Structural organization of the nucleolus as a consequence of the dynamics of ribosome biogenesis

Abstract

The nucleolus is a domain of the cell nucleus in which transcription, maturation, and assembly of ribosomes take place. The size and organization of the nucleolus are directly related to ribosome production. In higher eukaryotes, three principal nucleolar structures (FC, DFC, and GC) are defined by electron microscopy. This organization reflects the compartmentation of the machineries related to rDNA transcription, ribosomal RNA processing, and assembly of the two (40S and 60S) ribosomal subunits. The dynamics of these processes play a key role in this organization. The assembly of the nucleoli in telophase/early G1 depends on pre-existing machineries (transcription machinery and processing complexes) and partially processed 45S rRNAs inherited through mitosis. The 45S rRNAs nucleate the PNBs and order the dynamics of nucleolar assembly. The nucleolus is associated with several chromatin domains in addition to the NOR-bearing chromosomes and it has a specific relationship with the nuclear envelope. © 2011 Springer Science+Business Media, LLC.