Human Sperm Could One Day Be Made From Bone Marrow

German scientists have created early versions of human sperm cells in the laboratory from bone marrow.
The study is being published in the journal Reproduction: Gamete Biology.
The scientific team was led by Professor Karim Nayernia, who was then at the University of Göttingen in Germany but who has now moved to the UK and is based at the Northeast England Stem Cell Institute (NESCI), at the Centre for Life in Newcastle upon Tyne.

Prof Nayernia and colleagues isolated human "mesenchymal" stem cells from bone marrow they had extracted from male volunteers and stimulated them using a type of vitamin A to develop into male reproductive cells or "germ cells".

The presence of genetic markers showed that the germ cells also contained "spermatagonial stem cells", an early stage version of male sperm cells.

In the male body, spermatagonial stem cells eventually become fully mature sperm cells, but Prof Nayernia and colleagues were not able to take them this far in the laboratory. The cells stopped at the pre-meiosis, or cell division stage.

In an earlier study, also led by Prof Nayernia, scientists were able to make spermatagonial cells from the bone marrow of mice, insert them in the testes of live mice and watch them divide (go through meiosis) and develop into mature sperm cells.

Also, in 2006, Prof Nayernia and his team revealed that they had successfully bred seven live mice made from mouse eggs fertilized with sperm cells developed from embryonic mouse stem cells.

Commenting on the results of the latest experiment, Prof Nayernia said:

"We're very excited about this discovery, particularly as our earlier work in mice suggests that we could develop this work even further."

Prof Nayernia's next step, with other NESCI scientists, will be to get the spermatagonial stem cells to develop into fully mature sperm in the laboratory. He said this could take 3 to 5 years.

He said that this kind of research takes time because the science has to develop within an ethical and social framework in view of the potential applications for fertility treatment in humans.

One of their first goals is to find out why the cells stopped at the meiosis stage, the final phase before becoming mature sperm.

They are considering the possibility that when this stage occurs in the male testes, another group of cells called "sertoli cells" help to "nurse" the sperm cells through division and maturation. It might be possible also to produce sertoli cells from stem cells taken from bone marrow.

The researchers hope their work will one day lead to new treatments to help infertile men, for example after going through chemotherapy.

Other scientists, while welcoming the breakthrough say that there is still a long way to go before sperm cells produced in this way can be shown to fertilize a human egg.

Others are saying that a raft of difficult ethical questions have to be addressed before applications to human fertility can be considered, for example should this open the door to female only sperm cells, where a woman could make a baby with another woman?

And there are also questions about the long term genetic effects that creating sperm in this way might have on the health and development of embryos and the children and adults they eventually become.

What is Meiosis?

Meiosis is a special kind of cell division that sperm and egg cells go through. In humans it takes several stages to both divide and at the same time reduce the number of chromosomes from 46 to 23 so that when the sperm from one human fertilizes the egg of another, the recombined chromosome count of is 46 again.

Sperms and eggs are known as gametes, because they only have 23 chromosomes, whereas the fertilized egg is a zygote, because it is a viable future organism with all its requisite chromosomes present and correct.
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