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By Rabiya S. Tuma
Freelance Writer

ZOOM IN: Joe Gall, who has been studying frog oocytes since the '50s, was able to measure optical density of nucleoli by attaching a CCD camera to a scope.
Joe Gall, a faculty member at the Carnegie Institute of Washington in Baltimore, has been studying chromosomes and nuclear structures in frog oocytes since the 1950s. During that time, he and others speculated on the density of various structures within the nucleus, including the nucleoli, which appear very dense and heavy using traditional light microscopic techniques.

Last year, Gall hooked up a CCD camera to his 40-year-old Zeiss interferometer microscope. (Such microscopes are commonly used in materials science but are not frequently found in biology labs.) This enabled his team to measure the optical density of the nucleoli, coiled bodies, and the nucleoplasm that surrounds them. "I was quite surprised at how low-density everything was in the [nucleus]," Gall says. His group calculated that the nucleolus contains about 21.5 percent protein, whereas only 10.6 percent of the nucleoplasm is protein.

The interferometer microscope measures the change in the optical path of two light beams — one that passes through the material of interest, and one that does not. It is exquisitely sensitive when viewed by eye, Gall says, but the addition of the CCD camera enables his group to move from examining qualitative differences to quantitative ones.

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