Abstract
Polycomb group (PcG) proteins contribute to the formation and maintenance of a specific repressive chromatin state that prevents the expression of genes in a particular space and time. Polycomb repressive complexes (PRCs) consist of several PcG proteins with specific regulatory or catalytic properties. PRCs are recruited to thousands of target genes, and various recruitment factors, including DNA-binding proteins and non-coding RNAs, are involved in the targeting. PcG proteins contribute to a multitude of biological processes by altering chromatin features at different scales. PcG proteins mediate both biochemical modifications of histone tails and biophysical modifications (e.g., chromatin fiber compaction and three-dimensional (3D) chromatin conformation). Here, we review the role of PcG proteins in nuclear architecture, describing their impact on the structure of the chromatin fiber, on chromatin interactions, and on the spatial organization of the genome in nuclei. Although little is known about the role of plant PcG proteins in nuclear organization, much is known in the animal field, and we highlight similarities and differences in the roles of PcG proteins in 3D gene regulation in plants and animals.
Highlights
IntroductionPolycomb group (PcG) proteins were unified in a common family on the basis of their similar impact on development and their transcriptional repressive function, but they have various molecular activities [3,4,5,6]
This study revealed that local chromatin compaction precedes the establishment of H3K27me3 and provides a better substrate for PRC2 activity [81]
Important aspects of this first dimension include recruitment at specific genomic regions, modification of histone tails, compaction of nucleosomes, and interplay with other factors to form Polycomb-repressed chromatin domains that shape the epigenetic topography of the genome
Summary
Polycomb group (PcG) proteins were unified in a common family on the basis of their similar impact on development and their transcriptional repressive function, but they have various molecular activities [3,4,5,6]. Beyond their originally identified roles in controlling the sequence and timing of developmental switches and in maintaining cell and organ identity both in animals and plants [7,8], it is clear that PcG proteins accomplish a variety of functions. We present a brief overview of the molecular functions, recruitment, and regulation of PcG, with an emphasis on new research that highlights the roles of PcG proteins at different nuclear scales
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