Fruit Fly Klutzes Give Clues to Human Hearing, Touch

From the WebMD Archives

March 23, 2000 (Boston) -- They would probably make lousy dance partners, but a bunch of fruit flies so uncoordinated that they cannot even get food into their mouths is providing scientists with evidence of a gene that controls how sensations such as hearing, touch, and body position are conveyed to the brain. The research is reported in the March 24 issue of the journal Science.

And although it's a long conceptual leap from fruit fly to human, the findings may help medical researchers understand and perhaps treat or prevent certain inherited forms of deafness, suggest Richard G. Walker, PhD, and colleagues from the University of California, San Diego.

Fruit flies are the workhorses of genetic laboratories, because all of the genes that make the pesky little creatures what they are have been identified and catalogued. Many of the genes, in fact, are similar to those found in higher animals, including humans. Also, because fruit flies are born, grow up, breed, and die within two months, scientists can study how changes in specific genes in one generation of flies can affect their posterity for many generations to come.

But what do flies with two -- make that six -- left feet have to do with the realm of the senses? The answer has to do with the mechanisms that allow cells in the body to respond to a physical or mechanical stimulus such as a touch or a sound wave.

"Biologists have a pretty good idea of how chemicals work to signal cells [with] odors, tastes -- things like that, and we have a very good idea about the molecules involved in [responding] to light. We are virtually clueless as to how mechanical stimuli are translated into signals in cells," says Martin Chalfie, PhD, professor of biology at Columbia University in New York, who reviewed the study for WebMD. "Mechanical information is utilized by touch, hearing, balance, stretch, position, blood pressure, [and is even] important in regulating the amount of bone that you have."

To see whether they could find a gene that controlled how sensing cells send information to the brain, Walker and colleagues narrowed in on three strains of flies that couldn't find their way out of a lab dish, let alone out of a paper bag. The flies all had mutations in a specific gene that caused them to be so uncoordinated that their first act as full-fledged adult flies was to fall into their sticky food and die.

Continued

Although some genetic mutations are lethal, the flies died not because they inherited a fatal defect but because they couldn't figure out where they were or how to get food, which for normal fruit flies is as easy as falling off a log. "If you take them and put them in a non-sticky environment such as a piece of filter paper and you feed them, they'll probably live for a long time," says Walker in an interview with WebMD.

Fruit flies sense motion by means of ultrasensitive hairs on their bodies. Even a microscopically small deflection of the hairs will usually cause an electrical signal to shoot to the insects' brain, telling them "you have been stimulated, do something!" But in the mutant flies, the loss of or damage to the gene apparently kept the signals from ever making it to their minuscule noggins.

The reason all this matters is that the sensory hairs on fruit flies are strikingly similar in many ways to tiny hair-like cells within the inner ear of humans that are partly responsible for turning sound, in the form of vibrations, into an electrical signal that is then sent to the brain, which then says, "Oh yeah, I heard that."

Although no one has as yet identified a human equivalent for the fruit fly gene, it has also been found in another darling of genetics laboratories, the roundworm. The presence of the gene in both flies and worms (which biologically are two very different kettles of fish) suggests that the gene has played an important role in evolutionary history and is probably hanging around just waiting to be discovered in vertebrates -- that is, those of us with backbones, the authors say.

They speculate that if such a gene can be found, it could be used as the basis for strategies to prevent or perhaps even reverse some inherited forms of deafness.

Vital Information:

  • Researchers have found a gene in fruit flies that controls how sensations such as hearing, touch, and body position are related to the brain.
  • Fruit flies sense motion via tiny hairs on their bodies and translate that sensation into electrical signals for the brain, in much the same way that hair-like cells in the inner ear of humans help convert sound into electrical signals for the brain.
  • No one has yet found a similar gene among vertebrate animals, but researchers hope that one will be found and further our understanding and treatment of some types of deafness.
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