Scientists discover function for antisense RNA

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Scientists discover function for antisense RNA

http://www.news-medical.net/?id=21044

Researchers have found that a class of RNA molecules, previously

thought to have no function, may in fact protect sex cells from self-

destructing. These findings will be published in the November 17

issue of the journal Cell.

Central to this discovery is the fundamental process of gene

expression. When a gene is ready to produce a protein, the two

strands of DNA that comprise the gene unravel. The first strand

produces a molecule called messenger RNA, which acts as the

protein's template. Biologists call this first strand of DNA

the " sense " or " coding " transcript. Even though the other strand

doesn't contain a protein recipe, it may also, on occasion, produce

an " anti-sense " RNA molecule, one whose sequence is complementary to

that of the messenger, or sense, RNA. Antisense RNA has been

detected for a number of genes, but is largely considered a genetic

oddity.

Using common baker's yeast, Cintia Hongay, a postdoctoral researcher

in the lab of Whitehead Member and MIT Professor Gerald Fink,

discovered that in the case of a gene called IME4, the antisense RNA

blocks the sense RNA. In other words, the gene disables its own

ability to make protein.

" This is the first case where a specific function in a higher cell

for antisense RNA has been found, " says Fink, senior author on the

paper. " This points to an entirely new process of gene regulation

that we've never seen before in eukaryotic cells. "

There is a method to this sense/antisense madness, one that has a

kind of yin and yang quality. When conditions around yeast cells are

good and rich in nutrients, the cells divide by mitosis--that is,

the DNA duplicates so each daughter cell receives exactly the same

number of chromosomes as the original cell. However, when the yeast

cells are starving, IME4 switches on and activates a process called

meiosis. Here, the cells divide into germ-cell spores that, like

mammalian egg and sperm cells, have half the number of chromosomes.

Yeast spores withstand this harsh environment far more ably than the

larger cells from which they originate.

But in some cases, flipping the meiotic switch can be catastrophic.

If a cell with only one copy of each chromosome (a haploid cell) is

forced into meiosis, the progeny won't survive. Fortunately, such

destructive meiotic division is avoided in haploid cells because

they continually produce IME4 antisense RNA, blocking the production

of sense RNA. Antisense IME4, then, safeguards against meiosis in

cells that can't handle it.

" This is the first time that we've found a function for antisense

RNA, that is not RNAi, in a higher cell type, " says Hongay. " In

fact, it's really the first time we've seen a gene regulate itself

in this way. "

" For years scientists have evaluated genomes by measuring the sense

RNA, with antisense transcripts thought to have no meaning at all, "

says Fink. " Here we've found a process in which antisense RNA

regulates sense RNA. This same process may occur in the sex cells of

mammals. In fact, considering how widespread these antisense

transcripts are, I wouldn't be surprised if these findings

eventually lead us to discover an entirely new level of gene

regulation. "

Hongay is now searching the yeast genome for other genes that might

be regulated by antisense RNA.

http://www.mit.edu