Download Purdue Agricultures Cellular clues Animal sciences researchers

Cellular clues
Animal sciences researchers look for links
between egg quality and disease development
By Susan A. Steeves
C
hronic cramping in her left foot was Linda Hinkle’s first clue that something was wrong. A twitch in her left ring
finger and then stiffness in her neck and shoulder areas were the next symptoms.
It took a year, but, at age 56, Hinkle finally had the diagnosis—Parkinson’s disease, an ailment that causes tremors in
limbs, rigidity, slowness of movement and loss of balance. Most people have heard of the disease because of famous
people stricken with it—Katharine Hepburn, Pope John Paul II, Mohammed Ali and Michael J. Fox.
Whether in well-known people or your neighbor, Parkinson’s can progress at various rates and affect each person
somewhat differently. These variations explain why sometimes diagnosis takes a long time and the illness sometimes
initially is thought to be a different neurodegenerative disorder, such as multiple sclerosis or Alzheimer’s disease.
Purdue University researchers are investigating very basic factors that may underlie disease development. Their work
could lead to new treatments and even cures for Parkinson’s, which develops in adulthood, and many other illnesses.
Eggs, the single cells that create life
Three Purdue Agriculture scientists are focused on the egg, or oocyte, the single cell in all vertebrate animals that joins
with sperm to trigger cell division, the beginning of an embryo. They want to determine why some eggs develop into
embryos while others don’t, and why some embryos develop abnormally.
What researchers Rebecca Krisher, Zoltan Machaty and Ryan Cabot learn will aid in finding answers to what triggers
many diseases, from infertility to Parkinson’s.
All three animal scientists are members of the Center for Comparative Medicine, a collaboration between Purdue
University’s Department of Animal Sciences and School of Veterinary Medicine and the Indiana University School of
Medicine. Researchers from the center are devoted to studying genes and disease processes that are the same or similar in
both animals and humans.
Krisher, Machaty and Cabot are asking two fundamental questions: “How does egg quality affect its development?”
and “What factors impact egg quality and newly fertilized eggs and embryos?”
“The more I learn about oocytes, the more I realize how important they are in development,” Krisher says. “They have
an effect on embryo development, fetal development, postnatal development. They affect the development processes of a
lot of different cells. We have evidence from work in mice that quality of the egg and how it is manipulated in the lab can
cause adult-onset diseases.”
Nuclear transfer to pinpoint diseases
This potentially explains why only 1 percent of the 500,000 U.S. Parkinson’s cases and 6.3 million worldwide are
considered inherited, according to the National Institutes of Health’s National Institute of Neurological Disorders and
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Stroke. Hinkle doesn’t know why she developed the disease. “No one in my family had it, and I didn’t know anyone with
it. I come from a long line of healthy people.”
One tool that aids Purdue researchers in their quest to explain such sporadic disease is called “nuclear transfer.” This
technique allows scientists to make the earliest stage of an embryo—a zygote—in the laboratory. Nuclear transfer is how
the cloned sheep Dolly was produced in a Scottish lab in 1996.
Nuclear transfer involves removing the chromosomes from an animal’s egg and then fusing the “enucleated egg” to a
cell from the same type of animal. Machaty, Krisher and Cabot use pig eggs for this process. The donor cell, which
replaces the egg’s DNA-carrying nucleus, carries new DNA, the blueprint that will produce desired traits. Producing
livestock this way can create animals such as pigs with less fat or sheep with more wool. Nuclear transfer also has opened
an important research avenue—the possibility of producing animals that can serve as research models to investigate
human and animal diseases.
“Nuclear transfer is a tool for production agriculture as well as for biomedical research models,” Cabot says. “Using
that technique, scientists can learn a lot of the basic information we need to answer many questions about disease by
making pigs that demonstrate human disease, called ‘models,’ or pigs that have improved production traits.”
Animal models to study disease
Animal models can facilitate researchers’ probes into why the biochemical malfunctions of genes, and proteins they
manufacture, cause Parkinson’s, diabetes, infertility and a myriad of other disorders. Currently, most animal models for
diseases are mice, rats, Drosophila (fruit fly), C. elegans (a tiny, almost-microscopic worm) and even zebra fish.
Machaty and Purdue College of Pharmacy researcher Chris Rochet say that the points at which proteins abnormally
connect with other molecules can cause disease. “Proteins interacting with each other cause biochemical reactions that tell
cells how to behave,” Machaty says. “They can determine whether a brain cell—a neuron—will live or die.”
Protein interaction is one area that Rochet studies in his research, which focuses on neurological and muscular
disorders. In Parkinson’s, which is one of those illnesses, something causes cells that manufacture a chemical messenger
called “dopamine” to die. Dopamine, which affects brain processes that control movement, is manufactured in a part of
the brain called the “substantia nigra.”
Rochet uses neurons from mice, rats and human patients for his research in lab dishes. He also collaborates with
scientists who use mice and rat models to investigate Parkinson’s and other degenerative neuromuscular diseases.
Although mice and rat models that have defective genes linked to Parkinson’s are available, none fully exhibit the
disease. Because of that deficiency, a model closer to human physiology would help advance Parkinson’s research, Rochet
says. “There is speculation that the rodent dopamine-producing substantia nigra system is somewhat different from that
in people,” Rochet says. “Pig models might be a good compromise. I’m excited about that possibility.”
One hindrance to creating a viable Parkinson’s pig model for research is the extremely low success rate of producing
full-term animals through nuclear transfer. Only 1 to 3 percent of the zygotes produced with the technique develops to
full term and becomes a viable animal. Purdue’s animal sciences researchers want to improve the odds by discovering
how egg quality and manipulation affect nuclear transfer and fertility.
“Pigs would be an excellent model because they are much closer to human makeup than are mice; a pig embryo is
roughly the same size as a human embryo,” Cabot says. “But, if we want to use the pig as a model for specific types of
human disease, to test different production characteristics or to produce pigs with resistance to disease, we need to
understand what affects the survival and development of the egg.”
What eggs need
Putting the pig eggs and cells through nuclear transfer or in-vitro fertilization will help explain how those
manipulations allow or hinder embryo development. It also will reveal what eggs and embryos need to grow both in a
natural pregnancy and in a laboratory dish. Human in-vitro fertilization success rates could benefit from animal research,
Krisher says.
Seeing how the egg and zygote develop means finding ways to improve reproduction in livestock, humans and
endangered animals, she says. She already has demonstrated with laboratory animals that biochemical processes in
oocytes affect establishment of pregnancy, embryonic survival, fetal development and adult onset disease. “If we can
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produce better embryos by improving egg quality, then we may be able to create models to study diseases like
Parkinson’s and infertility so we can find better treatments and cures,” Krisher says.
That would mean a lot to people suffering from neurodegenerative disorders, like Hinkle. Although she participates in
a boxing class and
water aerobics and tackles such ad-ventures as a week at Disney World with her two grown
children and their families, she admits that the disease has slowed her down.
Helping patients
Currently, Hinkle takes a cocktail of medicines. When she gets tired she goes into the “shuffle mode,” a common
complaint of Parkinson’s sufferers. She doesn’t work anymore and doesn’t drive much, except to her exercise classes and
grocery shopping. A friend and fellow Parkinson’s patient wants her to go to Europe for 12 days. “In the past, I would
have just gone, but I’m not sure about that type of trip now,” Hinkle says. “Sometimes, when I’m shopping with family or
friends, I get tired and just say, ‘Park me here.’”
At age 60, a very upbeat Hinkle is handling the disease and its effects quite well. For that, she says, her doctor, Joanne
Wojcieszek, deserves much of the credit.
Wojcieszek, an IU School of Medicine associate professor of neurology and director of the IU Movement Disorder
Center, says that Hinkle is a textbook case of spontaneous, or sporadic, non-inherited Parkinson’s disease. Eighty-five
percent of Parkinson’s cases are spontaneous and are diagnosed in people at about age 60. Inherited cases are those
caused by a malfunctioning gene, and the disease usually is identified before the victims are 40 years old.
“Exercise and reducing stress are important for managing Parkinson’s disease,” Wojcieszik says. “These lifestyle
adjustments also can help minimize the amount of medication the patient needs.”
From lab to patient
But basic research is the first step to determine causes of disease. According to the National Institute for Neurological
Disorders and Stroke, it was just in the past decade that scientists realized some Parkinson’s cases are inherited. Studying
when and why the involved genes and proteins don’t function properly may uncover causes for both inherited and
sporadic instances of the illness, the institute’s experts say.
Purdue researcher Machaty says that he, Krisher and Cabot believe their research will answer some questions and
eventually help people like Hinkle. “Theoretically, it’s possible to make copies of animals with certain traits—transgenic
animals—to improve them,” Machaty says. “The importance to human medicine is that we could make models to
understand the biochemical mechanisms of certain human diseases. Our research may aid in developing and testing new
drugs and finding cures. The bottom line is how our research into egg quality and nuclear transfer can contribute to
progress in treating everything from infertility to Parkinson’s disease. We think it will be significant.”
Contact Susan A. Steeves at [email protected]
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