Download A Yale geneticist and a Chinese lab are creating the Amazon.com of

 A Yale geneticist
and a Chinese lab are creating
the Amazon.com of medical research animals.
Margot Sanger-Katz ’02
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yale alumni magazine | may/june 2010
M
ice like to bury marbles. If
you give a laboratory mouse
a handful of marbles, it will
often bury a few into the bedding in its cage. But one particular mouse in Yale genetics
professor Tian Xu’s lab will bury marbles all day
long. That mouse is missing a gene. Having seen it at
work, Xu and his colleagues now think the gene may
be related to behavioral problems like obsessivecompulsive disorder.
Another mouse of Xu’s appears to have the mouse
equivalent of male-pattern baldness. It grows lovely
white fur all over its body, but its head is bare.
Studying the gene this mouse is missing could help
scientists understand what causes some men to lose
the hair on their heads.
Tian Xu ’90PhD, who has developed an innovative system for easily producing mice missing single
genes, is raising thousands of mutant mice in a
laboratory complex in China—mice that don’t grow
work. Texas A&M Health Science Center professor
Richard Finnell, for instance, studies spina bifida,
a birth defect that can lead to lifelong paralysis. In
2006, he developed a mouse with damage to a gene
called FKBP8, which controls the development of
the spinal column. (He calls the mouse “Stacey.”) He
has used its descendants ever since in his research
on the environmental factors that contribute to the
birth defect.
All told, scientists have so far succeeded in knocking out about a fifth of the 24,000 genes that have
been mapped in the mouse genome. Xu’s break-
fa c i n g pa g e : m a x o p p e n h e i m /g e t t y i m a g e s . t h i s pa g e : c o u r t e s y t i a n x u ’ 9 0 p h d .
At Fudan University, Tian Xu
created a simple system for
disabling genes—a sort of
assembly line for mutant mice.
properly, mice that have kidney disease, mice with
neurological problems, mice that lack sex appeal—
in hopes that researchers around the world can use
those mice to better understand human development and disease. His goal is a “functional map” of
the mouse genome, linking every gene in the mouse
to its function in the species.
Such a tool has never been created for a mammal,
and it could have major implications for human
medicine. Humans and mice share about 99 percent of their genes, making mice, which are small,
inexpensive to raise, and (relatively) short-lived, an
ideal animal model for studying human disorders
and testing possible treatments. Biologists have
been studying mice for decades, using them to learn
about physical and mental development, cancer, and
heart disease, among other subjects. The scientists
who developed the first system for disabling single
genes in mice won the Nobel Prize in Medicine in
2007.
Over the last two decades, scientists who needed
mice missing specific genes have used gene splicing and other methods to engineer them for lab
through, developed at Fudan University in Shanghai,
where he has an adjunct faculty appointment, was in
creating a simple and inexpensive system for disabling different genes quickly and efficiently—a sort
of assembly line for mutants. In the first 18 months
of his project, he’d already reached the 5,000-gene
mark that took previous scientists 20 years.
Instead of the painstaking work of splicing coded
bits into mouse DNA, placing the manipulated DNA
Tian Xu’s mutant mice glow
pink under ultraviolet light,
thanks to a custom-built
piece of mobile DNA.
m a r g o t s a n g e r - k at z ’02 is senior staff editor of the
Yale Alumni Magazine.
yale alumni magazine | may/june 2010
35
years, at a fraction of the cost required to complete
the project the traditional way.
“There’s a significant advantage to doing this
stuff in China, because it’s just so cheap,” says Colin
Fletcher, program manager for the National Institutes of Health’s (NIH) Mouse Knockout Project,
Humans and mice share about
which has funded part of Xu’s research. The project
99 percent of their genes.
is also funding other scientists to knock out 8,500
genes in mouse stem cells using more-conventional
with a disabled gene simply by mating two specially technologies; its goal is to make a complete “library”
prepared mice. One of the mice has a piece of genetic of knockout mouse stem cells available to researchmaterial called a transposon, which can jump within ers. In China, Fletcher says, Xu’s work sees cost
the genome of the reproductive cells, inserting itself savings in building construction and lab equipment,
at random to disable an existing gene. The other but particularly in labor. A technician who would
earn a salary of more than $30,000 in the United
makes an enzyme that activates the jumping gene.
Breed the two together, and each of their offspring States can be hired for about $4,500 in China.
will be born with one inactive gene, a different gene
he breeding facility occupies two of
in each. The process doesn’t require molecular biolothe four buildings in a huge comgists, just skilled technicians who can care for the
plex at Fudan University in Shangmice and run basic tests to determine which gene
hai, the Fudan-Yale Biomedical
is missing.
Research Center. The first buildTransposons are common in plants and insects,
ing, with about 25,000 square feet
and scientists have used a similar technology to
create mutants in insect species. But before Xu, no of mouse space, went up in just six months, Xu says,
one had been able to find a transposon that would and the other buildings followed quickly. The fourth
work efficiently in mammals. And, in a clever twist, and largest addition, still under construction, will
into embryonic stem cells, and then implanting
those cells into pregnant mouse wombs—a process
that can take an individual lab as long as a year and
cost more than $50,000—Xu can breed a mouse
m o u s e i l l u s t r at i o n s : s h o n a g h r a e .
T
Tian Xu’s lab at Fudan
University, in Shanghai,
has created a system for
producing thousands
of mutant mice to help
researchers investigate
the functions of genes
and develop treatments
for disease. The artist’s
conceptions on this and
following pages illustrate
some of the mutants the
lab has already developed.
36
he has figured out a way to color-code the mice so
that technicians can tell instantly whether a mouse
is normal or a mutant: the mutant mice carry a gene
that makes them glow pink under an ultraviolet
lamp.
The mutants are bred in a lab in China large
enough to house 150,000 mice at a time. Overseen
by about 150 Chinese lab technicians and scientists—and U.S. researchers via webcam—the lab is
breeding its way through the mouse genome. Xu
expects to disable nearly every mouse gene in a few
yale alumni magazine | may/june 2010
add 100,000 square feet of space, most of it for mice.
“This really made it possible to do it large-scale,”
Xu says, marveling at the speed of the Chinese
construction effort. The complex not only houses
his project, but also aids Fudan faculty research
and offers training for talented graduate students
and postdocs—some of whom Yale may eventually
attract to do research here.
The collaboration with Fudan was Xu’s own suggestion, in part because he received his undergraduate training in genetics there. He grew up in China,
Tian Xu’s big innovation was finding a special type of mobile
DNA that could jump around the mouse genome and inactivate
genes. To generate new mutants, his lab breeds two special
mice. One is engineered to carry a copy of the mobile genecalled a transposon. The other produces an enzyme that
activates the transposon. When you breed the two special mice
together, each of their offspring will have one gene that’s been
inactivated by the transposon, which inserts itself at random
into the normal genetic material. Because of a special protein in
the transposon, each of the resulting mice will appear pink
under an ultraviolet lamp.
TRANSPOSON
ENZYME
To raise more mice with the same mutated gene, the lab next
breeds a pink mouse to a normal mouse. Because each mouse
has two copies of every gene, and only one copy in the pink
mouse is altered, only half of the resulting offspring will share
the mutation. They can be easily spotted by their color.
c h a r t : m a r k z u r o l o ’ 0 1 m fa .
But mice with one mutated copy of a gene and one
normal copy don’t always demonstrate
mutations. To raise mice with both copies of the
gene inactivated, the lab breeds pink mice from
the same litter together. Some resulting offspring
will be born missing both copies of the gene—and
appear a darker pink.
the son of intellectuals who suffered under the
Cultural Revolution, and is quick to credit Yale for
giving him opportunities—when he was a graduate
student on fellowship who spoke little English and
The lab is breeding its way through
the mouse genome.
when he was an assistant professor with a novel idea
for a project on mice. But he says he is also eager to
give back to Fudan, a school with highly regarded
biology departments and numerous Yale connections. (Xu, who is the vice chair of the Yale genetics
department and holds a prestigious five-year grant
as a Howard Hughes Medical Institute investigator,
is the director of the Fudan-Yale Center.)
In its post-tercentennial push to globalize its
research, Yale has created several such collaborations with Chinese universities. The projects fulfill
President Richard Levin’s mission to “become a
truly global university,” says Fawn Wang of Yale’s
Office for International Affairs, who is tasked with
setting up the Yale-China partnerships. But they also
allow Yale researchers to complete major research
on the cheap. Xu’s mouse buildings were built with
grants from the Chinese government; Yale brought
$1 million in NIH grant funding for the research,
but didn’t raise donor gifts or contribute any money
from its general fund. “This is such a world-class
university,” Wang says. “They can use our name to
apply for money.”
Although costs are low for the lab at Fudan,
Xu says he has been careful to ensure that the lab
maintains the same high standards for animal care
that would be employed in a Yale facility. He works
at the facility for about one week out of every month
and says the mouse areas are climate-controlled,
roomy, and constantly monitored. Fudan is responsible for animal care, but Yale’s contract with Fudan
specifies that it has to meet NIH animal care standards. As with other subcontractors, Yale does not
yale alumni magazine | may/june 2010
37
undertake on-site inspections. But a representative
of Yale’s Institutional Care and Animal Use Committee toured the facility with President Levin when
it opened, Xu says, and pronounced it better than
some animal labs in New Haven. He considers it an
important visit, “so we were not attacked for running a sweatshop.”
the diagnostic work begins even before the mutant
mice are born. About 15 percent of genes appear
to be so vital to survival that mice without them
die in utero. Some of those that survive will have
visible problems: they won’t grow normally, or they
have patchy fur, or they grow tusks. Others require
more advanced testing. Every mouse has its blood
reeding the mice is just the first
step. Because such a small portion of
the genome is currently understood,
Xu’s next project is figuring out what
effect each disabled gene will have
on the development, health, and
behavior of the mice. And diagnosing the problems is a complex business, because Xu’s method of
knocking out genes is random. Unlike the molecular
biologists who disable a selected gene because they
think it may be related to diabetes or cancer, Xu has
The mice get colonoscopies and
CT scans. Motor control is tested
on tiny balance beams.
no way to control which genes will be deactivated by
his breeding process. So when each mouse is born,
he needs to test it for a whole battery of different
abnormalities.
Back at Yale, Xu is at work creating the “most
advanced mouse hospital on earth.” Parts of that
hospital are already functional, in his current lab at
the Boyer Center for Molecular Medicine. A miniature CT (computed tomography) scanner sits in the
corner of a laboratory room, along with a hot plate
(used to detect pain response) and other mousetesting equipment. But the mouse hospital will
soon be a part of Yale’s new West Campus, where
substantial mouse vivarium space will be devoted to
Xu’s project. “I was trained as a PhD in genetics to
become a mouse doctor,” Xu jokes.
Yun You, an associate research scientist at Yale
who is managing the mouse testing effort, says
disorders, and trouble with breeding. Xu hopes this
method will reveal many more genes of medical
importance than would have been discovered the old
way, by guesswork.
As the lab learns more about the function of each
gene, Xu and his colleagues will publish scientific
papers and enter the information about each mouse
into a central Internet database. That website is
already live with about 1,200 known genes. Scientists can use the site as a sort of catalog, then contact
Xu with an order if a particular mutant would aid
their research. Xu wants to create a shopping-cart
system, so that scientists can search for traits and
genes and order frozen embryos or live mice in a few
simple steps.
“They’re all available,” says Jon Soderstrom, managing director of the Yale Office of Cooperative
Research, who is helping Xu patent the mice and set
B
Some mutant mice
develop obvious
problems, like baldness
or difficulty absorbing
nutrition; others require
testing to identify the
functions affected when a
given gene is disabled. This
research is done at Yale.
At first, scientists thought
one particular mutant (at
center) was sterile. After
further investigation, they
found that the mouse’s
reproductive biology was
fine—but females refused
to mate with it.
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yale alumni magazine | may/june 2010
drawn and its heart rhythm scanned. The mice get
colonoscopies, X-rays, and CT scans. Motor control
is tested on tiny balance beams. Mouse memory
is tested using special mazes. Behavior tests look
for depression, fearfulness, obsessive-compulsive
up a for-profit corporation to manage the mouseselling effort. “They’ll all be cataloged, and you’ll
be able to go online and click through and put your
order through.”
That concept is similar to a website the NIH has
built for its knockout mouse project, but is vastly
different from how knockout mice were obtained for
research in the past. Until recently, there has been
no comprehensive database listing knockouts and
because his method creates live breeding pairs. The
NIH library will provide modified stem cells that
are many complex steps away from living research
animals, because scientists must transfer them into
mouse embryos that they then breed for several
generations.
Research has also shown that different mutant
technologies can yield subtly different effects, and
Xu’s mice may be favored by certain scientists. “Our
no reliable way for scientists to put in requests, even
for those mice that were ready. Though Yale’s plan is
to make money from mouse distribution, the project’s overall goal is to make mice widely available, at
lower prices than those of most labs that currently
offer mutant mice to researchers.
Stefan Somlo, a nephrologist who works across
the street from Xu, read an early published report
about Xu’s mutants, and found a mouse that was
perfect for his own work on a common inherited
kidney disease that causes cysts and kidney failure.
He hopes the transposon-created mouse will help
him find out whether therapies that turn the gene
on and off will influence the progress of the disease.
“This is an enabling technology for us,” he says.
work is complementary,” says Kent Lloyd, a veterinarian and research physiologist at the University of
California–Davis who is working on the NIH knockout project.
Xu wants to create a shoppingcart system, so that scientists can
search for traits online and order
live mice in a few simple steps.
Xu’s mice may help
scientists understand the
biological underpinnings
of behavior. His lab at Yale
is looking for mutants that
demonstrate symptoms
of mental illness, like
fearfulness, depression,
or obsessive-compulsive
behaviors. Researchers
have already found one
mouse that obsessively
buries marbles in its cage.
Xu is also carving out his own project in the
mouse genome. He knows that most of the mice he
creates will benefit other researchers, but he’s taken
an interest in a few mutants they’ve already uncovs NIH scientists rush towards a ered. One particularly promising mutant has trouble
similar goal—a complete library absorbing nutrients in its digestive system. It is born
of knockout mice—it is unclear with chronic diarrhea and ultimately dies after sufwhether Xu’s mice will become fering many of the same symptoms seen in starving
the favored research animals or children. Xu thinks the mouse could serve a double
simply one of several options for value. By determining how to improve the effiscientists. But if it works, Xu’s massive experiment ciency of its digestive system, Xu hopes he can help
could serve as a demonstration project for how develop treatments to mitigate starvation in parts
to catalog an entire genome quickly. He’s already of the world where food is scarce. He also hopes the
shown that a similar transposon technology can mouse’s inefficient digestive system will help him
be used to create mutant rats, and he believes it find ways for humans who eat junk food and live
could work in other mammal species that may be sedentary lives to avoid the ravages of diabetes and
preferable for some kinds of research. Moreover, Xu heart disease. It’s a very American question for a
says his mice are likely to be less expensive to use Chinese mouse.
A
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