The technique, published in the March 24 issue of the journal 'Nature,' might help reveal the molecular steps involved in formation of sperm and lead to new treatments for male infertility, a condition that affects one in six couples.
Biologists have been trying to synthesize mammalian sperm outside body for almost a century. But, it is only now that a team of researchers from Japan have succeeded in understanding the mechanism by which the paired chromosomes swap DNA during meoisis, and prepare sperm cells to fuse with the egg.
"The report is quite exciting because it represents the fulfilment of a goal held by many reproductive biologists over many years," naturenews.com quoted Mary Ann Handel, an expert in reproductive genetics at the Jackson Laboratory in Bar Harbor, Maine, as saying.
Study on mice
Lead researcher Takehiko Ogawa along with his colleagues at Yokohama City University discovered that the key to growing sperm through meiosis in vitro conditions lies in a simple change to standard culture conditions.
For the study purpose, the researchers took slivers of fragments of testes from neonatal mice and cultured them in fetal bovine serum, a typical ingredient of cell cultures.
To track sperm development, they used a fluorescent protein that marked cells undergoing, or that had undergone, meiosis, the Daily Mail reports.
Initially, none of the factors mixed in the culture medium stimulated sperm formation, not even factors known to promote sperm maturation.
In a trial and error method, the researchers then replaced the fetal bovine serum with a serum-free medium, KnockOut Serum Replacement, which is often used to grow embryonic stem cells.
Breakthrough study findings
After several weeks of bathing the sample in the culture medium, researchers found that nearly half of the samples contained cells with flagella, tail-like projections, which help sperms in swimming and reaching the egg.
When these sperm were injected into egg cells, the surrogates delivered dozens of fertile offsprings.
Though it is illegal to use lab-grown sperm in the UK, and may raise ethical concerns, the researchers are planning to test the technique in samples collected from men.
“I want to apply our method to other species including humans. The sperm produced in our system should be safe,” Ogawa said.
Study findings stir debate
The United States fertility and cancer experts have welcomed the advance saying, “Anti-cancer therapies can impair male fertility. Whereas men can opt to freeze their sperm before treatment, young boys don’t produce mature sperm, so lack this choice. Work in mice offers hope for such patients.”
Dr Allan Pacey, a Sheffield University fertility expert, on the other hand, stressed that techniques that work in mice do not always work in people.
He added, “This is a very interesting study. There have been several attempts to create or “grow” animal sperm in the laboratory by various different approaches. However, none have been wholly successful and when the sperm have been used, the pups born have not been healthy and have soon died.
“To be able to “grow” sperm in this way would be useful so that we could study the process of sperm production. Because sperm develop in the testicle, and we cannot yet replicate this in the laboratory, it is not totally clear how sperm are formed and why in some men it doesn’t work properly.
“This could help discover new drugs or treatments to stimulate infertile men to produce more or better sperm. It also may help preserve the fertility of some males.
“I think this study is a small but important step in understanding how sperm are formed which may, in time, lead to us being able to routinely grow human sperm in the laboratory,” Pacey added.