APR 28, 2015 11:51 AM PDT

Neurons Busily Rewrite Their DNA Nonstop

WRITTEN BY: Judy O'Rourke
Scientists from Johns Hopkins have found that neurons are not risk-averse, if fact, they use minor "DNA surgeries" to toggle their activity levels 24/7.

Since these activity levels are important in learning, memory, and brain disorders, the researchers believe their finding will shed light on several key questions.
These are images of mouse neurons from the hippocampal region of the brain. Levels of the surface receptor GluR1, orange, are shown in unmodified neurons, left, and in those with increased levels of Tet3, right.
"We used to think that once a cell reaches full maturation, its DNA is totally stable, including the molecular tags attached to it to control its genes and maintain the cell's identity," says Hongjun Song, PhD, professor of neurology and neuroscience, Johns Hopkins University School of Medicine's Institute for Cell Engineering. "This research shows that some cells actually alter their DNA all the time, just to perform everyday functions."

This DNA alteration is called DNA demethylation. Methyl groups are regulatory tags that are permanently bound to cytosines, the C's in DNA's four-letter alphabet. Removing them is a multistep process that requires excising a tagged cytosine from the long string of paired "letters" that make up a chromosome and, ideally, replacing it with an untagged cytosine.

Because the process involves making a cut into DNA, it leaves the DNA somewhat vulnerable to mutations, so most cells use the process sparingly, mostly for correcting errors. But recent studies had turned up evidence that mammals' brains exhibit highly dynamic DNA modification activity-more than in any other area of the body-and Song's group wanted to know why all this risky business was going on in such a vulnerable tissue as the brain.

The main job of neurons is to communicate with other neurons through connections called synapses. At each synapse, an initiating neuron releases chemical messengers, which are intercepted by receptor proteins on the receiving neuron. Neurons can toggle the "volume" of this communication by adjusting the activity level of their genes to change the number of their messengers or receptors on the surface of the neuron. When Song's team added various drugs to neurons taken from mouse brains, their synaptic activity-the volume of their communication -- went up and down accordingly. When it was up, so was the activity of the Tet3 gene, which kicks off DNA demethylation. When it was down, Tet3 was down too.

Then, they flipped the experiment around and manipulated the levels of Tet3 in the cells. Surprisingly, when Tet3 levels were up, synaptic activity was down; when Tet3 levels were down, synaptic activity was up. So do Tet3 levels depend on synaptic activity, or is it the other way around?

Another series of experiments showed them that one of the changes occurring in neurons in response to low levels of Tet3 was an increase in the protein GluR1 at their synapses. Since GluR1 is a receptor for chemical messengers, its abundance at synapses is one of the ways neurons can toggle their synaptic activity.

The scientists say they have discovered another mechanism used by neurons to maintain relatively consistent levels of synaptic activity so that neurons can remain responsive to the signaling around them.

"If you shut off neural activity, the neurons 'turn up their volume' to try to get back to their usual level and vice versa. But they can't do it without Tet3," Song says.

He adds that the ability to regulate synapse activity is the most fundamental property of neurons. "It's how our brains form circuits that contain information," he says. Since this synaptic flexibility seems to require mildly risky DNA surgery to work, Song wonders if some brain disorders might arise from neurons losing their ability to "heal" properly after base excision. He thinks this study brings us one step closer to finding out.

A summary of the study, titled "Tet3 regulates synaptic transmission and homeostatic plasticity via DNA oxidation and repair," was published online in the journal Nature Neuroscience on April 27.

[Source: Johns Hopkins Medicine]
About the Author
  • Judy O'Rourke worked as a newspaper reporter before becoming chief editor of Clinical Lab Products magazine. As a freelance writer today, she is interested in finding the story behind the latest developments in medicine and science, and in learning what lies ahead.
You May Also Like
AUG 27, 2018
Genetics & Genomics
AUG 27, 2018
A Better Way to Classify Bacteria
The classification of organisms into groups, taxonomy, has taken an important step forward....
SEP 18, 2018
Microbiology
SEP 18, 2018
The Earliest Influences on the Microbiome Have a Lasting Impact
We coexist with microorganisms, and many of them play an important role in our health....
SEP 27, 2018
Genetics & Genomics
SEP 27, 2018
Learning What Causes Algae Blooms to Turn Toxic
According to the EPA, algal blooms threaten every state and in our changing climate, they may be more common....
SEP 29, 2018
Videos
SEP 29, 2018
CRISPR Technology may Have Serious Drawbacks
The CRISPR gene-editing system has been touted as a miraculous tool, but it has its problems....
OCT 15, 2018
Microbiology
OCT 15, 2018
Surprising Source of Hospital-acquired Infections is Found
Is it a sick visitor, a dirty hospital gown, or the unwashed hands of a clinician? No, the infection is coming from inside the patient!...
OCT 18, 2018
Genetics & Genomics
OCT 18, 2018
Expanding the List of Genes That Cause Multiple Sclerosis
For many years, researchers have been searching for the genetic influences that affect the development of MS....
Loading Comments...