PREMATURE ASSEMBLY OF NUCLEOLUS-DERIVED FOCI INDUCED BY A REVERSIBLE HYPOTONIC SHOCK TREATMENT OF METAPHASE
CV1 AND HeLa CELLS
O. O. Zharskaya, O. V. Zatsepina 1
A. N. Belozcrsky 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
The assembly of nucleolus-derived foci (NDF) in the cytoplasm of telophase cells is an early stage of nucleolus
reassembly during mitosis. In current literature, significant attention is paid to the molecular composition of NDF and their
participation in reassembly of the mature nucleolus. However, very little is known about mechanisms controlling the NDF formation.
The authors have demonstrated for the first time that a reversible action of low ionic strength buffers (lypotonic shock
treatment) on living mitotic human HeLa and green monkey CV1 cells triggers a premature assembly of NDF at metaphase. Like the
true NDF, i. e., those assembled in telophase mitosis, NDF prematurally induced at metaphase contain RNA and proteins required
for rRNA processing (fibrillarin, B23/nucliophosmin, C23/nucleolin), but lack UBF, an auxiliary factor of RNA polymerase I.
We have assumed that a reversible action of hypotonic shock on metaphase cells may result in temporal increase in intracellular
[Ca2+](i) that, in its turn, may induce a premature assembly of NDF under isotonic conditions. The structural
integrity of the mitotic spindle apparently plays an essential role in the response of metaphase cells to hypotonic shock
treatments.
Key words: nucleolus, mitosis, nucleolus-derived foci, mechanisms of the NDF assembly
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