ReTro: The first long-lived rhesus monkey clone

Scientists in China have reported the successful cloning of a rhesus monkey using somatic cell nuclear transfer, a technique that was used to create Dolly the sheep. The cloned monkey, named ReTro, has survived for more than two years, making it the longest living clone of its species.

Somatic cell nuclear transfer (SCNT) is a method of cloning that involves transferring the nucleus of a body cell, such as a skin cell, into an egg cell that has had its own nucleus removed. The egg cell, which now contains the donor’s DNA, is then stimulated to start developing into an embryo. The embryo can be implanted into a surrogate mother, where it can grow into a baby that is genetically identical to the donor.

ReTro: The first long-lived rhesus monkey clone
ReTro: The first long-lived rhesus monkey clone

SCNT has been used to clone various mammals, such as sheep, cows, pigs, and dogs. However, cloning primates, such as monkeys and humans, has been much more challenging. The first primate clones, two cynomolgus monkeys, were produced in 2018 using SCNT. However, no rhesus monkey, a widely used model for biomedical research, had been cloned using this technique until now.

How did the researchers clone ReTro?

The researchers, led by Falong Lu, Zhen Liu, and Qiang Sun from the Chinese Academy of Sciences, performed a comparative analysis of the genomes and epigenomes of embryos and placentas derived from SCNT and from natural fertilization. They found that SCNT embryos and placentas had abnormal patterns of DNA methylation, a chemical modification that affects gene expression. They also found that SCNT placentas had defects in their structure and function, such as calcification and hyperplasia.

To overcome these problems, the researchers devised a strategy called trophoblast replacement (TR), which involves replacing the outer layer of cells of the SCNT embryo, which forms the placenta, with cells from a normal embryo. They reasoned that this would improve the health and development of the cloned fetus and the surrogate mother.

Using this technique, the researchers produced 109 SCNT-TR embryos and transferred them into 29 surrogate mothers. Only one pregnancy resulted in a live birth, a male rhesus monkey named ReTro. ReTro was born on November 27, 2021, and has been healthy and normal for more than two years. He is the first rhesus monkey clone to survive well after birth using SCNT.

Why is this research important?

The researchers claim that their study demonstrates the feasibility and safety of cloning rhesus monkeys using SCNT-TR. They also suggest that their findings could help improve the understanding and efficiency of SCNT in other mammals, including humans.

Cloning rhesus monkeys could have several applications for biomedical research, such as creating genetically identical models for studying diseases, testing drugs, and developing therapies. It could also help conserve endangered primate species and preserve their genetic diversity.

However, the research also raises ethical and social concerns, such as the welfare of the animals involved, the potential misuse of the technology, and the implications for human cloning. The researchers acknowledge these issues and call for more public discussion and regulation of primate cloning.

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