Louise Brown, the world's first "test-tube baby", was conceived 40 years ago when Patrick Steptoe and Robert Edwards fertilised her mother's egg with her father's sperm in a laboratory dish. In vitro fertilisation, the field that they founded, has enabled millions of people worldwide to overcome infertility and have healthy babies.
IVF has improved substantially since 1978 — for example through technology that injects sperm directly into the egg — but some forms of infertility remain untreatable. A couple in which the man produces no sperm or the woman has no eggs cannot have a baby without a donor.
Now science is pointing the way to more radical treatments for cases of infertility in which sperm or eggs are absent or too low in quality for today's IVF techniques to work. Experiments with mice show that synthetic sperm and eggs can be created using stem cell technology.
The road to enabling men and women who cannot benefit from IVF to have children, will be long and difficult but the mouse studies suggest that this will eventually be possible.
The first successful creation of functioning mouse sperm in the lab was reported last year by the Chinese Academy of Sciences Institute of Zoology. Researchers converted embryonic stem cells, which can become any type of tissue, into immature sperm cells called spermatids. These were injected into mouse eggs, which were fertilised successfully. The resulting embryos, implanted in female mice, developed into healthy pups.
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The experiment showed that meiosis, the special process of cell division and genetic rearrangement required to form germ cells (sperm and eggs), can be achieved in the lab by treating stem cells with a cocktail of chemicals and hormones in the presence of testicular tissue.