Improvements in a technique for making “three-parent babies” could reduce the risk of passing on faulty mitochondria, the energy-producing organelles in cells.

Less than 2 percent of mitochondria were defective in most human embryos created from this refined “pronuclear transplantation” procedure, researchers report online June 8 in Nature.

Pronuclear transplantation is one of two ways to transfer nuclear DNA from a mother’s egg that has faulty mitochondria to a donor egg with healthy mitochondria. After fertilization, the mother’s and father’s chromosomes don’t merge but are encased in separate membranes inside the mother’s egg. In pronuclear transplantation, researchers remove both of these DNA packages, known as pronuclei, and inject them into an empty donor egg.
Any resulting children would inherit DNA from three parents: most from their mother and father, with a small amount of mitochondrial DNA from the egg donor. DNA transplant techniques may prevent mothers from passing mitochondrial diseases to their children. Such diseases, which result from mutations in mitochondrial DNA, particularly affect energy-hungry organs, including the brain and muscles.

Last month, researchers reported that even small amounts of defective mitochondria carried into the healthy egg might propagate and negate the effect of the therapy (SN Online: 5/19/16).

In the new study, flash-freezing the mother’s egg, removing pronuclei soon after they form (about eight hours after fertilization) and other refinements greatly reduced the amount of defective mitochondria transplanted into donor eggs. Of embryos created, 79 percent carried less than 2 percent of defective mitochondria, report reproductive biologist Mary Herbert of the Wellcome Trust Centre for Mitochondrial Research in Newcastle upon Tyne, England, and colleagues.

That decrease in defective mitochondria doesn’t eliminate the risk of disease resurgence, but greatly reduces it, says Herbert. “The focus of our current research is to get that carryover as close to zero as we possibly can.”

SAN DIEGO — A clue about why life on Earth chooses only one mirror-image form of certain molecules might lie in a gas cloud tens of thousands of light-years away.

For the first time, researchers have detected a chiral molecule, propylene oxide, in interstellar space. Chiral molecules, which come in two mirror-image versions, show up in many of life’s building blocks, such as the amino acids that make up proteins as well as sugars. The finding may be a step toward understanding why life prefers one of these versions over another.
The results were presented June 14 at a meeting of the American Astronomical Society and published online the same day in Science.

Chiral molecules are like opposing hands. Left hands and right hands mirror each other, but no amount of turning will get them to match when overlaid. Matching configurations of a chiral molecule are labeled as either left-handed or right-handed.

Amino acids and sugars come in both styles of handedness. But life on Earth exclusively uses left-handed amino acids and right-handed sugars. “This is one of the longest standing mysteries in the origin of life,” Brett McGuire, a chemist at Caltech, said at a news briefing.

Chiral molecules have shown up in meteorites with a slight preference for one configuration. McGuire and colleagues went looking for chiral molecules in space to see whether some interstellar intervention could preferentially seed a solar system with one handedness. The researchers sifted through radio observations from the Green Bank Telescope in West Virginia of a gas cloud dubbed Sagittarius B2. The nebula sits near the center of the galaxy and has historically been a rich hunting ground for interstellar molecules.

McGuire and colleagues found that the cloud was loaded with the chiral molecule propylene oxide. The stockpile has a mass equal to about 80 percent of Earth’s mass, said McGuire, and if compressed into a liquid blob, it would occupy a volume over five times that of our planet. The observations don’t reveal whether the cloud has a preference for one handedness over another; that will have to wait for future observations. But “we’re in the best position we could possibly be,” said McGuire, to figure out if life’s chiral exclusivity has an interstellar origin.