[The growth dynamics of nucleoli and their silver stainability in the cell cycle of ESK cells in a monolayer culture]. / Dinamika rosta iadryshek i ikh okrashivaemosti serebrom v kletochnom tsikle u kletok SPEV v monosloinoi kul'ture.

The cell cycle progression of individual pig embryo kidney (PK) cells was followed by time-lapse microphotography. Evidence has been presented that every detachment of cells from the substrate for subculturing leads to nearly a twofold decrease in the average number of nucleoli per nucleus. However, this number is progressively increased with every generation of flattened cells on the substrate. It appears that these nucleolar alterations reflect the nucleolar fusion in the suspended cells and the disruption of fused nucleoli during mitosis in the cells on the substrate. The configuration of nucleoli within the nuclei of cells on the substrate remains very stable through interphase, despite the movements of the nucleus, as a whole, in the plane of monolayer. The nucleoli grow through all the stages of interphase. The increase in the nucleolar size is highly coordinated with the increase in nuclear size and in the silver stainability of the nucleoli.

[The kinetics of the transition to DNA synthesis in the cell cycle of sister cells of the ESK line in culture]. / Kinetika perekhoda k sintezu DNK v kletochnom tsikle u sestrinskikh kletok linii SPEV v kul'ture.

The proliferation kinetics of a cultured pig embryo kidney cell line, PK, was studied by time lapse cinemicrography and 3H-TdR autoradiography. The duration and variability of all phases of the cell cycle was estimated. Evidence is presented that the variation in the cell cycle transit time of both unrelated and sibling cells results mainly from the variation in transit of G1-phase. These results indicate that the kinetics of the entry of cells into the S-phase represents the first order kinetics and does not contradict the transition probability model of cell cycle control. Analysis of the labeling pattern of sister cells reveals a clear correlation of the sister cells G1 transit time.

[The effect of picolinic acid and iron ions on the proliferation of SPEV cells]. / Vliianie pikolinovoi kisloty i ionov zheleza na proliferatsiiu kletok SPEV.

The effect of picolinic acid (PA) on SPEV cell proliferation is found to be different from that on normal and virus transformed NRC cells, and on spontaneously transformed CHO cells. It is shown that SPEV cells are arrested by PA at the end of G1-phase and at the beginning of S-phase and probably in G2-phase of the cell cycle. Ferrous ions remove the G1/S block induced by PA to permit the cell transfer through S-phase. On the one hand, PA chelates ferrous ions from the cells, and on the other one it inhibits the replicative DNA synthesis. It can be suggested that PA may arrest the SPEV cell growth affecting the iron-depend stable radical formation which is introduced into the active centre of ribonucleotiDE reduCTase. This results in the lower enzyme activity.

Ultrastructural changes in nucleoli and fibrillar centers under the effect of local ultraviolet microbeam irradiation of interphase culture cells.

As shown previously, ultraviolet (uv) microbeam irradiation of one of the two mature nucleoli within an interphase cell nucleus causes significant diminution and inactivation of the irradiated nucleolus and compensatory growth and activation of the nonirradiated one. In the present work we describe the results of an ultrastructural study of this phenomenon. The changes in the nucleoli were examined by means of complete series of ultrathin sections obtained from seven irradiated pig kidney cells. The compensatory hypertrophy of the nonirradiated nucleoli is shown to be accompanied by a nearly twofold increase in the number of fibrillar centers (FCs) and by a decrease in their linear dimensions compared with the control cells of the same ploidy. In the degraded nucleoli the number of FCs decreases, but their dimensions increase. Ultraviolet microbeam irradiation causes dramatic diminution of the dense fibrillar component within the irradiated nucleoli as well. The nucleolar capacity for compensatory hypertrophy indicates that in addition to active ribosomal genes, mature nucleoli also contain "silent" genes capable of being activated under extreme conditions to sustain the required level of rRNA synthesis. It is assumed that activation of latent ribosomal genes is accompanied by FC "fragmentation" without a considerable increase in their total volume per cell.

[Silver staining of the nucleoli of pig embryonic kidney cells during the hyperactivation and inhibition of the synthesis of nucleolar RNA by UV microirradiation]. / Okrashivanie serebrom iadryshek kletok SPEV pri giperaktivatsii i ingibirovanii sinteza iadryshkovoi RNK u UF-mikrooblucheniem.

Silver staining of the nucleoli in pig embryo kidney cells (PK) was studied during the cell cycle and also upon mature nucleoli modifications induced by UV microirradiation. During anaphase only four silver-stained granules were revealed in each daughter set of chromosomes in the four nucleolus-organizing regions (NORs). In the following 1-2 hours, the number of granules in the NORs rapidly increased up to 25-30 per nucleus. During the next 20-25 hours of the cell cycle, the number of silver-stained granules was slowly doubling as the nucleoli grew in size. UV microirradiation of one nucleolus in the nucleus with two nucleoli induced a profound degradation of the injured nucleolus and a compensatory hypertrophy of the intact one. Such nucleolar modifications were accompanied by redistribution of the silver-stained granules between the injured and non-injured nucleoli and by alterations in the levels of nucleolar RNA synthesis in the NORs. These data support a hypothesis that silver-stained proteins may be involved in the regulation of the nucleolar activity.

[Ultrastructure of the interphase nucleoli of pig embryonic kidney cells during their compensatory hypertrophy and degradation due to local UV microirradiation]. / Ul'trastruktura interfaznykh iadryshek kletok SPEV pri ikh kompensatornoi gipertrofii i degradatsii, vyzyvaemykh lokal'nym UF-mikrooblucheniem.

As shown elsewhere, the ultraviolet (UV) irradiation of one of the two nucleoli of the interphase cell nucleus results in inactivation and degradation of the irradiated nucleus and in the compensatory growth and activation of the nonirradiated one. In the present work we studied the ultrastructure of degraded and hypertrophied nucleoli in PK-cells with the aid of serial ultrathin sections. The compensatory hypertrophy of the nucleoli was shown to be accompanied by a significant increase in the number of fibrillar centers (FC) and a decrease in their linear size compared with the control ones; in the degraded nucleoli, the FCs number went down, while the size of FCs increased. Overall, the structural changes of the degraded nucleoli upon their UV microirradiation corresponded to those caused by the action of other known inhibitors of rRNA. The capacity of nucleoli for compensatory hypertrophy indicates that apart from the operating ribosomal genes, the cell also contains latent r-genes which may be activated under extreme conditions so as to sustain the required level of rRNA synthesis. It is suggested that such an activation is accompanied by a "fragmentation" of the original FCs into smaller and more numerous ones.

[The effect of the intracellular level of free iron on cell proliferation in culture]. / O vliianii vnutrikletochnogo soderzhaniia svobodnogo zheleza na proliferatsiiu kletok v kul'ture.

Dependence of changes in the intracellular free iron content upon cellular proliferation has been studied on mammalian cells in vitro. It has been established that picolic acid (PA)--a natural metal chelating agent of variable valency--inhibits the proliferation of cultivated pig embryo kidney cells (SPEV). Simultaneously the free iron quantity was decreased 2-fold as compared with the norm. PA block was removed by substituting PA-containing cultivated media for the PA-free one. It was accompanied by complete recovery of the free iron quantity in the cells. The regulation of cell proliferation is likely to correlate with the intracellular free iron content.

[Variability of the duration of the cell cycle in pig embryo kidney cells in monolayer culture and correlation of the cycle duration in sister cells]. / Variabel'nost' prodolzhitel'nosti kletochnogo tsikla u kletok SPEV v monosloinoi kul'ture i korreliatsiia prodolzhitel'nosti tsikla u sestrinskikh kletok.

The distribution of generation time of sister cells for the exponentially proliferating monolayer SPEV culture was obtained with time lapse cinemicrographic technique. The distribution is characterized by the average generation time equal to 24.3 hour, with the variation coefficient, asymmetry coefficient and correlation coefficient for sister pair cell being, respectively, 17%, 0.2 and 0.78. The results obtained are compared with the prediction of "a random transition" in the cell cycle.

[Thickness of mammalian cells in culture, the absorption of UV radiation in the cells and the related shift in action spectra]. / Tolshchina kletok mlekopitaiushchikh v kul'ture, pogloshchenie UF izlucheniia v kletkakh i sviazannyi s nim sdvig spektrov deistviia.

The thickness of SPEV cells in monolayer with different cell densities was measured by means of 3-dimensional reconstruction from serial vertical sections. No significant changes in the mean cell thickness were detected despite the wide range of volume and cell density variations. UV absorption at different wave-lengths was measured in various sites of single cells. It is shown that the well known shift between peaks of the UV action spectrum for mammalian and bacteria cells may result from the cell self-shielding at short wavelengths.