Philipp Oberdoerffer & David A. Sinclair
Eukaryotes come in many shapes and sizes, yet one thing that they all seem to share is a decline in vitality and health over time — a process known as ageing. If there are conserved causes of ageing, they may be traced back to common biological structures that are inherently difficult to maintain throughout life. One such structure is chromatin, the DNA–protein complex that stabilizes the genome and dictates gene expression. Studies in the budding yeastSaccharomyces cerevisiae have pointed to chromatin reorganization as a main contributor to ageing in that species, which raises the possibility that similar processes underlie ageing in more complex organisms. Chromosomes are arguably the most difficult structures a cell has to maintain over a lifetime. The DNA in each chromosome experiences thousands of chemical alterations and DNA breaks in a single day, and the information each encodes requires strict regulation to maintain cellular identity and function. To manage these tasks, eukaryotes have evolved a complex packaging system known as chromatin, in which DNA is wrapped around a protein core of four different histone dimers and forms a nucleosome, the basic building block of chromatin. Recent studies have indicated that chromatin is a highly dynamic form of nuclear organization that influences DNA stability and gene-expression patterns1, 2. The level of chromatin compaction can be modulated through the chemical modification of histones (Box 1) or of DNA. The more densely the nucleosomes are packed, the more protected is the DNA from chromosomal damage3, but the less accessible it is for transcription2. Highly compacted, transcriptionally silent chromatin is known as heterochromatin, whereas more accessible chromatin is known as euchromatin (Box 2).
Xanya Sofra Weiss
Xanya Sofra Weiss
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