Polycomb response elements (PREs) are regulatory switch elements that can direct the genes that they control to be either active or silenced. Once decided, this on or off state is maintained through subsequent cell divisions. We do not know how the switching works, or how it is copied to newly replicated chromosomes. Experiments that switch a silenced PRE to an active state have provided insights into both questions. A PRE switched experimentally can remember its previously silenced state and return to (...) it after several cell divisions. In the most recent study of this phenomen on,(1) the data show that several distinct variables affect the ability of PREs to “remember” and restore their previous state. The authors' interpretation of these results is discussed here. BioEssays 23:566–570, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

Noncoding RNA has arrived at centre stage in recent years with the discovery of “hidden transcriptomes” in many higher organisms. Over two decades ago, noncoding transcripts were discovered in Drosophila Hox complexes, but their function has remained elusive. Recent studies1-3 have examined the role of these noncoding RNAs in Hox gene regulation, and have generated a fierce debate as to whether the noncoding transcripts are important for silencing or activation. Here we review the evidence, and show that, by taking developmental (...) timing into account, some of these apparently conflicting results can be resolved. We examine current models that explain these data and explore alternative interpretations. BioEssays 30:110–121, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

For stem cells, life is full of potential: they have a high capacity to proliferate and a wide choice of future identities. When they differentiate, cells leave behind this freedom and become ever more committed to a single fate. Intriguingly, the Polycomb and Trithorax groups of proteins are vital to the very different natures of both stem cells and differentiated cells, but little is known about how they make the transition from one cell type to the other. A recent paper1 (...) throws light on this mystery, showing that the Polycomb proteins dramatically change their behaviour at a crucial moment of differentiation. BioEssays 28: 330–334, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

How fast? How strong? How many? So what? Why do numbers matter in biology? Chromatin binding proteins are forever in motion, exchanging rapidly between bound and free pools. How do regulatory systems whose components are in constant flux ensure stability and flexibility? This review explores the application of quantitative and mathematical approaches to mechanisms of epigenetic regulation. We discuss methods for measuring kinetic parameters and protein quantities in living cells, and explore the insights that have been gained by quantifying and (...) modelling dynamics of chromatin binding proteins. (shrink)