A team of scientists from the Riken Centre for Developmental Biology in Kobe, Japan have cloned healthy mice from the cells of animals frozen 16 years ago. The technique they used involved taking the nucleus of a cell from a frozen mouse and injecting it into a mouse egg from which the nucleus had been removed - SCNT (somatic cell nuclear transfer). The team, headed by Dr Teruhiko Wakayama, published the study in Proceedings of the National Academy of Sciences.
The findings came as a surprise for two main reasons. Firstly, the team found that it was easiest to clone mice from thawed brain cells; clones have never before been created from brain cells. Secondly, the frozen cells had burst and the existing wisdom has always said that DNA from burst cells would be too badly damaged to create clones.
Also, clones have never before been created from tissue frozen without pre-treatment. As a consequence, this study has ignited hope that cloning of endangered species could be helped by zoos freezing animals as they die, without the need for specialist equipment. Robert Lanza of Advanced Cell technology in Massachusetts, US, which has cloned the endangered gaur, said 'Many zoos are not in the position to collect cells and freeze them, but they can put a dead animal in a plastic bag and throw it in the freezer'.
Dr Wakayama and his team have similar hopes for the implications of their work. 'Cloning animals by nuclear transfer provides an opportunity to preserve endangered species,' they wrote, 'However, it has been suggested that the 'resurrection' of frozen extinct species (such as the woolly mammoth) is impracticable, as no live cells are available, and the genomic material that remains is inevitably degraded'.
Many scientists have advised caution, not least because, as Dr Wakayama points out, it is as yet unknown whether sufficiently intact nuclei could be extracted from frozen mammoth cells. Professor John Armitage, director of tissue banking at Bristol eye hospital, pointed out that 'to extrapolate these findings to animals held for thousands of years, perhaps under varying temperature conditions, is still a big leap'.
There are other reasons to be cautious too; there is much work to be done to discover whether these findings are replicable and applicable to larger extinct species; a suitable species would have to be identified to provide recipient eggs and surrogate mothers; and there are ethical considerations. 'You have to think about why you would do it and where you would put it' says Bill Holt, head of reproductive biology at the Zoological Society of London, speaking to the Guardian. 'Let's suppose we create a mammoth and put it in a zoo. Then what? Do we want a herd?'