Researchers from the Children's Hospital Boston/Harvard Medical School and the Whitehead Institute for Biomedical Research in Massachusetts, US, have created sperm from stem cells and used these cells to fertilise an egg. Their research, which took place in mice, was published in the 10 November online edition of the science journal Nature. It is hoped that the research will help scientists to better understand infertility and may provide the basis for new treatments.
Using embryonic stem cells (ES cells) derived from mouse embryos, the researchers first created a line of germ cells (primitive cells that develop into either sperm or egg cells) that showed continuous growth. Early embryos contain a small number of this type of cell, which are hard to isolate. By creating a germ cell line in the laboratory, the scientists hope to be able to study more closely the unique properties of this type of cell. It is hoped that the study of these cells will yield insights into gene imprinting (the process by which certain genes are switched off during early embryo development, according to whether they were inherited from the father or mother), cloning and cell reprogramming.
In the second stage of their research, the scientists used the germ cells to create functional sperm cells under laboratory conditions. These were not 'fully-fledged' sperm - they had no tails, for example. Earlier this year, scientists from the University of Pennsylvania, US, found that embryo cells grown in the laboratory could be coaxed into making eggs and egg-nurturing cells similar to those found in the body. As yet, none of these laboratory-produced eggs have been successfully fertilised with mouse sperm to make healthy embryos. The new investigation, led by stem cell biologist Dr George Daley, was looking at 'the other side of the reproductive equation'. When the researchers injected the laboratory-created sperm cells into eggs, one in five of the eggs were fertilised, creating embryos with a full set of chromosomes. The next step, say the researchers, is to transfer these embryos into mice: 'We will see if they make pups', said Dr Niels Geijsen, lead author of the study. 'This will tell us how normal the gamete really is'.
According to work published in the Proceedings of the National Academy of Science in September, Japanese scientists, based at the Mitsubishi Kagaku Institute of Life Sciences in Japan, have also produced normal, functioning mouse sperm from mouse ES cells which, said the researchers, had been used to fertilise an egg. Daley's group, however, is the first to conclusively show that laboratory-produced sperm is fertile. Hans Schoeler, who led the research team that created eggs from ES cells, said the sperm-based research was a 'very careful and beautiful study' that complemented his earlier findings.
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Stem cells used to create fertile sperm in mice