Gene Expression Can Occur In The Form Of Discrete ‘Pulses' Of Gene Activity

[Guest guest]

Gene Expression Can Occur In The Form Of Discrete `Pulses' Of Gene

Activity

http://www.medicalnewstoday.com/medicalnews.php?newsid=44941

Scientists at the Albert Einstein College of Medicine of Yeshiva

University have observed for the first time that gene expression can

occur in the form of discrete " pulses " of gene activity. The

researchers used pioneering microscopy techniques, developed by Dr.

Singer and colleagues at Einstein, that for the first time

allow scientists to directly watch the behavior of a single gene in

real time. Their findings appeared in the current issue of Current

Biology.

When a gene is expressed or " turned on, " genetic information is

transferred from DNA into RNA. This process, known as transcription,

is crucial for translating the gene's message into a functional

protein. Diseases such as cancer can result when genes turn on at the

improper time or in the wrong part of the body.

Researchers customarily use microarrays (also known as " gene chips " )

to assess gene expression in tumors and other tissues. But with

millions of cells involved, microarrays reflect only " average " gene

expression. Just how a gene is transcribed in a single cell-

continuously, intermittently or some other way-has largely been a

mystery.

Now, in observing a gene that plays a major role in how an organism

develops, the Einstein researchers observed a phenomenon that until

now has been indirectly observed and only in bacteria: pulses of

transcription that turn on and off at irregular intervals. Dr. Singer

and his co-workers used a fluorescent marker that sticks to the gene

only when it is active. Under a microscope, this fluorescent marker

appears when the gene turns on, then disappears (gene " off " ) and then

appears again (gene " on " ).

The focus of the study was a gene important in the life cycle of the

social amoeba Dictyostelium, thousands of which sometimes aggregate

into a single slug-like mass. This developmental gene plays a major

role in transforming the " slug " into a stalk-like structure called a

fruiting body, which releases new amoebae.

" The pulsing we observed in this gene would allow it to very

precisely regulate development, " says Dr. Singer, the study's senior

author and professor and co-chair of the Department of Anatomy &

Structural Biology at Einstein. He likens a gene to a thermostat:

" Heating a home all the time would be wasteful and would overheat the

house, " he says. " The solution is a thermostat, which injects a

little bit of heat when needed and then turns off. Similarly, a cell

needs the gene to be turned on-but too much activity at the wrong

time can be a problem, so the solution is to have small bursts of

activity. "

Still to be discovered, says Dr. Singer, is how the pulsing mechanism

itself is controlled. In addition, these findings pertain to

developmental genes, which are turned on selectively and only in

certain tissues. " Other genes-so-called constitutive genes-are

regularly expressed by all the cells of an organism, " Dr. Singer

notes. " We'd like to find out whether these genes pulse as well. "

Also involved in this study were R. Chubb (now at University

of Dundee in the U.K.), Tatjana Trcek and Shailesh M. Shenoy.

Albert Einstein College of Medicine of Yeshiva University