Apart from nuclear compartmentalization (see previous post), effect of transcription factors and histone modifications, another general regulation mechanism of gene expression exists which transcedes the generations and carries the epigenetic information. Methylation at CpG sites in the promoters is a known repressor of transcription; these methylations however portray a rather static landscape of gene regulation; i.e. until now. Authors of this paper make the case for a dynamic scene regarding methylation status at the CpG dinucleotides. Their results (e.g. see the figure below) show a cyclical methylation and de-methylation of pS2 promoter with a periodocity of ~100 minutes (compared to the constitutively expressed promoter PPIA).
The role of this sinuoidal methylation/de-methylation is unknown but one can envisage many key properties that may emerge from this behavior. For example, a general circadian rhythm may be in charge, thus controling the time-scale in which the genes are expressed relative to each other. Moreover, this rhythmic expression, in fact, is capable of increasing the efficiency by which the transcript levels can be controlled.
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