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Scattered Light Reveals Size and Shape Of The Nucleus

A new technology based on the interpretation of light reflected off cells will make it faster and more efficient for researchers to document how the nucleus, which contains a cell’s DNA and controls its actions, changes shape in response to its environment. The technique will enable researchers for the first time to watch some changes in the living cell as they happen.

The Duke University bioengineers who developed the new method and demonstrated its effectiveness believe that this approach will give scientists an additional tool to better understand the nucleus and provide more avenues for research into new therapies for disease.

Currently, measuring the nucleus is a painstaking cell-by-cell process, taking about one day to process 100 cells. The new method can screen hundreds of cells in as little as five minutes, the Duke researchers said. The new system also allows scientists to observe the nucleus in real time; conventional methods typically involve “fixing” and staining individual cells, revealing information about that instant in time only.

“We know that changes, or deformations, of the nucleus can impact how the genes within that nucleus are expressed,” said Kevin Chalut, lead author of a paper published May 29, 2008 in the Biophysical Journal. Chalut is a post-doctoral fellow in the Pratt School of Engineering labs of both Adam Wax, assistant professor of biomedical engineering and Kam Leong, professor of biomedical engineering.

“The results of our experiments demonstrate the ability of this technique to rapidly and accurately measure changes in the shape of the nucleus in response to external stimuli,” Chalut said. “We expect that these advances should enable cell biologists and tissue engineers to better understand the how changes in the shape of the nucleus influence the cell in studies of living systems.”

The light scattering technology is known as angle-resolved low coherence interferometry (a/LCI). In this process, light is shined into a cell and sensors capture and analyze the light as it is reflected back. The technique is able to separate the unique patterns of the nucleus from the other parts of the cell and provide representations of its changes in shape in real time.

“The exciting part of these experiments is that it demonstrated a new application of our technology,” said Wax, whose research focuses on biophotonics, or the use of light in medical research. “We have already shown that it could act as an early cancer detection system by detecting pre-cancerous cells in linings of tissues. These findings will permit researchers to pursue more and different investigations at the cellular level.”

Chalut tested the a/LCI technique on two different living cell types – cartilage cells from pigs and immune system cells known as macrophages from mice.

Working with researchers in the laboratory of Farshid Guilak, a Duke biomedical engineer and co-author on the paper, Chalut was able to measure how the shape of the nucleus within a chondrocyte, a type of cartilage cell, changed as the salinity of the environment around the cells changed.

“Ordinarily, increases in salinity cause cells to shrink, which has a direct effect on the nucleus within,” Chalut said. “Since Dr. Guilak’s research focuses on novel treatments for osteoarthritis, the ability to understand the response of the nucleus to environmental cues could help him to develop new tissue engineering approaches.”

Chalut also worked in the lab of Leong, a co-author who studies the use of novel biomaterials and nanoparticles for genetic and immune system therapies.

“We used the new system to look at how nuclei in mouse macrophages responded to different types of cellular scaffolding,” Chalut said. “The traditional way to study this phenomenon would be to introduce the scaffolding, and then over a period of time look at individual cells to see how the nucleus responded. The a/LCI permits us to complete experiments more quickly and to widen the scope of experiments we can perform.”

The Duke team plans additional collaborative studies with bioengineers and medical researchers using the a/LCI technique to show how different nuclear shape changes correlate with the expression of different genes.

The research was supported by the National Science Foundation, National Institutes of Health and the National Cancer Institute. Other members of the research team were Duke’s John Finan and Michael Giacomelli; and Sulin Chen of Johns Hopkins School of Medicine.