Research explores spread of ‘parasitic’ DNA

A new study has been published which sheds light on how strands of parasitic DNA proliferate as part of the ageing process.

Genomes of all organisms contain elements that, when not suppressed, copy themselves and spread, potentially affecting health. It has already been discovered that these parts, known as  "retrotransposable elements" (RTEs), are able to free themselves from the genome's control in cultures of human cells.

The new research, conducted at Brown University, examined the process in mice and found that RTEs became increasingly able to break free and copy themselves as the animals aged. This process was found to occur in cancerous tumours but can be combated by restricting calories.

Jill Kreiling, a research assistant professor at Brown, said: "This may be a very important mechanism in leading to genome instability. A lot of the chronic diseases associated with ageing, such as cancer, have been associated with genome instability."

It is not known whether the proliferation of RTEs only has negative effects. However, scientists do know that the body tries to control the rogue elements by wrapping them in a tight configuration known as heterochromatin. The study found that heterochromatin became more common in mouse tissues as they aged, although some tissues containing RTEs were loosened up.

The new study shows that the proliferation of RTEs is linked to the ageing of the whole organism. Although previous studies demonstrated the process at work in cell cultures, the process of replication in such cultures does not mirror that which occurs during ageing.

Researchers examined cells from the liver and skeletal muscle of mice aged five, 24 and 36 months. They found elevated expressions of RTEs in both types of tissue after 24 months and the RTEs also copied themselves and showed up elsewhere in the genome.

Mice which were adequately nourished but fed 40 per cent fewer calories than animals on a normal diet were found to have fewer RTEs. A restricted calorie intake is known to mitigate the ageing process in different animal models.

There was also an observed correlation between the presence of RTEs and tissues affected by naturally-occurring cancers, but there is not yet sufficient evidence to establish a causal link.