3D imaging reveals that only half of a chromosome is DNA

Credit: Pixabay
Credit: Pixabay

A newly developed microscopy technique by scientists at the University of Edinburgh has allowed them to study the structure of chromosomes in unprecedented detail, leading to new insights. The method known as 3D-CLEM combines light and electron microscopy with computational modelling software to produce high-resolution 3D images of chromosomes.

Since their discovery in 1882, chromosomes have been the focus of intensive study and their complete organisation and structure have remained a mystery, inspite of major technical advances.

The 3D models of all 46 human chromosomes produced by this method has revealed that DNA makes up only half of the material inside chromosomes – far less than was previously thought. Up to 47 percent of their structure is a mysterious sheath that surrounds the genetic material.

While the precise function of this sheath is unknown, researchers suggest it may keep chromosomes isolated from one another during the key process of cell division.

Researchers say this so-called chromosome periphery could help to prevent errors from occurring when cells divide – a hallmark of some forms of cancer and diseases associated with birth defects.

The imaging technique we have developed to study chromosomes is truly groundbreaking. Defining the structure of all 46 human chromosomes for the first time has forced us to reconsider the idea that they are composed almost exclusively of chromatin, an assumption that has gone largely unchallenged for almost 100 years.

Dr Daniel Booth School of Biological Sciences

DNA content

Analysis of the images reveals that material containing DNA and supporting proteins – known as chromatin – accounts for between 53 and 70 percent of the total contents of chromosomes. The remaining 30 to 47 percent is composed of the chromosome periphery.

The study was published in the journal Molecular Cell, was funded by The Wellcome Trust. The research was carried out in collaboration with the Kazusa DNA Research Institute, Japan, National Cancer Institute, US, and the University of Liverpool.

“We now have to re-think how chromosomes are built and how they segregate when cells divide, since the genetic material is covered by this thick layer of other material.”