Chinese scientists have officially announced an important achievement. They note that previously known cloning technologies were not suitable for this species, so it was necessary to slightly complicate the procedure by which the famous sheep Dolly was cloned.

Detail

The rhesus macaque is one of the most common primate species. They are adapted to living in a wide variety of conditions. These animals are among the animals raised in vivariums and used for medical, ethological and neurobiological research.

They initially tried to use the traditional SCNT method for cloning, thanks to the emergence of Dolly the sheep. In the case of SCNT, the nucleus of a somatic cell (i.e., a cell not intended for direct reproductive purposes) is transferred to an egg cell whose nucleus has been previously removed. Very few embryos survive in this method. Despite this, scientists have managed to obtain clones of various animal species, especially the Javan macaque (Macaca fascicularis). Rhesus macaques would be the second monkeys to be cloned, but technology stopped working on them; It turned out that none of the implanted embryos were viable.

To find out what the problem was, researchers from the Chinese Academy of Sciences in Shanghai compared 484 SCNT embryos obtained from rhesus macaques with 499 embryos obtained through traditional in vitro fertilization. Both types of embryos developed similarly before being transferred to the surrogate mother. then the clones started to fail.

Further studies showed that structural changes occur that affect the activity of genes without changing the DNA sequence. Genes that are often “read” differently from the maternal and paternal genomes during fetal development have lost their distinct structures in cloned embryos. This “brazenness” was particularly strong in placental cells; These cells also turned out to be thicker than they should be and contained other defects.

To solve the problem, researchers developed a method that involves replacing the trophoblast, the outer layer of cells in the developing embryo that will later form the bulk of the placenta. It was removed from SCNT embryos and replaced with trophoblasts from IVF embryos (in vitro fertilization). The embryo received a natural placenta, but the fetus itself remained a clone.

Thus, it was possible to reduce the likelihood of developmental defects. A total of 113 cloned rhesus macaque embryos were created, 11 of which were implanted into seven surrogate mothers, resulting in two pregnancies. In one case, twins died on day 106 of pregnancy (rhesus macaques are pregnant for 164 days). The second animal gave birth to a healthy male rhesus macaque named ReTro. He has been alive for 17 months.

According to Nature, the method that gave birth to ReTro is less efficient than SCNT. But cloning monkeys is an important tool for scientists. These same primates are important for studying diseases such as depression and anxiety and for evaluating the effectiveness and safety of medications, especially antidepressants; thus, the effects of the drugs can be monitored in both animals.