Genome complexity: splitting maintains identity (Introduction)

by David Turell , Friday, November 17, 2023, 18:54 (161 days ago) @ David Turell

Using markers;

https://www.sciencedaily.com/releases/2023/11/231116150849.htm

"A new theoretical model helps explain how epigenetic memories, encoded in chemical modifications of chromatin, are passed from generation to generation. Within each cell's nucleus, researchers suggest, the 3D folding patterns of its genome determines which parts of the genome will be marked by these chemical modifications.

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"The research team suggests that within each cell's nucleus, the 3D folding pattern of its genome determines which parts of the genome will be marked by these chemical modifications. After a cell copies its DNA, the marks are partially lost, but the 3D folding allows each daughter cell to easily restore the chemical marks needed to maintain its identity. And each time a cell divides, chemical marks allow a cell to restore its 3D folding of its genome. This way, by juggling the memory between 3D folding and the marks, the memory can be preserved over hundreds of cell divisions.

"'A key aspect of how cell types differ is that different genes are turned on or off. It's very difficult to transform one cell type to another because these states are very committed," says Jeremy Owen PhD '22, the lead author of the study. "What we have done in this work is develop a simple model that highlights qualitative features of the chemical systems inside cells and how they need to work in order to make memories of gene expression stable."

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"In their new study, Mirny and his colleagues wanted to answer the question of how those epigenetic marks are maintained from generation to generation. They developed a computational model of a polymer with a few marked regions, and saw that these marked regions collapse into each other, forming a dense clump. Then they studied how these marks are lost and gained.

"When a cell copies its DNA to divide it between two daughter cells, each copy gets about half of the epigenetic marks. The cell then needs to restore the lost marks before the DNA is passed to the daughter cells, and the way chromosomes were folded serves as a blueprint for where these remaining marks should go."

Comment: cell division must have these complex controls which are irreducibly complex and must be designed