Cells on the Move Are Fussy About Footing

From embryonic development to wound healing and cancer metastasis, cells move. But like runners on a track, they won’t go very fast on a surface that’s too hard or too soft to get the right amount of grip.

“That was a key realization,” says University of Minnesota biomedical engineering professor David Odde.” Cells are very responsive to the mechanical stiffness of their environment. It affects how cells [mature from embryonic to adult form] and migrate within the body, but it was not clear how this happens.”

Odde and his colleagues have built and tested a mathematical model of how cells respond to varying degrees of stiffness in the tissues on and through which they travel. They predicted, and found, that for a given cell there is an optimal stiffness–a sweet spot–for it to move.

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What slime molds tell us about ourselves

Some of Margaret Titus’s students are a little taken aback to learn how much they have in common with the slime mold Dictyostelium discoideum. Called “social amoebae” for their habit of joining together to save themselves when food is scarce, they may hold the key to understanding how a host of human cellular processes work—or go awry.

When human white blood cells or metastasizing cancer cells move through our bodies, or when nerve cells are forming connections with each other, they send out slender exploratory extensions called filopodia. And when “Dicty” cells search for food, they do the same thing. If any of these cells’ filopodia pick up signals that point them in a favorable direction, the rest of the cell follows; this is what directs their movement to the food source.

“I call filopodia ‘the cat’s whiskers of a cell,’” says Titus, a professor in the Department of Genetics, Cell Biology and Development. “Proteins called myosins, which act as mo-tors for many cells, are needed to make them, and we found the same basic operating principles in filopodia-forming myosins used by both Dicty and humans.” Continue reading

The sound of music


Suppose a flute player and a bass player are playing a tune where they must hit notes simultaneously. A new University of Minnesota study suggests that if a high flute note comes a tad earlier than its bass counterpart, the audience probably won’t notice. But if the bass note comes early, they will.

Also, the ability to detect a lack of synchrony between a low note and a high note had nothing to do with whether either note came on the beat; all that mattered was the order in which the notes were played.

The study revealed quirks in how humans process and perceive musical sounds that have evolutionary significance. And because it concerns how the inner ear and brain work together, it could aid in the design of better hearing aids or cochlear implants.

“These surprising results have given us more insight into the complex interactions that occur between the ear and brain when we perceive sound,” says Andrew Oxenham, a psychology professor and study author.

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Forty years with tigers

Tiger in tall grass

Tiger at night, caught in a camera trap in Nepal. Photo credit: David Smith.

Few tiger biologists venture into dens to photograph and collect data on cubs. But University of Minnesota tiger researcher David Smith has done it twice, once with the mother just 200 yards away.

Using radio and GPS collars, Smith has tracked tigers for 40 years with one goal in mind: to achieve larger and more secure tiger populations by keeping their prey abundant and their habitat connected rather than patchy. This matters because top predators are critical to ecosystem health.

So are Smith’s graduate students. Most come from Nepal, Thailand, Bangladesh, Cambodia, China, Taiwan or the Philippines. Degrees completed, they return home and mobilize local people for conservation efforts.

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Turning sugar into plastics, polyesters – and new industries

Kechun Zhang

With the world hungry for more and better nutrients, antibiotics, plastics and other materials, a cheap and sustainable source must be found. Enter Kechun Zhang, who works with the most abundant of all: sugar.

“Sugar is the basis of life,” explains Zhang, a 2015-17 McKnight Land Grant Professor in the College of Science and Engineering’s Department of Chemical Engineering and Materials Science (CEMS). “Everything is made of sugar or sugar-derived materials. Plants turn carbon dioxide into sugar, and it’s fed into all of life, including the cellulose in plant cell walls and the starches in seeds.”

Zhang and his colleagues—notably Regents Professor Frank Bates and chemistry professor Mark Hillmyer—have used various sugars as feedstocks to produce the building blocks of plastics, elastic materials (including spandex) and other products. This year, the three researchers founded the company Valerian Materials to manufacture the building blocks (monomers) of high-performance, biodegradable plastics and other polymers from renewable stocks instead of petroleum. Continue reading

Glial cells: guardians of brain activity

Gilal cells

After a stroke, blood flow through capillaries is hard to restore, even when the blood clot is removed. In Alzheimer’s disease, blood flow to some brain areas is compromised. In diabetic retinopathy, diabetes patients’ retinas deteriorate. The problem may be a compromised blood supply that can’t meet the demands of neurons.

In all these conditions, neurons are starved for the oxygen and glucose they need to function properly. Normally, when neurons in the brain or retina are working and need extra nourishment, some type of signal prompts nearby blood vessels to dilate and let more blood through. Pinpointing the nature and origin of such signals is critical to finding treatments for conditions in which it is lost or weakened.

But the signals don’t necessarily pass directly from neurons to blood vessels. University of Minnesota researchers have shown that in the retina, cells called glia—Latin for “glue”—respond to neuronal activity by signaling capillaries within the retina to dilate, increasing capillary blood flow by up to 26 percent. Their report is a cover story for the Journal of Neuroscience.

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Why prostate cancer treatment falls short

A common treatment for prostate cancer targets only one type of cancer cell, leaving patients vulnerable to a second type that continues to multiply, according to work at the University of Minnesota and Minneapolis Veterans Affairs Medical Center (VAMC).

“The problem is that some of the cancer cells are dependent on androgens–testosterone and other male hormones–and some cancer cells require estrogens,” says research leader Akhouri Sinha, a professor in the Department of Genetics, Cell Biology and Development, the Masonic Cancer Center, and the VAMC. “[A common treatment] is to drastically reduce the supply of androgens, but that leaves the estrogen-dependent cancer cells to grow and thrive.

“It’s like trying to shut off a river by damming only the main channel, while letting water in the side channels continue to flow.”

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Investing in nature pays off

China’s rapid economic growth has taken a toll on its environment, threatening the work that ecosystems do for free in the form of “ecosystem services” that benefit people. For example, healthy ecosystems store carbon, filter nutrients to provide clean water, prevent erosion, mitigate floods and sandstorms, and provide habitats that preserve biodiversity.

In 2000 China began investing in the restoration of its ecosystems to increase its “natural capital.” By 2009 the country had spent more than $50 billion on the effort. Writing in a recent issue of Science, a panel of researchers—including the U’s Stephen Polasky, Regents Professor of Applied Economics—reports a favorable result. Six of seven ecosystem services improved during the decade 2000-2010, and China’s ecosystem-restoration policies likely contributed significantly to four: carbon sequestration, soil and water retention, and sandstorm mitigation.

Polasky, along with coauthors from the United States and China, says the Chinese experience shows that improving ecosystem services can coexist with economic growth—a lesson that could be applied in other countries, including the United States. Also, its benefits ought to appeal to parties on both sides of the political divide.

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Fail-safe for faulty cell division found

When a cell divides by the process of mitosis, its chromosomes perform a well-choreographed ballet.

First, each makes a copy of itself. The copies, held together as pairs, line up in a ring around the middle of a football-shaped structure called the mitotic spindle. The chromosomes are then pulled apart, with the members of each pair migrating to opposite poles of the spindle. This creates two sets of chromosomes, one in each of the two daughter cells.

But if any chromosomes “lag”—that is, fail to line up and segregate properly—the daughter cells end up with too many or too few chromosomes. This condition, called aneuploidy, is a common feature in cancer development.

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‘Dirty’ mice may be better models of human biology

Researchers have long noted disparities between the functioning of the human immune system and that of laboratory mice. Could it be because, unlike us, they live in antiseptic cages, shielded from exposure to infectious organisms?

A landmark, University of Minnesota-led study lends credence to that idea. It has found that immune cells of lab mice bear relatively little resemblance to those of adult humans. Instead, they resemble the immature immune cells of newborn babies, who also have been sheltered from the unhygienic real world. But when lab mice were cohoused with less pampered “dirty” mice from pet shops, their immune systems matured to a state much more like that of adult humans.

While not discounting any previous work with lab mice, the researchers make the case that studying cohoused mice “could provide a relevant tool for modeling immunological events in free-living organisms, including humans.” The work is published in Nature.

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How size and lifestyle rule the plant world

Papaver alpinum

University of Minnesota researcher Peter Reich, along with numerous colleagues around the world, have found what scientists have long suspected: that despite Earth’s rich diversity of plant life, only relatively few combinations of traits are successful.

Drawing on a data set of 46,085 plant species, the researchers gave each an identity based on its scheme for growing, surviving and reproducing. Describing plants this way gives scientists a way to predict how different vegetation will respond to climate change, most crucially by the amount of carbon it can scrub from the atmosphere.

“This paper tells you about constraints on evolution,” says Reich, a Regents Professor of forest resources. “We need better models to understand and predict how vegetation globally will change with climate change. To do that, knowing more about the small number of ways plants vary can help us build more predictive models.”

The study appears in the journal Nature.

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Gravitational waves rock the physics world

About 1.3 billion years ago, a pair of black holes suddenly spiraled in on each other and merged, creating a new spinning black hole—all in just one-fifth of a second. The immense energy released by this cosmic cataclysm generated waves that shook the very fabric of space and rippled out through the cosmos.

In 1916 Albert Einstein’s theory of general relativity predicted that events like this would produce such ripples in the fabric of space, which he called gravitational waves. But they would be so weak that he thought they would never be detected.

So with today’s announcement that a team of some 1,000 scientists from the Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) project—including University of Minnesota researcher Vuk Mandic and his colleagues—has just detected gravitational waves, it doesn’t take an Einstein to see the excitement rippling through the scientific world. The waves stem from the black hole merger described above, and their discovery validates Einstein’s prediction and opens new avenues for understanding the Universe.

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