BIOTECHNOLOGY - Inshyna N.M. - 2009

CHAPTER 3. CELL ENGINEERING

Animal Cloning

Cloning is a set of Procedures used to obtain clones—genetically identical organisms that serve as exact copies of a single ancestor.

Cloning of Multicellular Organisms is carried out by transplanting somatic Cell nuclei into an enucleated fertilized egg. Using this method, J. Gurdon cloned frogs in 1977. In 1981, L. Shettles obtained 3 cloned human embryos, but halted their development. Later (in 1987), human embryo Cells were separated and a human embryo was cloned up to the 32-cell stage; the resulting embryos were destroyed.

Experiments on human cloning are prohibited. The Council of Europe adopted a convention banning human cloning, which was signed by 19 states. In December 2004, Ukraine adopted a law prohibiting human reproductive cloning. Cloning of human Organs is permitted in Belgium and the Netherlands.

In 1997, Dolly the sheep was cloned, followed by a heifer in 1998, and Drosophila in 2004. Animal cloning is performed through somatic cell nuclear transfer. The Nucleus is removed from a fertilized egg and replaced with a somatic Cell Nucleus; after embryo implantation into the Uterus, an Organism identical to the somatic cell donor develops. The egg donor and the somatic cell donor must not be the same individual.

Fig. 3.1 illustrates the scheme of cloning Dolly the sheep. The nucleus is removed from the egg using a micropipette. Mammary gland epithelial cells are cultured and induced to enter the G₀ phase (resting phase). Cell Fusion is then performed, after which the cells are implanted into the uterus of a surrogate mother, where further embryonic development takes place.

Dolly's case provided the first proof of the pluripotency of a differentiated adult cell nucleus.

It is worth noting that cellular transformation has certain drawbacks. Animals produced by cloning using somatic cell nuclear transfer technology suffer from a high rate of late-term miscarriages and offspring born with congenital defects.

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Fig. 3.1. Scheme of cloning Dolly the sheep

Some scientists have expressed doubts regarding the integrity of the experiment that produced Dolly the sheep. It is believed that the evidence of Dolly's origin is not 100% genetically reliable. The experimenters failed to prove that Dolly and her mother shared identical genetics, making it impossible to definitively establish whether Dolly is truly a clone of an adult animal. The mammary epithelium cells used to create Dolly were taken from a ewe that died 3 years before Dolly was born. The cells had been stored in liquid nitrogen for other purposes. In the sheep cloning experiment, 277 eggs were fused with mammary gland cells, and out of the 29 resulting embryos, only one developed into a viable organism. However, it remains a possibility that the donor nucleus was actually taken from an undifferentiated embryonic cell present within the mammary epithelium of the donor organism. A successful Replication of the experiment would dispel all doubts.