Chinese scientists have successfully cloned a rhesus monkey (Macaca mulatta) using a novel procedure that solves common developmental abnormalities seen in cloned embryos. Notably, rhesus monkeys are phylogenetically similar to humans, sharing approximately 93% of their DNA, making them useful models for studying human physiology, anatomy, and disorders. The new process differs from that used to clone Dolly the sheep. The monkey, dubbed ReTro, is already over two years old, a significant milestone in primate cloning.
Traditional cloning techniques, such as somatic cell nuclear transfer (SCNT), have generally resulted in low birth and survival rates for cloned embryos
For the first time, researchers at the Chinese Academy of Sciences in Shanghai successfully cloned a rhesus monkey using a modified cloning approach that involved replacing the cloned embryo’s placenta, which plays an important role in supporting the growth and development of the fetus, with a placenta from embryos produced through in-vitro fertilisation (IVF). By doing so, the scientists decreased developmental abnormalities that normally prevent cloned embryos from surviving, resulting in the species’ first successful cloning.
Traditional cloning techniques, such as somatic cell nuclear transfer (SCNT), have generally resulted in low birth and survival rates for cloned embryos, particularly in monkeys. This is the process used to clone Dolly the sheep and other mammals. Previous attempts to clone long-tailed macaques in 2018 resulted in only two surviving monkeys from 109 cloned embryos. In 2022, a rhesus monkey cloned by SCNT lived for fewer than 12 hours.
The researchers implanted 11 cloned rhesus monkey embryos into seven surrogates, yielding two pregnancies
The researchers discovered that placentas were not altered during the cloning process, which resulted in aberrant development. To address this issue, instead of using the entire cloned embryo, including the outside layer forming the placenta, scientists isolated the inner cells contributing to the animal’s body development and transplanted them into a non-cloned outer embryo. This novel method was intended to promote the formation of a normal placenta. This resulted in the development of a “natural placenta” while keeping the fetus’ cloned nature.
The researchers implanted 11 cloned rhesus monkey embryos into seven surrogates, yielding two pregnancies. One of the surrogates gave birth to ReTro, a healthy male rhesus monkey who has lived for almost two years. However, there are still hurdles to improving the cloning process. According to LluÃs Montoliu, a geneticist at the Spanish National Center for Biotechnology, cloning studies with low efficiency can be challenging to achieve success. Scientists hope to use cloned monkeys for drug testing and behavioural studies, reducing the number of animals required in trials and eliminating genetic background contamination.
