If you thought DNA was stable inside mature cells, you were wrong. Apparently, neurons are constantly changing to adapt to their environment. Minor surgeries are conducted toggling activity levels every single day. In effect, neurons constantly rewrite their DNA as needed. This information was discovered by John Hopkins scientists and published in the journal Nature Neuroscience on the 27th day of April this year.
Hongjun Song, Ph.D. says, “DNA, in a cell, is not always stable. It is being altered all the time in order to function. Even molecular tags, which maintains the cell’s identity, are constantly being altered.”
The DNA’s four letter alphabet contains C’s, or cytosine. Regulatory tags, or methyl groups, are bound to these cytosines. To remove them, tagged cytosines would have to be replaced with untagged cytosines. Cells use this process, but sparingly, because the process requires cutting into the DNA, where cutting can cause mutations. Even so, studies show that mammals’ brains conduct DNA altering processes on a regular basis, even more so than other areas of the body. This poses a question for Song:“Why is all this activity occurring in such a sensitive area of the body?”
Neurons communicate with each other through synapses. One neuron releases chemical messengers and the receiving neuron intercepts the message using protein receptors. These neurons can adjust the settings – how many messages, or how many messengers transmitting the communication. This all occurs on the surface of the neuron.
Song’s team added drugs to neurons of mouse brains. This procedure gauged synaptic activity. The volume went up, and the activity of Tet3 gene went up as well, starting DNA methylation. When the volume was down, the Tet3 gene was down as well.
Conducting the experiments in the opposite manner showed surprising results. When Tet3 was up, activity was down and vice versa.
An additional experiment shows that if Tet3 is down, then a protein at the synapse called GluR1 is elevated. GluR1 is a receptor for chemical messengers and allows for the various toggling needed for neurons and synaptic activity.
Scientists have found a way to retain levels of synaptic activity so that neurons can stay responsive to their surroundings. If activity increases, then Tet3 levels increase, as well as excisions of tagged cytosines. When this happens, the levels of GluR1 decrease at the synapses. This reduces strength and brings activity levels back to their previous state. So basically, Tet3 levels respond to synaptic activity levels and the other way round.
“If you stop neural activity, then neurons “turn up the volume”. This is done to get back to their normal activity level. Of course, it takes Tet3 to accomplish this feat,” says Song.
Considering the brain undergoes such risky behavior, it stands to question whether our brains experience damage due to unsuccessful excision. It doesn’t matter, however, and the activity will continue. It is a fundamental property of neurons to be able to regulate activity, so it’s a risk that will have to be taken.