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MONDAY, June 15 (HealthDay News) -- Biologists say they have discovered a clever packaging scheme that allows the genetic material in sperm to have far more influence over development of a fertilized egg than had been imagined.
The discovery has potential applications in helping infertile men, said Brad Cairns, a professor of oncological sciences at the University of Utah and a leader of the team reporting the finding in the June 14 online edition of Nature.
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The vast majority of the DNA molecules that carry genetic information are tightly packaged in sperm cells, Cairns said. That tight packaging enables a win in what is literally a race for life because the first sperm to reach an egg fertilizes it, and the tightest packages are the most streamlined.
"But when it comes to development, the sperm is at a real disadvantage," Cairns said. "The vast majority of their genes are tightly packed in material that is not helpful in giving them full expression."
In every cell other than sperm, DNA molecules are wrapped around structures called histones, an arrangement that allows for easy transmission of their genetic instructions. But only 4 percent of sperm DNA is arranged around histones. The other 96 percent is in a dense, impenetrable material called protamine.
"The hypothesis has been that this 4 percent of DNA in histones is randomly distributed," Cairns said. "We challenged the hypothesis and found that the DNA that is in histones is not randomly distributed but is located at important genes for embryonic development."
The discovery was made by using DNA from sperm at the University of Utah's in vitro fertilization clinic. "We isolated the DNA attached to histones and sequenced it," Cairns said. "We found genes that are important in guiding the development of the embryo."
The discovery raises "obvious questions" about the importance of DNA packaging in sperm on human fertility, he said.
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