...return of the matrix

cIlwain was sure that the structure they were seeing was holding the cell together. Before examining the cell, they extracted its soluble protein using 10-normal sodium hydroxide, which "dissolves protein like crazy," as McIlwain says. The substance had extracted about 60 percent of the total protein from the cell. "You remove half the protein, but you still get something that looks like a cell," Hoke says. This convinced them that the cell contained insoluble proteins that were controlling its size and shape.

The two also found success with experiments that followed. "For a while, every experiment we did was suggested by Penman's work, and we could predict how it was going to come out," McIlwain says. The experiments showed that the size and shape of the isolated framework changed after nerve injury, that the framework contained all the missing protein, and that the framework was very insoluble.

.: With an unusual thin-sectioning technique, McIlwain and Victoria Hoke got this image of a matrix in spinal motor cells. When McIlwain found the long-forgotten idea of such a matrix in a textbook, he dashed off these notes and sketch. Click to enlarge. :.

McIlwain has no doubt about the matrix. He's one of the few. One criticism: when Penman was promoting this idea, some scientists argued that one part of the thin-sectioning method — removing the wax and drying the cells with a technique called critical point drying — could be altering how the fine details of the framework appeared.

McIlwain concedes that could be true. But whatever the fine details of the framework, something is maintaining the cells' size and shape, even after McIlwain removes the soluble proteins. "I think these are the true bones of these cells," he says.

The explanation satisfies him enough that he's willing to spend the next few years — the end of his career — refining this work. "I'm happy to just stand right in line behind Porter and Penman and say, well, I took your ideas and applied them to neurons, and by golly, they seem to check out," he says.

o agree with McIlwain, scientists will have to change they way they think about cells. Bringing about such a "paradigm shift" is not easy. "It's hard for scientists to believe that something this fundamental has been overlooked," McIlwain says. "The whole idea of the cytoskeleton is so familiar that it's hard for scientists to accept new ideas about it."

If the proteins in the matrix are indeed insoluble, they're going to be hard to identify. McIlwain is betting that mass spectrometry — a tool of the new field of proteomics — will help. He has begun sending human cell samples to Carolina's Proteomics Core Facility. There researchers break the proteins down into their small chains, known as peptides, and run them through a mass spectrometer to determine their mass. Then McIlwain can use the human genome to identify the peptides, giving him a clue as to which proteins they come from.

McIlwain believes that the framework is not made of the usual cytoskeleton proteins. These proteins are soluble, and the way he sees it, the matrix is not. "I may be able to show that there's some interesting new protein in motor neurons," he says.

McIlwain hopes that proteomics will help scientists see the "insoluble world" in cells. "This world exists in nonneuronal cells as well as in neurons," McIlwain says. "We've got to come to grips with it."

"It doesn't happen very often that you just feel like something comes along and synthesizes what you're doing," he continues. "For me the real reward has been in getting an answer that really made good sense."

This work was funded by two small grants from UNC-Chapel Hill — a University Research Council grant and a Medical Alumni Foundation Endowment grant.

Angela Spivey is the associate editor of Endeavors magazine.
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