Key genes for sperm and egg formation identified

US scientists have succeeded in creating early-stage sperm and eggs cells from human embryonic stem cells (ES cells). By studying these artificially created {GLINK sperm and eggs, the research team have identified three key genes that are involved in the development of these cells. The findings, published in the journal Nature, may one day lead to a cure for some causes of infertility.

In humans, eggs and sperm are formed in the ovaries and testes from germ cells. Because germ cells are created in the very early embryo, the development of germ cells has been very difficult to study and little is known about the genetic processes involved. The new study, by a team at Stanford University, California, US, identified a cocktail of proteins that stimulated human ES cells into forming first germ cells and then early-stage sperm and egg cells. They then used genetic modification techniques to turn different genes on and off in the ES cells, and observed how this influenced the development of the germ cells and their maturation into sperm and eggs. They identified one gene called DAZL that is crucial to germ cell formation and two other genes called DAZ and BOULE that are involved in the later stages of egg and sperm development.

Professor Renee Reijo Pera, who led the team, said: 'our goal is to understand how you make eggs and sperm. We know almost nothing about human reproductive development, and this gives us a new way to investigate it. The hope is some day to help those who are infertile'.

It is believed that many cases of infertility are caused by underlying genetic problems that affect the development of germ cells or their ability to become mature sperm or eggs. This advance in recreating and studying these processes in the laboratory may eventually lead to ways of curing these underlying problems. Professor Reijo Pera explained: 'Figuring out the genetic "recipe" needed to develop human germ cells in the laboratory will give us the tools we need to trace what's going wrong for [infertile] people'.

This research raises the possibility that in the future, scientists may be able to create fully mature sperm and egg cells from ES cells or even adult skin cells that had first been modified to behave like ES cells (so-called induced pluripotent stem cells). In theory, this could become the ultimate cure for infertility. However, Professor Reijo Pera said that the in vitro derived (IVD) reproductive cells are currently 'highly genetically modified' and 'it would not be appropriate to use them to make an embryo'. The use of IVD gametes in reproduction is banned in the UK.