The researchers froze dried skin cells from the tails of mice and stored them for up to nine months before trying to create clones of them. The freeze-drying process killed the cells, but the scientists found that they could still create early-stage cloned embryos by placing the dead cells into mouse eggs that had their nuclei removed.
These early-stage mouse embryos, known as blastocysts, were used to create stem cell stocks that underwent another round of cloning. Stem cells were injected into mouse eggs that lacked their own nuclei, resulting in embryos representative of term-delivered mice. The first cloned mouse was followed by 74 more. To test whether the clones had healthy fertility, nine females and three males were crossed with normal mice. All females gave birth.
Despite the results, the process was inefficient – freeze-drying damaged the DNA in skin cells – and the success rate in creating healthy male and female rat mice was only 0.2 to 5.4%. In some cells, the Y chromosome was lost, resulting in female mice being born from cells obtained from male animals.
Source: Ferra