Not 'Junk DNA' After All: Tiny RNAs Play Big Role Controlling Genes

October 26, 2007

A study by researchers at the Yale Stem Cell Center for the first

time demonstrates that piRNAs, a recently discovered class of tiny

RNAs, play an important role in controlling gene function.

Haifan Lin, director of the stem cell center and professor of cell

biology at Yale School of Medicine, heads the laboratory that

originally identified piRNAs. Derived mostly from so-called " junk

DNA, " piRNAs had escaped the attention of generations of geneticists

and molecular biologists until last year when Lin's team discovered

them in mammalian reproductive cells, and named them.

The lab's current work suggests that piRNAs have crucial functions

in controlling stem cell fate and other processes of tissue

development.

In this study Lin and his Ph.D. student, Hang Yin, discovered more

than 13,000 Piwi-associated piRNAs in fruit flies. One particular

piRNA, they found, forms a complex with the protein known as Piwi,

which then binds to chromatin, a strategic region in the genome that

regulates the activity of the gene. Chromatin's role is to package

DNA so that it will fit into the cell, to strengthen the DNA to

allow cell division, and to serve as a mechanism to control gene

expression.

" This is important in maintaining self-renewal of stem cells, " Lin

said. " These small RNAs might provide new tools to harness the

behavior of stem cells and other biological processes related to

diseases. "

" This finding revealed a surprisingly important role for piRNAs, as

well as junk DNA, in stem cell division, " Lin said. " It calls upon

biologists to look for answers beyond the one percent of the genome

with protein coding capacity to the vast land of junk DNA, which

constitutes 99 percent of the genome. "

This research was supported by the Mather's Foundation and the

National Institutes of Health.

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