The Polycomb group (PcG) system represses the transcription of important developmental regulators and perpetuates this repression across multiple cell divisions. Inputs from outside the cell can influence PcG function by recruiting additional chromatin factors to PcG-regulated loci or by downregulating the PcG genes themselves. These types of PcG system modulation allow context-dependent induction of genes during development, in cancer, and in response to changes in the environment. In this review, we outline instances where molecular players in this process have been recently identified, comparing and contrasting different ways in which derepression is achieved, and projecting directions for future research.
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