Relationships between clusters of interchromatin granules and chromatin fibers.

Among nuclear compartments, interchromatin granule clusters (IGCs) are widely regarded as biomolecular condensates implicated in the regulation of gene expression, leading to the production of distinct mRNA species. Nevertheless, their functional dynamics within the nuclear environment remain largely elusive. In this study, we employed multiple transmission electron microscopy approaches to investigate the spatial and structural relationships between IGCs and chromatin. Our observations in HeLa cells demonstrate that IGCs establish physical connections with chromatin fibers. Furthermore, we show that the periphery of IGCs is enriched in decondensed chromatin domains and transcriptional sites. Quantitative analyses reveal that, upon α-amanitin treatment, the number of decondensed chromatin sites near IGCs is significantly reduced compared with untreated cells. In untreated conditions, a positive correlation emerges between IGC size and the abundance of adjacent decondensed chromatin regions. Based on these findings, we propose a model of IGC organization, considering their contacts with chromatin.