Spanish scientists say they have created rudimentary sperm-like cells from skin and bone marrow cells taken from adult males.
'What to do when someone who wants to have a child lacks gametes (eggs or sperm)?' asked Dr Carlos Simon, the scientific director of the Valencia Infertility Institute, where the research was carried out. 'This is the problem we want to address: to be able to create gametes in people who do not have them.'
Primordial human germ cells have been created from embryonic stem cells (see BioNews 785), and primordial mouse germ cells have been created from adult stem cells (see BioNews 841). But this is the first time that primordial human germ cells have been created from adult human stem cells.
The researchers first took skin and bone-marrow cells and induced them to become stem cells. They then introduced six key genes which they had identified as crucial to the process of meiosis, in which cells of the early embryo develop into germ cells and which have only half the usual number of chromosomes. These germ cells go on to become sperm or eggs in the developing fetus.
After introducing these six key genes, they bathed the stem cells in a specially developed cocktail of growth factors, and were able to coax around one percent of the cells to undergo meiosis.
They were confident that this had happened because the cells began to express genes normally expressed during and after meiosis. The cells also showed evidence of epigenetic reprogramming – a process that occurs during embryo development in which the DNA is reset during each generation.
Crucially, they found that one percent of the cells were haploid – having half the usual number of chromosomes. When they injected them into mouse testes, there was some evidence that they continued to develop there.
'This is a sperm but it needs a further maturation phase to become a gamete. This is just the beginning,' said Dr Simon.