Chinese scientists in Shanghai have successfully cloned two identical long-tailed macaques, named Zhong Zhong and Hua Hua.The pair were born a in December 2017 and are the first primates to ever be successfully cloned.
Critics say that this opens the door to human cloning, although Mu-ming Poo, director of the Institute of Neuroscience at the Chinese Academy of Sciences said, “I would think that the society and general public and the government will not allow the extension of application of these methods from non-human primates to humans.”
Instead, the goal is to create cloned monkeys that can be used to study human genetic diseases, said Poo, who co-authored a new study describing the results.
Like Dolly the sheep, the first animal successfully cloned (in 1996), the two baby monkeys were created in a process called somatic cell nuclear transfer. Researchers take an egg cell, or oocyte, and remove its nucleus (which holds its DNA) for this procedure. Then, they take a body, or somatic, cell from the animal they’d like to clone and remove its nucleus, transferring that nucleus into the empty egg. The cell is then allowed to divide and grow for a number of days to reach a multicell blastocyst stage. The blastocyst is then implanted in a surrogate mother monkey’s uterus to develop into a fetus and, hopefully, a baby.
Scientist have cloned other animals such as mice, rats dog and cows, but up until now no one has been able to clone a nonhuman primate, said Poo.
“Maybe the differentiated somatic nuclei of the primate species are unable to express the genes that are required for embryo development,” he said.
According to the researchers, the breakthrough in primate cloning was in reprogramming the donor nuclei. They did not alter the DNA sequence itself to do this reprogramming, but rather the way that individual genes were expressed in a process known as epigenetics. This allowed the scientists to reactivate the genes required for embryonic development. Zhen Liu, a study co-author and postdoctoral researcher at the Institute of Neuroscience said that the technology required to do this epigenetic modulation was developed in the past few years.
The researchers created 79 cloned oocytes that were implanted into 21 surrogate mothers, using connective tissue cells, called fibroblasts, from the fetuses of long-tailed macaques (Macaca fascicularis) as donors. Six pregnancies occurred and two developed to full term.
The researchers also tried cloning cells from adult monkeys, with less success. Poo explained that it is likely that adult cells are harder to reprogram than more flexible fetal cells.
Fetal fibroblasts are easy to grow in the laboratory, and they are also easy to edit genetically. The goal, said Poo, is to introduce genetic mutations of the same sort that cause human diseases such as Parkinson’s.
“Then, the clones will be [an] ideal model for that particular disease, for screening drugs that will cure the disease,” Poo said.
The researchers hope to produce gene-edited macaque clones to do this kind of research within a year.