The department provides electron mi-croscopic facilities for research in molecular biology, virology and cell biology.

Based on electron-microscopic, im-munocytochemical and biochemical studies, the principle of "discreteness" of chromo-some organisation in higher eukaryotes has been proposed. According to this principle, chromosome is built up from hierarchical system of structural levels of chromatin fibber compactization (nucleomeres, chromomeres, chromosomal bands).

Centriolar cycle was described and it was shown that maturation of the centriole continues for one and a half cell cycle. It was found that majority of microtubules radiating from the centrosome are 1-2 um long. Free microtubules appear in the cytoplasm of an interphase cell by three different pathways. Spontaneous assembly is a major source of free (non-centrosomal) microtubules in epithelial cells. Stability of the minus end is necessary for free microtubules formation.

New centrosomal protein-kinase of Xenopus laevis was described. Distribution of this protein has cell cycle-dependent manner. EG2 bind to the microtubules and is involved in bipolar mitotic spindle assembly.

With a help of light and electron imu-nocytochemistry we studied specific peculi-arities in behaviour of the major nucleolar proteins involved in the key steps of ribosome biogenesis. In vivo and in vitro models a structural association of the nucleolar protein B23/nucleophosmin with the poles of the mi-totic spindle was demonstrated. An experi-mental approach that allows to reproduce the dynamics of the structural nucleolar altera-tions normally occur during mitosis was elaborated for the interphase nucleoli of cul-tured mammalian cells.

The special type of chondriom organi-sation - mitochondrial reticulum has been found, in which individual mitochondria are connected through specific junctions. An ex-perimental evidence was obtained for "electrical cable" function of mitochondrial reticulum.

1. Zatsepina O.V., Polyakov V.Yu., Chentsov Yu.S. Chromonema and chromomeres - structural units of mitotic and interphase chromosomes. Chromosoma (1983) 88, 91-97.

2. Vorobjev I.A., Svitkina T.M., Borisy G.G. Cytoplasmic assembly of microtubules in cultured cells. J. Cell Science (1997) 110, 2635-2645.

3. Zatsepina O.V., Dudnic O.A., Chentsov Yu.S., Thiry M., Spring H., Trendelenburg M.F. Reassembly of nucnctional nucleolus following in situ unravelling by low-ionic-strength treatment of cultured mammalian cells. Exp. Cell Res. (1997) 233, 155-168.

4. Roghi C., Giet R., Uzbekov R., Morin N., Chartrain I., Le Guellec R., Couturier A., Doree M., Philippe M., and Prigent C. The Xenopus Protein Kinase pEg2 Associated with the Centrosome in the Cell Cycle-Dependent Manner, Bind to the Spindle Microtubules and is involved in Bipolar Mitotic Spindle Assembly. J. Cell Sci. (1998) 111, 157-172.

5. Amchenkova A.A., Bakeeva L.E., Chentsov Yu.S., Skulachev V.P., Zorov D.B. Coupling membranes as energy-transmitting cables. I. Filamentous mitochondria clusters in cardiomyocytes. J.Cell Biology (1988) 107, 485-491.