November 20, 2013 | Media Contact: David Orenstein | 401-863-1862
In yeast at least, the aging process appears to reduce an organism’s ability to silence certain genes that need to be silenced. Now researchers at Brown University who study the biology of aging have shown that the loss of genetic control occurs in fruit flies as well. Results appear online in the journal Aging.
PROVIDENCE, R.I. — Biologists at Brown University have found a way to measure the effects of aging by watching the ebb and flow of chromatin, a structure along strands of DNA that either silences or permits gene expression. In several newly published experiments they show that gene silencing via chromatin in fruit flies declines with age.
They also showed that administering life span extending measures to the flies, such as switching them to a lower calorie diet or increasing expression of the protein Sir2, restores the observed loss of gene silencing due to age.
“For many years it has been suggested that one of the issues that occurs with age, leading to cellular dysfunction, is that some genes that should be silenced lose that silencing,” said Dr. Stephen Helfand, senior author of the study published online Nov. 15 in the journal Aging. “It hasn’t been very well demonstrated to take place other than in yeast. So what we were trying to do in flies is see whether genes that are normally repressed lose their repression.”
The answer they report is that the phenomenon is true in flies too.
The variegations of age
To achieve those findings, Helfand and lead author Nan Jiang exploited a phenomenon called “position effect variegation.” PEV is the variation of a gene’s expression that comes from the gene existing at the border between euchromatin, a loose wrapping of DNA that readily permits gene expression, and heterochromatin, a tight wrapping that keeps it locked down. The scientists hypothesized that as organisms age, heterochromatin might recede, allowing more genes that had once been silenced to become exposed for expression — like a seashell becoming revealed to a passing beachcomber as the tide recedes.