Summary: The nucleus--a close-knit community of dynamic structures.

The 75th Cold Spring Harbor Symposium on Nuclear Organization and Function explored topics ranging from nucleosomes to nuclear pores. Exciting new genomic and imaging technologies have been used to characterize the nuclear interior, which consists of stable chromatin territories, dynamic domains, and self-organizing nuclear bodies. Histone variants and chaperones, posttranslational modifications, and ATP-dependent remodelers mediate nucleosome dynamics, regulated by Polycomb and other chromatin-associated proteins. Epigenetic memory is an emergent property of chromatin dynamics that is key to understanding how differentiated cells can become reprogrammed. Nuclear body composition and structure are becoming increasingly well understood, although their functions, if any, remain speculative. The nuclear envelope is strengthened by a fibrous lamin network that anchors chromosomes and represses gene expression, and disruption can lead to disease. Nuclear pores regulate the flow of substrates and products, using unstructured polypeptides to filter small molecules and flexible walls that allow large macromolecular assemblages to pass through. At mitosis, nucleosomes collapse into tightly packed nonfibrous cylinders that are then pulled to opposite poles at their kinetochores, where novel centromeric nucleosomes, mitotic motors, and spindle microtubules come together. By considering these complex processes in the context of the nucleus, the Symposium provided a coherent view of the genome in its native habitat.