Scientists Devise Technique That Allows Zebrafish to Replace
Mouse as Key Lab Animal in Gene Modification Research
Mar. 5, 2001 | 2:08 p.m.
ATTENTION: Science editors
WEST LAFAYETTE, Ind., March 5 (AScribe News) --

In the post-genomic world, the lowly zebrafish may be king.

Scientists at Purdue University have developed a technique that
allows zebrafish to pass genetic modifications to its offspring.

The discovery will lead to researchers being able to study genes
and proteins in a less expensive way.

The two-inch, black-striped zebrafish - known primarily as the
last fish living in your kid's aquarium - is quickly becoming famous
in the scientific world as the best animal to use when studying
genetics - even better than the mouse.

``Because zebrafish are relatively inexpensive and easy to
maintain compared to genetically modified mice, this discovery
could greatly accelerate new genetic experiments in vertebrates,''
says Randy Woodson, director of Purdue's Office of Agricultural
Research Programs.

These new experiments would provide information into Alzheimer's,
heart disease, certain types of cancer and other diseases.

The zebrafish is an essential tool to a new branch of science called
proteomics, also sometimes known as post-genomics. Proteomics
refers to the study of an organism's proteins, just as genomics
refers to the study of an organism's genetic material. Proteomics
is a natural follow-up to the mapping of various organisms'
genomes, including the human genome.

``With the human genome project they're sequencing genes,
and each of those genes causes the body to produce various
proteins at different times,'' says Paul Collodi, associate professor
of animal sciences at Purdue and primary investigator on the
research project. ``If you want to understand what the genes
actually do, you have to study the function of the proteins they
produce, and the zebrafish makes a nice model for that.''

Scientists study proteins and gene function by disabling a
single gene, and then raising clones of that test subject to
see how they develop without the missing gene.

Such experiments are called knockout experiments, because
the gene is turned off, or knocked out.

Over the past decade, plant scientists have used a small mustard
plant, called Arabadopisis, to conduct gene knockout experiments
in crops and plants. But until now it has been difficult to conduct
knockout experiments in animals.

In mice - until now the only animal in which the gene knockout
technique works - a genetically modified embryo cell, called an
embryonic stem cell, is inserted into a developing mouse embryo.

An embryonkC@MQ5 cell is an early embryo cell that has not
yet begun to differentiate into various tissues.

The embryo is then transferred into the womb of a female mouse
using surgical techniques. After the embryo develops into an adult,
some of the modified stem cells will give rise to eggs and sperm that
contain the modification. Such a process is laborious and expensive.
As a result, transgenic mice can cost thousands of dollars each.

``With mice you have maybe a dozen embryos to work with, and
you have to do surgery to transplant the embryos back into the
mother,'' Collodi says. ``Compare that to the zebrafish embryo where
we can modify 100 embryos an hour, and, because the embryos
develop outside the mother, we don't have to do surgery.
The entire developmental phase takes only about four days.''

Because of the expense and effort required to produce a
transgenic mouse, scientists have been searching for another
vertebrate animal that would allow these gej%:ic experiments.

The technique has been tried in chickens, cows, pigs, sheep
and other species of fish without success.

Collodi says the problem has been that, in species other than
the mouse, once the embryo cells containing the gene are
transferred into a developing embryo and that embryo develops
into adulthood, the animal does not produce functional eggs
and sperm. Therefore, the gene cannot be passed on to
subsequent generations.

``Getting embryonic stem cells to develop into functional eggs
or sperm once they were placed in an embryo has been the holy
grail for us,'' Collodi says. ``Recently, we've been able to grow
these cells in the lab and then transfer them into a zebrafish embryo.

We've been able to show that the cells contribute to the germ line
of the embryo. That's a big advance for us.''

However, Collodi says the next step is to extend the length of
time cells are kept growing in the lab so that gene can be inserted.
`We've been able to grow the embryo cells in the laboratory for
a short time. Now we have to extend the length of time. If we want
to make a knockout we have to be able to keep the cells growing
in the laboratory for several weeks. Now they last just a few days.''

Collodi's technique was published in the Feb. 27 issue of the
Proceedings of the National Academy of Science, and was
funded by Sea Grant and the U.S. Department of Agriculture.

Mark Hermodson, head of Purdue's Department of Biochemistry,
says genetic sequencing information will mean little if the
function of the proteins isn't discovered.

``But traditionally that's been fairly unproductive work, to be
honest,'' he says. ``The straight genetics approach is to knock
out the gene in genetically modified mice and see what symptoms
arise. That's very tedious and expensive. Transgenic mice are not
cheap.''

Zebrafish, on the other hand, can be raised in standard 20-gallon
aquariums by the thousands.

Although this is basic research, Collodi says the technique might
help advance several fields.

``From an agricultural point of view, transgenics and gene
knockouts can be used to control reproduction, disease rate,
growth rate and many things that are very valuable in livestock,''
he says. ``This technology could be used to make sterile animals
so that transgenic animals can't breed if they escape to the
environment.''

Related Web sites:
Collodi's Web page: http://www.ansc.purdue.edu/faculty/collo.htm
Hermodson's Web page: http://www.biochem.purdue.edu/hermodson.htm
Zebrafish information network: http://zfish.uoregon.edu/

Media Contact:
Paul Collodi, Animal Sciences, 765-494-9280; pcollodi(at)ansc.purdue.edu
Randy Woodson, Office of Agricultural Research Programs, 765-494-8362; wrw(at)aes.purdue.edu
Steve Tally, Purdue News Service, 765-494-9809; tally(at)aes.purdue.edu
Mark Hermodson, 765-494-1637; hermodson(at)aclcb.purdue.edu

PHOTO: A publication-quality photograph is available at
http://news.uns.purdue.edu and at http:ftp://ftp.purdue.edu/pub/uns/.
Photo ID: Collodi.zebrafish
PHOTO CAPTION: Purdue animal scientist Paul Collodi peers through
an aquarium full of zebrafish in his laboratory. Thanks to recent
developments in his lab, the familiar tropical fish may soon be used
by scientists to discover new insights into the genetics of diseases.
(Purdue Agricultural Communications photo by Tom Campbell.)

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