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Aug 13, 2012

Selfish DNA Abounds in Worms

  • Selfish DNA is not limited to arrogant athletes and your ex. Oregon State University researchers have discovered a form of the genetic material within the mitochondria of the roundworm that hurts its host organism by reducing its chances of survival—and provides clues to studying aging in humans.

    Until now, ‘selfish’ mitochondrial DNA (mtDNA) had been found in plants—where it can affect flowering and has sometimes caused sterility in more than 150 species—but not in animals. Selfish mtDNA differs from healthy mtDNA in that it tends to copy itself faster than other DNA, has no function useful to the cell, and in some cases actually harms the cell.

    “We speculate that selfish mtDNA in animals, though sometimes characterized as rare, might be more widespread (particularly in species where self-reproduction occurs), but has remained a cryptic phenomenon owing to difficulties in discovering heteroplasmic selfish mtDNA variants, demonstrating transmission advantages and characterizing phenotypic effects of particular mtDNA elements,” researchers concluded in their study, published online in the journal PLoS One.

    According to “Selfish Little Circles: Transmission Bias and Evolution of Large Deletion-Bearing Mitochondrial DNA in Caenorhabditis briggsae Nematodes,” the discovery came about almost accidentally during research on the nematode, a type of small roundworm.

    “At first we thought it must be a laboratory error,” Dee R. Denver, Ph.D., an OSU associate professor of zoology and the study’s corresponding author, said in a statement. “Selfish DNA is not supposed to be found in animals. But it could turn out to be fairly important as a new genetic model to study the type of mitochondrial decay that is associated with human aging.”

    Roundworms with selfish mtDNA had fewer offspring and less muscle activity than those without. These and other defects are surprisingly similar to the decayed mtDNA in aging humans—as is the fact worms contain more selfish mtDNA as they age.

    Researchers hypothesize that the population sizes of the nematode may be too small to eliminate the selfish mtDNA through normal evolution: “It might suggest that natural selection doesn’t work very well in this species,” OSU postdoctoral fellow Katie Clark said in the statement.

    Read the PLoS study at

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