British scientists say they've come one step closer to creating sperm and eggs from embryonic stem cells, a practice that has beneficial implications for couples faced with infertility. The feat was unveiled at a medical conference in Copenhagen, Denmark last week.1
The scientists in the laboratory of Dr. Harry Moore with the Centre for Stem Cell Biology at the University of Sheffield in England found that human embryonic stem cells can develop outside the body into the early forms of cells that eventually become sperm and eggs. The findings imply that such stem cells could someday be used to grow sperm and eggs for assisted reproductive therapies, the researchers stated.
"We derived six embryonic stem cell lines from embryos donated for research … by couples undergoing IVF treatment," explained Behrouz Aflatonian, a PhD student in Moore's lab, who presented the research at the conference.
Stem Cells: Unique Precursors
Embryonic stem cells are those derived from embryos created in in-vitro fertilization (IVF) procedures. These embryos are donated to research with the consent of the donors. Stem cells are primitive cells from the embryo that have the potential to become a wide variety of specialized cell types, such as those that make up the heart, pancreas, muscle, or brain.2 In this case, the stem cells were being used with the aim of becoming sperm and egg cells.
Stem cells are significant because they are the master cells of the body—capable of dividing and renewing themselves over long periods. They are also unspecialized cells, but give rise to specialized ones.2
More Questions to be Answered
For their experiment, Moore and his team allowed the embryonic stem cells to evolve into collections of cells known as embryoid bodies. They were then tested for gene activity. Within several weeks, it was found that a very small proportion of the embryoid bodies began to turn on some of the genes found in human primordial germ cells—the ancestral cells that eventually become sperm and eggs.
"Some cells also expressed proteins only found in maturing sperm," Aflatonian explained. "This suggests that human embryonic stem cells have the ability to develop into primordial germ cells and early gametes [reproductive cells], as has been shown previously for mouse embryonic stem cells."
But he stressed that much more research needs to be done before stem cells can be used to grow sperm and eggs used in assisted reproduction. "Producing functional gametes is much more difficult because we have to recreate for the cultured cells the environment of the developing follicle for egg development or the tissue of the testis for sperm," Alfatoonian said.
In addition, Moore's group wants to determine whether stem cells derived from embryos can also grow into cells that produce the hormones for sperm and egg development.
"Ultimately, it might be possible to produce sperm and eggs for use in assisted conception treatments," Moore predicted. "This is a long way off, and we would have to prove it was safe because, for example, the culture process may cause genetic changes."
Another significant implication is that this process could help scientists understand why some infertile couples fail to produce their own sperm and eggs. It may have something to do with toxic chemicals in the environment, the researchers theorize. These chemicals, such as pesticides, mimic the action of hormones and theoretically interfere with human development at the stage where eggs and sperm cells are forming.
But another implication is a controversial process known as embryo cloning. Genetic material is removed from the nucleus of a donated, unfertilized egg and replaced with genetic material from a cell in the patient's body, such as a skin cell. The egg is then artificially stimulated to divide and create an early-stage embryo, from which stem cells that could theoretically be used to create sperm and eggs.
Moore stresses his research does not involve a form of reproductive cloning, as some critics may charge. That's because only one set of gametes—either sperm or eggs—would potentially be developed this way, and then used in IVF with naturally produced sperm or eggs, creating a unique embryo.
"We would then have completed the circle of making human embryonic stem cells from eggs that came from human embryonic stem cells," he explained. "What came first, the chicken or the egg?"
1. European Society of Human Reproduction and Embryology 21st Annual Meeting. 2005 Jun 19-22. Copenhagen, Denmark.
2. National Institutes of Health. Stem Cell Information. Available at: http://stemcells.nih.gov/info/basics/basics3.asp. Accessed Jun 21, 2005.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.