23-Jul-2020 - Imperial College of London

Formation of quadruple helix DNA tracked in live human cells for the first time

The biology of DNA must be rethink

The formation of four-stranded DNA has been tracked in living human cells, allowing scientists to see how it works, and its possible role in cancer.

DNA usually forms the classic double helix shape discovered in 1953 - two strands wound around each other. Several other structures have been formed in test tubes, but this does not necessarily mean they form within living cells.

Quadruple helix structures, called DNA G-quadruplexes (G4s), have previously been detected in cells. However, the technique used required either killing the cells or using high concentrations of chemical probes to visualise G4 formation, so their actual presence within living cells under normal conditions has not been tracked, until now.

A research team from the University of Cambridge, Imperial College London and Leeds University have invented a fluorescent marker that is able to attach to G4s in living human cells, allowing them to see for the first time how the structure forms and what role it plays in cells.

Rethinking the biology of DNA

One of the lead researchers Dr Marco Di Antonio, who began the work at the University of Cambridge in the laboratory of Professor Sir Shankar Balasubramanian and now leads a research team in the Department of Chemistry at Imperial, said: "For the first time, we have been able to prove the quadruple helix DNA exists in our cells as a stable structure created by normal cellular processes. This forces us to rethink the biology of DNA. It is a new area of fundamental biology, and could open up new avenues in diagnosis and therapy of diseases like cancer.

"Now we can track G4s in real time in cells we can ask directly what their biological role is. We know it appears to be more prevalent in cancer cells and now we can probe what role it is playing and potentially how to block it, potentially devising new therapies."

The team thinks G4s form in DNA in order to temporarily hold it open and facilitate processes like transcription, where the DNA instructions are read and proteins are made. This is a form of 'gene expression', where part of the genetic code in the DNA is activated.

G4s appear to be associated more often with genes involved in cancer, and are detected in larger numbers within cancer cells. With the ability to now image a single G4 at a time, the team say they could track their role within specific genes and how these express in cancer. This fundamental knowledge could reveal new targets for drugs that interrupt the process.

Natural formation

The team's breakthrough in being able to image single G4s came with a rethink of mechanisms usually used to probe the working of cells. Previously, the team had used antibodies and molecules that could find and attach to the G4s, but these needed very high concentrations of the 'probe' molecule. This meant the probe molecules might be disrupting the DNA and actually causing them to form G4s, instead of detecting them naturally forming.

Dr Aleks Ponjavic, now an academic in the Schools of Physics & Astronomy and Food Science and Nutrition at the University of Leeds, jointly lead the research in the laboratory of Professor Sir David Klenerman and developed the method of visualising the new fluorescent marker with microscopy.

He said: "Scientists need special probes to see molecules within living cells, however these probes can sometimes interact with the object we are trying to see. By using single-molecule microscopy, we can observe probes at 1000-fold lower concentrations than previously used. In this case our probe binds to the G4 for just milliseconds without affecting its stability, which allows us to study G4 behaviour in their natural environment without external influence."

For the new probe, the team used a very 'bright' fluorescent molecule in small amounts that was designed to stick to the G4s very easily. The small amounts meant they couldn't hope to image every G4 in a cell, but could instead identify and track single G4s, allowing them to understand their fundamental biological role without perturbing their overall prevalence and stability in the cell.

The team were able to show that G4s appear to form and dissipate very quickly, suggesting they only form to perform a certain function, and that potentially if they lasted too long they could be toxic to normal cell processes.

Facts, background information, dossiers
  • DNA G-quadruplexes
  • single molecule microscopy
More about Imperial College of London
More about University of Cambridge
  • News

    Powering a microprocessor by photosynthesis

    Researchers have used a widespread species of blue-green algae to power a microprocessor continuously for a year - and counting - using nothing but ambient light and water. Their system has potential as a reliable and renewable way to power small devices. The system, comparable in size to a ... more

    Study help to pinpoint cancer culprits

    DNA analysis of thousands of tumours from NHS patients has found a ‘treasure trove’ of clues about the causes of cancer, with genetic mutations providing a personal history of the damage and repair processes each patient has been through. In the biggest study of its kind, a team of scientis ... more

    Scientists identify the cause of Alzheimer’s progression in the brain

    For the first time, researchers have used human data to quantify the speed of different processes that lead to Alzheimer’s disease and found that it develops in a very different way than previously thought. Their results could have important implications for the development of potential tre ... more

  • Videos

    Fighting cancer: Animal research at Cambridge

    Animal research plays an essential role in our understanding of health and disease and in the development of modern medicine and surgical techniques. As part of our commitment to openness, this film examines how mice are helping the fight against cancer. It takes a in-depth look at the faci ... more

    Killer T Cell: The Cancer Assassin

    How does a Killer T Cell Kill its target?The new film captures the behaviour of cytotoxic T cells – the body’s ‘serial killers’ – as they hunt down and eliminate cancer cells before moving on to their next target. more

    The Super-Resolution Revolution

    Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, and in three dimensions. Here, Professor Clemens Kaminski describes how a new era o ... more

More about University of Leeds
  • News

    Higher blood fats make cells share stress

    In patients with metabolic diseases, elevated fat levels in the blood create stress in muscle cells - a reaction to changes outside the cell which damage their structure and function. An international research team led by the University of Leeds and with participation by the University of B ... more

    Protein complex prevents toxic aggregation of proteins

    A protein complex within the cell has been found to play a key role in preventing the toxicity of proteins which build up amyloid plaques and can lead to neurodegenerative disorders such as Alzheimer’s and Huntington’s disease. Researchers from the Universities of Konstanz (Germany), Leeds ... more

    Libraries for Proteins

    Combinatorial libraries are a key component of the chemist's toolkit for ligand screening. Dynamic combinatorial libraries add a new dimension by interlinking synthesis and screening. Now, British scientists have developed a dynamic combinatorial library for the screening of supramolecular ... more