Published On: Sat, Apr 28th, 2018

A New Mysterious Form of DNA Seen Inside Human Cells for the First Time

It's DNA, but not as we know it. The new shape looks entirely different to the double-stranded DNA double helix and it has only been witnessed under artificial conditions in the laboratory, and not inside cells

i-motif DNA structure inside cells/ photo Chris Hammang

Never before been directly seen inside living human body cells, researchers in Sydney, Australian have identified a new DNA structure – called the i-motif.

The new findings look like a twisted ‘knot’ rather than the well-known double helix. Currently, It is unclear what the function of the i-motifs is. But scientists believe that i-motif might play an important role in how and when the DNA code is ‘read’.

The iconic ‘double helix’ shape of DNA which uncovered in 1953 by James Watson and Francis Crick, has captured the public imagination.

However, it’s now known that short stretches of DNA can exist in other shapes, in the laboratory at least.

Our DNA code provides precise instructions for how our bodies are built, and how they work. All 6 billion composed of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

Although researchers have seen the i-motif before and have studied it in detail, it has only been witnessed in vitro – that is, under artificial conditions in the laboratory, and not inside cells.

actually, researchers have debated whether the DNA ‘knots’ would exist at all inside living cells – the new findings said: YES.

“When most of us think of DNA, we think of the double helix,” says Associate Professor Daniel Christ who co-led the research. “This new research reminds us that totally different DNA structures exist – and could well be important for our cells.”

Associate Professor Marcel Dinger who co-led the research with Prof. Christ explained: “The i-motif is a four-stranded ‘knot’ of DNA. In the knot structure, C letters on the same strand of DNA bind to each other – so this is very different from a double helix, where ‘letters’ on opposite strands recognize each other, and where Cs bind to Gs [guanines].”

The iconic 'double helix' was discovered in 1953 by James Watson and Francis Crick

To detect the i-motifs inside cells, the researchers developed a new tool. It is a fragment of an antibody molecule that could specifically recognize and attach to i-motifs. Using fluorescences techniques to pinpoint where the i-motifs were located scientists were able to identify numerous spots of green in the nucleus.

“What excited us most is that we could see the green spots – the i-motifs – appearing and disappearing over time, so we know that they are forming, dissolving and forming again,” says Dr Mahdi Zeraati, whose research underpins the study’s findings.

They showed that i-motifs formed at particular points in the cell’s ‘life cycle’ when the DNA is being actively ‘read’.

They also appear more in promoter regions, which are areas of DNA that control whether genes are switched on or off. And in telomeres, ‘end sections’ of chromosomes that are important in the aging process.

‘We think the coming and going of the i-motifs is a clue to what they do. It seems likely that they are there to help switch genes on or off, and to affect whether a gene is actively read or not’, said Dr Zeraati.

Researchers hope this finding will set the stage for a new push to understand what this new DNA shape is for and whether it will impact our understanding of health and disease.

The new findings, from the Garvan Institute of Medical Research, are published today in the leading journal Nature Chemistry.

 

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