PGD. Notably, these included nocadazole and cytochalasin B, which depolymerise microtubules and microfilaments, making the cytoplasm and cell membranes less rigid and therefore less prone to damage when removing karyoplasts. Both drugs can disrupt chromosome segregation and cell division. However the panel was reassured that there is substantial evidence to show that these agents wash out easily and, as long as that is done, they should not persist to stages that might be affected. To reintroduce the isolated karyoplasts into the enucleated recipient oocyte or zygote, it is necessary to use cell fusion. Inactivated Sendai virus, which is both gentler and more efficient than other methods18, was found to be necessary in both the rhesus macaque monkey and human studies. It is essential that the Sendai virus is properly inactivated and that this procedure is performed in a separate facility. As long as care is taken, the use of this fusogen should be entirely safe. Prior to MST or PNT methods being used clinically, the safety of all the procedures will need to be subject to proper safety and risk assessment, as with any similar procedure.
4.3.4 Nuclear-mitochondrial interactions: A concern has been raised that there might be a failure of correct nuclear-mitochondrial interaction following MST or PNT because the donor mtDNA may be of a haplogroup different from that with which the maternal nuclear genome has been functioning. Mitochondria from separate human lineages can be classified according to similarities or differences in their DNA sequence into many different haplogroups. The more evolutionary distant the separation of two maternal lineages, the greater the differences between mitochondrial haplogroups. This is as typified by comparisons between European and African mtDNA. However, there is no evidence for any mismatch between the nucleus and any mtDNA haplogroup, at least within a species. Fifty per cent of nuclear genes are paternally inherited and are consequently alien to the mtDNA; backcrossing can replace the nuclear DNA entirely in a few generations. Furthermore, mitochondrial disease has not been noted to be more frequent amongst mixed-race children. However, if further concerns were raised, it would be possible to match mtDNA haplogroups from the egg donor and the mother.
18 A variety of electrical and chemical methods (electrofusion or polyethylene glycol) are typically employed in similar experiments involving rodents and domestic animals. However, the original method as developed in mice by McGrath and Solter made use of inactivated Sendai virus.
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