In eukaryotic organisms chromatin is duplicated during cell division to ensure faithful transmission of both genetic and epigenetic information, maintaining in the daughter cells the memory of the chromatin status of their progenitors. The epigenetic inheritance during DNA replication is crucial to maintain cellular identity following cell division.
The role of Polycomb Repressive complexes (PRC1 and PRC2) is essential for the temporal regulation of gene repression involved in different developmental processes, but how these complexes may interact with the DNA replication machinery to contribute to the mitotic inheritance of cellular identity in the daughter cells remains unknown.
Researchers at CBGP have provided an attractive model for targeting of PRC2 complex to newly synthesized DNA for reestablishment of repressive epigenetic marks after dilution by replication, which has important implications in the understanding of epigenetic inheritance in eukaryotic organisms. They have taken advantage of viable PRC2 and DNA polymerase mutations in Arabidopsis to address the mechanism underlying the maintenance of the epigenetic states during replication. They have also presented sound evidence supporting a role for the catalytic subunit of DNA polymerase ϵ in preserving high H3K27me3 levels at floral target loci. Using flowering time control as a subject, they have examined the function of the Pol ϵ in epigenetic transcriptional silencing and demonstrated the genetic and molecular interaction of this replication protein with PRC2.
Altogether, the data they have presented suggest the existence of interplay between the DNA replication machinery and the PcG complexes in the control of different plant developmental processes, including flowering time, through a mechanism involving epigenetic transcriptional gene silencing and might help to explain how these complexes preserve chromatin modification states during DNA replication.