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A New Study discovers That A Mysterious Structure Comprises Up To 47% Of Each Chromosome

In schools, we are taught that in the nucleus of each cell, DNA molecules are strongly packed around proteins known as histones to form our chromosomes. But a new study has found that there’s way more to chromosomes than the 25,000 or so genes they comprise, researchers have found that a mysterious 'sheath-like' arrangement accounts for up to 47% of each chromosome.

Human chromosomes. Credit: Wellcome Images

Our understanding, for more than a century, of chromosomes has been built on the guess that they are made from a multipart of histone proteins and DNA called chromatin, formed inside the nucleus of every cell.

Since their finding in 1882, chromosomes have been the topic of concentrated study, but the facts of their interior structure have got away, in no small fragment because chromosomes are absolutely invisible in the cell’s core, except the cell is dividing. When a cell splits through meiosis or mitosis, the chromatin inside develops more strongly packed, triggering the chromosomes to turn into 'supercoiled' and observable under a microscope. Most of what scientists know about chromosomes was establish by witnessing chromosomes during cell separation, but because we can merely observe them under definite conditions, we have been working with an unfinished picture of what a chromosome truly looks like.

To advance our capability to observe the interior structures of chromosomes, scientists from the University of Edinburgh in Scotland established a new way called 3D-CLEM, which syndicates light and electron microscopy with computational demonstrating software to produce the main high-resolution three-dimensional images of all 46 human chromosomes. After demonstrating the length, width, volume, surface area, and DNA filling density of all average human chromosomes, they found something that could have great consequences for our undeveloped understanding of a chromosome’s inner structure.

Daniel Booth is a biologist and also the member of the team, he says, "Describing the structure of altogether 46 human chromosomes for the first time required us to review the idea that they are collected almost totally of chromatin, and guess that has gone principally unchallenged for more or less 100 years,".

In their study, Booth and his team found that chromatin merely accounted for between 53 and 70% of the entire contents of chromosomes. An arrangement is known as the chromosome periphery, something that scientists have caught sights of in the past, but had no actual idea or concept of knowing how broad it was, accounted for the lasting 30 to 47% of the 46 chromosomes. That means for any assumed chromosome, DNA, and its backup proteins might only make up half of the total contents.

They write in their paper, "This first presentation of 3D-CLEM exploration produced the extraordinary, and astonishing, a decision that a very big percentage of the complete volume of mitotic genes is not composed of chromatin, but is instead in the boundary compartment,". At this step, it's imprecise what the purpose of this structure really is, but the scientists suspect it could turn into a kind of 'sheath', keeping genes inaccessible from each another throughout cell division. This is maintained by previous study representing that the structure is at least partially formed as a consequence of the protein Ki-67, a marker for cellular propagation that muddles to the chromosome surface to keep sister chromatids isolated.

If this actually is the job of the chromosome sheath, it means the structure shows a vital role in stopping errors from happening when cells divide, something that can give a clue of birth defects and numerous forms of cancer. Despite its function, there's still a lot we do not know about this mysterious arrangement or structure we are not sure if it behaves like a liquid or a solid film, and it is not clear how it effects the structural variations of chromatin throughout the cellular division. So it appears like it’s back to the diagram board for one of the most important elements of a living cell.

As one of the team member, Bill Earnshaw, says: "We now have to reconsider how chromosomes are made and how they separate when cells split since the genetic material is protected by this dense layer of other material."

The study has been published in Molecular Cell.

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