Cloning animals can become more effective
Embryologists have found out the reasons for the failures of cloning experiments
Scientists from the USA and France studied gene expression as clones develop and found out why most cloned embryos die in the early stages of development. The scientists presented their findings on the pages of the Proceedings of the National Academy of Sciences (Biase et al., Massive dysregulation of genes involved in cell signaling and placental development in cloned cattle conceptus and maternal endometrium).
It's been 20 years since the successful cloning of Dolly the sheep. The animal was cloned by transferring the nucleus of a somatic cell into an egg. In this process, the nucleus from the adult cell is transferred to an unfertilized egg, from which its own nucleus is previously removed. With the help of an electric "shock", embryologists activate cell growth, and then implant the resulting cell into the uterus of a surrogate mother.
However, the probability of successful cloning of cattle is still extremely low. Less than 10% of the total number of cloned animals survive to birth. Among the reasons for such failures: embryo death, failure in the implantation process and the development of a defective placenta.
Embryologists decided to examine tissues from cloned cow embryos obtained from the same cell line on the 18th and 34th days of development. The scientists also examined uncloned cows conceived by artificial insemination.
Using RNA sequencing, embryologists examined gene expression in cloned cows during implantation and found several genes with abnormal expression. Such expression can lead to the rapid death of cloned embryos. Studying the extraembryonic tissue of cloned cows on the 18th day, the researchers found anomalies in the expression of more than five thousand genes.
On the 34th day of development, the nature of gene expression in cows conceived by artificial insemination changed, and the surviving cell clones were able to successfully implant into the uterus and begin to form a placenta.
"Our results confirm that the interaction between the uterus and extraembryonic tissue is crucial during implantation," said study co–author Oliver Sandra. "Now we understand why cloning experiments fail, and we can improve this process."
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16.12.2016