3rd quarter 2006

First functional sperm created from embryonic stem cells

Scientists in Göttingen, Germany, have bred mice by fertilising eggs with sperm made from embryonic stem cells. Prior to this, researchers had succeeded in differentiating embryonic and somatic stem cells into male and female germ cells in laboratory cultures, but had not been able to produce any live offspring. "This is the crucial result of our research," said Prof. Wolfgang Engel, Director of the Institute of Human Genetics of Georg-August University in Göttingen.

These findings on the artificial maturation of functional male germ cells are a milestone towards a better understanding of how sperm are formed in mammals. "The research is primarily of a basic nature," Engel said. "It enables us to better understand the biological aspects of germ cell formation and investigate in greater detail how the genome is reprogrammed during germ cell formation."

By adding certain growth factors to the culture medium, the murine embryonic stem cells were stimulated to develop into male germ cells. The greatest obstacle was to induce meiosis, during which the number of chromosomes is reduced by half.

Overall, the sperm derived from embryonic stem cells resulted in the birth of seven mice. They were either unusually small or big compared to normal mice, and lived from five days to five months. The abnormal size and early death of the mice are due to an incomplete reprogramming of the genome during germ cell formation. The researchers did not succeed in completely reproducing all of the complicated steps of sperm development in the culture dish.

"We would now like to replicate our findings in monkeys to find out whether the method also works in primates," Engel said. Conducting such experiments with human embryonic stem cells is illegal in Germany.