Focusing on the Electron Microscopy Facility
By Mika Ono
Malcolm Wood, director of TSRI's Electron Microscopy Facility,
adjusts the focus, contrast, brightness, and magnification
of the black-and-white image of a blood vessel on a screen,
looking for clues to a problem of excess bleeding. Still not
satisfied, he moves on to see if he can glean more insight
from the next sample.
"The ability to see and to understand what you are seeing
is critical in microscopy," says Wood. "Experience does help
interpreting the images, as does the confidence to interact
with the equipment. You can't just accept the first image
on the screen as real."
Many scientists at TSRI send samples to the Electron Microscopy
Facility to draw on the expertise of Wood and his staff, microscopists
Theresa Fassel and Brian Smith. Assistant Professor Henrik
Ditzel, for one, wanted to identify the location of several
proteins on neutrophils, a kind of white blood cell highly
destructive of microorganisms, to help understand a type of
autoimmune reaction.
"Malcolm was very helpful," says Ditzel. "It's great to
have high-quality core facilities like this one on campus.
They make the progress of research much faster."
The Electron Microscopy Facility, which participates in
15 to 20 TSRI research projects a month, houses two electron
microscopes in the basement of the Molecular Biology/Skaggs
Institute Building and a confocal and a deconvolution microscope
in the basement of the Stein Building. Projects are turned
around in three days to two weeks or more, depending on the
requirements of the job and the number of samples provided.
Electron microscopy, a technique developed in the 1930s,
can magnify a sample theoretically to the angstrom level,
a level at which individual molecules can be detected. To
prepare a sample for electron microscopy, cells are fixed
and embedded in resin for support, then cut into extremely
thin slices—70 nanometers thick—using a diamond
knife. The sections are then picked up on a mesh grid and
stained with heavy metals such as uranium or lead for contrast.
In the electron microscope, the various lenses are electromagnets
that essentially manipulate the beam of electrons in a manner
comparable to the glass lenses of the light microscope. In
the transmission electron microscopes, the beam of electrons
passes through the sample and the electrons impact the phosphorescent
screen to create the image of the sample.
"Essentially, in electron microscopy you are looking at
a shadow of the parts of the cell that have differentially
taken up heavy metals," explains Wood. "In this shadow, you
can identify structures."
Although electron microscopy offers extremely high magnification
and better resolution than the light microscope, preparing
samples for this technique can be a time-consuming process.
"In immuno-electron microscopy, it's often a balancing act
to find a concentration of chemicals that will preserve cells
without destroying antigenicity," Wood says. "In light microscopy,
sample preparation is more straight-forward. Although the
magnification it offers is not as high, light microscopy has
an important role to play as a guide for further research."
In addition to its drop-off service, the Electron Microscopy
Facility offers an open-access program in which researchers
can learn to use the microscopes and go on to work with them
independently. Training, which is conducted by the facility's
staff, usually lasts 10 to 12 hours for electron microscopes,
8 to 10 hours for light microscopes.
"People are sometimes surprised when they use the instruments
for the first time," says Wood. "In general, you don't see
the images shown in a textbook. More often, the structures
appear at an unexpected angle or plane. You have to think
three-dimensionally while looking at two dimensions."
For more information on the Electron Microscopy Facility,
contact Wood, x4-8186 or e-mail mwood@scripps.edu.
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Malcolm Wood directs the Electron Microscopy Facility, which
participates in 15 to 20 TSRI research projects each month.
Photo by Tom Gatz.
This image from an electron microscope shows part of an alpha
cell from mouse pancreatic islets.
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