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Biology through a lens
Rockefeller’s Bio-Imaging Resource Center provides a place where scientists can watch the processes of life unfold on the tiniest of scales
Much of biology is, at its essence, the study of very tiny things. Cells, the building blocks of all living organisms, are on average just one-tenth of a millimeter in diameter. From there — organelles, chromosomes, proteins — things just get smaller. To understand the processes that take place on such a miniscule scale, you need a microscope. And that’s where the situation gets complicated.
See the microscopes
in action.
Unlike the souped-up magnifying glasses of a few decades ago, today’s microscopes are enormously expensive, highly specialized devices. Depending on what you’re trying to see, you might need precise lasers to activate dyes, spinning discs to filter light at extremely high speeds, robotic stages capable of tracking moving objects, or sophisticated software that can stitch together a series of two-dimensional images into a three-dimensional model. Some microscopes forgo light altogether and use streams of electrons to create images of objects as small as a few millionths of a millimeter in size.
“With all these complicated, expensive microscopes available, no individual lab could afford to have them all,” says Alison North, director of Rockefeller’s Frits and Rita Markus Bio-Imaging Resource Center. North’s optical microscopy facility on the second floor of the Bronk building, and the electron microscopy facility she oversees on the first floor of the Rockefeller Research Building, are home to 12 scopes worth in excess of $5 million. Scientists from any of the university’s 70-plus laboratories pay modest hourly fees to use some of the most sophisticated imaging technology available. When they’re all in use, the microscopes in North’s facility can generate as much as 250 gigabytes of digital images and movies per week.
“Considering that a single microscope can cost half a million dollars or more, it’s far more efficient for the university to invest in a centralized facility that can be used by everybody than it is to purchase equipment on a lab-by-lab basis,” North says.

An explosion in imaging

Traditionally, many of the questions in cell biology have used the tools of molecular biology to make observations indirectly. Now, with improved technologies and an explosion of genetic studies, scientists can see many cellular processes directly, and even watch them unfold in real time.
“The question that everybody’s interested in now is what are the genes doing?” says North. “Genes make proteins, and people want to know what the proteins are responsible for. The first step toward answering that question is asking where they are in the cell — and looking into a microscope is the only way to learn the answer.” By attaching a fluorescent marker to an intriguing protein, scientists can track where the protein travels within a cell, and note what structures it interacts with. Well over half of the users of the Bio-Imaging Resource Center are trying to localize proteins in this way.
An increasing number of researchers are also doing live cell imaging, in which a series of images are linked together to create a movie. “This is really where things get interesting,” North says. “You can see what happens during development, what changes during disease and how cells and proteins move around. Only in the last 10 years has this been a widely available option for scientists.” In addition, a small percentage of the center’s users require more basic structural studies of a specific sample — a comparison between healthy and diseased tissue, for example.
“A lot of the work is done in parallel; first you watch a live cell to follow changes in the cellular organization, then fix your sample in order to get a more detailed look at where everything is. Different microscopes are designed to best answer certain questions. By combining several techniques, you can get a much more comprehensive analysis of your problem than if you focus only on one type of microscope, even if it is the latest and greatest,” North says.

Fireworks in a cell

North has been fascinated with microscopes since she was a teenager. “I looked down my first fluorescence microscope in my second year of university, and that was it. I said this is what I want to do,” she says. She completed graduate work and two postdocs in cell biology, but always specialized in microscopy. She came to Rockefeller to establish the bio-imaging center from Manchester,U.K., in 2000. “Maybe it’s the artist in me that was drawn to this career. I see the images that come out of our facility and they remind me of fireworks. When people see them they simply say ‘Wow!’” North says.
The light microscopy facility provides training and guidance, but generally lets scientists do their own imaging. For certain jobs, North or Dan Elreda, an image analysis specialist, will collaborate with scientists. In the electron microscopy facility, two microscopists, Helen Shio and Eleana Sphicas do most of the imaging. “Our job is primarily to provide expertise,” says North. “If you want to get good images, you have to know when the cells look happy. You also have to know which microscope is most suitable for your experiment, and how to use it to get the best possible results.”

Turning images into discoveries

Collecting images is not as easy as many budding scientists believe, and magnification only gets you so far. In order to produce useful images, microscopists have to also consider resolution, the ability to distinguish between closely placed objects, and contrast, the required variation in intensity necessary to create a visible image. Sample preparation is also important. If a sample is poorly prepared, for instance if there’s a lot of background staining or if the wrong chemicals have been used to fix a certain structure, or even if the wrong thickness of glass coverslip has been used, no amount of technology will be able to create a good image.
And then there’s the tricky business of interpreting images. “This is where things can get very murky, and often people see what they want to see,” North says. Consider, for example, the situation of a scientist trying to determine the function of a particular protein. Microscopy can tell him or her where in a cell a protein is located, but it may not tell whether or not that protein is active. It can’t tell whether the protein is interacting with other proteins at that location.
“Because I’m removed from the scientific project and I’m not looking for anything specific, I have a more objective viewpoint, which can be useful when scientists are trying to determine if they are indeed seeing what they think they are seeing in a particular image,” North says.

October 15, 2004



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