For the first time, the clone of a monkey, a rhesus macaque, called ReTro, was born healthy and lived for over two years, after the embryo was provided with a healthy placenta. The result, obtained in China, promises to make primate cloning more effective, thus paving the way for the possibility of obtaining stem cell reserves to obtain miniature organs (organoids) with which to study the mechanisms underlying infertility and many diseases that affect humans. Published in the journal Nature Communications, the research was conducted by the Chinese Academy of Sciences.
The result is the result of a huge number of experiments, coordinated by Zhen Liu and Qiang Sun. In 2018, the latter had obtained the first disease-carrying monkey embryos. The first author of the research is Zhaodi Liao. The new method consists of perfecting the nuclear transfer technique that in 1997 had led to the announcement of the birth of Dolly the sheep, the first clone of a mammal. The technique consists of transferring the nucleus of an adult cell, i.e. the structure of the cell that encloses the DNA, into an oocyte deprived of its nucleus; In this way, the cell is induced to regress to a very primitive and undifferentiated stage, to the point that if it is transferred to the uterus it is able to give rise to an embryo.
With this technique, clones of many species of mammals have been obtained since the time of Dolly the sheep. However, in the case of monkeys, especially rhesus macaques, the efficiency of this technique has always been very low, to the point that so far in only one case had an embryo survived birth by a few hours.
That placental development was the weak point of primate cloning emerged when researchers from the Chinese Academy of Sciences compared the genetic characteristics of monkey embryos at a primitive stage of development (blastocysts) obtained by in vitro fertilization and those obtained by cloning. Abnormalities in the development of cloned embryos have been identified, both in the transmission of genetic information to the embryos and the placenta, and in the size of the placenta. To overcome these obstacles, the authors of the research isolated the embryonic tissue that gives rise to the individual (called the internal cell mass) from the one that gives rise to the placenta (trophoblast) and that does not come into play in the formation of the embryo; They then transferred the internal cell mass of the clone to another embryo, obtained with the ICSI technique (which consists of inserting a single sperm into a mature oocyte) and deprived of the cells that give rise to the embryo. In this way, the clone found himself having a healthy placenta. "Using this approach, we obtained the birth of a healthy rhesus monkey clone that survived for over two years," the researchers note. "Although this result concerns only one monkey clone, the new technique could prove successful in being able to clone primates in the future."
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