In findings published Wednesday in the scientific journal Cell, a team of scientists from the Chinese Academy of Sciences in Shanghai, China have announced the first-ever cloning of a primate from post-embryonic cells, namely two macaque monkeys. They used somatic cell nuclear transfer, the same method that was used to create Dolly the sheep in 1996.
In somatic cell nuclear transfer, scientists remove the nucleus, which is the organelle that contains the chromosomes, from an unfertilized ovum, or egg cell, and implant the nucleus from a somatic cell, or non-reproductive cell, into that ovum. The ovum is then stimulated and develops in the normal way, growing into a whole organism that has the same nuclear DNA as the donor organism, though it will have all of the ovum’s mitochondria and other cellular machinery. Clones like these have been described as identical twins to their donors, but younger.
The scientists implanted 21 ova into surrogate mother monkeys, resulting in six pregnancies, two of which produced living animals. The young clones were named “Zhong Zhong” and “Hua Hua,” both derived from Zhōnghuá, the Chinese-language word for the Chinese people. They are both cynomolgus monkeys, or crab-eating macaques (Macaca fascicularis). The scientists also attempted to clone macaques using nuclei from adult donors. They implanted 42 surrogates, resulting in 22 pregnancies, but there were still only two infant macaques, and they died soon after birth. The Scotland-based team that created Dolly the sheep in 1996 required 277 attempts and produced only one lamb.
Generally, the older the donor organism, the more difficult it is to get the DNA from the harvested nucleus to reactivate the genes that allow the clone organism to grow. Previous efforts to clone rhesus monkeys (Macaca mulatta) using embryonic donor cells have been successful, but this attempt used significantly older donors: fetal fibroblast cells, which are key cells in connective tissue, and adult monkey cumulus cells.
“We’re excited — extremely excited,” said study co-author Muming Poo. “This is really, I think, a breakthrough for biomedicine.” He went on to say that the cloned monkeys could be used as test subjects for the study of neurological diseases such as Parkinson’s and Huntington’s. Primates are already a popular model organism for neurological studies. In the United States, for example, non-human primates are used in less than 0.3% of all animal experiments, most of them involving neuroscience, and macaques in particular are a well-established animal model of atherosclerosis, which causes heart disease.
“I think it’s a very exciting landmark. It’s a major advance,” agreed reproductive biologist Dieter Egli of Columbia University. “It should be possible to make models of human disease in those monkeys and study those and then attempt to cure it.”
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