Structure, organization, and dynamics of promyelocytic leukemia protein nuclear bodies.

The interphase nucleus compartmentalizes its components to give rise to a highly organized and tightly controlled environment. Individual chromosomes occupy discrete areas, termed “chromosome territories,” that are separated from each other by a channel called the “interchromosomal domain” (reviewed in Lamond and Earnshaw 1998). Actively transcribed genes tend to be at the periphery of chromosomal territories, whereas newly made RNA transcripts localize into the interchromosomal domain, where they can undergo further processing and transport. Movement within the nucleus (Ferreira et al. 1997) may permit chromosomes to enter “factories” that contain all the necessary enzymatic machinery for replication (reviewed in Jackson 1995). Of the many discrete domains identified throughout the nucleus, the largest are nucleoli, sites of ribosomal RNA synthesis and processing, and sites of preribosomal particle assembly (reviewed in Scheer and Weisenberger 1994). Other subnuclear bodies that appear as punctate structures under immunofluorescence (IF) microscopy include various dynamic structures involved in the maintenance and replication of DNA and RNA synthesis, processing, and transport (reviewed in Nickerson et al. 1995): replication foci, transcript foci, speckled domains, coiled bodies, gems, and promyelocytic leukemia protein (PML) nuclear bodies. Spliceosomal small nuclear (sn) ribonucleoprotein (RNP) components and a subset of non-snRNP splicing factors can be found concentrated in discrete subnuclear domains called “coiled bodies” (Matera and Frey 1998 [in this issue]). It is becoming increasingly apparent that the nucleus has an organization and contains a number of discrete macromolecular domains that coordinate a variety of nuclear processes.