Forget-me-now: Memory loss gene found in mice

Whether painful memories linger or fade may be
down to the expression of a single gene, according to researchers at Massachusetts Institute of Technology (MIT), USA.

As time passes, newer, happier experiences
gradually replace older, more traumatic memories. This is called 'memory
extinction'. A study, published in
the journal Neuron, has shown a gene known as Tet1 is critical to the
process of memory extinction. Improving the expression of Tet1 may benefit
people with post-traumatic
stress disorder (PTSD), the researchers believe.

Professor Li-Huei Tsai,
director of the Picower Institute for
Learning and Memory at MIT, told Discovery
News: 'Once a fear memory is formed, to extinguish that memory a new
memory has to form. The new memory competes with the old memory and eventually
supersedes the old memory'. It is thought this process is disrupted in people
with PTSD.

To investigate the
role of Tet1 in memory extinction, Professor Tsai and her team studied mice with the Tet1
gene knocked out. The researchers conditioned the mice to fear a particular
cage where they received a mild electric shock. Once conditioned, the mice were
put in the cage but not shocked by the researchers. After time, mice with
regular Tet1 levels lost their fear of the cage; the Tet1 knockout mice did
not.

Lead author Dr Andrii
Rudenko explained that mice lacking Tet1 could not forget about the electric
shock: 'They don't relearn properly. They're kind of getting stuck and cannot
extinguish the old memory'.

The team believes
Tet1 regulates memory extinction by controlling the expression of a handful of
other 'memory genes'. This is achieved by removing DNA methylation.

High methylation
levels on DNA prevent genes from being switched on, and lower levels allow the
genes to be expressed. The research team observed that mice without Tet1 had
very high levels of methylation on important memory genes. This makes it very
difficult for mice lacking Tet1 to ‘switch on’ their memory genes to replace a
traumatic memory.

Researchers hope this research will lead to new
treatments for PTSD and other anxiety disorders, although this will likely take
more than a decade.

British mental health charity, Mind,
estimates that around three percent of the general population is 'likely to be
affected by PTSD at some point'.