Research Highlights

Our pick of the latest scientific literature

This miniature ‘brain’ was grown from human embryonic stem cells.

This miniature ‘brain’ was grown from human embryonic stem cells. Credit: E. Karzbrun/Nature Phys.

Biophysics

‘Brains in a dish’ show how wrinkles form

Uneven growth of brain layers helps to create characteristic folds.

Miniature ‘brains’ in a dish have provided a guidebook to the physical forces that give the human cerebral cortex its classic wrinkled appearance.

Previous experiments used polymer gels to model the formation of the brain’s folds, a process crucial to the organ’s development. To move such studies into living cells, Orly Reiner and her colleagues at the Weizmann Institute of Science in Rehovot, Israel, grew ‘organoids’ — 3D clumps of cells — that mimicked the developing brain.

The team confined the organoids, which were grown from human cells, to small compartments. Wrinkling developed during the second week of maturation, and was triggered, in part, by the faster growth of the organoid’s outer regions compared with its inner regions. Treatment with a drug that inhibits the action of a key component of the cell skeleton led to smoother organoids.

The results suggest that organoids can offer a useful model for early brain development.

False-colour image of fossilized diatoms, single-celled algae that may trigger underwater landslides.

False-colour image of fossilized diatoms, single-celled algae that may trigger underwater landslides. Credit: Steve Gschmeissner/SPL

Geology

The slippery cause of huge underwater landslides

Ancient layers of buried algae may represent a weak link.

Buried layers of microscopic fossils could be responsible for some of the world’s biggest landslides.

Earth’s largest known landslides happened underwater. A slide off what is now Norway, for example, triggered a 20-metre-high tsunami that swamped nearby coastlines 8,150 years ago. But little is known about why such slides occur, especially on gently sloping seafloors.

Morelia Urlaub at the Geomar Helmholtz Centre for Ocean Research Kiel in Germany and her colleagues studied sediments extracted from the Cap Blanc slide, which occurred off northwest Africa 149,000 years ago. The team also analysed images generated by bouncing seismic waves off bands of sediment buried beneath the seafloor.

A squishy layer of fossilized diatoms — microscopic algae — was the weak link that gave way to cause the slide, the authors say. Such diatom layers are common on continental slopes and could have played a part in other massive underwater landslides.

Two cells of the dinoflagellate Alexandrium catenella

A lethal nerve agent called saxitoxin is produced by marine plankton (above) and freshwater bacteria. Credit: Donald Anderson

Biochemistry

How bacteria build a deadly toxin

Insights into an enzyme could yield new anaesthetics.

Scientists have revealed the first steps involved in a microbe’s synthesis of a potent nerve toxin. The advance could help to make the compound, saxitoxin, medically useful.

Saxitoxin is made by aquatic bacteria and plankton. Although humans can die from eating shellfish contaminated with it, the compound’s nerve-blocking activity might make it useful as a long-lasting anaesthetic. Alison Narayan at the University of Michigan in Ann Arbor and her colleagues investigated an enzyme involved in manufacturing saxitoxin in the bacterium Cylindrospermopsis raciborskii T3.

First, the authors determined which chemical ingredients the enzyme uses as a feedstock. Then the team fed alternate forms of one ingredient to the enzyme, which made saxitoxin precursors that differed slightly from the one produced under natural conditions.

The modified precursors could lead to forms of saxitoxin mild enough to act as a drug rather than a poison.

A vampire bat dines on livestock blood, which is high in protein and low in carbohydrates.

A vampire bat dines on livestock blood, which is high in protein and low in carbohydrates. Credit: Nicolas Reusens/Barcroft Media/Getty

Evolution

A vampire bat’s secrets to blood-sucking

Gory diet might poison bats without aid from microbiome.

Feasting on blood brings nutritional challenges, but vampire bats overcome these with a little help from their gut bacteria.

Lisandra Zepeda Mendoza at the University of Copenhagen and her colleagues analysed the genomes of the common vampire bat (Desmodus rotundus) and its gut microbes to understand how the animal thrives on a blood-based diet, which is rich in protein but poor in vitamins and carbohydrates.

The team found that the bat has evolved adaptations to cope with nutrient shortages, such as genes that help the animal to maximize the use of any available carbohydrates. The bat’s gut bacteria also boast special genes that help the animals to metabolize urea and other nitrogen-based waste products from its blood-heavy diet. The bat’s gut microbes might improve the creature’s ability to fight off blood-borne pathogens, as well.

Paper test strips showing positive and negative results

Paper test strips reveal whether a CRISPR test has found disease-related DNA. Credit: Zhang lab, Broad Institute of MIT and Harvard

Biotechnology

CRISPR’s powers unleashed for disease detection

Two techniques use the popular gene editor for good — and one can be used far from the laboratory.

Trace amounts of specific DNA and RNA can be detected using the gene-editing technique CRISPR.

Two tests, developed by independent teams, rely on basic CRISPR machinery: a bacterial enzyme, and, riding with it, a piece of ‘guide’ RNA that attaches only to specific stretches of DNA or RNA. For both test methods, the researchers added the enzyme–RNA complex, along with marker molecules, to a sample of genetic material. If the guide RNA found its target — for example, a bit of RNA from the Dengue virus — the enzyme would be activated, prompting the markers to light up.

One of the techniques, devised by Jennifer Doudna at the University of California, Berkeley, and her colleagues, can distinguish between highly similar strains of the human papilloma virus. The other, first reported last year by Feng Zhang at the Broad Institute of MIT and Harvard in Cambridge, Massachusetts, and his colleagues, has now been upgraded to show results on paper test strips, allowing use of the test in field settings far from any lab.

Optical image of the Andromeda galaxy

The Andromeda galaxy (shown in an artist’s depiction) and the Milky Way share a spiral shape and perhaps a similar mass.

Astronomy and astrophysics

The Milky Way’s big sister gets shrunk down to size

The Andromeda galaxy might be only half as massive as thought.

The Andromeda galaxy, the closest to the Milky Way, might be more of a lightweight than astronomers thought.

Previous measurements have put Andromeda’s mass at about twice that of the Milky Way, although estimates vary from around the same to three times as heavy.

To refine the estimates, Prajwal Kafle of the University of Western Australia in Crawley and his colleagues studied the motion of Andromeda’s stars, which orbit the galaxy’s centre. From the speeds of 86 of Andromeda’s fastest stars, the researchers were able to infer a galactic speed limit — the velocity at which a star would escape Andromeda’s gravitational pull. This allowed the team to calculate the galaxy’s mass: around 800 billion solar masses, on par with the Milky Way.

The revised figure could help to explain why fewer satellite galaxies orbit Andromeda than expected, say the authors.

A termite-eating ant tends to a nest-mate (marked with green) that has lost two legs.

A termite-eating ant tends to a nest-mate (marked with green) that has lost two legs. Credit: Erik Frank

Animal behaviour

The life-saving care provided by ant medics

Treatment of injured nest-mates greatly improves survival.

Some ants nurse nest-mates wounded in battle in an effort to prevent infection.

Squads of the termite-eating ant Megaponera analis raid termite foraging sites, often losing limbs in the process. Erik Frank and his colleagues at the University of Würzburg in Germany collected raiding ants in Comoé National Park, Côte d’Ivoire, amputated either two or five legs to simulate injuries from a raid, and placed the injured warriors next to the trail leading back to the ants’ nest.

The team found that heavily injured ants were left behind, but those with two lost limbs were carried back to the nest in 45% of trials. Inside the nest, injured ants’ wounds were groomed by nest mates, possibly to remove dirt and apply antimicrobial substances. Treated ants were 70% more likely to survive the first 24 hours after injury than untreated ants.

Wild flowers bordering a field

Bees prosper in farmland criss-crossed by many field borders. Credit: Christoffer Askman/Image Source Salsa/Alamy

Agriculture

Bees thrive when fields have borders

Croplands with more divisions benefit pollinators.

Decreasing the size of farm fields and creating more borders between them helps wild pollinators to flourish, whereas increasing crop diversity does not.

Annika Hass at the University of Göttingen in Germany and her colleagues surveyed the number of bees and hoverflies — flies that eat nectar and pollen — in 229 fields across 4 European countries. The team found that wild bees became more abundant as field size shrank and the extent of field borders rose. Borders might help pollinators by providing safe travel routes through fields, the researchers say.

But bee abundance fell as crop diversity rose, the team adds. One possible explanation for that trend: increases in crop diversity might have been driven by the planting of crops that require more fertilizers and herbicides.

The researchers recommend implementing agricultural policies that counteract the trend towards large farm fields.

Oil palm plantations in the rainforest

Roads and oil-palm plantations slice into a rainforest on the Malaysian island of Borneo. Credit: Matthias Klum/NGC

Conservation biology

Tropical forests are near a breaking point

In 50 years, the average size of a forest could be smaller than a football pitch.

If deforestation continues at its current pace, only small and isolated patches of tropical forest will survive half a century from now.

Agriculture, logging and urbanization have chopped great swathes of tropical forest into fragments, disrupting habitats and reducing biodiversity. To assess the damage, Franziska Taubert of the Helmholtz Centre for Environmental Research in Leipzig, Germany, and her colleagues studied high-resolution satellite images, which revealed more than 130 million fragments of tropical forest across 3 continents. Sections smaller than 10,000 hectares account for roughly 10% of forests.

The researchers also found that tropical forests are nearing a critical point. If deforestation continues, runaway fragmentation will lead to an explosion in the number of forest segments, and average size will plummet from 17 to 0.25 hectares over the next half century.

Tree clearing should be slowed and reforestation increased to restore tropical-forest cover in the next few decades, the authors say.

Ancient people in what is now Sweden mounted human skulls on wooden sticks, perhaps as a funerary display.

Ancient people in what is now Sweden mounted human skulls on wooden sticks, perhaps as a funerary display. Adapted from Fredrik Hallgren/The Cultural Heritage Foundation.

Anthropology

Stone Age people laid staked skulls in watery grave

Complex ritual included creation of stone pavement on lake bottom.

Prehistoric residents of what is now Sweden mounted the heads of some of their dead on wooden stakes before consigning them to the waters of a small lake.

Anna Kjellström at Stockholm University and her colleagues recovered two staked skulls and the remains of at least eight other individuals from an expanse of large, closely packed stones on a prehistoric lake bottom. The people who laid the stones and deposited the remains were hunter-gatherers living 7,500 to 8,000 years ago.

Seven of those left in the lake had suffered blows to the skull well before their deaths. The proportion of damaged to undamaged skulls and the positions of the injuries suggest that the trauma resulted from violence, rather than accidents, the authors say.

Correction: An earlier version of this article erroneously referred to Anna Kjellström as the team's leader.

Scanning electron micrograph of interface between two photonic crystals with different topological properties

An artificially shaded view of the honeycomb structure on a device that bends light. Credit: S. Barik et al./Science

Optics and photonics

Photons hug the curves with help from special physics

Topology inspires a light-routing device with minimal scatter.

A newly designed device routes photons along twisting paths with minimal scattering by exploiting ‘topological’ effects. In physics, topological properties are those that do not change when a shape is deformed; as such, they can preserve the direction of electrical currents and protect light waves from disturbances.

Mohammad Hafezi and his collaborators at the University of Maryland in College Park etched triangular holes into a transparent slab of insulating material. The holes, which were arranged in a honeycomb pattern, were slightly larger in one half of the slab than in the other, a design that gave the two sections different topological properties.

Thanks to this split, single photons emitted by a light source in the slab could travel only along the boundary between the sections. The device’s design also prevented the light from scattering when it swerved around bends and forced polarized light to travel in only one direction.

Analysis of bacteria from hundreds of soil samples has yielded a new family of antibiotics.

Analysis of bacteria from hundreds of soil samples has yielded a new family of antibiotics. Credit: Sean Brady

Microbiology

Dirt yields potent antibiotics

Soil microbes make compounds that kill resistant pathogens.

Microorganisms found in dirt have yielded antibiotics that can kill pathogens resistant to multiple drugs.

One gram of soil contains at least 1,000 bacterial species. To explore the medical potential of that diversity, Sean Brady at the Rockefeller University in New York City and his colleagues analysed roughly 2,000 soil samples collected across the United States. The researchers extracted DNA from the samples and screened it for genetic sequences involved in the production of antibiotics by various bacteria.

The search turned up a new family of antibiotics that the team named ‘malacidins’. The compounds kill many formidable pathogens, including a microbe resistant to vancomycin, which is considered to be the antibiotic of last resort. When applied to the skin of rats, the new antibiotics sterilized wounds infected with methicillin-resistant Staphylococcus aureus (MRSA), a bacterium that can ravage large expanses of tissue.

A vacuum system and electronics for a laser are among the components required for a portable atomic clock housed in a trailer.

A vacuum system (right) and electronics (left) for a laser are among the components required for a portable atomic clock housed in a trailer. Credit: PTB

Physics

Portable atomic clock scales new heights

High-precision timepiece takes stock of gravitational effects in a mountain tunnel.

For the first time, scientists have used an advanced timepiece called an optical clock to make measurements outside a laboratory setting.

General relativity predicts that gravity slows the passage of time. This means that time flows more languidly at Earth’s low points than on mountain peaks, because points closer to Earth’s core feel the planet’s gravitational tug more strongly. To measure this effect, Christian Lisdat at the German National Metrology Institute in Braunschweig and his colleagues designed an optical clock — an ultra-precise atomic clock — that can be mounted in a car trailer. Such devices typically require a highly stable laboratory environment.

After moving their invention to a tunnel in the French Alps, the researchers used the clock’s exceptionally precise timekeeping to calculate the gravitational effect on time at the clock’s new location. Comparisons with reference data from a lab at a lower altitude showed that the portable clock’s measurements were consistent with conventional surveying techniques, although less accurate.

With improvements, the clock could be used to measure land heights with an accuracy of 10 centimetres, making it useful in remote settings where conventional surveys are difficult, the authors say.

Comparison of Astyanax mexicanus surface fish and Pachón cavefish

Mexican cavefish (right) lack eyes and sleep little, whereas their relatives (left) that live on the surface have eyes and sleep a lot. Credit: J. B. Jaggard et al./eLife/CC BY 4.0

Animal behaviour

Fish forgo sleep thanks to a molecule in the brain

Chemical helps blind cavefish to survive on catnaps.

Even the most sleep-deprived human has nothing on a Mexican cavefish. These blind creatures have long been scientific curiosities because of their habit of sleeping just 1.5 hours a day on average — about four times less than related, sighted populations of the species (Astyanax mexicanus) that live at the surface.

A new investigation might have found an explanation for the unusual behaviour: the fish’s brain produces excessive amounts of a molecule called hypocretin/orexin (HCRT), which regulates wakefulness and appetite. Alex Keene at Florida Atlantic University in Jupiter and his colleagues discovered that the brain of the Mexican cavefish contains almost twice as many HCRT-packed neurons as that of the surface-dwelling variety.

When the team gave the fish drugs that reduced the effects of HCRT on the brain, the cavefish slept up to three times longer than untreated fish. The finding suggests that high levels of HCRT help to keep them awake.

Non-invasive activation of neurons in the reward center of the mouse brain

Brain cells (red dots) in mice can be activated by near-infrared light shone onto the animals’ heads. Credit: S. Chen et al./Science

Neuroscience

How to control neurons deep in the brain with light

Nanoparticles serve as a relay for optogenetic manipulation.

Nanoparticles could allow researchers to manipulate mouse neurons with light — without opening the skull.

Optogenetics uses light to activate proteins on the surfaces of neurons in the brain. The proteins then stimulate activity in the neurons. The most widely applied method requires probes to be implanted into the brain, prompting Shuo Chen of the RIKEN Brain Science Institute in Wakoshi, Japan, and his colleagues to seek a less-invasive technique.

Working in mice, the team injected light-responsive nanoparticles deep into a brain region involved in memory. The researchers then shone near-infrared light — which can pass through bone and tissue — onto the animals’ heads. The nanoparticles converted the beam into blue-green light, which in turn stimulated neurons that affect how mice respond to a perceived threat.

The technique will enable less-invasive optogenetic manipulation of deep brain regions compared to what was previously possible, the authors say.

Scanning electron micrograph of an ependymoma cell and a natural killer cell

A natural-killer cell (pink) sidles up to a tumour cell (yellow). Credit: Eye of Science/SPL

Cancer

Natural-killer cells sound the alarm against cancer

Immune cells help to marshal the body’s soldiers against tumours.

Immune cells called natural-killer cells play a key part in the body’s campaign against cancer, according to a study of mouse and human tumours.

Previous research has shown that the immune system relies on versatile troops called dendritic cells to recognize tumour cells and initiate rejection. But it has been unclear what makes these cells flock to cancerous tissues. Jan Böttcher and Caetano Reis e Sousa of the Francis Crick Institute in London and their colleagues found an answer: chemicals produced by natural-killer cells attract a class of dendritic cell to tumours in mice.

The researchers examined genes that tend to be active in natural-killer cells. Patients who had the highest levels of activity in those genes tended to live longer than patients showing lower gene activity. But the researchers also found that tumours can produce a compound called prostaglandin E2, which impairs the function of natural-killer cells and dendritic cells.

A toad contemplates a bombardier beetle, which could prove difficult to digest.

A toad regurgitates a bombardier beetle, which can spray the gullets and stomachs of its predators with scalding chemicals. Credit: S. Sugiura & T. Sato/Biol. Lett.

Animal behaviour

Bombardier beetle lives on by causing indigestion

Insect has a superheated surprise for anything that swallows it.

A species of bombardier beetle can survive being eaten by squirting a boiling-hot chemical over predators’ innards, causing them to vomit.

Some bombardier beetles are known to release chemicals heated to about 100 °C from their rear ends when attacked. But whether — or how — this strategy helps them to escape from predators has not been clear. Shinji Sugiura and Takuya Sato at Kobe University in Japan fed the bombardier beetle Pheropsophus jessoensis to two species of toad, Bufo japonicus and B. torrenticola.

Within two hours of the meal, nearly half the toads had regurgitated the insects, which were all alive and well. When toads were fed beetles treated to exhaust their reserves of scalding spray, only 5% of the amphibians spat out their meals, suggesting that the spray helps the beetle to escape from predators.

The Mojave rattlesnake’s venom can kill a human, but it preys mainly on rodents.

The Mojave rattlesnake’s venom can kill a human, but it preys mainly on rodents. Credit: Daniel Heuclin/NPL

Ecology

Rattlesnake gardeners sow plant diversity

Mouse eats seeds, snake eats mouse, snake spreads seeds.

Seeds consumed by a mouse can still sprout and grow — if the mouse is eaten by a rattlesnake.

Randall Reiserer at the University of California, Berkeley, and his colleagues examined 50 museum specimens of rattlesnake encompassing three species: sidewinder (Crotalus cerastes), Mojave rattlesnake (C. scutulatus) and Southwestern speckled rattlesnake (C. pyrrhus). In the snakes’ stomachs and intestines, the researchers discovered a total of 971 seeds that had been collected by rodents such as pocket mice (Chaetodipus) before snakes ate the rodents.

Seeds cannot germinate after passing through a rodent’s digestive system, but the team found germinated seeds inside some of the snakes’ guts. This suggests that the reptiles can inadvertently rescue seeds that rodents collect and store in their cheek pouches. Predators such as rattlesnakes could help to disperse viable seeds far from the parent plant, making them important for ecosystem dynamics, the authors say.

A woman in her pomelo plantation.

A Thai farmer checks her pummelos, an ancestor of many popular citrus fruits. Credit: UNDP/Thierry Falise/LightRocket/Getty

Plant sciences

The sweet and sour story of citrus

DNA reveals when life first gave us lemons.

From sweet oranges to sour lemons, all citrus fruit traces its roots to the southeast foothills of the Himalaya, says an international team of scientists.

Fruits of the genus Citrus are among the most commonly grown worldwide, yet the group’s origins have been elusive. To investigate, Manuel Talon at the Valencian Institute of Agricultural Research in Spain and his colleagues analysed the genomes of 58 wild and domesticated citrus plants. They found that citrus spread rapidly from its origins in southeast Asia nearly 8 million years ago as monsoon rains weakened and a drier climate prevailed.

The analysis showed that lemons, limes, oranges and grapefruits all trace some of their roots to three fundamental ancestors: citrons, mandarins and pummelos. Pummelo ancestry, for example, conferred larger size.

The findings also confirm some of the branches of the citrus family’s evolutionary tree. Kumquats and desert limes had previously been attributed to separate genera, but the authors squeeze them into Citrus.

Nuclear physics

Heaviest known element has electrons that break the mould

Oganesson nuclei are bathed in an electron haze.

Electrons generally orbit atomic nuclei in distinct shells, but calculations show that the outer electrons of oganesson, the heaviest element found so far, may instead orbit the nucleus as a gas.

Oganesson decays quickly, making it a challenge to probe experimentally. Instead, Peter Schwerdtfeger at Massey University Auckland in New Zealand and his colleagues calculated the energy levels of electrons around oganesson nuclei. For greater accuracy, the researchers took into account what are known as ‘relativistic effects’ — the influence of the element’s high nuclear charge, which is much greater than that of lighter elements.

The team found that in oganesson, the outermost electron orbits become indistinct, creating an outer layer that is almost an electron gas. Oganesson is classified as a noble gas, but the findings suggest that it may behave differently from other members of its group and may even be solid at room temperature.