Fluvial mapping of Mars

 It took fifteen years of imaging and nearly three years of stitching the pieces together to create the largest image ever made, the 8-trillion-pixel mosaic of Mars' surface. Now, the first study to utilize the image in its entirety provides unprecedented insight into the ancient river systems that once covered the expansive plains in the planet's southern hemisphere. These three billion-year-old sedimentary rocks, like those in Earth's geologic record, could prove valuable targets for future exploration of past climates and tectonics on Mars.

The work, published this month in Geology, complements existing research into Mars' hydrologic history by mapping ancient fluvial (river) ridges, which are essentially the inverse of a riverbed. "If you have a river channel, that's the erosion part of a river. So, by definition, there aren't any deposits there for you to study," Jay Dickson, lead author on the paper, explains. "You have rivers eroding rocks, so where did those rocks go? These ridges are the other half of the puzzle." Using the mosaic, as opposed to more localized imagery, let the researchers solve that puzzle on a global scale.

Mars used to be a wet world, as evidenced by rock records of lakes, rivers, and glaciers. The river ridges were formed between 4 and 3 billion years ago, when large, flat-lying rivers deposited sediments in their channels (rather than only having the water cut away at the surface). Similar systems today can be found in places like southern Utah and Death Valley in the U.S., and the Atacama Desert in Chile. Over time, sediment built up in the channels; once the water dried up, those ridges were all that was left of some rivers.

The ridges are present only in the southern hemisphere, where some of Mars' oldest and most rugged terrain is, but this pattern is likely a preservation artifact. "These ridges probably used to be all over the entire planet, but subsequent processes have buried them or eroded them away," Dickson says. "The northern hemisphere is very smooth because it's been resurfaced, primarily by lava flows." Additionally, the southern highlands are "some of the flattest surfaces in the solar system," says Woodward Fischer, who was involved in this work. That exceptional flatness made for good sedimentary deposition, allowing the creation of the records being studied today.

Whether or not a region has fluvial ridges is a basic observation that wasn't possible until this high-resolution image of the planet's surface was assembled. Each of the 8 trillion pixels represents 5 to 6 square meters, and coverage is nearly 100 percent, thanks to the "spectacular engineering" of NASA's context camera that has allowed it to operate continuously for well over a decade. An earlier attempt to map these ridges was published in 2007 by Rebecca Williams, a co-author on the new study, but that work was limited by imagery coverage and quality.

"The first inventory of fluvial ridges using meter-scale images was conducted on data acquired between 1997 and 2006," Williams says. "These image strips sampled the planet and provided tantalizing snapshots of the surface, but there was lingering uncertainty about missing fluvial ridges in the data gaps."

The resolution and coverage of Mars' surface in the mosaic has eliminated much of the team's uncertainty, filling in gaps and providing context for the features. The mosaic allows researchers to explore questions at global scales, rather than being limited to patchier, localized studies and extrapolating results to the whole hemisphere. Much previous research on Mars hydrology has been limited to craters or single systems, where both the sediment source and destination are known. That's useful, but more context is better in order to really understand a planet's environmental history and to be more certain in how an individual feature formed.

In addition to identifying 18 new fluvial ridges, using the mosaic image allowed the team to re-examine features that had previously been identified as fluvial ridges. Upon closer inspection, some weren't formed by rivers after all, but rather lava flows or glaciers. "If you only see a small part of [a ridge], you might have an idea of how it formed," Dickson says. "But then you see it in a larger context -- like, oh, it's the flank of a volcano, it's a lava flow. So now we can more confidently determine which are fluvial ridges, versus ridges formed by other processes."

Now that we have a global understanding of the distribution of ancient rivers on Mars, future explorations -- whether by rover or by astronauts -- could use these rock records to investigate what past climates and tectonics were like. "One of the biggest breakthroughs in the last twenty years is the recognition that Mars has a sedimentary record, which means we're not limited to studying the planet today," Fischer says. "We can ask questions about its history." And in doing so, he says, we learn not only about a single planet's past, but also find "truths about how planets evolved... and why the Earth is habitable."

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Brain imaging predicts PTSD after brain injury

 Posttraumatic stress disorder (PTSD) is a complex psychiatric disorder brought on by physical and/or psychological trauma. How its symptoms, including anxiety, depression and cognitive disturbances arise remains incompletely understood and unpredictable. Treatments and outcomes could potentially be improved if doctors could better predict who would develop PTSD. Now, researchers using magnetic resonance imaging (MRI) have found potential brain biomarkers of PTSD in people with traumatic brain injury (TBI).

The study appears in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, published by Elsevier.

"The relationship between TBI and PTSD has garnered increased attention in recent years as studies have shown considerable overlap in risk factors and symptoms," said lead author Murray Stein, MD, MPH, FRCPC, a Distinguished Professor of Psychiatry and Family Medicine & Public Health at the University of California San Diego, San Diego, La Jolla, CA, USA. "In this study, we were able to use data from TRACK-TBI, a large longitudinal study of patients who present in the Emergency Department with TBIs serious enough to warrant CT (computed tomography) scans."

The researchers followed over 400 such TBI patients, assessing them for PTSD at 3 and 6 months after their brain injury. At 3 months, 77 participants, or 18 percent, had likely PTSD; at 6 months, 70 participants or 16 percent did. All subjects underwent brain imaging after injury.

"MRI studies conducted within two weeks of injury were used to measure volumes of key structures in the brain thought to be involved in PTSD," said Dr. Stein. "We found that the volume of several of these structures were predictive of PTSD 3-months post-injury."

Specifically, smaller volume in brain regions called the cingulate cortex, the superior frontal cortex, and the insula predicted PTSD at 3 months. The regions are associated with arousal, attention and emotional regulation. The structural imaging did not predict PTSD at 6 months.

The findings are in line with previous studies showing smaller volume in several of these brain regions in people with PTSD and studies suggesting that the reduced cortical volume may be a risk factor for developing PTSD. Together, the findings suggest that a "brain reserve," or higher cortical volumes, may provide some resilience against PTSD.

Although the biomarker of brain volume differences is not yet robust enough to provide clinical guidance, Dr. Stein said, "it does pave the way for future studies to look even more closely at how these brain regions may contribute to (or protect against) mental health problems such as PTSD."

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Flag leaves could help top off photosynthetic performance in rice

 The flag leaf is the last to emerge, indicating the transition from crop growth to grain production. Photosynthesis in this leaf provides the majority of the carbohydrates needed for grain filling -- so it is the most important leaf for yield potential. A team from the University of Illinois and the International Rice Research Institute (IRRI) found that some flag leaves of different varieties of rice transform light and carbon dioxide into carbohydrates better than others. This finding could potentially open new opportunities for breeding higher yielding rice varieties.

Published in the Journal of Experimental Botany, this study explores flag leaf induction -- which is the process that the leaf goes through to "start up" photosynthesis again after a transition from low to high light. This is important because the wind, clouds, and movement of the sun across the sky cause frequent fluctuations in light levels. How quickly photosynthesis adjusts to these changes has a major influence on productivity.

For the first time, these researchers revealed considerable differences between rice varieties in the ability of flag leaves to adjust to fluctuating light. They also showed that the ability to adjust differs between the flag leaf and leaves formed before flowering. Six rice varieties chosen to represent the breadth of genetic variation across a diverse collection of more than 3000 were analyzed as a first step in establishing if there was variation in ability to cope with fluctuations in light.

In this study, they discovered the flag leaf of one rice variety that began photosynthesizing nearly twice (185%) as fast as the slowest. Another top-performing flag leaf fixed 152% more sugar. They also found large differences (77%) in how much water the plant's flag leaves exchanged for the carbon dioxide that fuels photosynthesis. Additionally, they found that water-use efficiency in flag leaves correlated with water-use efficiency earlier in development of these rice varieties, suggesting that water-use efficiency in dynamic conditions could be screened for at younger stages of rice development.

"What's more, we found no correlation between the flag leaf and other leaves on the plant, aside from water-use efficiency, which indicates that both kinds of leaves may need to be optimized for induction," said Stephen Long, Illinois' Ikenberry Endowed University Chair of Crop Sciences and Plant Biology. "While this means more work for plant scientists and breeders, it also means more opportunities to improve the plant's photosynthetic efficiency and water use. Improving water use is of increasing importance, as agriculture already accounts for over 70% of human water use, and rice is perhaps the largest single part of this."

Confirming their previous study in New Phytologist, they found no correlation between data collected in fluctuating and steady-state conditions, where the rice plants were exposed to constant high light levels. This finding adds to a growing consensus that researchers should move away from research dependent on steady-state measurements.

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Big bumblebees learn locations of best flowers

 Big bumblebees take time to learn the locations of the best flowers, new research shows.

Meanwhile smaller bumblebees -- which have a shorter flight range and less carrying capacity -- don't pay special attention to flowers with the richest nectar.

University of Exeter scientists examined the "learning flights" which most bees perform after leaving flowers.

Honeybees are known to perform such flights -- and the study shows bumblebees do the same, repeatedly looking back to memorise a flower's location.

"It might not be widely known that pollinating insects learn and develop individual flower preferences, but in fact bumblebees are selective," said Natalie Hempel de Ibarra, Associate Professor at Exeter's Centre for Research in Animal Behaviour.

"On leaving a flower, they can actively decide how much effort to put into remembering its location.

"The surprising finding of our study is that a bee's size determines this decision making and the learning behaviour."

In the study, captive bees visited artificial flowers containing sucrose (sugar) solution of varying concentrations.

The larger the bee, the more its learning behaviour varied depending on the richness of the sucrose solution.

Smaller bees invested the same amount of effort in learning the locations of the artificial flowers, regardless of whether sucrose concentration was high or low.

"The differences we found reflect the different roles of bees in their colonies," said Professor Hempel de Ibarra.

"Large bumblebees can carry larger loads and explore further from the nest than smaller ones.

"Small ones with a smaller flight range and carrying capacity cannot afford to be as selective, so they accept a wider range of flowers.

"These small bees tend to be involved more with tasks inside the nest -- only going out to forage if food supplies in the colony are running low."

The study was conducted in collaboration with scientists from the University of Sussex.

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Discovery boosts theory that life on Earth arose from RNA-DNA mix

 Chemists at Scripps Research have made a discovery that supports a surprising new view of how life originated on our planet.

In a study published in the chemistry journal Angewandte Chemie, they demonstrated that a simple compound called diamidophosphate (DAP), which was plausibly present on Earth before life arose, could have chemically knitted together tiny DNA building blocks called deoxynucleosides into strands of primordial DNA.

The finding is the latest in a series of discoveries, over the past several years, pointing to the possibility that DNA and its close chemical cousin RNA arose together as products of similar chemical reactions, and that the first self-replicating molecules -- the first life forms on Earth -- were mixes of the two.

The discovery may also lead to new practical applications in chemistry and biology, but its main significance is that it addresses the age-old question of how life on Earth first arose. In particular, it paves the way for more extensive studies of how self-replicating DNA-RNA mixes could have evolved and spread on the primordial Earth and ultimately seeded the more mature biology of modern organisms.

"This finding is an important step toward the development of a detailed chemical model of how the first life forms originated on Earth," says study senior author Ramanarayanan Krishnamurthy, PhD, associate professor of chemistry at Scripps Research.

The finding also nudges the field of origin-of-life chemistry away from the hypothesis that has dominated it in recent decades: The "RNA World" hypothesis posits that the first replicators were RNA-based, and that DNA arose only later as a product of RNA life forms.

Is RNA too sticky?

Krishnamurthy and others have doubted the RNA World hypothesis in part because RNA molecules may simply have been too "sticky" to serve as the first self-replicators.

A strand of RNA can attract other individual RNA building blocks, which stick to it to form a sort of mirror-image strand -- each building block in the new strand binding to its complementary building block on the original, "template" strand. If the new strand can detach from the template strand, and, by the same process, start templating other new strands, then it has achieved the feat of self-replication that underlies life.

But while RNA strands may be good at templating complementary strands, they are not so good at separating from these strands. Modern organisms make enzymes that can force twinned strands of RNA -- or DNA -- to go their separate ways, thus enabling replication, but it is unclear how this could have been done in a world where enzymes didn't yet exist.

A chimeric workaround

Krishnamurthy and colleagues have shown in recent studies that "chimeric" molecular strands that are part DNA and part RNA may have been able to get around this problem, because they can template complementary strands in a less-sticky way that permits them to separate relatively easily.

The chemists also have shown in widely cited papers in the past few years that the simple ribonucleoside and deoxynucleoside building blocks, of RNA and DNA respectively, could have arisen under very similar chemical conditions on the early Earth.

Moreover, in 2017 they reported that the organic compound DAP could have played the crucial role of modifying ribonucleosides and stringing them together into the first RNA strands. The new study shows that DAP under similar conditions could have done the same for DNA.

"We found, to our surprise, that using DAP to react with deoxynucleosides works better when the deoxynucleosides are not all the same but are instead mixes of different DNA 'letters' such as A and T, or G and C, like real DNA," says first author Eddy Jiménez, PhD, a postdoctoral research associate in the Krishnamurthy lab.

"Now that we understand better how a primordial chemistry could have made the first RNAs and DNAs, we can start using it on mixes of ribonucleoside and deoxynucleoside building blocks to see what chimeric molecules are formed -- and whether they can self-replicate and evolve," Krishnamurthy says.

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Carbon capture: Faster, greener way of producing carbon spheres

 A fast, green and one-step method for producing porous carbon spheres, which are a vital component for carbon capture technology and for new ways of storing renewable energy, has been developed by Swansea University researchers.

The method produces spheres that have good capacity for carbon capture, and it works effectively at a large scale.

Carbon spheres range in size from nanometers to micrometers. Over the past decade they have begun to play an important role in areas such as energy storage and conversion, catalysis, gas adsorption and storage, drug and enzyme delivery, and water treatment.

They are also at the heart of carbon capture technology, which locks up carbon rather than emitting it into the atmosphere, thereby helping to tackle climate change.

The problem is that existing methods of making carbon spheres have drawbacks. They can be expensive or impractical, or they produce spheres that perform poorly in capturing carbon. Some use biomass, making them more environmentally friendly, but they require a chemical to activate them.

This is where the work of the Swansea team, based in the University's Energy Safety Research Institute, represents a major advance. It points the way towards a better, cleaner and greener way of producing carbon spheres.

The team adapted an existing method known as CVD -- chemical vapour deposition. This involves using heat to apply a coating to a material. Using pyromellitic acid as both carbon and oxygen source, they applied the CVD method at different temperatures, from 600-900 °C. They then studied how efficiently the spheres were capturing CO2 at different pressures and temperatures

They found that:
 

• 800 °C was the optimum temperature for forming carbon spheres
• The ultramicropores in the spheres that were produced gave them a high carbon capture capacity at both atmospheric and lower pressures
• Specific surface area and total pore volume were influenced by the deposition temperature, leading to an appreciable change in overall carbon dioxide capture capacity
• At atmospheric pressure the highest CO2 adsorption capacities, measured in millimolars per gram, for the best carbon spheres, were around 4.0 at 0 °C and 2.9 at 25 °C.

This new approach brings several advantages over existing methods of producing carbon spheres. It is alkali-free and it doesn't need a catalyst to trigger the shaping of the spheres. It uses a cheap and safe feedstock which is readily available in the market. There is no need for solvents to purify the material. It is also a rapid and safe procedure.

Dr Saeid Khodabakhshi of the Energy Safety Research Institute at Swansea University, who led the research, said:

"Carbon spheres are fast becoming vital products for a green and sustainable future. Our research shows a green and sustainable way of making them.

We demonstrated a safe, clean and rapid way of producing the spheres. Crucially, the micropores in our spheres means they perform very well in capturing carbon. Unlike other CVD methods, our procedure can produce spheres at large scale without relying on hazardous gas and liquid feedstocks.

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Primordial black holes and the search for dark matter from the multiverse

 The Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) is home to many interdisciplinary projects which benefit from the synergy of a wide range of expertise available at the institute. One such project is the study of black holes that could have formed in the early universe, before stars and galaxies were born.

Such primordial black holes (PBHs) could account for all or part of dark matter, be responsible for some of the observed gravitational waves signals, and seed supermassive black holes found in the center of our Galaxy and other galaxies. They could also play a role in the synthesis of heavy elements when they collide with neutron stars and destroy them, releasing neutron-rich material. In particular, there is an exciting possibility that the mysterious dark matter, which accounts for most of the matter in the universe, is composed of primordial black holes. The 2020 Nobel Prize in physics was awarded to a theorist, Roger Penrose, and two astronomers, Reinhard Genzel and Andrea Ghez, for their discoveries that confirmed the existence of black holes. Since black holes are known to exist in nature, they make a very appealing candidate for dark matter.

The recent progress in fundamental theory, astrophysics, and astronomical observations in search of PBHs has been made by an international team of particle physicists, cosmologists and astronomers, including Kavli IPMU members Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov.

To learn more about primordial black holes, the research team looked at the early universe for clues. The early universe was so dense that any positive density fluctuation of more than 50 percent would create a black hole. However, cosmological perturbations that seeded galaxies are known to be much smaller. Nevertheless, a number of processes in the early universe could have created the right conditions for the black holes to form.

One exciting possibility is that primordial black holes could form from the "baby universes" created during inflation, a period of rapid expansion that is believed to be responsible for seeding the structures we observe today, such as galaxies and clusters of galaxies. During inflation, baby universes can branch off of our universe. A small baby (or "daughter") universe would eventually collapse, but the large amount of energy released in the small volume causes a black hole to form.

An even more peculiar fate awaits a bigger baby universe. If it is bigger than some critical size, Einstein's theory of gravity allows the baby universe to exist in a state that appears different to an observer on the inside and the outside. An internal observer sees it as an expanding universe, while an outside observer (such as us) sees it as a black hole. In either case, the big and the small baby universes are seen by us as primordial black holes, which conceal the underlying structure of multiple universes behind their "event horizons." The event horizon is a boundary below which everything, even light, is trapped and cannot escape the black hole.

In their paper, the team described a novel scenario for PBH formation and showed that the black holes from the "multiverse" scenario can be found using the Hyper Suprime-Cam (HSC) of the 8.2m Subaru Telescope, a gigantic digital camera -- the management of which Kavli IPMU has played a crucial role -- near the 4,200 meter summit of Mt. Mauna Kea in Hawaii. Their work is an exciting extension of the HSC search of PBH that Masahiro Takada, a Principal Investigator at the Kavli IPMU, and his team are pursuing. The HSC team has recently reported leading constraints on the existence of PBHs in Niikura, Takada et. al. (Nature Astronomy 3, 524-534 (2019))

Why was the HSC indispensable in this research? The HSC has a unique capability to image the entire Andromeda galaxy every few minutes. If a black hole passes through the line of sight to one of the stars, the black hole's gravity bends the light rays and makes the star appear brighter than before for a short period of time. The duration of the star's brightening tells the astronomers the mass of the black hole. With HSC observations, one can simultaneously observe one hundred million stars, casting a wide net for primordial black holes that may be crossing one of the lines of sight.

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Discovery about how cancer cells evade immune defenses inspires new treatment approach

 Cancer cells are known for spreading genetic chaos. As cancer cells divide, DNA segments and even whole chromosomes can be duplicated, mutated, or lost altogether. This is called chromosomal instability, and scientists at Memorial Sloan Kettering have learned that it is associated with cancer's aggressiveness. The more unstable chromosomes are, the more likely that bits of DNA from these chromosomes will end up where they don't belong: outside of a cell's central nucleus and floating in the cytoplasm.

Cells interpret these rogue bits of DNA as evidence of viral invaders, which sets off their internal alarm bells and leads to inflammation. Immune cells travel to the site of the tumor and churn out defensive chemicals. A mystery has been why this immune reaction, triggered by the cancer cells, does not spell their downfall.

"The elephant in the room is that we didn't really understand how cancer cells were able to survive and thrive in this inflammatory environment," says Samuel Bakhoum, a physician-scientist at MSK and a member of the Human Oncology and Pathogenesis Program.

According to a new study from Dr. Bakhoum's lab published December 28 in the journal Cancer Discovery, the reason has to do, in part, with a molecule sitting on the outside of the cancer cells that destroys the warning signals before they ever reach neighboring immune cells.

The findings help to explain why some tumors do not respond to immunotherapy, and -- equally important -- suggest ways to sensitize them to immunotherapy.

Detecting Dangerous DNA

The warning system Dr. Bakhoum studies is called cGAS-STING. When DNA from a virus (or an unstable cancer chromosome) lands in a cell's cytoplasm, cGAS binds to it, forming a compound molecule called cGAMP, which serves as a warning signal. Inside the cell, this warning signal activates an immune response called STING, which addresses the immediate problem of a potential viral invader.

In addition, much of the cGAMP also travels outside the cell where it serves as a warning signal to neighboring immune cells. It activates their STING pathway and unleashes an immune attack against the virally infected cell.

Previous work from the Bakhoum lab had shown that cGAS-STING signaling inside of cancer cells causes them to adopt features of immune cells -- in particular, the capacity to crawl and migrate -- which aids their ability to metastasize. This provided part of the answer to the question of how cancer cells survive inflammation and aid metastasis in the process. The new research shows how the cancer cells cope with the warning signals that activated cGAS-STING releases into the environment. A scissor-like protein shreds the signals, providing a second way the cells can thwart the threat of immune destruction.

Examples of human triple negative breast cancer staining negative (left) and positive (right) for ENPP1 expression. Examples of human triple negative breast cancer staining negative (left) and positive (right) for ENPP1.

The scissor-like protein that coats cancer cells is called ENPP1. When cGAMP finds its way outside the cell, ENPP1 chops it up and prevents the signal from reaching immune cells. At the same time, this chopping releases an immune-suppressing molecule called adenosine, which also quells inflammation.

Through a battery of experiments conducted in mouse models of breast, lung, and colorectal cancers, Dr. Bakhoum and his colleagues showed that ENPP1 acts like a control switch for immune suppression and metastasis. Turning it on suppresses immune responses and increases metastasis; turning it off enables immune responses and reduces metastasis.

The scientists also looked at ENPP1 in samples of human cancers. ENPP1 expression correlated with both increased metastasis and resistance to immunotherapy.

Empowering Immunotherapy

From a treatment perspective, perhaps the most notable finding of the study is that flipping the ENPP1 switch off could increase the sensitivity of several different cancer types to immunotherapy drugs called checkpoint inhibitors. The researchers showed that this approach was effective in mouse models of cancer.

Several companies -- including one that Dr. Bakhoum and colleagues founded -- are now developing drugs to inhibit ENPP1 on cancer cells.

Dr. Bakhoum says it's fortunate that ENPP1 is located on the surface of cancer cells since this makes it an easier target for drugs designed to block it.

It's also relatively specific. Since most other tissues in a healthy individual are not inflamed, drugs targeting ENPP1 primarily affect cancer.

Finally, targeting ENPP1 undercuts cancer in two separate ways: "You're simultaneously increasing cGAMP levels outside the cancer cells, which activates STING in neighboring immune cells, while you're also preventing the production of the immune-suppressive adenosine. So, you're hitting two birds with one stone," Dr. Bakhoum explains.

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