Three papers published online Nature Cell Biology analyse a component of chromatin - the complex of DNA and protein that makes up chromosomes - and identify two new modifications that expand the 'chromatin code'. The research also shows that a variant of this component mediates 'epigenetic memory' - a process of key importance to cloning.
The DNA of a human cell totals about two meters. To prevent the vast stretches of DNA turning into a tangle, the genome is spooled tightly around protein complexes called histones. Recent research has shown that histones also regulate gene activity and a growing number of reversible chemical modifications of these proteins -- collectively called the 'chromatin code' -- have been uncovered and found to regulate gene expression.
Roland Schüle and colleagues identify a new letter in the alphabet of the chromatin code in the form of phosphorylation of a histone called H3 and show that this letter allows genes packaged around the phosphorylated H3 to be activated. In a related paper, Michael Rudnicki and colleagues unravel how Pax7, a key regulator of muscle gene activity, works. By recruiting an enzyme that adds another letter, a methyl-group, to H3 it regulates genes that govern the differentiation of certain stem cells into muscle cells. Finally, John Gurdon and colleagues show how a gene maintains its activity status during the cloning procedure, when a nucleus from a differentiated donor tissue is transplanted into an egg. The memory of the gene status is dependent on a specific variant of H3 called H3.3. Remarkably, this memory was shown to be maintained while the cells of the egg multiply twenty four times.
Roland Schüle (ZKF, Uniklinik-Frauenklinik, Freiburg, Germany)
Michael Rudnicki (Ottawa Health Research Institute, Ontario, Canada)
John Gurdon (Wellcome Trust/Cancer Research UK Gurdon Institute, Cambridge, UK)
Abstracts available online:
(C) Nature Cell Biology press release.
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