Research Highlights

Our pick of the latest scientific literature

  • Volume 550
  • Issue 7675

Immunology

Immune cells go home to die

Neutrophil white blood cells can end up back in the bone marrow once their job is done.

Neutrophils are white blood cells produced in the bone marrow that can fight infection and inflammation by ingesting harmful microorganisms. But some evidence has suggested that if neutrophils do not die in a wound, they might leave and cause inflammation elsewhere in the body. 

Now researchers have found that the cells sometimes return to the bone marrow and self-destruct.

Paul Kubes at the University of Calgary in Canada and his colleagues used fluorescence imaging to track the activity of these cells in mice with damage to the liver. They watched as neutrophils infiltrated wounds and cleaned up DNA fragments, as expected. But 24 hours later, many of the cells had returned to the bone marrow and initiated their own deaths. This round trip could be essential for the resolution of inflammation, the authors say.

How the Sun’s corona can be millions of degrees hotter than its surface has been a mystery.

How the Sun’s corona can be millions of degrees hotter than its surface has been a mystery. NASA/SDO

Astronomy and astrophysics

Tiny, fleeting flares might heat Sun’s corona

Short-lived ‘nanoflares’ could explain why the Sun’s outer atmosphere can be several million degrees hotter than its surface.

Fleeting ‘nanoflares’ that are too small to see directly could explain why the Sun’s outer atmosphere, or corona, can be millions of degrees hotter than its surface. 

Giant eruptions of ionized gas occasionally release energy into the Sun’s outer layers, but this happens too rarely to explain the zone’s usual temperature of 1 million to 3 million kelvin.

Shin-nosuke Ishikawa at the Japan Aerospace Exploration Agency in Kanagawa and his colleagues looked for another potential source of heat: a plethora of small, short-lived explosions. The team compared X-ray observations of a region of the Sun made using a research rocket with data on the same area collected by the US Geostationary Operational Environmental Satellite. Although no distinct flares were indicated by the satellite data, the X-ray maps showed a faint emission, suggestive of a small amount of plasma at an extraordinary 10 million kelvin. The presence of nanoflares could explain this finding, say the authors. They add that the results will constrain models of how these flares could be distributed.

Ice formed six-leaved-clover patterns on hydrophobic surfaces, and sunflower-like arrangements on hydrophilic ones.

Ice formed six-leaved-clover patterns on hydrophobic surfaces, and sunflower-like arrangements on hydrophilic ones. J. Liu et al./PNAS

Physics

Watching how surface properties affect ice growth

Water-repellent surfaces trigger formation of crystals shaped like six-leaved-clover.

Ice crystals grow on solid surfaces in two distinctly different ways, depending on the degree to which the surface attracts or repels water. Jianjun Wang at the Chinese Academy of Sciences in Beijing and his colleagues triggered ice formation using silver iodide nanoparticles, and watched as crystals formed on hydrophilic and hydrophobic surfaces.

When ice formed on the former, it grew along the surface, producing sunflower-like patterns (bottom). On the latter, it minimized its contact with the substrate by growing away from the surface at an angle, and forming six-leaved-clover shapes (top). 

Although the influence of factors such as temperature and humidity on ice formation has been well studied, the influence of surface properties is less well understood. The new findings could inform the design of surfaces that need to repel ice, such as windscreens.

Climate sciences

Dry summers ahead for US–Mexico border region

Higher abundance of carbon dioxide in the atmosphere means less rainfall for northwest Mexico.

Summer in northwestern Mexico and the southwestern United States is expected to become palpably drier as a result of rising atmospheric carbon dioxide levels.

Abundant summer rain over parts of this region is crucial for replenishing the limited local water supply. But scientists have been uncertain how climate change might affect the seasonal monsoon rainfall, owing to the coarse resolution and inconsistency of models of atmospheric circulation. 

Using an improved climate model that accounts for small-scale atmospheric processes such as convection, Salvatore Pascale of Princeton University in New Jersey and his colleagues found that summer rainfall in the region would drop by up to 40% in response to doubling CO2 levels. The projected weakening of the North American monsoon, the authors suggest, is driven mainly by rising global sea surface temperatures, which tend to suppress rain-generating atmospheric convection. More climate-adaptation measures and better freshwater management will be needed across the region, the researchers say.

When the signals from blood vessels are dimmed, lymph vessels can be seen in primate brains on magnetic resonance imaging scans.

When the signals from blood vessels are dimmed, lymph vessels can be seen in primate brains on magnetic resonance imaging scans. M. Absinta et al./eLife (CC0 1.0)

Neuroscience

Scans light up the ‘drain pipes’ in human and monkey brains

Discovery follows previous finding of lymphatic systems in rodents.

Waste-removal ‘drain pipes’ have been observed in the brains of humans and non-human primates for the first time.

Lymphatic vessels in the brain were first hypothesized in 1816, but they were not seen until 2015, when researchers working in mice found them in the meninges — membranes that protect the brain.

Lymphatic vessels are hard to spot because they closely resemble blood vessels. Using a magnetic dye in combination with high-resolution magnetic resonance imaging (MRI), Daniel Reich of the US National Institutes of Health in Bethesda, Maryland, and his team were able to dim the signal from blood vessels while scanning the brain, thus revealing a network of lymph vessels in humans and marmoset monkeys.

Because it used MRI, the technique has immediate application for studying how these drainage vessels affect a variety of neurological disorders, the researchers say.

Genomics

Ancient encounters of the Neanderthal kind

New genomes from ancient hominids further entangle their respective family trees.

All humans whose ancestors lived outside Africa carry pieces of Neanderthal DNA. Two ancient-genome studies now suggest that human and Neanderthal populations may have mated more often than was previously thought.

A team led by Kay Prüfer and Svante Pääbo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, generated a high-quality genome sequence from 50,000-year-old remains of a Neanderthal female found in Vindija Cave in Croatia. Her genome, like one previously sequenced from Neanderthal remains found in a Siberian cave, contain traces of gene flow from Homo sapiens. But the Neanderthals who left their mark on modern humans were more closely related to the Croatian individual than to her Siberian relative. 

Another team, led by Eske Willerslev at the Natural History Museum of Denmark in Copenhagen, sequenced 5 genomes from a 34,000-year-old Homo sapiens burial site in Russia. One individual carried more Neanderthal ancestry than do non-Africans today, possibly also reflecting additional mating episodes between humans and Neanderthals.

Despite claims of recent sightings in Tasmania, most researchers think the thylacine died out decades ago.

Despite claims of recent sightings in Tasmania, most researchers think the thylacine (Thylacinus cynocephalus) died out decades ago. Popperfoto/Getty

Zoology

Drought drove Tasmanian tiger from Australian mainland

Genomes of extinct marsupial predator reveal ancient family history.

The last known Tasmanian tiger, or thylacine, died in 1936 on the island for which it was named. But, by then, the animal had been extinct on the Australian mainland for more than 3,000 years.

Jeremy Austin and his colleagues at the University of Adelaide in Australia collected samples from thylacine (Thylacinus cynocephalus) museum specimens. They sequenced DNA contained in cell structures called mitochondria for 51 animals, including 15 from mainland Australia. Mapping of the relationships between animals suggests that there were two separate mainland populations — a larger, more genetically diverse population in the west and a smaller, less-diverse population in the east and Tasmania — that diverged about 30,000 years ago.

When Europeans settled on Tasmania in the 1800s, the thylacine population seems to have been expanding after long being kept small and genetically similar by centuries-long drought. This severe dry spell could have contributed to the species’ extinction on the mainland, where it was more severe.

New Content Item

Budgies come in two distinct colour combinations; now researchers think they have worked out why. Getty

Genetics

Pinpointing pigment genes for parrot pets

Enzyme identified that makes budgies yellow and green or blue and white.

Researchers have identified the genetic trait that controls whether the parrots widely known as budgerigars (Melopsittacus undulatus), or budgies, will be yellow and green or blue and white.

By sequencing DNA from 234 budgies, Carlos Bustamante at Stanford University in California and his colleagues determined that a pigment that gives yellow feathers their colour is linked to an enzyme called MuPKS. Yeast expressing the enzyme turned the same bright yellow as the parrot feathers. The researchers found that a single amino-acid substitution in MuPKS halted its activity, making feathers blue and white in some birds.

MuPKS does exist in the genomes of other bird species, but it is expressed at a rate hundreds to thousands of times higher in parrots. And that’s why, for example, we don’t see any crows or chickens in vibrant blues or yellows, the authors say.

CRISPR systems are used by microbes to fight off attacks, such as from the Pseudomonas aeruginosa bound to an invading phage DNA

CRISPR systems are used by microbes to fight off attacks, such as from the Pseudomonas aeruginosa bound to an invading phage DNA (shown in orange here). V. Falconieri/Subramaniam lab/NCI/NIH

Molecular biology

CRISPR seen in action

Cryo-electron microscopy paints a picture of how the system binds to DNA.

Electron-microscope images reveal how a CRISPR system marks specific DNA sequences for destruction.

Microbes use CRISPR as a defence system to fend off viruses and other invaders, and geneticists have harnessed it to alter DNA sequences in a process called gene editing. 

Sriram Subramaniam at the National Cancer Institute in Bethesda, Maryland, and his colleagues used cryo-electron microscopy to watch a CRISPR system from the bacterium Pseudomonas aeruginosa as it bound to DNA. The team found that this process causes large structural changes in an enzyme complex called Csy — which recognizes the target DNA — and the fragment of ‘guide’ RNA that steers Csy to its target. These changes could be important for allowing other enzymes to cut the targeted DNA. The team also showed that three viral inhibitors of CRISPR work by preventing the binding of Cys to its target.

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