REGULARITIES IN THE ASSEMBLY OF NUCLEOLUS-DERIVED FOCI IN VARIOUS CULTURED MAMMALIAN CELLS DURING MITOSIS
O. O. Zharskaya, O. V. Zatsepina 1
A. N. Belozersky Institute of Physical and Chemical Biology, Moscow State University
and M. M. Shemyakin-Yu. A. Ovchinnikov Institute of Bioorganic Chemistry RAS, Moscow, Russia;
1 e-mail: zatsepina_olga@mail.ru
During mitosis, rebuilding of the nucleolus is a step-wise process that, above all, includes an assembly of
nucleolus-derived foci (NDF) in the cytoplasm of telophase cells. In this study, we performed a comparative analysis of NDF
formation in mitotic cells of various mammalian cell cultures, such as green monkey CV1 cells, human HeLa cells, mouse 3T3 cells,
and pig PK cells, both in control and following inhibition of rRNA synthesis by actinomycin D or by an adenosine analogue, DRB.
The results obtained show that in all examined cell types NDF are formed shortly after or simultaneously with the onset of
chromosome segregation to the poles of the mitotic spindle. However, an efficiency of NDF assembly, i. e. the number of NDF per
anaphase or telophase cell, and the portion of anaphase and telophase cells containing NDF vary in different cell cultures,
being most prominent in CV1 and HeLa cells. In these cells, the vast majority of NDF accumulate several proteins of the mature
nucleolus, such as B23/nucleophopmin, C23/nucleotin, fibrillarin, and, to a lesser extent, Nop52. The rRNA harbored by NDF is
synthesized several hours prior mitosis, and plays an essential role the maintenance of NDF structural integrity. Starting from
early stages of the assembly onwards, the NDF are predominantly located in the area occupied by aster microtubules of the mitotic
spindle.
Key words: nucleolus, mitosis, nucleolus-derived foci, nucleolar proteins
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