Glowing sugars light up zebrafish

Using artificial sugar and some clever chemistry, University of California, Berkeley, researchers have made glow-in-the-dark fish whose internal light comes from the sugar coating on their cells.

This novel method of fluorescently tagging the sugar chains, or carbohydrates, that coat cells is a new tool for those studying development in the zebrafish, a laboratory organism popular because its transparent embryos allow easy observation of living cells as they develop over time.

"Most people think of carbohydrates as food, but the surface of any cell in our body is adorned with a ton of sugars as well as proteins that allow cells to communicate with other cells and invading pathogens," said UC Berkeley graduate student Jeremy M. Baskin. "People have had for many years the ability to image specific proteins, but not carbohydrates. We have developed for the first time methods for labeling and imaging carbohydrates inside an intact animal."

"An understanding of how, when and where cells dust themselves with sugar may shed light on how stem cells develop into tissues, as well as turn up markers of disease, such as cancer, or strategies for battling infectious organisms," said first author Scott T. Laughlin, who, like Baskin, is a graduate student in the Department of Chemistry.

One big advantage of the technique is that it is non-toxic and can be used to study living cells, Baskin said, whereas other methods of tagging cell-surface carbohydrates cannot be performed on living specimens.

Baskin and Laughlin, together with Carolyn Bertozzi, UC Berkeley professor of chemistry and of molecular and cell biology, and developmental geneticist Sharon L. Amacher, associate professor of molecular and cell biology, reported their results in the May 2 issue of the journal Science. Bertozzi also is director of the Molecular Foundry at Lawrence Berkeley National Laboratory, a Howard Hughes Medical Institute investigator, and the T.Z. and Irmgard Chu Distinguished Professor of Chemistry at UC Berkeley.

"We have genes in our body coding for proteins, but proteins get modified in lots of different ways, one of which is by addition of sugars that stick out on the cell surface and change the way the protein interacts with the environment," Amacher said. "One of the big mysteries is how the pattern of sugar modification changes during development, or in cancer cells versus non-cancer cells, for example. The exciting work Carolyn is now doing is finding ways that we can actually see the sugar labels on proteins."

Scientists have known for more than a century how to attach fluorescent dyes to proteins, and have used the technique to study protein trafficking in cell culture and even in whole organisms, though often at the expense of killing the cells or organism. Bertozzi has focused on making it just as easy to study the sugars on cells, in part to investigate their role in such diseases as tuberculosis and influenza. In the latter, the flu virus enters cells by way of hemagglutinin, a sugar-protein complex on the viral surface that attaches to sugars on the surface of host cells. But sugars clearly have roles in cell-to-cell communication that have yet to be discovered.

One technique Bertozzi has developed is to feed cells an artificial sugar that looks so much like the real thing that cells are tricked into incorporating the sugar into their carbohydrate chains. Once the sugar becomes part of the forest of carbohydrates adorning a living cell, she then uses a non-toxic chemical reaction to attach small organic labels to it. Simple, highly selective and non-toxic chemical reactions like this have come to be called click chemistry.

In their work on zebrafish, Baskin, Bertozzi and their colleagues soaked zebrafish embryos in the artificial sugar N-azidoacetylgalactosamine, which the embryo cells then used as a carbohydrate building block to replace the natural sugar N-acetylgalactosamine. The researchers then modified a chemical reaction that is normally toxic to cells to eliminate the toxic copper catalyst and employed this reaction to attach a small fluorescent molecule, a fluorophore, to the "azido" part of the unnatural sugar.

The copper-free click chemistry worked with three separate fluorophores, enabling the researchers to make two-to five-day-old zebrafish cells glow red, green and even near infrared, which is invisible to the eye but can be detected by some microscopes. They were able to observe differences over time in when and where on a single cell the sugar appeared, sugar movement through the cell interior, and in which tissues the sugar showed up.

"We're hoping to extend the technique to other sugars, too," Baskin said, noting that of the nine sugars used by vertebrates to build carbohydrates, Bertozzi's lab has found artificial surrogates for four of them. "We also want to try getting (artificial sugar) to work in different organisms and different disease models, such as cancer models in mice. Basically, we are providing this as a tool for the general community to use."

Amacher, who studies tissue patterning in the very early zebrafish embryo, is anxious to work with the labeling technique, but is waiting until Bertozzi's group gets it to work in hours-old embryos, at a stage when muscles and organs begin to form.

"Once they get the labeling technique to work at very early times, it is going to be an even more exciting collaboration, and hopefully, a continuing one," she said.

Source: UC Berkeley

Related stories:

Future MP3 players may eat sugar to recharge
(PhysOrg.com) -- Just as humans scoff sugary food to keep energised, so might your future iPod to charge its “bio-battery”.
TB Bacterium Uses Its Sugar Coat To Sweeten Its Chances Of Living In Lungs
(PhysOrg.com) -- Common strains of tuberculosis-causing bacteria have hijacked the human body’s immune response to play tricks on cells in the lungs, scientists say.
Existing anti-obesity drugs may be effective against flu, hepatitis and HIV
Viruses dramatically increase cellular metabolism, and existing anti-obesity drugs may represent a new way to block these metabolic changes and inhibit viral infection, according to a study published today in the journal Nature Biotechnology.
Killer carbs -- Monash scientist finds the key to overeating as we age
A Monash University scientist has discovered key appetite control cells in the human brain degenerate over time, causing increased hunger and potentially weight-gain as we grow older.
Engineer Taps Heat-Loving Bacteria for Hydrogen
A North Carolina State University engineer has been awarded a $1.6 million grant from the U.S. Department of Energy to learn more about the microbiology, genetics and genomics behind how and why heat-loving bacteria called thermotogales produce large amounts of hydrogen with unusually high efficiencies. These microorganisms are found all over the globe in areas which are naturally hot – including volcanic sediments, hot springs and brines from deep oil wells.
New Yeast Trick for Eating Favorite Food
It is well known that yeast, the humble ingredient that goes into our breads and beers, prefer to eat some sugars more than others. Glucose, their favorite food, provides more energy than any other sugar, and yeast has evolved a complex genetic network to ensure that they consume as much glucose as possible whenever it is available. UC San Diego bioengineers have recently identified a previously unknown mechanism that allows yeast to shut down the metabolism of another sugar, galactose, when they sense glucose in the environment.
Compound that Helps Rice Grow Reduces Nerve, Vascular Damage from Diabetes
You may want to soak your brown rice. Researchers have found that a compound that helps rice seed grow, springs back into action when brown rice is placed in water overnight before cooking, significantly reducing the nerve and vascular damage that often result from diabetes.
All Sweeteners May Not Be the Same When Managing Type 2 Diabetes and Complications
(PhysOrg.com) -- Recent research by Kalidas Shetty of the University of Massachusetts Amherst and Lena Galvez Ranilla of the University of San Paolo, Brazil, shows that when it comes to managing Type 2 diabetes, all sweeteners may not be the same. Some sweeteners, including date sugar and less refined, dark brown sugars, showed potential for managing Type 2 diabetes and related complications − information that could help Type 2 diabetics make better dietary choices.

News discussion:

General Science news