Abstract
Chromatin is organized and compacted in the nucleus through the association of histones and other proteins, which together control genomic activity. Two broad types of chromatin can be distinguished: euchromatin, which is generally transcriptionally active, and heterochromatin, which is repressed. Here we examine the current state of our understanding of repressed chromatin in Caenorhabditis elegans, focusing on roles of histone modifications associated with repression, such as methylation of histone H3 lysine 9 (H3K9me2/3) or the Polycomb Repressive Complex 2 (MES-2/3/6)-deposited modification H3K27me3, and on proteins that recognize these modifications. Proteins involved in chromatin repression are important for development, and have demonstrated roles in nuclear organization, repetitive element silencing, genome integrity, and the regulation of euchromatin. Additionally, chromatin factors participate in repression with small RNA pathways. Recent findings shed light on heterochromatin function and regulation in C. elegans, and should inform our understanding of repressed chromatin in other animals.
Highlights
Chromatin is organized and compacted in the nucleus through the association of histones and other proteins, which together control genomic activity
Its tendency to aggregate and create repressive subnuclear compartments means that it can indirectly influence the organization of euchromatin and gene expression (Francastel et al 2000; Sexton et al 2007)
There are many types of repressed chromatin, reflecting a range of modifications and ligands, heterochromatin was traditionally split into two classes that largely reflect the properties of the underlying DNA
Summary
Chromatin is organized and compacted in the nucleus through the association of histones and other proteins, which together control genomic activity. The LEM-2-associated domains are enriched for H3K9-methylated histones, and their perinuclear positioning is largely dependent on this mark, which is recognized by a nuclear envelope-associated chromodomain protein, CEC-4 (Towbin et al 2012; Gonzalez-Sandoval et al 2015).
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