Histone dynamics, heritability and variants

Published on October 1, 2007 Updated on May 16, 2022   38 min

A selection of talks on Cell Biology

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In this talk, I'd like to discuss with you the issue concerning histone dynamics, their heritability, and their existence in the form of variants.
DNA in the nucleus is present in the form of chromatin, and that consists of a complex together with proteins. The main proteins found in chromatin are called histones. They are small, basic proteins called H3, H4, H2A, and H2B for the core histones and H1 for the linker histone. They ensure the compaction of DNA in the nucleus. In the human cells about 2 meters of DNA will fit in a volume of about a few micrometers for the diameter of common somatic cells. And this is represented here with a tennis ball on the right-hand panel. So that will impose a problem of accessibility to the DNA for all DNA transactions, which thus necessitates dynamic properties in order for all the metabolic pathways of the DNA level to operate. The additional aspect that histones can bring in the chromatin organization is a source of information. Indeed, this organization can contribute to a differential use of genetic information provided by the DNA and thus, ensure a functional diversity in the different cells. Then the question that ensues is, how is it established, and how can it be inherited? If we now come to compaction,
which is the first aspect I wanted to present, in the chromatin organization as depicted by this watercolor, which was drawn by Nicolas Bouvier from the ?"???? you can see that there are different levels that ensure this compaction in the nucleus. First, you have the DNA in the form of a helix, which is wrapped around the core histones to form the nucleosome—the sort of tennis ball that was represented before— which then folds up further to give chromatin fibers, which further fold up and then organize in the nucleus to form different domains. So this high level of compaction is dynamic, and the enzymes that have to get access to DNA have to deal with this kind of organization. So if we get back to the DNA helix