Making a worm do more than squirm

Satirist Stephen Colbert envisions his “Colbert Nation” mentally marching in lockstep with his special brand of patriotism.  But scientists have done him one better, by creating tiny worm-bots completely under their control.

Rather than comedic persuasion, these scientists are using a dot of laser light. With it they can make a worm turn left, freeze or lay an egg. The researchers report their work online January 16 in Nature Methods.

The new system, named CoLBeRT for “Controlling Locomotion and Behavior in Real Time,” doesn’t just create a mindless zombie-worm, though. It gives scientists the ability to pick apart complicated behaviors on a cell-by-cell basis.

“This system is really remarkable,” says biological physicist William Ryu of the University of Toronto, who was not involved in the research. “It’s a very important advance in pursuit of the goal of understanding behavior.”

Transparent and small, the nematode C. elegans is particularly amenable to light-based mind control. Another benefit of the worm is that researchers know the precise location of all 302 of its nerve cells. But until now, there wasn’t a good way to study each cell by itself, especially in a wriggling animal.

“This tool allows us to go in and poke and prod at those neurons in an animal as it’s moving, and see exactly what each neuron does,” says study coauthor Andrew Leifer of Harvard University.

The system is based on the emerging field of optogenetics, in which light is used to turn cells on or off. Leifer and his colleagues genetically engineered light-responsive molecules into particular groups of cells in the worm.

Then, a computer program that the team developed figures out where in the microscope’s field of view a target cell is. Once the cell is pinpointed, the program directs lasers so that a tiny beam of light hits the cell.

“When we’re shining light on a neuron, we’re hitting that neuron and nothing else,” Leifer says.

The whole process, from finding the cell to light hitting its target, takes about 20 milliseconds. As the worm’s position changes, that information is fed back into the computer program, and the laser is adjusted. If the worm crawls too far, a motorized microscope stage brings the animal back.

One of the biggest benefits of the new method, Ryu says, is that it works in a roving animal. “The worms are not held down in any way — they’re freely moving. There aren’t many systems where you can look at such truly free organisms.”

In early tests of their technique, Leifer and his team forced worms to freeze, change directions, turn left or right, and even lay eggs. In later tests, the team focused on two nerve cells that help the worm respond to touch. Researchers knew that a gentle tickle on the head causes worms to move backward, but after too many touches, the worms grow desensitized and stop responding. By mimicking touches with light, the researchers found that a weary cell that’s been touched too many times can also tire out its partner cell that hasn’t been touched, suggesting that these cells don’t act alone.

Another group of scientists, led by Jeffrey Stirman of Georgia Tech in Atlanta, reports a similar technique for worm mind-control, also online January 16 in Nature Methods. Ryu says the two methods are similar. The CoLBeRT method appears to be a little faster, he says, but if the worm is crawling slowly, the method used by Stirman’s group may offer more precise laser targeting. “Do both papers contribute to understanding behavior at a holistic level? Yes, definitely.”

Neuroengineer Ed Boyden of MIT says the new work could allow scientists to figure out how every cell in an animal works together to generate a behavior. “The ability to

target a single cell is really important, because it allows you to understand precisely what each of these cells does.”
For more info- http://www.sciencenews.org/view/generic/id/68860/title/Making_a_worm_do_more_than_squirm

Earth Is Twice as Dusty as in 19th Century, Research Shows

The study, led by Natalie Mahowald, associate professor of earth and atmospheric sciences, used available data and computer modeling to estimate the amount of desert dust, or soil particles in the atmosphere, throughout the 20th century. It's the first study to trace the fluctuation of a natural (not human-caused) aerosol around the globe over the course of a century.

Mahowald presented the research at the fall meeting of the American Geophysical Union in San Francisco Dec. 13.

Desert dust and climate influence each other directly and indirectly through a host of intertwined systems. Dust limits the amount of solar radiation that reaches the Earth, for example, a factor that could mask the warming effects of increasing atmospheric carbon dioxide. It also can influence clouds and precipitation, leading to droughts; which, in turn, leads to desertification and more dust.

Ocean chemistry is also intricately involved. Dust is a major source of iron, which is vital for plankton and other organisms that draw carbon out of the atmosphere.

To measure fluctuations in desert dust over the century, the researchers gathered existing data from ice cores, lake sediment and coral, each of which contain information about past concentrations of desert dust in the region. They then linked each sample with its likely source region and calculated the rate of dust deposition over time. Applying components of a computer modeling system known as the Community Climate System Model, the researchers reconstructed the influence of desert dust on temperature, precipitation, ocean iron deposition and terrestrial carbon uptake over time.

Among their results, the researchers found that regional changes in temperature and precipitation caused a global reduction in terrestrial carbon uptake of 6 parts per million (ppm) over the 20th century. The model also showed that dust deposited in oceans increased carbon uptake from the atmosphere by 6 percent, or 4 ppm, over the same time period.

While the majority of research related to aerosol impacts on climate is focused on anthropogenic aerosols (those directly emitted by humans through combustion), Mahowald said, the study highlights the important role of natural aerosols as well.

"Now we finally have some information on how the desert dust is fluctuating. This has a really big impact for the understanding of climate sensitivity," she said.

It also underscores the importance of gathering more data and refining the estimates. "Some of what we're doing with this study is highlighting the best available data. We really need to look at this more carefully. And we really need more paleodata records," she said.

Meanwhile, the study is also notable for the variety of fields represented by its contributors, she said, which ranged from marine geochemistry to computational modeling. "It was a fun study to do because it was so interdisciplinary. We're pushing people to look at climate impacts in a more integrative fashion."
For more info- http://www.sciencedaily.com/releases/2011/01/110110055748.htm