Back is the name of a monkey born on July 16, 2020 in China. It appears to be a normal specimen of Macacus rhesus, but in reality it is a clone. Remarkably, this is the first cloned monkey of this species to survive healthy into adulthood. To announce it in the journal Natural Communications, it was the Chinese Academy of Sciences that achieved this result by perfecting the technique that led to the birth of the first cloned mammal in 1996 Dolly the sheep. The technique used by the Chinese team is called Somatic cell nuclear transfer (SCNT). But what is it made of and what possible uses does it have in the medical field?
The somatic cell nuclear transfer technique for cloning
THE Somatic cell nuclear transfer This is the process that consists of the transplantation of adult cell nuclei into eggs or blastocysts, which, stimulated to develop by electrical or chemical inputs, produce pluripotent cells. The resulting embryo is genetically identical to the donated nucleus and has been used primarily for two purposes: therapeutic and for purposes reproductive. If the embryo is used for tissue development in vitro, the purpose is considered therapeutic, while if it is implanted in a uterus, a clone and the goal will be the reproduction of an individual identical to the donor.
The problems with this technology
In one of the previous cloning experiments using the SCNT technique, only one monkey out of a total of 35 implanted fetuses was born alive, but unfortunately it died the next day. What's happened? Subsequent histological examinations revealed Malformations of the placenta of cloned embryos, particularly noticeable hyperplasia and calcification. In addition, reduced or absent DNA methylation was found in embryos. Imprinting on the genes passed on from the mother by day 17 of embryonic development. What does that mean? In the case of hypomethylation, i.e. a loss of methyl groups in the DNA, instability of the embryo's genome can occur. As for the lack of maternal imprinting, the explanation is somewhat more complex.
Imprinting is an epigenetic process that does not change the sequence of genes, but rather their expression in the individual's phenotype. Imprinting occurs both maternally and paternally and requires that one of the two alleles (expressions, variants) of the same gene be excluded from activation, depending on the sex of the parent from which the chromosome in question comes. If the imprinting is of maternal origin, the maternal allele is silenced and the paternal allele is expressed and vice versa. The loss of maternal imprinting suggested to experts the inheritance of epigenetic abnormalities of somatic cells during SCNT cloning.
The SCNT-TR technique used to clone the retro monkey
To address these issues, researchers incorporated a strategy called Trophoblast Replacement (Throphoblast Replenishment TR) into the SCNT protocol, thereby obtaining the SCNT-TR technique. THE TR method consists of injecting the inner cell mass of embryos obtained using the SCNT technique into the blastocele (from which the cell mass is extracted) of embryos that have undergone intracytoplasmic sperm injection (ICSI), a medically assisted reproductive technique that is already regularly used in human conception. With this methodology, Retro was born.
What are the effects?
The news of the birth and continued existence of Retro for more than two years is fundamental for at least two reasons: the first is the previous one No M. rhesus monkey has been cloned using the SCNT technique, the same as for Dolly the sheep. The second reason is thismedical application of the TR technique, which would repair damage to the developing trophoblast by replacing dysfunctional cells with healthy cells, thus preventing the development of fertilized embryos. This would be a promising strategy to improve the success rates of assisted reproduction.