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Science & Technology

Fruit fly genome

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From Diana J. Choyce
Apr 03 - 09, 2000

This past week marked a milestone in the history of science. At first glance it doesn't seem all that earth shattering. And the fact that it has to do with the lowly fruit fly makes it even more likely to be passed by the casual reader. But in fact this may be the beginning of a whole new era in the mapping of genes. Despite the controversy surrounding gene research, this discovery merits a closer look.

A team of 200 scientists from Celery Genomics Corp., the Berkeley and European Drosophila Research Projects have successfully sequenced the whole genome of the Drosophila fruit fly. A genome holds all the hereditary information of an organism. For the last 100 years genetic scientists have been studying the fruit fly. And in the last 20 years they have been focusing on mapping its genes by using recombinant DNA cloning and sequencing techniques.The federally funded Human Genome Project in 1990 selected Drosophila as a model organism for study. "The sequencing of the Drosophila genome represents the successful completion of one more important step in place to first sequence the relatively small genomes of important experimental organisms such as bacteria, yeast, flies and worms, before attacking the considerably larger human genome," said evolutionary geneticist Margaret G. Kidwell of the University of Arizona. "The smaller genomes are biologically interesting in their own right as well as serving as pilot projects to refine the tools for automated sequencing and computational analysis of the human genome."

Fruit flies are being used in studies because they are easy to breed and experiment on. They have produced volumes of information to scientists such as helping to understand the human aging process, insight into diseases like Parkinsons'. And they have also helped understand the simpler things humans do such as hearing, the sense of smell, sleeping and others as well. The fruit fly is the largest animal so far to have its genes sequenced. "In essence, we are nothing but a big fly,'' Charles Zuker, a professor of biology at the University of California San Diego, who studied fruit flies, said in a statement. "If there's one thing we've learned over the past 80 years, it's that model organisms like Drosophila are wonderful engines of discovery. They not only allow us to efficiently focus on problems that are hard to track in higher organisms, they also recapitulate much of the same biology as more complex forms.'' A comparison study of 289 of the known human disease genes has shown that 177 of the fruit fly genes matched. Researchers have also found that the p53 gene that causes many cases of human cancer has a similar appearance to one in the fruit fly. A cluster of genes associated with aging and degenerative diseases were found as well. Another study helped scientists gain insight into how human and other complex organisms hear, balance, and sense touch on a molecular level. "You literally have to hand-feed them, put food in their mouths, because they're so uncoordinated that they just can't function in any other way,'' Richard Walker said. "They are so uncoordinated that they just fall into their food, which is kind of sticky, where they get stuck and die.'' Zuker said the gene finding shows that complex senses such as touch and hearing depend on a very simple molecular function. "Our enjoyment of wonderful symphonies is nothing but the conversion of mechanical energy into electrical signals by the cells in our inner ear,'' he said. His team hopes to help doctors understand and treat hearing loss in a more efficient manner.

Other researchers at Brigham and Women's Hospital and Harvard Medical School in Boston said this week they had created fruit flies with symptoms of Parkinson's disease, which they hope to use to study the fatal and incurable brain disease. Scientists there have spliced a human gene that is often mutated in Parkinson's Disease into the DNA of the flies. This has produced the symptoms often associated with the disease such as shaking. Flies are popular for such research as they have a two month lifespan, are small, cheap, and develop rapidly. They share many of the same genes as humans and readily take in food that has drugs used for experiments. "At the level of individual nerve cells, flies are remarkably like humans," Feany says. "The same molecules that make neurons work, or not, as in Parkinson's disease in people do the same thing in fruit flies." Feany and his team harvest clumps of brain proteins from expired Parkinson's patients and graft them into the fly DNA. After the 40th day of growth the flies began to exhibit the trouble of keeping their balance and were unable to take the normally easy path to their food. the same neurons that die in Parkinson's patients, died in the flies, forming the telltale protein clusters on the remaining neurons. "These three features are the key manifestations of Parkinson's disease in people," Feany says. "We think, therefore, that flies are an excellent model of the human disease." "This will have a remarkable catalytic effect on Parkinson's research," comments Columbia University neurologist Robert Burke. "Once you have a model like this that includes all three features of Parkinson's, especially a convenient one like flies, it enables you to investigate more rapidly the death of neuron cells and begin to look into drugs." The short lifespan of fruit flies shortens and simplifies experiments. Scientists can also easily alter fruit fly genes. "When we understand both how the disease is initiated, and how it progresses," Feany says, "we will be able to design treatments targeted at prevention, arrest of the disease process and symptomatic relief."