Unfertilised mouse eggs used in successful nuclear transfer

Scientists in Japan have succeeded in performing cell nuclear transfer on mouse eggs left unfertilised after IVF. Lead scientist on the study Teruhiko Wakayama said, 'Before our findings, it was believed that only fresh eggs could be used. But if incompetent eggs can be cloned, then scientists could be given eggs that failed to be fertilised and would have been abandoned in fertility clinics'. The study appears in the latest issue of the journal Current Biology.

The team selected unfertilised mouse eggs six hours after insemination to act as nuclear recipients in a standard cloning procedure, in which the nucleus of the oocyte is removed and replaced with a donated one. The cells used to donate the nuclear material were selected from various mouse strains, including one that had been engineered to express green fluorescent protein. Rates of cloning were lower in the earliest stages of the procedure when compared to fresh eggs undergoing the same experiment. Once the procedure was successfully underway however, the proportion that proceeded normally evened out. They also found that egg cells stored at room temperature for a day showed similar rates of success in this type of cloning.

It is not yet clear whether the same outcomes would be derived using human eggs but the research has implications due to the controversy that surrounds the question of asking women to donate fresh eggs for this type of research. In the routine practice of IVF a proportion of extracted oocytes fail to fertilise and are discarded. Scientists in this study have named these eggs 'aged, fertilisation-failure' (AFF) oocytes. It is thought that using these eggs to perfect the technique of cell nuclear transfer could ease certain ethical concerns, particularly those concerning the potential harm to the women donating eggs for research, but not eradicate them altogether.

Caution was also expressed about the practical application of Professor Wakayama's research. Motoya Katsuki, President of Japan's National Institute of Basic Biology pointed out that, 'Scientists have never succeeded in creating a cloned organ that functions without problems, and most cloned animals so far - whether they are cows, rats or mice - have been sick and died young. You can't transplant sick organs to patients. Thus we haven't even reached the level of discussing the ethical issues in such medical science'. Professor Wakayama, who carried out the research at the Japanese government funded Riken research foundation, addressed the final concern toward this type of research when he insisted that the cloned embryos could not develop into cloned animals, telling reporters, 'A cloned embryo made of aged eggs which failed to fertilise is unlikely to have the capability of developing into a full offspring'. Such embryos could instead potentially be used as a source of embryonic stem cells.