Nuclear functions in space and time: gene expression in a dynamic, constrained environment.

All eukaryotic cells enclose their genome within a dedicated, membrane-bound organelle termed the nucleus, which functions to partition gene transcription from sites of protein translation in the cytoplasm. Despite a great deal of research effort, basic questions about chromosome structure and gene expression mechanisms remain to be answered, including the relationship between the spatial organization of the genome and the transcription machinery. Powerful in vivo approaches are allowing researchers to test established in vitro concepts within the dynamic cellular environment, while genome-wide screens have enabled rapid high throughput analyses of both structural and functional parameters. In several cases, as highlighted here, this has turned up surprising results and has forced a re-evaluation of models for nuclear structure and gene regulation.