Fruit-Fly Paralysis Spurs Discovery of Protein Required For Nervous-System Function

BUFFALO, N.Y. -- Studies of mutant fruit flies have led University at Buffalo pharmacologists to discover a previously unknown protein that plays a key role in the electrical signals that are the basis for nervous-system function.

The new protein is important in the function of sodium-channel alpha subunits, bagel-shaped proteins that open and close, controlling the flow of ions, which is the basis for electrical activity in the nervous system.

The finding allows researchers to begin to unravel the mysteries of the nervous system at a molecular level, not only in fruit flies, but possibly in other species, including humans. It also may have eventual application in the development of new treatments for diseases and clinical conditions in which sodium channels are involved.

The work was described in a paper published today in Cell.

The UB researchers have licensed the new protein to Merck & Co. as a rapid screening assay for new insecticides. A patent is pending on the protein and the new gene encoded by it.

"Sodium-channel alpha subunits in fruit flies are very similar to those of other species, including humans," explained Linda Hall, Ph.D., professor of biochemical pharmacology at UB and senior author of the Cell paper.

Hall explained that mutations in these alpha subunit proteins in both humans and flies lead to severe motor defects.

The researchers reasoned that mutations in other proteins that interact with alpha subunits may also cause similar motor defects. In their research, they focused on one such mutation: alterations in a gene called tipE (temperature-induced paralysis gene E) that cause fruit flies to become paralyzed when exposed to heat.

"This gene, pronounced 'tippy,' describes what happens when the flies are heated to human-body temperature -- they tip over and are paralyzed until the temperature is lowered to a comfortable room temperature when they get up again and go busily on their way," said Hall.

After determining where the tipE gene was located on the chromosomes, Hall and her co-authors studied the chromosomal region until they found several candidate genes.

The final proof that they had the gene responsible for the paralysis came from "gene therapy" experiments in which they replaced the mutant gene with a normal one and cured the fruit flies' paralysis.

They then sequenced the gene responsible for the cure, which allowed them to show it encoded a unique protein.

"There was nothing like it in the extensive databases from the genome projects," said Hall.

Using the tipE protein, Hall and her colleagues functionally expressed, for the first time in vitro, the para sodium channel, which causes paralysis or death when mutated.

Several groups had tried to make the gene for this sodium channel work in vitro, but none had been successful.

It turns out that both the tipE gene and the para gene are required for expression of this sodium channel during neural development.

When expressed during a specific period in the development of the fruit fly's nervous system, the gene endows the fly with properties that prevent the adult from becoming paralyzed at high temperatures.

"The gene is at its peak expression when the fruit fly's nervous system is undergoing reorganization," said Hall. "This is a critical time for the gene, when something key in development changes, but we don't yet know what that is."

The findings suggest that this protein may exist in many different species, from insects to mammals.

"The protein we discovered, tipE, may also be a missing key required to turn on sodium channels at appropriate times in other species," she said. "The fact that scientists have cloned sodium channels from other species, but have not been able to get them to function properly outside the organism, suggests there may be a factor missing and tipE may be that factor."

Hall added that if homologues of tipE regulate sodium-channel function in the human brain and heart, better treatments for diseases in these organs may be possible.

A sodium channel in the human uterus, which may be involved in the birthing process, may also be regulated by tipE, she said. By affecting sodium channels in the uterus, Hall said, it may be possible to develop more natural labor-inducing agents or prevent premature births.

Co-investigators on the paper are Guoping Feng, Ph.D., now Jane Coffin Childs Postdoctoral Associate at the Washington University School of Medicine; Péter Deák, Ph.D., now associate professor at Attila Jószef University (Hungary), and Maninder Chopra, Ph.D., postdoctoral associate at UB. Hall, Chopra and colleagues are continuing this work with support from a Jacob Javits Neuroscience Investigator Award from the National Institute of Neurological Disease and Stroke and by a grant from the Muscular Dystrophy Association.