For the first time, scientists say they created cloned primates using the same complicated cloning technique that made Dolly the sheep in 1996.
Shanghai scientists created two genetically identical and adorable long-tailed macaques. The monkeys are named Hua Hua and Zhong Zhong, a version of the Chinese adjective Zhonghua which means the “Chinese nation” or “people.”
The research was published in the journal Cell on Wednesday.
These two are not the first primates to be cloned. Scientists in 1999 created Tetra, a rhesus monkey, but used what researchers consider a simpler cloning method that produces a more limited number of off spring. In Tetra’s case, scientists split the embryos, much like what happens naturally when identical twins develop.
In the case of Hua Hua and Zhong Zhong, researchers used modern technology developed only in the last couple of years to enhance the technique used to clone Dolly, which is called somatic cell transfer, or SCNT. This is where scientists reconstruct an unfertilized egg. The researchers remove the egg’s nucleus — the part of the cell that contains most of its genetic information– and replace it with the nucleus from another cell. It’s then stimulated to develop into an embryo, which is transplanted into a surrogate mother. That same cell cluster can make more genetically matched animals.
When scientists made Dolly the sheep, years after she was born they used the same cell cluster to make four other sheep clones.
How it worked
The SCNT technique has worked to create about 20 different animals including frogs, mice, rabbits, pigs, cows and even dogs, but there have been “numerous attempts to clone non-human primate species, but they all failed,” said Mumming Poo, an author on the paper. Scientists long thought something in a monkey’s genes made the technique unsuccessful. The success of Poo’s team came from several factors, he said.
The team tweaked the SCNT procedure using new technology that helped with the nucleus transfer and the fusion of cells. The team spent three years perfecting the delicate procedure. Speed while performing the procedure helped, they learned, and scientists discovered clones created out of cells from fetal tissue did better than when they used adult cells.
“By optimizing the method, we obtained 79 well-developed embryos and implanted them in 21 female monkey surrogates,” Poo said. That resulted in six pregnancies and the births of the two monkeys in late 2017. They hope more monkey babies will be born soon from these embryos.
Scientists unaffiliated with the experiment say the limited success rate of the procedure suggests more work is needed before this practice becomes common. “While they succeeded in obtaining cloned macaques, the numbers are too low to make many conclusions, except that it remains a very inefficient and hazardous procedure,” said Robin Lovell-Badge, an embryologist and head of the Division of Stem Cell Biology and Developmental Genetics at the Francis Crick Institute.
“You do have to start with proof of principle,” said Jennifer Barfield, an assistant professor in biomedical sciences at Colorado State University, about the low number of births. She is not affiliated with the new study, but is working on reproductive technology research involving buffalo. She found the work interesting and important, “particularly for primates, where success hasn’t been that easy to come by.”