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Thursday, February 5, 2015

Making the Cells and Tissue Bigger, to Get a Better Look

Microscopic view of a histologic specimen of h...
Microscopic view of a histologic specimen of human lung tissue stained with hematoxylin and eosin. (Photo credit: Wikipedia)

A new laboratory technique enables researchers to see minuscule biological features, such as individual neurons and synapses, at a nearly molecular scale through conventional optical microscopes.

In a paper published recently in the journal Science, researchers at the Massachusetts Institute of Technology said they were able to increase the physical size of cells and tissue by as much as five times while still preserving their structure. They call the new technique expansion microscopy.

By extending the resolving power of conventional microscopes, Scientists can glimpse the protein structures that form ion channels and the outline of the membrane that holds the genome within a cell. The researchers have examined minute neutral circuits, gaining new insights into local connections in the brain and a better understanding of larger networks.

The maximum resolving power of conventional microscopes is about 200 nanometers. (A human hair is about 500 times wider.) In recent decades, scientist have struggled to push past these limits.

Last year, three scientists received a Nobel Prize for a technique in which fluorescent molecules are used to extend the resolving power of optical microscopes. But the technique requires specialized equipment and is costly.

With expansion microscopy, Edward S. Boyden of the M.I.T. Center for Neurobiological Engineering and his colleagues were able to observe objects originally measuring just 70 nanometers in cultured cells and brain tissue through an optical microscope. They were also able to produce super-resolution animations in which the viewer “flies” through a detailed three-dimensional image of a mouse hippocampus.

“We hope we have a technology that will allow you to scan the nervous system of entire animals,” Dr.Boyden said.

The idea began as a joke, according to Dr. Boyden. But he and two graduate students realized it might be feasible after exploring the work of Toyoichi Tanaka, who discovered a class of “intelligent” gels that respond to stimuli such as water.

One of those materials is a polymer used in diapers, which absorbs 200 times to 300 times its mass in water. The researchers realized it was perfect for forcing biological tissue to swell.

The researchers apply fluorescent dye to the sample. Then they infuse the tissue with the chemical building blocks of the polymer. The blocks form the polymer inside the tissue, which is then chemically “chopped up” so it can be enlarged. Then, just add water. The tissue expands, and the tiny structures traced in fluorescence burst into view.

Expansion microscopy may permit scientists to create three-dimensional models of large areas in the brain of animals, making it possible to map biological processes from one region to the next. And the technique may reveal the structures of individual proteins, structural detail inside cells and other biological features in near-molecular detail.

Dr. Boyden said the imaging technique will not directly capture dynamic processes in the brain, but it may make it possible to gain insight into brain function by taking samples before and after events.

Taken from TODAY Saturday Edition, The New York Times International Weekly, January 31, 2015