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from the issue of March 29, 2007
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Research may change views on DNA tests
BY KELLY BARTLING, UNIVERSITY COMMUNICATIONS
A doctoral candidate, a biologist who specializes in fish genetics and a psychologist focused on monkey behavior teamed up to make an exciting new discovery that can change scientists' views of genetic testing.
Their research at the University of Nebraska sheds light on how a pre-birth genetic exchange between marmoset twins plays a part in parenting behavior among the tiny New World monkeys.
Writing in the online edition of the Proceedings of the National Academy of Science, Corinna Ross, now at the University of Texas Health Center, showed how in utero genetic exchange between marmoset twins may help explain the unique patterns of parental care in this primate species. Marmosets (Callithrix kuhlii) typically give birth to twins. Fraternal twins, which develop from two separate fertilized eggs, often exchange embryonic stem cells through shared blood vessels early in development. This exchange produces genetic chimeras, or animals that carry the genes of their siblings in some tissues. Chimerism in marmosets is well recognized in their blood cells and bone marrow but had not been previously described in other bodily tissues.
In the study, Ross, Jeffrey French and Guillermo Orti show that chimerism is common in many of the tissues of twin marmosets, including reproductive cells such as sperm. These chimeric animals can then pass on their sibling's genes to their offspring, producing offspring that are not genetically their own.
"What we've discovered in this animal is that when an individual parents their offspring, they may actually be parenting their brother's offspring," said Corinna Ross, a postdoctoral fellow at UT's Barshop Institute for Longevity and Aging Studies. "And that's very odd - the fact that male marmosets sometimes fertilize their offspring with their brother's sperm."
This ambiguous paternity could underlie the highly cooperative parenting behaviors seen in marmosets - explaining why fathers and unrelated adults often care for infants. This genetic exchange could have driven the evolution of cooperative infant care in this group of primates, the authors suggest.
French said that this discovery, like so many in science, came unexpectedly. Ross initially was looking at different tissues in marmosets to find the best type for DNA paternity testing.
"Initially when I started my dissertation, I was interested in paternity, and whether fraternal twins can have a different father," Ross said.
"Every single tissue she looked at had evidence of chimerism," said French, a recognized expert on marmosets who runs the Callitrichid Research Center at UNO. The marmoset research center studies social behavior, reproduction and hormones of the species. Ross, originally from New York, later worked on her post-graduate studies with Orti at UNL after working in the Callitrichid lab.
"Cory was looking at molecular tools and markers to trace the genes, to see if they're exchanging genes or not. Because she needed individuals of known pedigree to do the genotyping on the tissues, she had access to all that at the marmoset center at UNO through the archiving and record-keeping of the specimens," said Orti, a biologist at UNL who advised Ross on the genetics aspects of the research.
UNO's marmoset colony, established in 1991, provided Ross with a wealth of geneologic information. The history of individuals and family groups is completely detailed and now goes back three and four generations.
The discovery not only opens up new clues into what's underlying the marmoset behavior, but also highlights important areas of research into chimerism, which could affect what scientists believe about DNA testing.
"We used to think chimerism was very rare and always led to negative effects, like sterility. Now, in the marmosets, we know it doesn't necessarily mean sterility, and more is being discovered and written about it all the time. Medical journals releasing papers about human chimerism, and there have been popular programs like the Discovery Channel's "I am my Own Twin." These studies are going to shed new light on paternity testing, what it means to be an individual, and other things that we take for granted," Ross said.
Ross said her current research, which also is using marmoset populations, is on aging and genetics. She said she is privileged to have had great mentors in Nebraska and that "it was a great environment that encouraged graduate students to excel. It led to this publication and being co-PI on an NSF grant. I've been really lucky in my career."
"This is a real tour de force for Cory," French said.
Genetic exchange between marmoset twins
• Study found that chimerism is common in many tissues of twin marmosets -including reproductive cells
• The chmeric animals can then pass a sibling's genes to their offspring, producing offspring that are not genetically their own
• Study suggests that ambiguous paternity could explain the highly cooperative parenting behaviors seen in marmosets -specifically why fathers and unrelated adults often care for infants
• Access the study online at www.pnas.org
GO TO: ISSUE OF MARCH 29
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