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Clues to aging found in stem cells’ genomes

Chicago, Feb. 13 — Stem cells that produce sperm use a genetic trick to stay perpetually young across generations, researchers at the University of Michigan (UM) Life Sciences Institute have discovered.

The results have been newly reported in the journal eLife.

Certain sections of the fruit fly genome get shorter with age. But remarkably, some reproductive cells can repair the shrinkage, and this genomic shrinkage may underlie aspects of aging and hint at ways that select cells might thwart it.

In the study, UM researchers focused on workhorse genes encoded in ribosomal DNA, or rDNA. These genes carry instructions for the parts that make up ribosomes, cellular machines that turn RNA molecules into every protein needed in the body.

In fruit flies, chains of rDNA genes are found on the X and Y chromosomes. Compared with young male fruit flies, old males had a shortage of rDNA genes on the Y chromosome, leaving them with a shrunken Y chromosome.

Moreover, this dearth of rDNA seems to be passed on from generation to generation. Geriatric fly fathers, those 40 days old, passed on their reduced number of rDNA genes to their sons, UM researchers found. These sons had considerably fewer copies of rDNA genes than sons born to younger fathers.

Then the researchers saw something surprising. In many cases, this rDNA loss reversed itself. At about 10 days of age, sons born to old fathers had recovered enough rDNA to be comparable to sons born to young fathers.

“This recovery was something we really didn’t expect,” said UM Life Sciences Institute faculty member Yukiko Yamashita.

The results suggest that rDNA rejuvenation in sons might be a crucial aspect of how stem cells persist from father to son. The researchers do not yet know whether such a reset can happen to female stem cells in the ovaries.

Until now, researchers had observed the phenomenon only in yeast. If the results hold true for humans, they could offer insight into how most cells deteriorate over time.

Being pushed, Yamashita would wager that some types of immortal cells in people can perform the same rejuvenating trick to prevent the rDNA declines that come with age.

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