PcGTrxG

PcGTrxG refers to the coordinated network of Polycomb Group (PcG) and Trithorax Group (TrxG) chromatin regulators that maintain transcriptional states across cell divisions. Originating from studies in Drosophila, PcGTrxG components are conserved across plants and animals and form an antagonistic system that preserves cellular memory during development and differentiation.

PcG complexes primarily enforce repression. The best characterized pairs are Polycomb Repressive Complex 1 (PRC1) and PRC2. PRC2 deposits the repressive histone mark H3K27me3, while PRC1 ubiquitylates H2A at lysine 119, reinforcing silencing and chromatin compaction. Recruitment often involves Polycomb response elements in Drosophila and, in mammals, CpG-rich regions, noncoding RNAs, and transcription factors that guide the complexes to target loci. PcG-mediated repression is crucial for silencing developmental regulators in inappropriate contexts and for maintaining stable gene expression programs.

TrxG complexes oppose PcG activity to promote gene activation. They include COMPASS-like assemblies and related SET-domain methyltransferases (such as MLL/SET1 family) that catalyze H3K4 methylation, an activating mark. Additional TrxG factors recruit chromatin remodelers and histone acetyltransferases to sustain accessible chromatin and transcription, supporting active transcription and rapid response to signals. The coexistence of activating marks (e.g., H3K4me3) with repressive marks at certain loci in stem cells creates bivalent domains, poised for activation or repression during differentiation.

Biologically, PcGTrxG controls key developmental decisions, stem cell maintenance, and lineage specification. Dysregulation is linked to developmental disorders and cancer. Research methods include ChIP-based assays, CUT&RUN, and genetic perturbations to map binding, catalysis, and functional outcomes in various organisms.