When they are not in their division phases, chromosomes are fluid, though not quite liquid. This discovery was made possible by the first-ever direct mechanical manipulation of chromosomes in the nucleus of live cells. Previously, chromosomes, which are extraordinarily long DNA molecules, were represented as entangled like loose balls of yarn and creating a sort of gel. This new publication’s findings present a completely different picture. Chromosomes are fluid and free to move, unrestricted by the other parts that make up the nucleus and can reorganize themselves. To reach these conclusions published in Science, scientists from CNRS, the Curie Institute, and Sorbonne University, working in the Nuclear Dynamics, Physical Chemistry and Cell Biology, and Cancer laboratories, in collaboration with scientists from the Massachusetts Institute of Technology, attached magnetic nanoparticles to a small portion of a chromosome in a living cell. Then, they stretched the chromosome, exerting different degrees of force, thanks to a micro-magnet outside the cell. Using this approach, the teams managed to measure the response of a chromosome to external forces, for the very first time in a living cell. Through these experiments, the scientists were able to see that the range of forces exerted naturally in the nucleus – for example by enzymes replicating DNA – is sufficient to substantially alter the conformation of a chromosome. This major discovery, at the interface between physics and biology, changes the hitherto established representation of chromosomes. It also adds new elements to our understanding of biological processes, the biophysics of chromosomes, and the organization of the genome. Reference: “Live-cell micromanipulation of a genomic locus reveals interphase chromatin mechanics” by Veer I. P. Keizer, Simon Grosse-Holz, Maxime Woringer, Laura Zambon, Koceila Aizel, Maud Bongaerts, Fanny Delille, Lorena Kolar-Znika, Vittore F. Scolari, Sebastian Hoffmann, Edward J. Banigan, Leonid A. Mirny, Maxime Dahan, Daniele Fachinetti and Antoine Coulon, 28 July 2022, Science.DOI: 10.1126/science.abi9810
