From snapshots to moving pictures: new perspectives on nuclear organization

The positioning of chromosomal domains in the interphase nucleus is proposed to facilitate gene regulation in simple cells such as yeasts and to coordinate patterns of gene expression and activation of origins of replication during cell differentiation in complex organisms. Over the past 10-12 years, detailed information on the organization of interphase chromosomes has accumulated from three-dimensional microscopy of fixed cells labeled by in situ hybridization and immunofluorescence techniques. Recently, time-lapse fluorescence microscopy of GFP-tagged domains has shown that interphase chromatin can be highly dynamic, moving distances >0.5 mum within seconds. Novel fluorescence techniques show that most nuclear proteins are also highly mobile. Both the rapid oscillations of chromatin and long-range movements of chromosomes suggest new mechanisms for spatial and temporal control of transcription and other nuclear events.