end. The only surviving horse genus, single-toed Equus, emerged about 5 million years ago.

“If you look closely, you can still see the vestigial remnants” of a bone that would have led to a side toe on a modern horse’s foot, says Brianna McHorse, a paleontologist at Harvard University.

To retrace the evolution of horse toes, McHorse and colleagues used CT scans to capture the internal structure of fossilized foot bones from 12 kinds of extinct horses. They also analyzed the feet of the closely related Central American tapir, which are oddly toed like Hyracotherium. A computer simulation then let researchers estimate how the bones would respond to the stresses of locomotion for each species, such as jumping over a hurdle or accelerating into a gallop. Then the scientists compared what happened when they applied the animal’s full body weight to just to the central toe, or spread it among multiple toes.

Side toes significantly increased the early horses’ ability to bear their own weight, the team found — the central toe of early horses would have fractured without help from other toes. As the era of modern horses approached and side toes dropped away, however, the middle toe bone grew thicker and hollower. These changes made the single-toed foot nearly as sturdy — resistant to bending and compression — as multiple toes.
As horses’ legs grew longer, the extra toes at the end of the limb would have been “like wearing weights around your ankles,” McHorse says. Shedding those toes could have helped early horses save energy, allowing them to travel farther and faster, she says. The study can’t determine what changes came first — whether bulking up the middle toe drove the loss of side toes, or the loss of side toes caused changes in the middle toe.

Horses aren’t the only animals to have lost toes or fingers to the evolutionary chopping block. “Digits have been lost many times in animals that walk, run, hop and fly,” says Kim Cooper, a biologist at the University of California, San Diego. Modeling how forces of locomotion act on an animal’s bones — living or extinct — could help scientists understand why.

The brain chemical missing in Parkinson’s disease may have a hand in its own death. Dopamine, the neurotransmitter that helps keep body movements fluid, can kick off a toxic chain reaction that ultimately kills the nerve cells that make it, a new study suggests.

By studying lab dishes of human nerve cells, or neurons, derived from Parkinson’s patients, researchers found that a harmful form of dopamine can inflict damage on cells in multiple ways. The result, published online September 7 in Science, “brings multiple pieces of the puzzle together,” says neuroscientist Teresa Hastings of the University of Pittsburgh School of Medicine.
The finding also hints at a potential treatment for the estimated 10 million people worldwide with Parkinson’s: Less cellular damage occurred when some of the neurons were treated early on with antioxidants, molecules that can scoop up harmful chemicals inside cells.

Study coauthor Dimitri Krainc, a neurologist and neuroscientist at Northwestern University Feinberg School of Medicine in Chicago, and colleagues took skin biopsies from healthy people and people with one of two types of Parkinson’s disease, inherited or spontaneously arising. The researchers then coaxed these skin cells into becoming dopamine-producing neurons. These cells were similar to those found in the substantia nigra, the movement-related region of the brain that degenerates in Parkinson’s.
After neurons carrying a mutation that causes the inherited form of Parkinson’s had grown in a dish for 70 days, the researchers noticed some worrisome changes in the cells’ mitochondria. Levels of a harmful form of dopamine known as oxidized dopamine began rising in these energy-producing organelles, reaching high levels by day 150. Neurons derived from people with the more common, sporadic form of Parkinson’s showed a similar increase but later, beginning at day 150. Cells derived from healthy people didn’t accumulate oxidized dopamine.
This dangerous form of dopamine seemed to kick off other types of cellular trouble. Defects in the cells’ lysosomes, cellular cleanup machines, soon followed. So did the accumulation of a protein called alpha-synuclein, which is known to play a big role in Parkinson’s disease.
Those findings are “direct experimental evidence from human cells that the very chemical lost in Parkinson’s disease contributes to its own demise,” says analytical neurochemist Dominic Hare, of the Florey Institute of Neuroscience and Mental Health in Melbourne, Australia. Because these cells churn out dopamine, they are more susceptible to dopamine’s potential destructive forces, he says.

When researchers treated neurons carrying a mutation that causes inherited Parkinson’s with several different types of antioxidants, the damage was lessened. To work in people, antioxidants would need to cross the blood-brain barrier, a difficult task, and reach the mitochondria in the brain. And this would need to happen early, probably even before symptoms appear, Krainc says.

“Without this human model, we would not have been able to untangle the pathway,” Krainc says. In dishes of mouse neurons with Parkinson’s-related mutations, dopamine didn’t kick off the same toxic cascade, a difference that might be due to human neurons containing more dopamine than mice neurons. Dopamine-producing neurons in mice and people “have some very fundamental differences,” Krainc says. And those differences might help explain why discoveries in mice haven’t translated to treatments for people with Parkinson’s, he says.

Over the past few decades, scientists have been accumulating evidence that oxidized dopamine can contribute to Parkinson’s disease, Hastings says. Given that knowledge, the new results are expected, she says, but still welcome confirmation of the idea.

These toxic cellular events occurred in lab dishes, not actual brains. “Cell cultures aren’t the perfect re-creation of what’s going on in the human brain,” Hare cautions. But these types of experiments are “the next best thing for monitoring the chemical changes” in these neurons, he says.

When it comes to some oddball fish, looks can be deceiving.

Polypterus, today found only in Africa, and its close kin have generally been considered some of the most primitive ray-finned fishes alive, thanks in part to skeletal features that resemble those on some ancient fish. Now a new analysis of fish fossils of an early polypterid relative called Fukangichthys unearthed in China suggests that those features aren’t so old. The finding shakes up the evolutionary tree of ray-finned fishes, making the group as a whole about 20 million to 40 million years younger than thought, researchers propose online August 30 in Nature.
Ray-finned fishes named for the spines, or rays, that support their fins — are the largest group of vertebrates, making up about half of all backboned animals. They include 30,000 living species, such as gars, bowfins and salmon. The group was thought to originate about 385 million years ago, in the Devonian Period. But the new research, using 3-D CT scans of the previously discovered fossils, shifts the fishes’ apparent origin to the start of the Carboniferous Period some 360 million years ago, says study coauthor Matt Friedman, a paleontologist at the University of Michigan in Ann Arbor.
One of the largest extinction events in Earth’s history marks the boundary between the Devonian and Carboniferous. “We know that many groups of backboned animals were hard hit by the event,” Friedman says. But after the massive die-off, ray-finned fishes popped up and, according to previous fossil evidence, their diversity exploded. The new finding “brings the origin of the modern ray-finned fish group in line with this conspicuous pattern that we see in the fossil record,” Friedman says. It suggests these vertebrates didn’t survive the event. They came after, then flourished.

The largest marsupial to ever walk the Earth just got another accolade: It’s also the only marsupial known to migrate seasonally.

Diprotodon optatum was a massive wombat-like herbivore that lived in what’s now Australia and New Guinea during the Pleistocene, until about 40,000 years ago. Now, an analysis of one animal’s teeth suggests that it undertook long, seasonal migrations like those made by zebras and wildebeests in Africa.

Animals pick up the chemical element strontium through their diet, and it leaves a record in their teeth. The ratio of different strontium isotopes varies from place to place, so it can provide clues about where an animal lived. Strontium isotope ratios in an incisor from one D. optatum revealed a repeating pattern. That suggests the animal migrated seasonally — it moved around, but generally hit up the same rest stops each year, researchers report September 27 in the Proceedings of the Royal Society B.

It’s the first evidence to show a marsupial — living or extinct — migrating in this way, says study coauthor Gilbert Price, a paleoecologist at the University of Queensland in Brisbane, Australia. It’s not clear exactly why this mega-marsupial might have migrated, but an analysis of the carbon isotopes in its teeth suggests it ate a fairly limited diet. So it might have migrated to follow food sources that popped up seasonally in different places, the authors suggest.

Pluto has no rings — New Horizons triple-checked. An exhaustive search for rings and dust particles around the dwarf planet before, during and after the spacecraft flew past Pluto in 2015 has come up empty.

“It’s a very long paper to say we didn’t find anything,” says team member Tod Lauer of the analysis, posted online September 23 at arXiv.org. But the nonresult could help scientists understand the contents of the outer solar system — and help plan New Horizons’ next encounter. The spacecraft is now on a course to a space rock in the Kuiper Belt, another 1.5 billion kilometers past Pluto.
Before New Horizons arrived at Pluto, the possible existence of rings was an urgent matter of safety. Hitting a particle as small as a sand grain could have damaged the spacecraft.

Searches with the Hubble Space Telescope in 2011 and 2012 turned up two previously unknown moons orbiting Pluto — Kerberos and Styx (SN: 11/28/15, p. 14) — and zero rings. Even so, many researchers expected to encounter rings, or at least some debris. The four outer planets in the solar system have rings, as do other small bodies in the solar system, like the tiny planetoid 10199 Chariklo (SN: 5/3/14, p. 10). And some studies suggest that Pluto probably had rings at one point in its past, left over from the collision that formed its largest moon, Charon.

Nine weeks before New Horizons’ closest approach to Pluto, a team jokingly called the “crow’s nest” acted much like a ship’s lookout for potential hazards, says Lauer, an astronomer with the National Optical Astronomy Observatory in Tucson, Ariz. The group examined images taken with the spacecraft’s Long Range Reconnaissance Imager camera, looking for ring particles reflecting sunlight or spots that moved against a starry background from one set of images to the next. Nothing turned up.

The team declared the spacecraft’s trajectory safe, and New Horizons flew sailed safely past Pluto on July 14, 2015 (SN Online: 7/15/15). After the flyby, the team turned New Horizons around to look back at Pluto, and towards the sun. This was a much better position to look for rings, as dust particles would pop into view when backlit by the sun like motes of dust in the light from a window.

“If you really want to know for sure whether there’s any dust there, the viewing geometries where you’re looking past the dust with the sun in the background, that’s the gold standard,” says Matthew Tiscareno of the SETI Institute in Mountain View, Calif., who studied Saturn’s rings with the Cassini spacecraft but was not involved in New Horizons.
It took the better part of a year for all the data from New Horizons to return to Earth, and several months after that to analyze it, but the team is now ready to call it: The rings really aren’t there — or at least they’re too diffuse to see.

That’s somewhat surprising, Lauer says. But the chaotic gravity of Pluto’s family of moons might make it too hard for rings to find stable orbits. Or the slight pressure generated by light particles streaming from the sun could constantly blow would-be ring particles away.

It’s also possible there just wasn’t that much dust there to begin with. New Horizons saw fewer craters on Pluto and Charon than expected, which could mean there are fewer small bodies at that distance from the sun smacking into Pluto and its moons and kicking up dust.

That could be good news for New Horizons’ next act. After five months in hibernation, the spacecraft woke up on September 11 and has set its sights on a smaller, weirder and more distant object: a space rock about 30 kilometers long called 2014 MU69 (SN Online: 7/20/17). Initial observations suggest it might be a double object, with two bodies orbiting closely or touching lightly.

New Horizons will fly past MU69 on January 1, 2019. In the meantime, the team is looking for hazards along the route. “We’re going to do a similar effort to what we did with Pluto,” Lauer says. “We’re going to get in the crow’s nest and get out our binoculars, as it were, and see if we’re going to be okay.”

Astronomers may have just spotted the first asteroid caught visiting the solar system from another star.

The Pan-STARRS 1 telescope in Hawaii discovered the object, initially dubbed A/2017 U1 and later named ‘Oumuamua, on October 18. More observations from other telescopes around the world suggest the object’s trajectory is at an unusually steep angle to the plane on which all the planets lie, and it does not orbit the sun. A/2017 U1’s slingshot route suggests it is a recent visitor to the solar system — and is now on its way out again. The discovery was announced in a bulletin published October 25 by the International Astronomical Union’s Minor Planet Center.
All asteroids previously seen come from within the solar system and circle the sun. Even comets, which come from a distant reservoir of icy rocks in the solar system called the Oort cloud and can have highly titled orbits, still orbit the sun.

Astronomers first pegged the object as a comet thanks to its elongated path, but additional telescope observations October 25 indicate it’s more likely that A/2017 U1 is an asteroid. Those observations revealed that the object looked like a single, sharp point of light, suggesting it is not a comet, which would have an extended icy halo. The asteroid, which is probably no more than 400 meters across, zoomed into the solar system at 25.5 kilometers per second and is now fleeing at 44 km/s.

The new data also supported the wacky trajectory, suggesting the object truly is a visitor from beyond. “It’s now looking very promising,” says planetary scientist Michele Bannister of Queen’s University Belfast in Northern Ireland, although she would still like to get more data to be sure. Astronomers are already planning to measure the colors in the asteroid’s reflected light to figure out what it’s made of, a clue to its origins.

Bit by qubit, scientists are edging closer to the realm where quantum computers will reign supreme.

IBM is testing a prototype quantum processor with 50 quantum bits, or qubits, the company announced November 10. That’s about the number needed to meet a sought-after milestone: demonstrating that quantum computers can perform specific tasks that are beyond the reach of traditional computers (SN: 7/8/17, p. 28).

Unlike standard bits, which represent either 0 or 1, qubits can indicate a combination of the two, using what’s called quantum superposition. This property allows quantum computers to perform certain kinds of calculations more quickly. But because qubits are finicky, scaling up is no easy task. Previously, IBM’s largest quantum processor boasted 17 qubits.

IBM also announced a 20-qubit processor that the company plans to make commercially available by the end of the year.

Bit by qubit, scientists are edging closer to the realm where quantum computers will reign supreme.

IBM is now testing a prototype quantum processor with 50 quantum bits, or qubits, the company announced November 10. That’s around the number needed to meet a sought-after milestone: demonstrating that quantum computers can perform specific tasks that are beyond the reach of traditional computers. Unlike standard bits, which represent either 0 or 1, qubits can indicate a combination of the two, using what’s called a quantum superposition. This property allows quantum computers to perform certain kinds of calculations more quickly. But because quantum bits are more finicky than standard bits, scaling up is no easy task. Previously, IBM’s largest quantum processor boasted 17 qubits.

A race is now on to commercialize quantum computers, making them available to companies that want to solve problems particularly suited to quantum machines, such as designing new materials or speeding up the search for new drugs. IBM also announced a 20-qubit processor that the company plans to make commercially available by the end of 2017. Meanwhile, Google has its own plans to commercialize quantum computers. The company’s quantum computing researchers are currently testing a 22-qubit chip and are designing a larger one.