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Fruit flies don’t bother me

By Jeyling Chou

March 3, 2003 9:00 p.m.

There are labs on the UCLA campus that contain vials and vials
of tiny, winged creatures. They live out their entire two-week life
cycle within these vials, consuming a mixture of cornmeal and
sugar.

They grow to reach only three millimeters, but fruit flies hold
a significance for human genetics that is exponentially greater
than their size.

No other organism has had their DNA as tweaked and altered as
the fruit fly, known as Drosophila melanogaster to scientists.
These insects have been the buzz word in genetics for the last
century.

Drosophila, with its completely sequenced genome, is a model
organism ““ one of several animals selected by the National
Institute of Health as useful for research and the development of
science.

Studies of Drosophila in the early 20th century led to a flying
advance in human genetics: the discovery that genes were located on
chromosomes.

Although Drosophila only has four chromosomes and humans 23,
nearly 60 percent of the genes are found in common.

Today, UCLA researchers continue to study Drosophila because
discoveries made on the miniscule fly level can be expanded and
applied broadly to human health and genetics.

“What we’ve learned by using genetic approaches in
studying the development of fruit flies is relevant to the
development of all creatures, including humans,” said Albert
Courey, a chemistry and biochemistry professor.

“Genes in Drosophila have counterparts in all animals that
play strikingly similar roles.”

Fruit flies are a model organism because of their ability to
multiply quickly and their short life span. This rapid breeding
makes it possible for researchers to create a fly with a genotype,
or genetic makeup, tailored exactly to the purpose of an
experiment.

Two types of flies with the genotypes the researcher wants to
cross are placed within the same vial and allowed to mate. The
resulting genotype can be passed on through successive generations
and maintained for several months.

Vials of live flies are then labeled with the specific genotype
and stored with a monthly renewed food supply.

Fly labs like the ones at UCLA can inexpensively keep hundreds
of vials, each containing Drosophila with a different genetic
variation.

“Flies are a fairly cheap, rapid test organism to give you
clues about what to do in other organisms,” said John
Merriam, a molecular, cell and developmental biology professor.

In a process called “fly pushing,” the flies are
studied under a microscope by pushing and sorting them according to
physical characteristics that result from their manufactured
genotype.

The flies are knocked out with carbon dioxide emitted from tiny
pores in the pad of the microscope. Specimen which are no longer
needed are simply scooped up and poured into a nearby flask
containing ethanol and dead flies, fittingly called “the
morgue.”

Specific mutations can be induced in the fly through the process
of various genetic crosses. The physical characteristics or
phenotypes of a particular mutation are often more visible in
Drosophila than in other organisms.

For example, Drosophila is found in the wild with naturally
occurring red eyes. Flies with white eyes can be created through
the isolation and reproduction of the gene which produces the white
mutation.

After a mutation is identified, the next step is to locate the
gene which causes that mutation, and ultimately, to discover the
function of the original gene.

Through this process in fruit flies, the thousands of genes and
their functions are slowly being paired.

“By using fruit flies you can discover roles for genes and
then look to see if the homologous genes in humans play homologous
roles,” Courey said.

“If you hadn’t done the fruit fly genetics first,
you’d never know what genes to look at in humans.”

With the sequencing of the entire human genome, many researchers
have begun to decipher the vast amounts of information in the
genetic code by working from the ground up, and from the simple to
the complex.

“If someone shows you a Cray supercomputer, and you
don’t know much about computers, before you start pushing
buttons, you might go to the store and buy a pocket
calculator,” said Frank Laski, MCDB professor.

“After you figure out the calculator, you can work your
way up until you’re ready to take on the complexity of the
supercomputer.”

Drosophila is that pocket calculator. The ultimate goal of the
research of these tiny insects is an application to the field of
human genetics.

“One hopes that we will find relevant genes which involve
direct relevance to human diseases ““ particularly cancer
““ such that if we understood why changes in the genes do what
they do, scientists could try to find drugs and ways to stop those
changes,” said Uptal Banerjee, professor and chair of the
MCDB department.

Humans and flies differ obviously in their phenotypes, but
researchers are increasingly realizing a genetic similarity across
all organisms.

“All living organisms share more or less the same set of
genes,” said John Marriam, an MCDB professor. “This has
become miraculously apparent in the last ten years with the various
genome projects.”

For example, the study of cell differentiation ““ how a
single cell from a fertilized egg divides and develops into a
complex organism ““ in a fruit fly can reveal much about the
same process that results in a human embryo.

During cell differentiation, precursor cells develop into
neurons, blood cells or muscle cells based on chemical signals from
the cells around them.

Drosophila and humans share many of the chemical and genetic
building blocks which control the development of a complex organism
from an undifferentiated ball of cells. The only difference is the
regulation of these genes.

“It’s as if you’re trying to figure out how to
use bricks and mortar to build a house or a bridge,” Banerjee
said.

“There’s a big difference in what the house looks
like and what the bridge looks like but the fundamental principles
behind building them are the same.”

Various UCLA researchers are focusing on specific parts of the
fruit fly ““ including the brain, ovary, and the eye ““
in hopes of applying what they find to the analogous part in
humans.

Researchers are optimistic about the future of human genetics
carried on the tiny buzzing wings of Drosophila.

“We’ve come a tremendous ways,” Merriam
said.

“Darwin would be proud of us.”

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Jeyling Chou
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