Polycomb Responds to Low Levels of Transcription

Publication date: 25 July 2017
Source:Cell Reports, Volume 20, Issue 4
Author(s): Georgina Berrozpe, Gene O. Bryant, Katherine Warpinski, Dan Spagna, Santosh Narayan, Shivangi Shah, Mark Ptashne
How is Polycomb (Pc), a eukaryotic negative regulator of transcription, targeted to specific mammalian genes? Our genome-wide analysis of the Pc mark H3K27me3 in murine cells revealed that Pc is preferentially associated with CpG island promoters of genes that are transcribed at a low level and less so with promoters of genes that are either silent or more highly expressed. Studies of the CpG island promoter of the Kit gene demonstrate that Pc is largely absent when the gene is silent in myeloid cells, as well as when the gene is highly expressed in mast cells. Manipulations that increase transcription in the former case, and reduce it in the latter, increase Pc occupancy. The average negative effect of Pc, we infer, is about 2-fold. We suggest possible biological roles for such negative effects and propose a mechanism by which Pc might be recruited to weakly transcribed genes.

Graphical abstract

Teaser

Berrozpe et al. assayed occupancy of the Polycomb mark H3K27me3 genome-wide and at a specific gene (Kit) when transcribed at different levels. They report that Polycomb is preferentially recruited to genes expressed at a low level.


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