Mitotic bookmarking of formerly active genes: keeping epigenetic memories from fading

Abstract

In order for cell lineages to be maintained, daughter cells must have the same patterns of gene expression as the cells from which they were divided so that they can have the same phenotypes. However, during mitosis transcription ceases, chromosomal DNA is compacted, and most sequence-specific binding factors dissociate from DNA, making it difficult to understand how the "memory" of gene expression patterns is remembered and propagated to daughter cells. The process of remembering patterns of active gene expression during mitosis for transmission to daughter cells is called gene bookmarking. Here we discuss current knowledge concerning the factors and mechanisms involved in mediating gene bookmarking, including recent results on the mechanism by which the general transcription factor TBP participates in the mitotic bookmarking of formerly active genes.

Figure 1

Model of TBP-mediated mechanism in “bookmarking” promoters of formerly active genes during mitosis. The model is not meant to imply that no nucleosomes are present on the promoters in mitotic cells, only that these regions are less compacted than most of the genomic DNA at this stage of the cell cycle.