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Introducing ANDi: The first genetically modified monkey
  
By Bijal P. Trivedi


ANDi (DNA inserted spelled backward) is the first transgenic monkey.

Oregon researchers have created the first genetically modified monkey. ANDi, a playful, coffee-colored rhesus monkey born on October 2nd 2000, has been engineered to carry a gene from another species. The work demonstrates that a foreign gene can be delivered and inserted into a primate chromosome. The researchers anticipate that gene insertions in the monkey will lead to primate models of human diseases—like Alzheimer's, diabetes, heart disease and obesity—that will offer a more robust testing ground for new drugs, gene therapy and modified stem cells.

"Our ultimate goal is to produce human disease models. Primates show human pathology better than mice, which, in many cases, are the only systems we have for modeling human diseases," says Anthony Chan, of the Oregon Regional Primate Research Center, in Beaverton. The report is published in this week's issue of Science.

Chan's goal was to show that a foreign gene can be inserted into a monkey's chromosome and produce a functional protein. The GFP gene was chosen because the protein it produces emits a fluorescent green glow that can easily be seen through a microscope. Eventually scientists want to insert human disease genes and study disease progression in monkeys, says Chan.

Tissue samples taken from ANDi's cheek, hair, umbilical cord and placenta confirm that the cells contain the GFP gene and corresponding mRNA; the molecule that bridges the gap between DNA and protein. However, when the tissue was examined under the microscope, no green protein could be seen.

"Maybe the quantity of protein is too small to be seen or maybe the mRNA is not being translated," says Chan. The team will continue to monitor ANDi for GFP; some transgenic animals do not produce any foreign protein until after the first year.


(LEFT)Virus particles carrying the GFP gene are injected into the unfertilized egg. The gene (white) is released from the virus and incorporated into the chromosome. (RIGHT)About 6 hours after introducing the virus scientists artificially fertilize the egg by injecting a sperm from a male rhesus. The fertilized egg then begins to grow and divide. Two to three days later when the egg has divided twice and become a four-celled embryo it is implanted into a surrogate mother.

To create ANDi, Chan and his colleagues injected 224 unfertilized rhesus eggs with a virus carrying the GFP gene. The virus's job is to integrate the gene into a random site on one of the chromosomes. Six hours later, each egg was artificially fertilized by sperm injection. Roughly half of the fertilized eggs grew and divided, reaching the four-cell stage. Forty were chosen and implanted into twenty surrogate mothers—two per mother. Of these, three healthy males were born and two twin males were stillborn. ANDi was the only live monkey carrying the GFP gene.

Curiously, green fluorescent protein was produced in both stillborn males. Their hair and toenails had a green glow when examined under fluorescent light. It is not clear whether their deaths were due to the protein or to the twin pregnancy, which is rare and risky in rhesus.

It will take considerably more research before monkeys like ANDi are common research animals in the lab. "We need to become more efficient at producing transgenic animals," says Chan. "We need to learn when is the best time to inject the virus, how long to wait before fertilizing the eggs, and when to implant the embryos. We need to adjust the timing of a lot of steps and make a lot of improvements," he added.

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Chan, A. W. S. et al. Transgenic monkeys produced by retroviral gene transfer into mature oocytes. Science 291, 309-312 (January 12, 2000).
 

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