Figure 3. Regulation of Cell-Cycle Checkpoints and DNA Damage Repair Pathways by PcG.

(A) The essential role of PcG proteins in somatic stem cell self-renewal is multifaceted. It involves the regulation of several cell-cycle checkpoints, DNA damage repair pathways, control of differentiation, and prevention of senescence and apoptosis programs. Cell-cycle regulators directly interacting with or repressed by PRC1 and/or PRC2 proteins are indicated in green (PRC1), purple (PRC2), and red (PRC1 and PRC2). The question mark indicates that the role of PcG proteins in the process remains to be confirmed.

(B) PRC1 proteins directly interact with Geminin and mediate its degradation, thereby stabilizing the DNA replication licensing factor CDT1. PcG proteins also interact with CDC6, colocalize with PCNA, and associate with late DNA replication origins.

(C) PcG proteins play an important role in maintaining genome integrity by regulating and interacting with multiple proteins and long noncoding RNAs (lincRNA) involved in DNA damage repair pathways. They also appear to participate in reactive oxygen species metabolism. The asterisk indicates that the involvement of the PRC1 complex in DNA damage-induced monoubiquitylation of lysine 119 of histone H2A (H2AK119ub1) remains unclear. The color code in (B) and (C) is the same as in (A).