Discovery of Nerve Cell ‘Motor’ Sparks Rivalries, New Research

In a cluttered basement room at the Marine Biological Laboratory, Ronald Vale cleared space on a counter, rummaged for a pair of tweezers and slowly squeezed a single, glistening drop of protoplasm from the nerve filament of a squid.

The precious substance, unique in the natural world, has enabled Vale and collaborators led by Thomas Reese to purify and identify a biological “motor” that they say is used by nerve cells to ferry supplies along their long, fibrous tendrils, or axons.

The finding, if confirmed, could have important consequences for the treatment of a variety of severe brain disorders, including Alzheimer’s disease and Lou Gehrig’s disease, in which nerve cells in the brain and spinal cord cease to function.

Defects in the biological motor could contribute to those diseases by making nerve cells unable to send signals. If so, the discovery of the motor should enable drug makers to design new treatments that would restore the cells’ function by repairing the motor.

“If you know what the molecule is, if you know how it works, pharmacologists can design drugs to stimulate it or slow it down,” said Roger Sloboda of Dartmouth College and the Marine Biological Laboratory. Sloboda is also studying the movement of chemicals inside squid nerve cells.

Bitter Rivalries

The story of the research that preceded the Reese findings is in many respects a triumph of the scientific method. But it is also a story of bitter personal rivalries, cries of unfair competition and assertions by some in the dispute that the discovery claimed by Reese and his colleagues would ultimately be proved wrong.

“I don’t think that’s the way it’s supposed to happen,” Reese said recently, looking back on the frenzied months of research and recriminations. “There were some difficult personalities.”

“This is competition gone overboard,” said Scott Brady, who works in a building next to Reese’s and is one of his most intense competitors. “As a result, I will not discuss my work in progress.” Brady’s work likewise deals with nerve-cell transport in squid.

The feud has led to an atmosphere of suspicion and secrecy that might be appropriate in the Pentagon but is highly unusual at scientific research establishments like the Marine Biological Laboratory.

In fact, Reese credits what he calls the “open university” feeling at the Marine Biological Laboratory with contributing to the discovery. “Everything is accessible, and everybody knows what everybody is doing,” he said.

Notebooks Locked Away

That has not been strictly true for the last couple of years. Researchers involved in the struggle to identify the protein in squid axons began locking laboratory notebooks away at night, and they refused to divulge the chemical recipes they were using in their work.

At the laboratory’s annual meeting in August, neither Reese nor Brady presented reports on their work, as might normally have been expected. “Everybody’s afraid to say anything,” said another competitor, who likewise decided not to speak at the meeting.

Reese’s scientific papers reporting the discovery of the protein motor he has dubbed kinesin (pronounced kih-NEE-sin) were published at the end of last year and the beginning of this year. But that did not mark the end of the competition.

Kinesin moves supplies in only one direction, from the center of a nerve cell to the tip of its axon. It appears that another protein is required to carry waste products back in the other direction. A second horse race to find this protein has already begun.

Furthermore, kinesin governs only so-called “fast” axonal transport, in which movement occurs at a rate of several inches a day. There are at least two forms of “slow” transport and one kind of intermediate transport, said Sloboda, an authority on axonal transport.

It is not yet known what protein motors are involved in these other forms of transport. Nor has anyone yet sorted out the role of these various forms of transport in human diseases, although they are almost certain to play some part.

No Conclusive Proof

Sloboda says that Reese has not yet proved conclusively that kinesin is responsible for fast transport.

Reese has shown that the protein can produce movement of specially treated microscopic glass beads in a laboratory setup that resembles conditions inside cells, Sloboda says. But Reese has not shown the same movement with actual vesicles--the little packets of chemicals that move inside cells.

“There’s no data presented yet that shows kinesin moves vesicles on microtubules,” Sloboda said. “It probably does, but ‘probably’ is worth two cents in science.”

Brady is even more dubious of Reese’s findings. “It could be that it’s unrelated to what happens in the axon,” he said. Brady has independently isolated a protein that he believes is responsible for the movement in axons, and he studies the actual movement of vesicles, not glass beads.

“We have several candidates,” Brady said. “What’s important is to note that there are alternate possibilities.”

“That’s true,” Reese said. “Kinesin might not be it. But so far, things are checking out.”

Sloboda and Susan Gilbert, who has just left his laboratory for Pennsylvania State University, have joined the fray with the isolation of yet another protein that is somehow involved in moving vesicles in axons. They report that it is different from both kinesin and Brady’s protein, and they are working to characterize it further.

Brady feels particularly aggrieved because he made the critical finding that allowed the isolation of kinesin, and yet Reese’s group seems to be getting the lion’s share of credit for the discovery of kinesin.

Brady showed that a substance called AMP-PNP would freeze the movement protein to microtubules, allowing it to be more easily isolated and identified. As Brady tells it, Reese seized upon that finding and simply outgunned him, because Brady could not match Reese’s financial resources.

Reese and his colleagues deny that they merely “threw money” at the problem, as Brady and others have charged. “The relevant discoveries were made without a lot of money,” said a member of the Reese team, Michael Sheetz of Washington University in St. Louis. “There wasn’t a lot of money thrown at it. There was a lot of time thrown at it.”

Works Alone

Brady, like most Marine Biological Laboratory scientists, spends summers in Woods Hole and the academic year at a university, in his case the University of Texas Health Sciences Center in Dallas. He works alone, on a small grant from the National Institutes of Health.

Reese heads a special year-round National Institutes of Health laboratory at the Marine Biological Laboratory and thus has considerably greater financial resources.

“I am the underdog, but I should not be underestimated,” Brady said. “I’ve worked with this system for 10 years.”

Most recently, Brady has identified a movement protein with properties that he says differ significantly from those of kinesin.

Reese and Sheetz believe that Brady’s protein is also kinesin, or a form of it. “The question was put at a conference--what are the differences,” Sheetz said. “And there aren’t many.”

The roots of the kinesin story go back at least to the 1930s, when J. Z. Young, an eminent British biologist, spent some time at the Marine Biological Laboratory. He became the first to investigate the so-called giant axon of the squid and to demonstrate its value for scientific research.

Large Nerve Cell

The giant axon is part of a nerve cell large enough to see without a microscope, unlike the nerve cells and axons in higher animals.

As Vale demonstrated, the squid’s giant axon allows extraction of the protoplasm--or more properly, axoplasm--from which kinesin was ultimately isolated.

The research by Young and those who have followed was done to answer basic scientific questions concerning the workings of axons. The possible value of the research in the treatment of human disease was far from the scientists’ minds, although most scientists believe as an article of faith that today’s basic research will have important practical applications tomorrow.

Work continued on squid axons after Young’s pioneering investigations. In the 1960s, Raymond Lasek of the Marine Biological Laboratory and Case Western Reserve University made important contributions to the understanding of transport within axons.

But certain crucial insights eluded Lasek and his colleagues, because the moving vesicles in the axons were too small to see, even with the most powerful microscopes.

That problem was solved in 1981, when Robert Allen of Dartmouth and the Marine Biological Laboratory developed what has come to be called video microscopy.

Allen attached a video camera to his sensitive, state-of-the-art microscope and found that radical alterations of the video contrast could produce 10 times more magnification than was possible with the microscope alone.

When the new video microscope was turned on squid axoplasm, researchers saw for the first time the jerky dance of vesicles along microtubules. “Seeing it on the screen was the greatest experience of my life,” Lasek said.

The development of video microscopy was not without its unpleasant aspects. Shinya Inoue, a year-round researcher at the Marine Biological Laboratory, was locked in fierce competition with Allen.

The two were not on speaking terms, said Nina Allen, Allen’s former wife. She too had her differences with Allen: She claims a share in the discovery of video microscopy and says Allen never gave her credit for her contributions.

The two divorced last year, several months before Allen died of cancer.

The development of video microscopy gave Brady, Reese and others the tool they needed to identify movement proteins. They could perform various chemical operations on the axoplasm and see whether the operations interfered with movement.

That was what allowed Brady to find the substance that froze the movement protein on the microtubules, and thus made possible its isolation.

New Research

Kinesin--or something like it--has now been identified in other types of cells, and its discovery promises to open a new arena of scientific research on the nature of movement within cells.

“The identification of a new motor has caused a number of fields to explode,” Gilbert said.

Researchers at the University of Colorado, for example, have found a protein like kinesin in sea urchin eggs that appears to be involved in the segregation of chromosomes into two pairs as cells divide. This segregation of chromosomes occurs in all animals, from sea urchins right up to humans.

Anthony Breuer of the Cleveland Clinic Foundation has found that abnormalities in fast axonal transport may play a role in Lou Gehrig’s disease, in which vesicles appear to move too fast along the microtubules.

The identification of kinesin and its relatives does not suggest that a cure for Lou Gehrig’s disease is at hand, but it is a step toward such a cure, Reese said.

“If you’ve got a degenerative disease, some part of the axon is not functioning,” he said. “One could list a number of degenerative diseases and point out that it is now possible to probe all of these to find the role of kinesin.”

However the dispute between Brady, Reese, Sloboda and other researchers turns out, it is clear that the competition has produced findings of potentially immense importance.

As Gilbert put it, “No one group could have done it alone.”