How Unborn Mice Get to Be Parents

US scientists have created sperm capable of fertilising an egg in a laboratory dish, using embryo stem cells. They hope to use unborn creatures as biological parents of a new generation of mice.

The experiment could lead to better understanding of cancer, birth defects and infertility. It may also one day help researchers turn adult stem cells into new treatments for diabetes, Parkinson's disease, or spinal injury.

There are no federal funds in the US for research with human embryo stem cells. But a team from the Children's Hospital Boston, the Harvard Medical School, and the Whitehead Institute for Biomedical Research report in Nature Online today that they worked with the next best thing: embryo stem cells from laboratory mice.

They used these to create embryo germ cells. These are the primitive cells in the embryo that mature into sperm or eggs. A team at the University of Pennsylvania has already made mouse eggs from embryonic stem cells. So far, these have proved infertile.

The sperm grown in the Boston laboratory were not fully-fledged. However, when injected into eggs, they fertilised them, to create embryos with full sets of chromosomes.

The next step will be to transfer the fertilised eggs into surrogate mother mice to see how they develop.