Increased functional load on mouse kidney proximal tubule epithelial cells causes changes in nucleolar 3-D architecture.

Ultrastructural 3-D analysis of nucleolar architecture and Ag-NOR protein distribution in mouse kidney-cortex proximal-tubule epithelium has been performed. A principal scheme of structural changes of the nucleolus and organization of its components during the intensification of pre-rRNA synthesis (dynamic model of a nucleolus) based on computer spatial modelling has been advanced. According to the nucleolar composition, three groups of cells, which differ from each other by rRNA synthesis, are defined in normal kidney. Most nephron proximal-section cells (about 52%) are characterized by lower activity of RNA synthesis. Such kind of cells are defined as group I (nucleolar diameter 0.7-1.5 microm) and always contain resting, ring-shaped or close to ring-shaped dense nucleoli, which have 2 or 3 fibrillar centers. Nucleoli of group II cells (about 37%, nucleolar diameter 1.5-2.5 microm) have a higher level of activity, contain 4-7 fibrillar centers, and their structural organization is close to reticulated forms due to the first indications of vacuolar network (identified as prereticulated nucleoli). The most active cells of group III (about 11%, nucleolar diameter 2.5-3.5 microm) include cells with typical reticulated nucleoli with a well expressed vacuolar network and numerous fibrillar centers (18-22). Increased functional load of the epithelium caused by unilateral nephrectomy and diuretic (4-chlor-H [2-furylmethyl] 5-sulphamyl-antranic acid) injection changed the proportion of the different cell groups: group I decreased (about 25%), whereas groups II and III increased (about 8% and 17%, respectively). The increase of nucleolar activity first causes a deformation of the individual fibrillar centers as well as complication and growth of their surface. Further, a progressive fragmentation of the fibrillar centers and the growth of their total volume is observed. The complication and growth of the total volume of Ag-positive zones is another indication of the nucleolar activation. The vacuolar system develops by a gradual fusion of small isolated cavities into a united vacuolar network. Nucleoli with 2-7 fibrillar centers are considered to be intermediate forms reflecting successive stages of its activation or inactivation: from the resting ring-shaped nucleolus via transient stages of increasing functional activity to the active reticulated nucleoli and vice versa. The observed differences in the nucleolar ultrastructure are regarded as evidence of the functional heterogeneity of cell populations within one functional segment of nephron.

[The dependence of the 3-dimensional organization and length of the nucleolonema in the hepatocyte nucleoli of normal and regenerating rat livers on the nucleosome structure of the intranucleolar chromatin]. / Zavisimost' trekhmernoi organizatsii i dliny nukleolonemy iadryshek gepatotsitov normal'noi i regeneriruiushchei pecheni krysy ot nukleosomnoi struktury vnutriiadryshkovogo khromatina.

A biochemical and ultrastructural stereo-morphological analysis, with special reference to spatial organization and length of nucleonema and Ag-positive zones, was performed for various modifications of nucleolonemal type nucleoli in normal and regenerating (6 and 22 hours after partial hepatectomy) rat hepatocytes. To determine possible disorders on nucleosomal and supranucleosomal levels, chromatin DNA degradation was carried out during micrococcal nuclease hydrolysis, followed by analysis of electrophoretically separated particles. Functional characterization of intranucleolar chromatin was performed by testing the rate of DNA degradation after DNAase I treatment as well as by detection of free G-C pairs during titration with actinomycin D. Transcriptional activity of nucleoli was determined according to the intensity of [14C]-UTP uptake with isolated nucleoli. It is shown that the total chromatin from control nucleoli contains nucleosomal fibrils, although deprived of high compactization level. Nucleosomes themselves are strongly destabilized. In activated nucleoli structural differences of chromatin are more perceptible. In 6 hour preparations the bulk of chromatin fibrils (about 70%) undergo a further relaxation and lose the nucleosomal structure. Therefore at this point of experiment, the maximum length of nucleolonema and Ag-positive zones was registered in addition to the highest quantity of free G-C pairs, and sensibility to DNAase I transcriptional activity of isolated nucleoli. 22 hours after hepatectomy, the transcriptional activity and functional parameters of intranucleolar chromatin markedly decreased compared to the 6 hour period. Simultaneously, the share of chromatin restituting the nucleosomal structure increased, while the length of nucleolonema was shorter than in nucleoli 6 hours after hepatectomy. The main results could be resumed in the following way: the general composition of nucleolonemal type nucleolus variations described in our experimental conditions is in close relation with the with the compactization grade of ribosomal DNP-fibrils.

Transcriptional activity and ultrastructure of morphologically different types of nucleoli isolated from hepatocytes of normal and hepatectomized rats.

Morphologically different types of nucleoli were isolated from liver of normal and partially hepatectomized rats, to allow their ultrastructure and transcriptional activity to be precisely correlated. Transcriptional activity was estimated from the intensity of incorporation of [14C]-UTP during periods of maximal RNA-polymerase I activity. RNA synthesis in hepatocyte nucleoli was maximal at 6 and 22 h after partial hepatectomy. The changes in transcriptional activity coincided with changes in nucleolar ultrastructure. Pseudonucleolonemal nucleoli, in which the prominent nucleolonemal network has a large dense fibrillar component and a small granular part, were first seen 6 h after the operation and showed the highest transcriptional activity. After 22 h, a second peak of RNA synthesis was recorded. Nucleolar size had almost doubled, and most hepatocytes showed hypertrophy of the granular component, indicative of intensified pre-rRNA processing.

[The 3-dimensional organization of the nucleolus and nucleolus-organizer regions of differentiated cells. IV. The structural and functional heterogeneity of the nucleoli in the epithelium of the proximal nephron in the mouse]. / Trekhmernaia organizatsiia iadryshka i iadryshkoobrazuiushchikh raionov differentsirovannykh kletok. IV. Strukturnaia i funktsional'naia geterogennost' iadryshek épiteliia proksimal'nogo otdela nefrona myshi.

By means of stereological and morphometrical analysis, the ultrastructure of nucleoli in epitheliocytes of mouse kidney cortex proximal tubuli has been studied. In accordance to the nucleolar composition, three main groups of nephrocytes with different levels of rRNA and protein synthesis were defined. Functional heterogeneity of proximal tubuli epithelium was established by correlation between different variants of ultrastructural organization of nucleoli and the total RNA synthesis activity, determined by 3H-uridine incorporation intensity. It has been shown that a greater part of cells (about 52%) in the nephron proximal section, which is characterized by slow RNA synthesis, causing a low functional activity of these cells, presumably represents a reparative cellular reserve. Such cells, defined as the 1st group cells, have resting, ring-shaped nucleoli with one fibrillar centre, and nucleoli similar to the ring-shaped ones but containing 2-3 fibrillar centres. Nucleoli of the 2nd group of nephrocytes (about 37%), most actively incorporating labeled precursor, contain 4-6 fibrillar centres. Their structural organization is closer to the reticular type of nucleoli. The 3rd most actively labeled group of nephrocytes includes cells with typical reticulated nucleoli. The number of fibrillar centres in the reticulated nucleoli is much higher (18-22) than in the 1st and 2nd groups of nephrocytes. Structural and functional polymorphism of nephrocytes was revealed not only in the proximal part of one nephron. During the increase in functional activity of nephrocytes, caused by unilateral nephrectomy, the quantitative correlation between cells related to these different groups was seen to change. The number of cells of the 1st group decreased by 24%, whereas that in the 2nd and 3rd groups increased by 9 and 15%, respectively. Nucleoli with 2-3 fibrillar centres are considered as transitional forms between the inactive ring-shaped nucleoli and the active reticulated nucleoli. Differences in the ultrastructure of nucleoli may be considered as an evidence of functional heterogeneity of nephrocytes within the proximal segment of nephron.

[The 3-dimensional organization of the nucleolus and the nucleolus organizer regions in differentiated cells. II. The reticular, vacuolized and nucleolonemal nucleoli of hepatocytes from the intact mouse liver and of hepatocytes stimulated to proliferation as a result of partial hepatectomy]. / Trekhmernaia organizatsiia iadryshka i iadryshko-obrazuiushchikh raionov differentsirovannykh kletok. II. Retikuliarnye, vakuolizirovannye i nukleolonemnykh iadryshki gepatotsitov intaktnoi pecheni myshi i gepatotsitov, stimulirovannykh k proliferatsii v rezul'tate chastichnoi gepatéktomii.

By means of stereological and morphological analysis, the dynamics of nucleolar structural changes in stimulated mouse hepatocytes has been studied. Reticulated and vacuolized nucleoli typical for normally functioning hepatocytes were shown to convert into the nucleolonemal nucleoli, first noticed 18 hours following operation. The process of activation of mouse hepatocyte nucleoli involves two steps. At the first step (within 1-18 hours following operation) a progressive growth of nucleoli volume, due to a simultaneous reduction of vacuolar sizes and growth of RNP component occurs. Such changes were observed in both groups of nucleoli being present in the intact mouse liver, because at this particular step a considerable decrease in the number of vacuolized nucleoli took place. Besides, in the stimulated hepatocyte nucleoli the number and total volume of fibrillar centers increase. However, in spite of their considerable changes, the nucleoli preserve the marks characteristic of the reticulated type. The second step of activation, noted 18 hours after stimulation of hepatocytes, includes more fundamental structural reconstructions. As the result, reticulated nucleoli obtain the nucleolonemal structure. At the same time, on the background of a further decrease in the individual volume and an essential growth of the total volume in the fibrillar centres, a spasmodic increase in the mass of the dense fibrillar component, which is associated with the formation of the continuous strand of the nucleolonema. All this is responsible for the complete changes in structural organization of nucleoli commonly seen in mouse hepatocytes. It is suggested that the cause of such a structural reconstruction may be due to the changes in topography of transcriptionally active regions of rDNA.

[The 3-dimensional organization of the nucleolus and the nucleolus organizer regions in differentiated cells. III. Changes in the nature of the distribution of argentophilic proteins in the nucleoli of mouse hepatocytes with stimulation of the hepatocytes to proliferation]. / Trekhmernaia organizatsiia iadryshka i iadryshko-obrazuiushchikh raionov differentsirovannykh kletok. III. Izmenenie kharaktera raspredeleniia argentofil'nykh belkov iadryshek gepatotsitov myshi pri stimuliatsii gepatotsitov k proliferatsii.

The stereological and morphological analysis of Ag-positive zones revealed the principal difference in quantity and distribution of Ag-NOR proteins in reticulated and nucleolonemal nucleoli of mouse hepatocytes. It is shown that reticulated nucleoli of resting hepatocytes are characterized with the presence of discrete rounded Ag-positive zones, whose quantitative parameters correspond to the fibrillar centers and dense fibrillar component taken together. The analysis of the three-dimensional structure of Ag-positive zones of nucleolonemal nucleoli has revealed considerable changes in quantity and distribution of Ag-NOR proteins due to proliferative stimuli. 22 hours following operation, a continuous, strongly winding strand of nucleolonema is revealed in the nuclei. Taking into account that Ag-NOR proteins are associated with the transcriptionally active regions of rDNA it may be suggested that this structural conversion was due to decondensation and activation of inactive regions of r-chromatin. A considerable growth of Ag-positive zone volume during the conversion of reticulated nucleoli into the nucleolonemal type may be explained by the increase in Ag-NOR protein contents.

[The 3-dimensional organization of the nucleoli of benign and malignant tumor cells from different human organs]. / Trekhmernaia organizatsiia iadryshek dobrokachestvennykh i zlokachestvennykh opukholevykh kletok razlichnykh organov cheloveka.

The method of ultrathin serial sections was used to perform a comparative ultrastructural and 3-dimensional analysis of nucleoli for the following variants of human tumours: benign (fibroadenoma) and malignant (infiltrating ductal carcinoma) tumours of one organ (mammary gland); malignant tumours of epidermal genesis in different organs (squamous cell carcinomas of skin, larynx, lung, gullet, uterus); two forms of malignant tumours (squamous cell and small cell carcinomas) of one organ (lung). The spatial models of nucleoli in these tumour cells are given. The specific signs in architecture of tumour nucleoli was found. Nucleoli of fibroadenomas have well pronounced 1-4 fibrillar centres forming a united system with a lacunar component and intranucleolar chromatin. Unlike benign tumour cells, nucleoli of infiltrating ductal carcinomas are characterized by large, prominent nucleoli containing giant, multiform fibrillar centres with a complicated surface, a well developed granular component and an unusually organized lacunar system. In squamous cell carcinomas of various localization, active, hypertrophied nucleoli with pseudonucleolonemal organization were found. The small cell carcinoma of lung differs from the squamous cell cancer of the same organ by dense, fibrillar nucleoli with a small amount of granular component located on the periphery of the nucleolar body. Nucleolar type reflecting the functional state of malignization process may serve as an additional diagnostic criterion for tumour identification.

[Activation of transcription function in lymphocytes after irradiation with He-Ne-laser]. / Aktivatsiia transkriptsionnoi funktsii v limfotsitakh pod vliianiem oblucheniia He-Ne-lazerom.

The influence of He-Ne-laser irradiation (lambda = 632.8 nm) in dose 56 J/m2 on the ultrastructure of the nucleolus from human peripheral lymphocytes was studied electronmicroscopically. After 1 h irradiation a well-expressed reaction of the nucleolus was observed in 70% of the lymphocytes under examination. Changes consist in the appearance of a wrong-shaped fibrillar center or in its fragmentation, the increase of RNP-containing fibrillar and granular components, and also in expansion of vacuoli. In a number of irradiated lymphocytes nucleoli with several fibrillar centres and with a strand-like organization of RNP part were observed. The size of these nucleoli increases. Following the accepted functional interpretations the observed changes can be connected with the intensification of RNA metabolism including the synthesis, processing of pre-rRNA and preribosome transport from the nucleolus. Similar rearrangements of the nucleoli were revealed in parallel experiments with phytohemagglutinin-treated lymphocytes. They were observed 1 h after the stimulation of lymphocytes. Taking into account the absence of mitogenic action of He-Ne-laser irradiation on lymphocytes, the ultrastructural changes of nucleoli under the action of irradiation are considered as functional activation of rRNA synthesis in the Go-period.

[The ultrastructure and possible role of the vacuolar component of hepatocyte nucleoli]. / Ul'trastruktura i vozmozhnaia rol' vakuoliarnogo komponenta iadryshek gepatotsitov.

A study was made of the nucleolar vacuoles in guinea pig hepatocytes that are poorly investigated for animal cells. A comparison of ultrathin sections, contrasted by heavy metals, with those treated according to Bernhard allowed to reveal the following intravacuolar structures: 1) fibrils 10-15 nm and 20-30 nm thick similar to perinucleolar chromatin fibrils; 2) RNP-granules 15-20 nm in diameter resembling the granular component of the nucleolus; 3) RNP-fibrils 15-20 nm thick with high electron density. The latter were visualized for the first time, their function still remains obscure. Upon stimulation of hepatocytes with partial hepatectomy, the vacuolar component changed. In 2.5 and 5 hours after the operation the vacuoles became smaller, the number of RNP structures of two types increased. Further, in 9 hours, the enlarging of vacuoles was accompanied by a sharp decrease in the number of these RNP-structures. The results obtained allow to suppose that the vacuoles of nucleolonemic nucleoli may be functioning elements, linking intra- and perinucleolar chromatin fibrils. They are depots for the RNP synthesized in the nucleolus; the rRNP is transported through the vacuolar system.

[Ultraimmunocytochemical diagnosis of squamous cell cancer of the digestive tract]. / Ul'traimmunotsitokhimicheskaia diagnostika ploskokletochnogo raka pishchevaritel'nogo trakta.

Procedure using fluorescent and peroxidase labeling and monoclonal antibodies to basal-cell antigen of multilayer epithelium showed the antigen to occur in squamous cell cancer irrespective of site and degree of cell differentiation; this, however, was not the case with tumors of other origins. Ultraimmunocytochemical method was used to identify localization of the antigen at cellular and subcellular levels, namely, in tonofilaments and desmosomes. Said situation is considered to suggest squamous cell carcinoma.

[Changes in the number and size of fibrillar centers in nucleolus inactivation during erythropoiesis]. / Izmenenie chisla i razmerov fibrilliarnykh tsentrov pri inaktivatsii iadryshek v protsesse éritropoéza.

The size and number of fibrillar centers (FCs) was shown to be proportional to or correlate with the ploidy of the cell, respectively. In the active nucleoli of erythroblasts, the numbers of FCs exceeds several-fold that of nucleoli organizing regions (NORs). In the course of maturation, the number of FCs becomes 3-10 times lower than that of NORs. The total size of FCs decreases three-fold during differentiation, although the size of individual FCs increases. Inactivation of ribosomal genes in the process of erythropoiesis seems to be accompanied by fusion of individual FCs and compaction of their tissue.

Changes in the number and volume of fibrillar centres with the inactivation of nucleoli at erythropoiesis.

The number and volume of fibrillar centres, the structural components of interphase cell nucleoli on the surface of which rRNA is synthesized, have been studied in differentiating erythroblasts of mouse embryo liver. Complete series of ultrathin sections of erythroblast nuclei have been used at the main stages of differentiation: proerythroblast, basophilic erythroblast, polychromatophilic erythroblast and normoblast. It has been shown that in the active nucleoli of proerythroblasts the number of fibrillar centres is correlated with cell ploidy and exceeds by several-fold the number of nucleolus-organizing regions of chromosomes. The total volumes of fibrillar centres in 2C (0.369 micron 3) and 4C (0.749 micron 3) proerythroblasts are proportional to number of nucleolus-organizing regions. With the maturation of erythroblasts the total number of fibrillar centres declines and in normoblasts it is 3- to 10-fold less than that of the nucleolus-organizing regions. The total volume of fibrillar centres in normoblasts (0.102 micron 3) is threefold smaller than that in proerythroblasts (0.369 micron 3), even though the mean volumes of individual fibrillar centres are significantly higher (0.0042 micron 3 in proerythroblasts and 0.039 in normoblasts). The optical density of fibrillar centres in normoblasts can be higher compared with that of proerythroblasts. It has been suggested that the inactivation of nucleoli at erythropoiesis is accompanied by the fusion of individual fibrillar centres and, possibly, by the compaction of their material.

[3-dimensional organization of the nucleolus and the nucleolus-organizing regions in differentiated cells. I. Ring-shaped nucleoli in the endotheliocytes, smooth-muscle cells and fibroblasts in the mouse]. / Trekhmernaia organizatsiia iadryshka i iadryshkoobrazuiushchikh raionov differentsirovannykh kletok. I. Kol'tsevidnye iadryshki éndoteliotsitov, gladkomyshechnykh kletok i fibroblastov myshi.

The method of ultra-thin serial sections was used to study the three-dimensional structure and to perform the quantitative analysis of ring-shaped nucleoli of kidney and liver endotheliocytes, smooth muscle cells of kidney arterioles and fibroblasts of mice. Spatial models of ring-shaped nucleoli with one fibrillar centre are given. For the quantitative analysis the following parameters were measured: the number and volumes of nucleoli, fibrillar centers, RNP-containing structures, the vacuolar system and the RNP-index (the latter is a ratio of RNP-part and fibrillar center volumes). Nucleoli of the same type of cells, occasionally in the same nucleus, were found to differ sharply in their fibrillar center shape. Differences in the mean volume values of nucleoli, fibrillar centers and the RNP-part between some cell populations are sufficiently well pronounced. Within the same population ring-shaped nucleoli have, as a rule, specific volume values of nucleoli, RNP and fibrillar centers. The comparison of quantitative data obtained on different cell types showed that the mean RNP-index values were the most stable parameter. The structural relation between fibrillar centers, intra- and perinucleolar chromatin and lacunar region is shown. The structural organization of intranucleolar chromatin and rRNA in the nucleolar body and in fibrillar centers is discussed.

[Reaction of monoclonal antibodies A 6/1 with the antigen determinant of ultrastructures of tumor cells in epidermal-type tegmental tissues]. / Reaktsiia monoklonal'nykh antitel A 6/1 s determinantoi antigena ul'trastruktur opukholevykh kletok pokrovnykh tkanei épidermal'nogo tipa.

Using indirect immunoenzyme assay and ultrathin sections, it was shown that antibodies against basal cell antigens react with tonofibril and desmosome filaments of squamous tissue carcinoma cells.

[Rearrangement of nucleoli in hepatocytes stimulated for proliferation and enhancement of their transcription function]. / Perestroiki iadryshek v stimulirovannykh k proliferatsii gepatotsitakh i usilenie ikh transkriptsionnoi funktsii.

The nucleoli of normally functioning guinea-pig hepatocytes that have a nucleolonemal (strand-like) organization differ from identical nucleoli of other cells. Their nucleolonema consists as a rule of a fibrillar component with 45S RNA and is poor in granulas that contain pre-rNA molecules of an intermediate size and 28S rRNA, a dense fibrillar component with nascent rRNPs in its composition was not revealed. In hepatocytes stimulated by a 2/3 liver resection rearrangements in nucleoli were found. This brought to a conclusion that rRNA metabolism undergoes some changes. In 2.5 and 5 hours after the resection the hepatocytes' nucleoli were characteristic of a greater thickness of strands and a smaller size of vacuoles, appearance of distinct zones of the dense fibrillar component and an increased amount of RNP-granules. All these observations taken together point out at an increased synthesis and processing of rRNA at early stages of the prereplicative period. In 9 hours the character of changes in nucleoli was different: the vacuoles were considerably widened, whereas the thickness of strands that consisted of a well-expressed dense fibrillar, fibrillar and granular components was lesser. Such rearrangement points out at an increased transport of preribosomes from the nucleolus, a high level of synthesis and processing of nascent RNP-product being maintained. The changes of nucleolar RNP-component were followed by appearance of greater blocks of perinucleolar condensed chromatin, which may be connected with "cutting-off" some tissue-specific genes and initiation of functioning of the mitotic operon genes.

[Immunomorphological (light and electron microscopic) diagnosis of human squamous cell cancer using monoclonal antibodies]. / Immunomorfologicheskaia (sveto- i élektronno-mikroskopicheskaia) diagnostika ploskokletochnogo raka cheloveka s pomoshch'iu monoklonal'ny kh antitel.

It is shown with fluorescent and peroxidase labels for antibodies that the antigen to which the monoclonal antibody A-6/2 is directed, is a marker for cells of the basal stratified epithelium (basal-cell antigen). This antigen persists in squamous cell carcinomas of various sites and degrees of differentiation, but does not occur in tumors of other origins. With electron immunocytochemistry, the antigen was found to be located in tonofilaments and desmosomes of human squamous cell carcinoma. The A-6/2 monoclonal and basal-cell antigen may be used when developing immunomorphologic (light- or electronmicroscopic) procedures for histogenetic diagnosis of these carcinomas.

[Changes in the ultrastructure of inactive circular nucleoli from mature rat lymphocytes at early stages of blast transformation]. / Izmenenie tonkoi organizatsii neaktivnykh kol'tsevidnykh iadryshek zrelykh limfotsitov krys na rannikh stadiiakh blasttransformatsii.

We studied the ultrastructure of lymphocyte nucleoli from rat peripheral blood within the first 6 hrs of their cultivation in the presence of phytohaemagglutinin (PHA). In the mixed population of intact lymphocytes there were observed several types of nucleoli, the localization and the ratio of individual nucleolar components being different. This seems to reflect functional peculiarities of these nucleoli. Some nucleoli are characteristic of the presence of several sites of intranucleolar condensed chromatin. However, all these nucleoli could be related to the so-called ring-shaped nucleoli with a fibrillar center surrounded by fibrillar and granular RNP-components, which points out to their low synthetic activity. The major changes in the nucleoli of stimulated lymphocytes were observed after the action of PHA within 1 hr. These changes were expressed in the elevation of electron density of the fibrillar centre and the loss by it of clear borders and correct shape, in the appearance of large zones of the dense fibrillar component with acquired an increased electron density, and also in the disappearance of condensed chromatin sites. By that time, there was revealed a peculiar shape of nucleoli with a "fragmented" fibrillar centre and the presence of vacuoles and strands consisting of fibrillar and granular RNP-components. The different types of changed nucleoli in the population of stimulated lymphocytes seem to be the consequence of a gradual transition of ring-shaped nucleoli to active nucleolonema-like ones. So, it is obvious that changes in the ultrastructure of nucleoli occur already by 1 hr after the PHA action. This points out to the intensification of pre-rRNA transcription that takes place by that time.

[Ultrastructure and behavior of the nucleoli and fibrillar centers during cell differentiation of liver erythroblasts of 12-day-old mouse embryos]. / Ul'trastruktura i povedenie iadryshek i fibrilliarnykh tsentrov v protsesse keltochnoi differentsirovki na primere éritroblastov pecheni 12-sutochnykh émbrionov myshi.

The transformation of nucleolus and its structural components in the main groups of erythroid cells (from pronormoblasts to reticulocytes and dividing ones) has been studied. It is shown that during inactivation of the nucleolus, the granular component is reduced, and the degree of chromatin condensation increases. Enlargement and "naking" of fibrillar centres are also observed. At the stage of basophilic and polychromatophilic erythroblasts, the nucleolus has a mushroom-like shape with well developed fibrillar centres, which lie at the border of the nucleolus. Nucleolar RNP components consist predominantly of a fibrillar component and forms "caps" of these mushroom-like structures. Therefore, at this stage "free" fibrillar centres are found on ultrathin sections, if the section plane runs only through the fibrillar centre, or through ring-shaped nucleoli, i.e. the fibrillar centre surrounded by sheet of nucleolar RNP fibrilles, when the mushroom-like nucleolus is cut tangentially. Using serial section technique, small round nucleoli with an extremely weakly developed RNP material or free fibrillar centres, resembling those in telophase nuclei, are shown on the terminal stage of nucleolus transformation. It is noted that the main groups of erythroid cells differ from each other not only in the chromatin condensation degree, but also in the development of nucleolus material and in the size of fibrillar centres. However, such differences exist in either cell group. Consequently, we can distinguish between cell populations being on different stages of maturation. On this basis, we described on intermediate population of cells, which possess signs of pronormoblasts and basophilic erythroblasts. In all the cases, strands of electron opaque material bound with the condensed chromatin are present in fibrillar centres.(ABSTRACT TRUNCATED AT 250 WORDS)

[Ultrastructure and functions of ring-shaped nucleoli, fibrillar centers and nucleolar vacuoles]. / Ul'trastruktura i funktsii kol'tsevidnykh iadryshek, fibrilliarnykh tsentrov i iadryshkovykh vakuolei.

Evidence on the ultrastructure of ring-shaped nucleoli in several cell types is reviewed. Detailed attention is paid to these structures in PEK culture cells after the action of actinomycin D, to infiltrating carcinomas of human breast after different degrees of malignization, and to hepatocytes of 11 day old chick embryos. On the basis of our own and literary data, the ring-shaped nucleoli are classified into two groups: 1) those with centrally located fibrillar centres, and 2) those containing large central vacuole. Connections of fibrillar centres with the nucleolus organizer regions in the interphase nucleolus and mitotic chromosomes are considered in detail. Literary and our own data on the genesis and functional activity of ring-shaped nucleoli with the central vacuole, as well as nucleoli with different degrees of vacuolization (vacuolized nucleoli) are specially analyzed. Cellular function, properties and significance of the central vacuole in low differentiated cells are discussed.

[Fibrillar centers in the nucleoli of a PEK cell culture after administration of actinomycin D]. / Fibrilliarnye tsentry v iadryshkakh kletok kul'tury SPEV posle deistviia aktinomitsina D.

A study was made of the fine structure of the light zone (fibrillar centres) that appear in the interphase nucleoli of PEK cell culture after the action of actinomycin D. The fibrillar centres contain densely packed homogeneous fibrils whose diameter ranged between 7-10 nm. Analysis of serial sections suggests that fibrillar centres may represent spherical zones within the nucleolus, displaying structural continuity with the intra- or perinucleolar chromatin and the perinucleolar nucleoplasm. The origin and some properties of fibrillar centres are discussed.