6th ESACP Congress, Heidelberg, April 7-11, 1999

A083
THREE-DIMENSIONAL COLOCALIZATION OF NUCLEOLIN, UBF AND DNA DURING INTERPHASE AND MITOSIS: A STUDY USING CONFOCAL MICROSCOPY AND VOLUME RENDERING
Klein C, Cheutin T, O'Donohue MF, Kaplan H, Lucas L, Ploton D

Unité Médian, EA 2063, IFR 53, Reims, France

3D localization of nucleolin, an rRNA maturation nucleolar protein, was studied during interphase and mitosis in human KB cells, using confocal microscopy and volume rendering visualization. Its localization was compared to that of DNA and UBF (Upstream Binding Factor), which remains associated to rDNA genes throughout the cell cycle. During interphase, the nucleolin labeling was localized in structures forming networks in the nucleoli and was essentially not colocalized with UBF which was present in numerous necklace structures. During prophase, the network organization of the nucleolin labeling was lost and this protein was present in large remnants of homogeneous aspect. These nucleolar remnants were thereafter expelled at the periphery of the metaphase plate, where they progressively desagregated in numerous cytoplasmic granules and a faint perichromosomic labeling. At this step, nucleolin was not detected in the NORs in contrast to UBF. During telophase, some cytoplasmic granules were found in close contact with prenuclei surface, even forming connections with intranuclear nucleolin already present in prenucleolar bodies (PNBs). Some of the PNBs were associated with NORs i.e. with UBF. In conclusion, during the cell cycle, nucleolin has a localization similar to other maturation-associated proteins, whose behaviour is totally different from that of transcription associated proteins.