Monkeys first primates to be cloned with method used to create Dolly the sheep

Researchers from institutions in Shanghai recently conducted a study, published in the Cell journal, to explore how they could enhance the technique used in 1996 to make Dolly.

To do so, they used a procedure known as somatic cell nuclear transfer or SCNT to build two genetically identical macaque monkeys named Hua Hua and Zhong Zhong, who were born about two months ago.

During SCNT, scientists reconstruct an unfertilized egg by removing the egg’s nucleus, which contains much of the DNA. They then replace it with the nucleus from another cell. Once it develops into an embryo, the egg is transplanted into a surrogate mother.

While SCNT has been used to create many animals, including frogs, mice, rabbits, pigs, cows and dogs, the cloning of monkeys, a human primate species, is the first. Tetra, a rhesus macaque born in 1999, was the first ever cloned primate, but the embryo splitting method was used.

Scientists made 79 attempts, which included six failed pregnancies and two clones that only lived a few hours after birth, before finding success. They overcame their challenges by introducing modulators that controlled the genes preventing embryo development and by transferring nuclei from fetal cells as opposed to adult ones. 

"We tried several different methods, but only one worked," senior author Qiang Sun said in a statement. "There was much failure before we found a way to successfully clone a monkey."

"It takes a lot of practice,” coauthor Muming Poo added. “Not everybody can do the enucleation and cell fusion process quickly and precisely, and it is likely that the optimization of transfer procedure greatly helped us to achieve this success."

Their results are significant, because scientists believe their discoveries will help doctors better understand human diseases.

“This will generate real models not just for genetically based brain diseases, but also cancer, immune, or metabolic disorders and allow us to test the efficacy of the drugs for these conditions before clinical use," Sun said.

As for now, the researchers are continuing to monitor Hua Hua and Zhong Zhong, who appear to be active and playful in videos from the lab. They report that they are bottle-fed and are growing normally compared to other monkeys their age. They also expect the birth of more clones within the next few months.