The “fluid” nature of chromosomes revealed for the first time

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The “fluid” nature of chromosomes revealed for the first time

An observation that changes the established representation of structure carrying the genes.

Each healthy human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes .

Chromosomes are particularly fluid, almost liquid, when they are not in the dividing phase, shows the work of French scientists, who succeeded for the first time to manipulate them mechanically and directly in living cells.

The human body is made up of billions of microscopic cells in the middle of which is a nucleus. This houses the chromosomes in which is found the DNA carrying the genes where the genetic information of an individual is written.

  • Each healthy human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes (44 autosomes and 2 sex chromosomes).
  • Each parent contributes 1 chromosome to each pair. Children get half of their chromosomes from their mother and half from their father.
  • Humans have two types of sex chromosomes, the X and the Y. Females have two X chromosomes and males have one X and one Y.
  • A trait (eye color, hair color, diseases, etc.) .) is a trait determined by genes.
  • Some traits may be the result of genetic mutations that are inherited or are the product of a new mutation.

Researchers associated with the Institut Curie, the Sorbonne University and the French Center for Scientific Research (CNRS) have succeeded in directly manipulating the chromosomes of living cells. By subjecting the chromosomes to different forces, using magnets, they discovered that the chromosomes are actually very fluid, almost liquid, outside of the cell division phases, explains the CNRS in a press release.

To date, the chromosomes were represented as tangled, like balls of wool, and forming a kind of gel. Recent work published in the journal Science (in English) give a different picture. They would be rather fluid, able to move and reorganize freely without constraint from the other constituent elements in the nucleus.

To arrive at this observation, Dr Antoine Coulon of the Institute Curie and his colleagues attached magnetic nanoparticles to a small portion of the chromosome of a living cell to then stretch it and exert different intensities of forces on it, thanks to the attraction of a micromagnet.

Using this approach, the teams have succeeded, for the very first time in a living cell, in measuring the response of a chromosome to external forces, notes the press release

This experiment has found that the scale of forces naturally exerted in the nucleus, for example by DNA-replicating enzymes, is sufficient to alter the conformation of the chromosome.

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This new knowledge is of great importance since, until today, our understanding of the physical principles that organize the genome in the nucleus has been limited by the lack of tools to exercise and directly measure forces on the chromosomes and to probe their material nature.

The approach developed by the French team now makes it possible to do this. It has made it possible to observe viscoelastic displacements of chromosomes over micrometers, in a few minutes, in response to external forces.

The technique thus makes it possible to bring new elements of understanding on biological processes, on the biophysics of the chromosome and on the organization of the genome. In addition, it opens up new research perspectives in areas ranging from chromosome mechanics to genome functions.

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