[DNA-containing polygonal structures detected in somatic nuclei of Bursaria ovata during preparation to cryptobiosis]. / DNK-soderzhashchie poligonal'nye struktury, vyiavliaemye v somaticheskikh iadrakh infuzorii Bursaria ovata pri podgotovke k kriptobiozu.

Supramolecular chromatin organization of the somatic nucleus (macronucleus--Ma) was studied in a free-living unicellular eukaryotic organism, the ciliate Bursaria ovata Beers 1952, at two late successive stages of its encystment (in the state of preparation to cryptobiosis). A modified Miller's method (Sergejeva et al., 1987) and the same technique in combination with high resolution DNA autoradiography were used. In chromatin spread preparations of Ma, not labeled by 3H-thymidine, numerous electron dense structures (rounded, stick-like and polygonal) were revealed, along with rarely occurring typical supramolecular chromatin structures, such as nucleosomic and not nucleosomic threads, nucleomeres, chromomeres, rosette-like looping chromatin, and electron dense chromonemes (Fig. 1). For DNA visualizing in the revealed polygonal structures, the vegetative cells (trophonts) of B. ovata were inoculated into the culture medium, containing 3H-thymidine and food (ciliates Paramecium caudatum). Here, the ciliates passed through 3-4 successive cell division cycles, thus progressively accumulating the radioactive DNA precursor in Ma. After washing the ciliates in 3H-thymidine-free culture medium, the process of their encystment was induced, and Ma were isolated by hand from the ciliates being at two late successive stages of encystment. Isolated Ma were dispersed in the low ionic solutions, as described elsewhere (Sergejeva et al., 1987). The carbon shadowed electron grids, that contained spread Ma preparations, were individually coated with photographic emulsion, according to the loop interference method (Angelier et al., 1976a; Bouteille, 1976). After a 6 month exposure at 4 degrees C, thymidine incorporation was revealed in fibril crowds, rosette-like structures (Fig. 2), and crystal-like plates of different size and morphology (Fig. 3). In all our experiments, non-specific localization of radioactive DNA precursor was not observed. The above data confirm undoubtedly our earlier assumption (Sergejeva et al., 1987; Sergejeva, Bobyleva, 1988) that the Ma chromatin of Bursaria may undergo crystallization during encystment, i.e. in the state of preparation to cryptobiosis. The present data enable us first to suggest that the looping rosette-like chromatin may be transformed into crystal-like structures ("exotic liquid crystal structures") by means of a peculiar loop packing within the limits of an individual resette (Fig. 2-4), these structural transformations taking place without any visible loop destruction. In this paper, we first describe new morphological types of polygonal plates, differing from those earlier reported elsewhere for the Ma of Bursaria (Sergejeva, Bobylova, 1988), and also from the plates earlier described in studies on liquid crystals both in vivo and in vitro (see: Gianonni et al., 1969; Lerman, 1974; Livolant, 1991: Leforestier et al., 1993, 1997, 1999). The technical approaches used in the present work enabled us to obtain, for the first time, a direct evidence of the presence of DNA in the crystallized structures of somatic nuclei of ciliates during their preparation to cryptobiosis, the DNA-containing polygonal structures being highly morphologically diverse. Further studies into the reasons of this diversity are needed.

[Effects of altered gravity on the culture of unicellular eucaryotic organisms, Bursaria truncatella (Ciliophora)]. / Vliianie izmenennoi sily tiazhesti na kul'turu odnokletochnykh éukarioticheskikh organizmov Bursaria truncatella (Ciliophora).

The paper reports the results of experiments with centrifugation and clinostating. Growth rate, cellular division and several morphofunctional characteristics of unicellular organisms of infusoria Bursaria truncatella in culture were studied under normal (1 g), elevated (hypergravity at 2 and 5 g), and compensated gravity. The data point to certain changes in the functional activity and morphology of cells consequent to long-time cultivation under these conditions. The observed regularities in the dynamics of B.truncatella growth and shifts in its physiology and morphology due to hypergravity or compensated gravity support our earlier proposed working hypothesis about the dominance of functional activity over morphological properties in sensitivity of unicellular organisms to perception and realization of the gravitational stimulus.

[Biomechanical aspects of the process of formation of food vacuoles in the infusoria Bursaria truncatella under changed gravity]. / Biomekhanicheskie aspekty protsessa obrazovaniia pishchevykh vakuolei u infuzorii Bursaria truncatella v usloviiakh izmenennoi sily tiazhesti.

Results from clinostatic and centrifugal laboratory experiments in which there has been evaluated an activity of digestive process in infusoria Bursaria truncatella by the content of vacuole numbers and its change in the cell under changed gravity are presented. It is indicated that the extended clinostatic exposure of infusoria stimulates their digestive activity and an increased gravity (centrifugation 2 g, 5 g) inhibits this process. In these examinations, an effort was made to explain the obtained results started from the propositions of cell biomechanics and bioenergetics. The mechanisms of gravity influence on this process have been proposed.

[Structure of the macronucleus chromatin of the ciliate Bursaria truncatella. III. Chromatin organization in resting cysts and during excysting]. / Struktura khromatina makronukleusa infuzorii Bursaria truncatella. III. Strukturnaia organizatsiia khromatina v tsistakh pokoia i v protsesse ékstsistirovaniia.

Structural organization of macronuclear chromatin of a ciliate Bursaria truncatella was studied electronmicroscopically by means of Miller's technique and negative staining of resting cysts and at excysting. In resting cysts practically all the macronuclear chromatin was shown to be organized into compact chromatin clumps 100-300 nm in size. At excysting a natural decompactization of the chromatin clumps occurred and radial loop-shaped chromatin fibres appeared around the clumps. Sometimes transcription units with a relatively small contour length of transcribed region and with high RNA-polymerase density were observed on the loops. The responsibility of such genes for the synthesis of proteins taking part in regulation of excystment and/or subsequent cell growth and differentiation is discussed.

[Structure of the interphase chromatin in the ciliata Bursaria truncatella macronucleus. II. Loop organization of inactive chromatin clumps]. / Struktura interfaznogo khromatina makronukleusa infuzorii Bursaria truncatella. II. Petel'naia organizatsiia glybok neaktivnogo khromatina.

Electron microscopic study of chromatin organization in isolated macronuclei of a ciliate Bursaria truncatella showed macronuclear chromatin to be organized in compact clumps 120--180 nm in diameter linked with each other by one or several chromatin fibres. Macronucleus being dispersed in a solution of low ionic strength, radial loops basically of nucleosomal structure start appearing around chromatin clumps. Long-time dispersing of macronuclear chromatin brings complete decompactization of chromatin clumps into a set of nucleosome fibres. The way the fibres of interphase chromatin are packed in a chromatin clump is discussed.

[Structure of the interphase chromatin in Bursaria truncatella macronucleus. I. Electron microscopic and autoradiographic study of the structural chromatin changes during differentiation and growth after division]. / Struktura interfaznogo khromatina makronukleusa infuzorii Bursaria truncatella. I. Elektronno-mikroskopicheskoe i avtoradiograficheskoe izuchenie strukturnykh izmenenii khromatina v protsesse differentsirovki i rosta infuzorii posle deleniia.

The structure of interphase chromatin from isolated individual macronuclei of Bursaria truncatella was studied at different moments after cell division. During the period 0,5-3 hours after division most of the macronuclear chromatin is represented by loose agglomerations of decondensed chromatin, where transcription complexes can be seen. The maximum quantity of decondensed chromatin is observed 0,5-1,5 hours after cell division. During the period 1,5-3 hours after the division the part of decondensed chromatin decreases along with the increase of the quantity of dense chromatin organized in chromatin clumps 0,12-0,18 mu in diameter. In completely developed vegetative cells nearly all the chromatin has the structure of closely packed chromatin clumps. Electronmicroscopic autoradiography data show that chromatin clumps are transcriptionally inert, whereas all the transcription processes take place in decondensed chromatin agglomerations. The structure of transcription complexes of B. truncatella macronucleus is discussed in detail.