An E(z) escape from Pacman ensures Polycomb silencing Free

Polycomb-mediated gene repression is a robust epigenetic mechanism that tightly regulates the expression of developmental genes. Much is known regarding the different proteins that make up Polycomb group (PcG) complexes and how they interact with chromatin; however, the mechanism that regulates the dynamic activity of PcG proteins during development is less well understood. Now, Susumu Hirose and colleagues uncover a novel role for Mbf1 protein in protecting the mRNA of E(z) – a core component of the Polycomb repressive complex 2 (PRC2) – from degradation. The authors show how expression of E(z) protein is severely compromised in Psc¹/+; mbf1²/+ Drosophila mutants and perform RNA-immunoprecipitation (RIP) experiments to demonstrate preferential binding of Mbf1 to E(z) mRNA. RNA protection assays show how the 5′-3′ exoribonuclease Pacman (Pcm), previously shown to degrade decapped mRNA, cannot degrade E(z) mRNA in the presence of Mbf1. The authors also perform RIP-seq analysis and identify other mRNAs regulated by Mbf1, namely GstD5, Ide, Tep2 and Pebp1. Taken together, these results demonstrate a role for cytoplasmic Mbf1 in the regulation of Polycomb-mediated gene silencing during development and open up new avenues of research into the regulation of mRNA stability by cytoplasmic Mbf1.