London, July 8 : Scientists have achieved a major breakthrough in making sperm-like cells from human embryonic stem cells.

Karim Nayernia, of the University of Newcastle Upon Tyne in the UK, has revealed that these cells can swim like sperm do.

He says that his team used the same technique to create sperm-like cells from human embryonic stem cells that he had used in 2006 to produced sperm from mouse embryonic stem cells.

The team labelled embryonic stem cells with a fluorescent marker attached to a particular gene that is expressed during reproductive-cell development, and cultured the cells in a medium that encourages differentiation into sperm cells.

The researchers observed that about three per cent of the resulting cells contained enough DNA for only one set of chromosomes, suggesting that meiosis had occurred.

Some of these cells also formed tails and were motile, they said.

Nayernia and his colleagues have yet to analyse methylation patterns in their sperm-like cells, or conduct a detailed study of the cells'' morphology.

While there work has been hailed by other scientists, the sperm-like cells created by the researchers will still require much more characterization before they can be used as an experimental model for the study of inherited diseases and infertility.

Another hurdle is that, in several countries, it may actually be illegal even if these cells were properly characterised.

Nayernia admits it, but still insists that his team's work was a "proof-of-principle experiment".

"We don''t claim that it is fully normal sperm, but they do have some of the right characteristics," Nature magazine quoted him as saying.

Meanwhile, he and his colleagues have also launched a project to produce sperm cells from induced pluripotent stem cells, which can be generated from adult cells.

The researchers believe that such cells would make it easier to derive sperm cells from many individuals.

"Then we can, for example, see whether environmental factors or genetic factors are affecting fertility, and which step of sperm production has been affected by those factors," he says. (ANI)