Cloning issues in reproduction, science and medicine : a consultation document / Human Genetics Advisory Commission and Human Fertilisation & Embryology Authority.

  • Great Britain. Human Genetics Advisory Commission.
Date:
1998
Catalogue details

Licence: Open Government Licence

Credit: Cloning issues in reproduction, science and medicine : a consultation document / Human Genetics Advisory Commission and Human Fertilisation & Embryology Authority. Source: Wellcome Collection.

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    Annex C EXPERIMENTS WHICH LED TO DOLLY AND SUBSEQUENT DEVELOPMENTS The first evidence that it was possible to clone vertebrate animals using nuclear replacement was in 1952. The first series of experiments, using cells from tadpoles as the source of donor nuclei, produced adults but at a very low efficiency. Although the cells used were highly specialised, they were not derived from adult frogs, so the cells might not have been fully differentiated. Later, clones of tadpoles were obtained by nuclear transfer from differentiated adult frog skin cells to an enucleated egg establishing that differentiation of cells involving selective gene expression does not require the loss or irreversible inactivation of genes. No viable adult frog developed from these tadpoles. In contrast, cloning by embryo splitting, from the 2-cell up to the blastocyst stage, has been extensively used in sheep and cattle to increase the yield of progeny from genetically high grade parents. Embryo splitting was first used to produce genetically identical sheep ten years ago at Cambridge. This technique has been used extensively in sheep since then. Because of the different pattern of early development, embryo splitting is much less successful in mice. From a scientific point of view, it would probably not be very effective in the human, although monozygotic (one-egg) twins and higher multiples occur naturally at a low incidence. The Ministry of Agriculture, Fisheries and Food (MAFF), the Biotechnology and Biological Sciences Research Council (BBSRC), industry and the European Union have funded research at the Roslin Institute on the development of nuclear replacement technology since 1991 because of its potential to contribute towards genetic improvement of livestock. In announcing the birth of two genetically identical normal lambs (Megan and Morag) in 1996, the Roslin Institute reported a new method of cloning sheep embryos, which involved first establishing cell cultures from single embryos. Nuclei from the cultured cells were transferred to enucleated unfertilised sheep eggs, particular attention being paid to the cell cycle stage of both donor and host cells, and the eggs were then artificially stimulated to develop. More recently, in creating Dolly, the Roslin Institute transferred a nucleus from a cell culture of adult sheep cells. Dolly appears to be the first and only example of an adult vertebrate which has been cloned from another adult. However, it has yet to be established whether the transferred nucleus was from a differentiated mammary gland cell or from a stem cell. It is not clear whether Dolly is normal or whether she could have subtle problems that might lead to serious diseases. Concern has been expressed that the use of an adult donor cell will have effects on ageing a