A fluorescence image of a mouse tibia, after the minerals and lipids from the bone were removed.

A fluorescence image of a mouse tibia, after the minerals and lipids from the bone were removed. Credit: Greenbaum et al./Sci. Transl. Med


Cells spotted in see-through bone

A technique that makes bone transparent helps researchers capture images of key cells.

A technique that makes mouse bones transparent allows researchers to capture images of specific cells.

Studying bone structure often requires samples to be destroyed, and taking images of cells within opaque bone is difficult. By contrast, soft tissues such as the brain can be made transparent using various techniques. Viviana Gradinaru at the California Institute of Technology in Pasadena and her colleagues have developed a way of doing this for bone by removing minerals and lipids, allowing light to pass through while keeping the tissue intact. They used the method to visualize mouse leg bones. The team also built a microscope and software that automatically mapped and quantified bone cells that had been engineered to fluoresce. Cells were analysed up to a depth of 1.5 millimetres — more than twice the depth achieved by previous bone-imaging methods.

The technique could allow the outer layers of the brain to be studied without the skull having to be removed, the authors say.

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Highlights from recent research

Astronomy and astrophysics

Is it a planet or a star?

A celestial planet-like object and its dusty disk blur the line between planets and stars.

Planets, young stars, and failed stars known as brown dwarfs may have more in common than astronomers thought.

Amelia Bayo at the University of Valparaiso in Chile and her colleagues studied OTS44, a planet-like object thought to be 160 parsecs away that is about 12 times the mass of Jupiter and is surrounded by a disk of swirling dust. Using the high-resolution Atacama Large Millimeter/submillimeter Array in Chile, the authors calculated the mass of the disk.

The relative difference in mass between it and OTS44 is similar to mass differences measured for brown dwarfs and young stars and the dust clouds that surround them. This suggests that OTS44 formed in a similar way to these objects, from a collapsing cloud of debris — which is odd, because it was thought to be too small to have formed this way.

The inset image was projected onto a plate of pigment-producing Escherichia coli, causing the bacteria to make the image on the right.

The inset image was projected onto a plate of pigment-producing Escherichia coli, causing the bacteria to make the image on the right. Credit: J. Fernandez-Rodriguez et al./Nat. Chem. Biol.

Synthetic biology

Colour pictures made in bacterial film

Engineered E. coli produce red, green and blue pigments based on light exposure.

A genetic system that contains 18 genes and other elements has allowed Escherichia coli to make different pigments according to the colour of light — red, green or blue — the bacteria are exposed to.

Christopher Voigt and his colleagues at the Massachusetts Institute of Technology in Cambridge designed the system to include genes encoding proteins that are sensitive to different wavelengths of light. Bacteria with the system produce pigments that are the same colour as the light they are exposed to. The team grew E. coli on a plate while projecting a coloured image onto it. Less than 24 hours later, the pigments generated formed an image that was identical to the original.

Engineering bacteria to recognize a variety of colours could be useful in fine-tuning the control of microbes from afar in a variety of biomedical applications, the authors say.


A pro-cancer protein that’s anti-pain

An immune-suppressing molecule is linked to pain sensitivity in mice.

A molecule made by some cancers and targeted by certain immunotherapies also blocks pain in mice.

Ru-Rong Ji at Duke University Medical Center in Durham, North Carolina, Yu-Qiu Zhang at Fudan University in Shanghai, China, and their colleagues studied the effects of PD-L1. This protein is inhibited by certain cancer immunotherapies because it suppresses the immune response to  tumours. The researchers found that PD-L1 is also made by healthy tissues such as the skin and spinal cord.  Inhibiting PD-L1 or deleting its receptor made mice more sensitive to pain. Conversely, injecting PD-L1 into rodents temporarily increased pain thresholds near the injection site, and reduced chronic pain caused by nerve injury. The activity of PD-L1 and its receptor dampens electrical activity in spinal nerve cells that transmit pain signals.

The findings could lead to new analgesics, the authors suggest. They add that patients being treated with cancer immunotherapies that block PD-L1 might need to have their pain levels monitored.


New target for cancer immunotherapy

An antibody that inhibits regulatory immune cells boosts anti-cancer responses in mice.

Regulatory T cells help to modulate the immune system, and those that express a protein called LAP are particularly potent suppressors of immune responses to cancer. The cells have been linked to poor outcomes in people with the disease. Howard Weiner at Brigham and Women’s Hospital in Boston, Massachusetts, and his colleagues have found a way to target these cells with an antibody that lowers LAP levels.

Treatment with the antibody diminished tumour growth in mice, and improved the effectiveness of an anti-cancer vaccine. Four months after treatment, the antibody had increased the number of CD8+ T cells, which are involved in immune memory. This suggests that inhibiting LAP could enhance the immune system’s ability to quickly recognize and respond to cancer cells.


Natural mutations hamper gene drives

Efforts to spread new gene variants across insect populations face genetic hurdles.

Natural genetic variation is likely to stymie gene drives, which are designed to deploy specific heritable mutations across a population of organisms, such as disease-carrying insects. 

Researchers have recently developed gene drives based on the CRISPR–Cas9 gene-editing system for fruit flies and malaria-transmitting mosquitoes. A team led by Michael Wade at Indiana University in Bloomington modelled whether natural genetic variation in an agricultural pest called the red flour beetle (Tribolium castaneum) could prevent the spread of a CRISPR-based gene drive. The team found that many wild beetle populations harbour genetic variants that, even when rare, would make beetles immune to gene drives that target three different genes.

Inbreeding, which is common in some disease-carrying insects, increases the prevalence of mutations that can inactivate gene drives.

The damselfish Dascyllus marginatus swims above the coral Stylophora pistillata.

The damselfish Dascyllus marginatus swims above the coral Stylophora pistillata. Credit: Nur Garcia-Herrera


Fish boost coral photosynthesis

The flicking fins of damselfish may be the reason for enhanced coral growth.

Damselfish living in and around coral reefs could be boosting coral growth by increasing ventilation.

Coral reefs and damselfish species have a mutually beneficial relationship. The fish hide from predators among coral branches, and in turn, they clean coral surfaces and protect them from predators. Corals that host the fish are known to grow faster. To learn why, Nur Garcia-Herrera at the Leibniz Center for Tropical Marine Ecology in Bremen, Germany, and her colleagues captured Dascyllus marginatus damselfish and colonies of the branching coral Stylophora pistillata in the northern Red Sea, and studied them in the lab. 

They found that fish living between the coral branches increased coral photosynthesis, probably because the fishes’ fin movements improved ventilation. Video cameras placed near coral reefs in the wild revealed that the fish spend up to 34% of daylight hours within the coral. The researchers estimate that the fish boost coral photosynthesis by 3–6%.

Tasmanian devils (Sarcophilus harrisii) transmit cancer to each other through biting.

Tasmanian devils (Sarcophilus harrisii) transmit cancer to each other through biting. Credit: D. Parer & E. Parer-Cook/Minden Pictures/FLPA


Transmissible tumours target the fittest devils

Social success may boost risk of Tasmanian devil facial tumour disease.

Many diseases tend to target the weakest animals in a population, but in Tasmanian devils, an aggressive transmissible cancer that causes devil facial tumour disease seems to infect the fittest. Animals that eventually become infected survive at a higher rate and reproduce more before dying of the disease than devils that don’t get the cancer.

Konstans Wells of Griffith University in Brisbane, Australia, and his colleagues used 10 years of data on 518 Tasmanian devils (Sarcophilus harrisii) in western Tasmania to build a model of survival, reproduction and cancer in the animals. They found that devils with cancer were fitter than those without tumours, and that animals with small tumours had higher average survival rates than those that were never infected. Female cancer hosts reproduced 1.3 times on average before dying, compared to 0.7 times for uninfected females, and had more offspring per litter.

The disease is spread through biting during mating and other interactions, and so the fittest animals could be becoming infected more often because they tend to be more socially dominant. The team’s data also suggest a decline in the rate of infection and transmission since 2012, which may be due to increasing disease resistance.

Moss samples collected from Ardley Island and other sites on the Antarctic Peninsula showed increasing moss growth due to rising temperatures.

Moss samples collected from Ardley Island and other sites on the Antarctic Peninsula showed increasing moss growth due to rising temperatures. Credit: Dan Charman

Climate change

Antarctica is going green

Global warming has increased moss growth at sites across the Antarctic Peninsula over the past half-century.

Much of Antarctica is covered in ice, but parts of its peninsula are instead blanketed in moss. Each year, more moss grows over the top of the previous season’s growth, providing a record of moss health over thousands of years. 

Matthew Amesbury at the University of Exeter, UK, and his colleagues isolated moss-bank cores dating back 150 years from three sites across the peninsula. They found that since 1950 moss growth and accumulation have increased markedly at all sites. This shift is probably due to the increasing global temperatures associated with climate change. 

Continued warming will probably trigger large-scale changes to Antarctic terrestrial ecosystems, the authors suggest.

Nanoscience and technology

Nanoprobe detects the force of swimming bacteria

The optical fibre is several times more sensitive than other techniques.

A thin optical fibre can detect the minuscule forces generated by swimming bacteria with a sensitivity at least 10 times greater than that achieved by atomic force microscopes. 

Probes used in atomic force microscopy are often bulky, and some other force detectors have low resolution. Donald Sirbuly and his colleagues at the University of California, San Diego, made a compact device from a tin dioxide fibre 200-400 nanometres in diameter, which they covered in a polymer and dotted with gold nanoparticles. The particles interact with light passing down the fibre. When forces — such as those generated by nearby swimming bacteria or beating heart cells — push the gold particles into the polymer, the interaction increases. This boosts the intensity of the light scattered by the nanoparticles. 

Using a microscope to pick up these changes, the authors detected forces as small as 160 femtonewtons (1 femtonewton is 10−15 newtons). The team plans to use the device to measure the behaviour of single cells.

A device with sticky gripper can lift a variety of irregularly shaped objects.

A device with sticky gripper can lift a variety of irregularly shaped objects. Credit: Sukho Song


Sticky gripper can lift flasks and tomatoes

A gecko-inspired adhesive could help robots to climb bumpy walls and grasp fragile objects.

The hairs that make geckos’ feet sticky have inspired the invention of adhesives for flat surfaces, but creating strong adhesives that can grab complex, 3D objects has proved a challenge. 

Metin Sitti at the Max Planck Institute for Intelligent Systems in Stuttgart, Germany, and his colleagues spread elastic microfibres, or ‘hairs’, across a soft, stretchy membrane, allowing it to mould and stick to a surface. The team attached this to a ‘gripper’ layer. Reducing the pressure inside the gripper spreads the load evenly across the sticky membrane, strengthening the bond between it and the target object. Changing the pressure in the system increased the membrane’s ‘stickiness’ 14-fold, allowing the device to suspend a variety of hard and soft objects, from fluid-filled flasks to tomatoes.

Materials science

3D-printed device makes clean steam

The evaporator uses solar energy to efficiently purify water.

Most evaporators that use solar heating rely on lenses or mirrors to concentrate sunlight, which makes it difficult to stop heat being lost to the environment and reduces efficiency. Liangbing Hu and his colleagues at the University of Maryland in College Park built a device using a 3D-printed material made of carbon nanotubes and graphene oxide, which absorbs 97% of incoming sunlight and rapidly warms up. This layer sits on a box with no bottom, which was 3D-printed using porous graphene oxide and nanostructured cellulose. When placed in shallow water, the walls of the box wick water to the top layer, where it is heated and escapes as steam.

The device used 85.6% of the absorbed energy to generate steam, which is one of the highest efficiencies achieved by evaporators. The approach could help to ease shortages in areas where water has to be sterilized or desalinated, the authors say.

The varroa mite (shown sitting on honeybee hairs in this scanning electron microscope image) is honeybee parasite that can spread viruses.

The varroa mite (shown sitting on honeybee hairs in this scanning electron microscope image) is honeybee parasite that can spread viruses. Credit: Erbe & Pooley/USDA/ARS/EMU


Beekeeping practices boost parasite risk

Suppressing natural honeybee behaviours in crowded apiaries could enhance the spread of mites.

Varroa mites (Varroa destructor) spread viruses, feed on honeybee larvae and could be contributing to widespread losses of bee colonies. Beekeepers try to control the pests using chemicals; but in an 11-month study of 120 commercial colonies, Gloria DeGrandi-Hoffman at the US Department of Agriculture in Tucson, Arizona, and her colleagues revealed that 55% of treated hives were still lost. 

A model that simulated varroa populations and bee interactions showed that natural swarming, which is suppressed in domesticated bees, keeps varroa populations down. That’s because swarming carries mites away from hives and reduces the number of bee larvae produced, shrinking the mites’ food supply. Furthermore, infected forager bees that raid other hives can quickly spread the mites when hives are close together. 

The authors think varroa might be impossible to control unless changes are made to the way bees are kept.

This planet-like object (artist's representation), called SIMP0136, was thought to be a brown dwarf.

This planet-like object (artist's representation), called SIMP0136, was thought to be a brown dwarf. Credit: NASA/JPL, slightly modified by Jonathan Gagné

Astronomy and astrophysics

A celestial case of mistaken identity

From failed star to lonely planet, an interstellar oddity gets a second look.

A nearby celestial object that astronomers thought was a failed star turns out to be a planet-like object that does not orbit a star.

The object, dubbed SIMP0136, is slightly more than 6 parsecs from Earth, in the constellation Carina. It was previously pegged as one of the closest known brown dwarfs, which are bigger than planets but too small to burn hydrogen in their cores as stars do.

But SIMP0136’s mass is only about 13 times that of Jupiter — putting it on the boundary between planets and brown dwarfs, according to Jonathan Gagné at the Carnegie Institution of Washington in Washington, DC and his colleagues, who observed the object using the Keck II telescope in Hawaii. 

Only a few free-floating planets have ever been found, so SIMP0136 offers astronomers a rare opportunity to explore an exoplanet atmosphere without interference from the light of a nearby star.

Enterococcus faecalis survives well in hospitals and can easily fend off antibiotics.

Enterococcus faecalis survives well in hospitals and can easily fend off antibiotics. Credit: Eye of Science/Science Photo Library


Why some drug-resistant bacteria thrive in hospitals

Adaptations to terrestrial life could be the key to their success. 

Two members of a group of gut microbes have evolved multi-drug resistance to become leading hospital-adapted pathogens. The bacteria, called enterococci, are thought to have diverged from an aquatic ancestor around 425 million years ago, when the first animals moved onto land. 

To find out why some enterococci have adapted so well to hospital life, Michael Gilmore at the Massachusetts Eye and Ear Infirmary in Boston, Ashlee Earl at the Broad Institute in Cambridge, Massachusetts, and their colleagues sequenced the genomes and studied the characteristics of 24 species of Enterococcus and 5 species from closely related genera. 

The team found that the enterococci share a core set of 1,037 genes. These encode enzymes that, among other things, produce a hardened cell wall that protects the bacteria from drying and from other harsh conditions on land. The adaptations could have enabled the microbes to flourish in hospitals and develop drug resistance, the authors suggest. 

Chemical biology

Small molecule shuttles iron into cells

A natural compound boosts absorption of the nutrient in animals with iron-transport deficiencies.

A small molecule can function like a protein transporter by moving iron into cells. This suggests a possible way of treating diseases such as anaemia that are caused by dysfunctional or missing iron-transport proteins.

Martin Burke at the University of Illinois at Urbana–Champaign and his colleagues tested the ability of iron-binding small molecules to move the metal into yeast cells that are missing an iron-transporting complex. They homed in on hinokitiol, a compound made by the Taiwan hinoki tree (Chamaecyparis taiwanensis). The molecule restored iron transport in human and mouse cells deficient in any one of three different transporter proteins. In rodents with these deficiencies, hinokitiol increased the absorption of iron into the gut roughly fourfold, and in one animal model returned it to normal levels.

The small molecule seems to collaborate with proteins in the cell to usher in iron after levels have built up outside the cell.


A filter-free way to purify water

Bubbling carbon dioxide in water can remove suspended particles.

Harnessing carbon dioxide to purify water uses less energy than typical filtration methods. 

Water is generally purified by being pumped across expensive membranes, which uses a lot of energy. Howard Stone at Princeton University in New Jersey and his colleagues have devised a way to eliminate the need for filters. They suspended 500-nanometre-wide polystyrene particles in water and exposed one side of the mixture to CO2. The gas dissolved in the water, generating an ion gradient that drove negatively charged polystyrene particles to one side and positively charged ones to the other so that they could be removed from the water.

Many microbes are charged, so this method could be used to remove bacteria and viruses without chlorination or ultraviolet treatment, the authors say.


Ancient protein resurrected in bacteria

Engineering an ancestral protein into E. coli makes it virus-resistant.

Viruses often commandeer their hosts’ proteins to turn infected cells into virus factories. Researchers have tried inactivating these proteins to boost virus resistance in plants, but this can harm the hosts. Jose Sanchez-Ruiz and his colleagues at the University of Granada in Spain have developed another way of doing this, using Escherichia coli, which can be infected by a bacteriophage — a bacterial virus — called T7. 

The authors focused on one of the bacterium’s thioredoxin genes, which T7 hijacks and uses to replicate during infection. They replaced this gene with one of several ancestral versions that encode forms of the protein that T7 has not encountered before. The team found that a bacterial thioredoxin from about 2.5 billion years ago conferred T7 resistance with minimal effect on the bacterium’s growth. 

This method could be used to make crops resistant to viruses, the authors say.  


Male hormones curb allergies in mice

The finding could explain why asthma affects more women than men.

Male sex hormones inhibit the development of key immune cells involved in asthma and other allergic responses.

Jean‑Charles Guéry at the French National Institute of Health and Medical Research in Toulouse, Cyril Seillet at the Walter and Elisa Hall Institute of Medical Research in Parkville, Australia, and their colleagues found that male mice have fewer of the cells – called group 2 innate lymphoid cells – and are less likely than females to develop airway inflammation when exposed to an environmental allergen. Castrating the males eliminated these differences. 

The progenitors of these immune cells have receptors that bind male sex hormones. Biochemical signalling through the receptor inhibited the cells’ development.

Hot springs formed these rock deposits, called geyserite, 3.5 billion years ago.

Hot springs formed these rock deposits, called geyserite, 3.5 billion years ago. Credit: T. Djokic et al./Nat. Commun. (CC BY 4.0)


Microbes liked it hot 3.5 billion years ago

Ancient rocks suggest that some of Earth’s earliest life may have emerged near hot springs.

The 3.48-billion-year-old Dresser Formation contains ancient evidence for life on the planet. A team led by Tara Djokic at the University of New South Wales in Kensington, Australia, analysed deposits from the formation and identified a type of rock called geyserite that is produced by terrestrial hot springs. The researchers also found signatures of microbial life, including layered rock structures called stromatolites, near the geyserite deposits. The study extends the geological record of life on land by nearly 600 million years.

The search for ancient life on Mars should focus on such environments, the authors suggest.


Marijuana improves memory in old mice

Low doses of marijuana’s active ingredient reverse the age-related decline of learning and memory skills.

Andreas Zimmer at the University of Bonn, Germany, and his colleagues studied mice aged 2 months (young), 12 months (mature) and 18 months (old). They implanted mini-pumps under the mice’s skin, and for 28 days these released either low doses of marijuana’s main active compound, delta-9 tetrahydrocannabinol (THC), or a solution without the drug. After this period, the THC-treated mature and old mice performed as well as untreated young animals in memory and learning tests, whereas THC-treated young mice performed considerably worse. 

In the brains of the treated mature and old mice, the structures of neuronal connections, or synapses, also reverted to those seen in untreated young animals, as did patterns of gene expression. All of these changes depended on the function of a brain receptor that binds certain neurotransmitters as well as THC.