Sharing of mitotic pre-ribosomal particles between daughter cells.

Ribosome biogenesis is a fundamental multistep process initiated by the synthesis of 90S pre-ribosomal particles in the nucleoli of higher eukaryotes. Even though synthesis of ribosomes stops during mitosis while nucleoli disappear, mitotic pre-ribosomal particles persist as observed in pre-nucleolar bodies (PNBs) during telophase. To further understand the relationship between the nucleolus and the PNBs, the presence and the fate of the mitotic pre-ribosomal particles during cell division were investigated.

Time-lapse, photoactivation, and photobleaching imaging of nucleolar assembly after mitosis.

Nucleolus assembly starts in telophase with the benefit of building blocks passing through mitosis and lasts until cytokinesis generating the two independent interphasic cells. Several approaches make it possible to follow the dynamics of fluorescent molecules in live cells. Here, three complementary approaches are described to measure the dynamics of proteins during nucleolar assembly after mitosis: (1) rapid two-color 4-D imaging time-lapse microscopy that demonstrates the relative localization and movement of two proteins, (2) photoactivation that reveals the directionality of migration from the activated area, and (3) fluorescence recovery after photobleaching (FRAP) that measures the renewing of proteins in the bleached area.

Influenza A H3N2 subtype virus NS1 protein targets into the nucleus and binds primarily via its C-terminal NLS2/NoLS to nucleolin and fibrillarin.

Background: Influenza A virus non-structural protein 1 (NS1) is a virulence factor, which is targeted into the cell cytoplasm, nucleus and nucleolus. NS1 is a multi-functional protein that inhibits host cell pre-mRNA processing and counteracts host cell antiviral responses. Previously, we have shown that the NS1 protein of the H3N2 subtype influenza viruses possesses a C-terminal nuclear localization signal (NLS) that also functions as a nucleolar localization signal (NoLS) and targets the protein into the nucleolus.

The nucleolus: structure/function relationship in RNA metabolism.

The nucleolus is the ribosome factory of the cells. This is the nuclear domain where ribosomal RNAs are synthesized, processed, and assembled with ribosomal proteins. Here we describe the classical tripartite organization of the nucleolus in mammals, reflecting ribosomal gene transcription and pre-ribosomal RNA (pre-rRNA) processing efficiency: fibrillar center, dense fibrillar component, and granular component.

Assembly and disassembly of the nucleolus during the cell cycle.

The nucleolus is a large nuclear domain in which transcription, maturation and assembly of ribosomes take place. In higher eukaryotes, nucleolar organization in three sub-domains reflects the compartmentation of the machineries related to active or inactive transcription of the ribosomal DNA, ribosomal RNA processing and assembly with ribosomal proteins of the two (40S and 60S) ribosomal subunits. The assembly of the nucleoli during telophase/early G(1) depends on pre-existing machineries inactivated during prophase (the transcription machinery and RNP processing complexes) and on partially processed 45S rRNAs inherited throughout mitosis.