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."
