PubMed Health⌕ Search

Biomedical subjects

V N Parfenov

Publications and source records attributed to V N Parfenov.

At least 37 records · Page 2Linked to original sources
PubMed1995

[The organization of dispersed nucleolar chromatin and the ultrastructure of the nucleoli in the oogenesis of the common frog].

The structure of the nucleoli and their chromatin from grass frog Rana temporaria oocytes during different stages of oogenesis has been studied. Light microscopic analysis of dispersed according Callan's method (Callan et al., 1987) nucleoli of third stage of oogenesis (Dumont, 1972) revealed that by decreasing ionic strength to 25 mM spherical nucleoli got the appearance of necklace-like structures. Their electronmicroscopic analysis following by Miller's technique (Miller, Beatty, 1969) showed that they represent rosette-like structures which are connected to each other by ribosomal transcriptional units. Loops of the rosettes also are formed by transcriptional units of ribosomal genes. By the decreasing of transcriptional activity of nuclei from oocytes of 5-6th stages of oogenesis from hibernating frogs the structure of dispersed chromatin has been changed. The number of beads along the necklace-like structure axis decreased. Electron microscopic analysis of spread nucleolar chromatin from oocytes of these stages revealed the increase of part of inactive nucleosomal chromatin and the decrease of the number of loops in rosettes. The study of nucleoli ultrastructure showed that their morphology depends on their chromatin structure. In nucleoli with higher activity in oocytes of third stage of oogenesis fibrillar centers have not been found. At the same time in partially inactive nucleoli of 6th stage of oogenesis (Winter season) it was possible to identify well developed typical fibrillar centers. In those cases when nucleoli were completely inactive during the same stage of oogenesis and were not stained with 3H-actinomycin D, fibrillar centers were absent.

Animals↗
PubMed1995

[The formation of the karyosphere in the oogenesis of insects and amphibians].

This review deals with the authors' own and literary data on the ultrastructural and cytochemical organization of insect and amphibian oocyte nuclei, with special attention being paid to the karyosphere and its capsule. The evidence provided is supplemented with data on isolated karyospheres in Rana temporaria oocytes. A conclusion is made that the karyosphere is a complex structure which contains all chromosomes in the limited space of the oocyte nucleus, and that these chromosomes are, as a rule, in the process of inactivation. It is inferred that the karyosphere capsule commonly appears in gigantic oocyte nuclei (more than 100 micron in diameter) containing extrachromosomal DNA. The analogy of capsule organization in different invertebrate and vertebrate species is discussed, in addition to the involvement of presumably homologous nuclear structures (e.g. derivatives of synaptonemal complexes and nuclear envelope) in capsule formation. It is assumed that the karyosphere capsule is a specially organized part of the nuclear matrix. The capsule provides nuclear compartmentalization and chromosome localization in the germinal vesicle. Studies of this sort open up new possibilities to further investigation of intranuclear morphogenesis.

Amphibians↗
PubMed1994

[Seasonal transformations in the lampbrush chromosomes and the morphogenesis of the karyosphere capsule in Rana temporaria oocytes detectable by an analysis of the isolated nuclear structures].

A study was made of the seasonal changes in lampbrush chromosomes, accompanying structures and the karyosphere capsule, isolated from diplotene oocytes of Rana temporaria of stages 3-6 of oogenesis, as classified by Dumont (1972). The frogs were collected from their hibernation sites. The formation of fibrillar material of the karyosphere capsule was followed from stage to stage. Isolation of nuclei by hand, and dispersal of their content was carried out as described by Callan (Callan, 1986; Callan et al., 1987). A modified Miller's method (Miller, Beatty, 1969) was used for the ultrastructural analysis. The examination of lampbrush chromosomes shows that they change from season to season (summer, autumn, winter), reaching the maximum size in summer (Fig. 2). In autumn their transcriptional activity decreases, although their size remains unchanged. In this period each transcription unit of lateral loops contains about IO RNP-fibrils per 1 mkm, whereas in summer their number is 20 per 1 mkm (Fig. 4, 5). A large number (about 100 per each bivalent) of spheroidal granules about 1.8 mkm in diameter appear around the autumn bivalent (Fig. 3). They constantly accompany the chromosomes and therefore are called satellites. In winter, the satellites are of variable diameter (0.8-5.3 mkm) and still bound to lateral loops of chromosomes. The loops are notably reduced, and the association of the satellites shortened, to aggregate into knots.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

[Intranuclear actin microfilaments in the oocytes of the common frog].

For identification and distribution of actin microfilaments in hand-isolated nuclei of R. temporaria oocytes (stage 6, according to Dumont, 1972) different methods were used: heavy meromyosin decoration, antiactin immunofluorescence with monoclonal antibodies, staining with rhodamine phalloidin, and electrophoresis in polyacrylamide gel. The nuclei of R. temporaria oocytes contain a considerable quantities of actin microfilaments which form intranuclear meshwork. Microfilaments are connected with the nucleoli, nucleolar RNP-complexes and nuclear envelope. Immunofluorescence with antiactin monoclonal antibodies reveals a strong staining of microfilaments and nucleoli. A slight staining of nucleoli is observed after the treatment of nuclei with rhodamine phalloidin. A specific role of intranuclear microfilaments in direct transport of nucleolar material from the nucleus into the oocyte cytoplasm, in stabilization of the karyosphere (the late diplotene oocyte complex of chromosomes with numerous nucleoli) is discussed in addition to its keeping in a definite region of the nucleus. A supposition is drawn on the functional significance of the connection between microfilaments and nuclear matrix. Based on our own and literature data, a conclusion is drawn, that the intranuclear filament actin may be one of the leading components in morpho-functional organization of the nucleus as the whole.

Actin Cytoskeleton↗
PubMed1985

[Intranuclear lipids in the late oocytes of the common frog].

The complex of chromosomes and nucleoli, constituting the karyosphere with a capsule, was removed micro-surgically from the late oocyte nuclei of Rana temporaria. Lipids of nuclei and of karyosphere were investigated using biochemical and autoradiographical methods in hormone-stimulated maturing oocytes in vitro. Neutral lipids (triglyceride, diglyceride, cholesterol ester) were found in the karyosphere substance by thin-layer chromatography. During oocyte maturation the incorporation of a precursor (3H-glycerol) into triglyceride was seen to increase much more than into lecithin. The autoradiography on the sectioned oocytes showed that the intranuclear level of 3H-glycerol was more densely distributed in the nucleolar zone over the material of a fibrous component of the karyosphere capsule. The level was also detected over the central part of the karyosphere in close proximity to the chromosomes. The involvement of lipids in organization of the complicated intranuclear complex of the karyosphere with a capsule is discussed. It is suggested that lipid accumulation in the area of the karyosphere fibrous component may reflect their functional relation with the oocyte nuclear matrix.

Animals↗
PubMed1984

[Nuclear ultrastructure of the oocytes from human antral follicles. Formation of the karyosphere].

The organization of the nucleus in the oocytes from human antral follicles was examined at the electron microscopic level. At this time all the chromosomes are aggregated around an inactivated nucleolus forming a karyosphere 5-7 micron in diameter. The nucleolus bears no granular component and consists of densely packed delicate fibrillar material. The peripheral zone resembling a ring 0.5 micron thick is separated in the nucleolus. Nucleolus-like bodies (NLB), consisting of granules 20 nm in diameter embedded in finely fibrillar material, are constantly observed in contact with the chromatin. The eventually formed karyosphere is a complex of intimately interconnecting structures--the nucleolus, chromosomes and NLB. However, the chromatin surrounding the nucleolus does not form a continuous (compact) mass as it is observed at the light microscopic level. It is determined that the human karyosphere is formed during the preovulatory period when the connection between oocyte and follicular cells of cumulus oophorus is lost. The duration of karyosphere existence in the human oocytes, and relation of the karyosphere to the processes of antral follicle atresia are discussed.

Adult↗
PubMed1984

[Characteristics of karyosphere formation in the lake frog. Electron microscopic data].

The ultrastructural organization of the karyosphere in oocytes of R. ridibunda during formation of its central body (CB) was examined. It is shown that the material of CB consisting of pores similar to those of the nuclear envelope makes some intimate contact with DNA-containing fibrillar micronucleoli (MN). In the zone of this contact a transfer of MN fibrils into CB is observed. The electron microscope data on the nucleolar origin of numerous MN are provided. It is suggested that MN supply the material for the formation of CB. The participation of r-DNA in this process is discussed.

Animals↗
PubMed1983

[Characteristics of karyosphere formation in the lake frog. Light microscopy data].

Morphological peculiarities of the oocyte nuclear organization were examined in R. ridibunda during winter and spring (February-March). Numerous nucleoli were seen to be assembled around regressive lampbrush chromosomes in the centre of the nucleus, and a central body was formed to which the chromosomes were attached. As result, a structural complex is constituted that involves a karyosphere and a capsule. Nucleoli are characterized by segregation and intensive fragmentation of their material. In result, a considerable part of nucleolar DNA is eliminated in the form of ring and polymorphous structures (micronucleoli). Besides the membranous component of nucleoli (nucleolar threads or tails) is lost. Towards the end of this period, nucleoli with complicated morphology become spherical again. The formation of the central body is started from the appearance of some small optically-light protein structures 5-20 nm in diameter (central body precursors-CBP). CBP are closely surrounded with ring micronucleoli to make intimate contact with the chromosomes and nucleolar threads. CBP commonly lie in one region of the nucleus not far from each other. The formation of a definitive central body obviously occurs due to a fusion of some small CBP. A conclusion is made of the nucleolar origin of the ring and polymorphous structures and of their essential role in the central body formation. The participation of chromosomal and eliminated nucleolar DNA in this process is discussed.

Animals↗
PubMed1982

[Nuclear organization of the oocytes from atretic follicles of the lake frog].

Oocytes of Rana ridibunda were examined by light and electron microscopy. A peculiarity of these oocytes is the availability of the vast local growings of the inner nuclear membrane, their expansion into the nucleus and the formation of cluster accumulations of membrane structures - intranuclear vesicles filled with fibrillar protein material. In the regions of nuclear membrane expansion some disturbances in the nuclear envelope are noted: disappearance of nuclear pores, replacement of membranes by filamentous material, and formation of nuclear membrane gaps. It is suggested that growings of the inner nuclear membrane are related to the isolation of cytoplasmic proteins penetrating into the nucleus. A general pattern of the karyospheric structure, characteristic of the normal developing oocytes, remains unchanged during degeneration as well. The karyosphere is a complex consisting of the central protein body (CPB), chromosomes associated with this body and numerous nucleoli surrounding the chromosomes. Some differences in details of the structure of karyosphere in the examined oocytes are revealed. Thus, the CPB in these oocytes consists of pseudomembranes, but autonomous pore complexes here occur seldom. The chromosomes have a tendency to fuse forming in some cases a unique network of the chromatin material associated with the material of CPB. In the contact zone the transfer of chromatin fibrils into pseudomembranes is observed. The nucleoli bear no granules and demonstrate a segregation of the fibrillar material. As the result, DNA-containing material of the fibrillar centre appears at the periphery of nucleoli. Analysis of our own and literature evidence on the morphology of the oocyte nuclei from the atretic follicles of different vertebrates, and on the structure of ciliate micronuclei degenerating during conjugation allows a conclusion on the identical response of sexual cells to different stimuli evoking degeneration.

Animals↗
PubMed1979

The karyosphere during late oogenesis in Rana ridibunda.

The organization of the nucleus in the oocytes of Rana ridibunda was examined during late diplotene at the light and electron microscopic level. At this stage the chromosomes are relatively condensed and assembled in the centre of the nucleus, constituting a karyosphere. The chromosomes here are associated with the central "protein sphere" (15--20 microns in diameter), obviously at their telomeres. Numerous nucleoli are accumulated around the chromosomes, forming a karyosphere capsule and contain segregated fibrillar and granular components; structures resembling perinucleolar chromatin and fibrillar bodies (spherules) are associated with the nucleoli. Granules 30 to 40 nm in diameter are seen to surround the fibrillar spherules. "Nucleolus-like bodies" consisting of granules 10 to 15 nm in diameter which are embedded in finely fibrillar material are often associated in contact with the chromosomes. The central sphere is an accumulation of annular structures similar to those of the pore complexes of the nuclear envelope. These structures are bound to the chromosome material, the "nucleolus-like bodies" and the fibrillar bodies. A participation of "nucleolus-like bodies" in the formation of the central sphere is suggested. A possible role of the nuclear protein matrix in the construction of the karyosphere elements is discussed.

Animals↗
PubMed1976

[Nuclear structures in the late oogenesis of Rana temporaria. III. Electron microscopic studies].

The ultrastructural organization of the vitellogenic oocyte nucleus (stage VI, according to Duryee, 1950) was studied in normal and in vitro hormone-stimulated maturing oocytes of Rana temporaria. At this stage, numerous nucleoli are gathered around the knot of highly contracted chromosomes (the karyosphere) thus making the karyosphere capsule. Light microscope observations reveal three zones in the capsule: a central fibrous zone separating the chromosomes from the nucleoli, a middle zone, consisting of numerous nucleoli and a distinct fibrous componen; in addition a fibrous zone on the capsule periphery is seen. The nucleoli are fibrillar, bear no proribosomal granules and do not synthesize RNA. This period is characterized by an intensive fragmentation and segregation of the nucleolar material. Numerous micronucleoli and nuclear bodies occur in the nucleus. The nucleoli are normally compound and irregular in shape to become spherical in hormone-stimulated maturing oocytes. In the central fibrous zone of the capsule, separating the chromosomes from the nucleoli, some peculiar abundant accumulations of annuli were detected lacking the membranes component. Annuli are linked with the fibrous material and are regularily packed making peculiar pseudomembranes (PMM). The chromatin is connected with PMM directly. In the middle zone of the capsule, accumulations of PMM are also seen, though less abundant and less regularly packed; along with annuli, membranous areas of various size and form are met in PMM. PMM are connected with the micronucleoli with filaments 20 nm thick. In the peripheral zone of the capsule, a variety of membranous structures is detected: intranuclear annuli lamellae, component of the capsule consists of different membranous and pseudomembranous (with annuli) structures. A question of the contribution of the chromatin material in the formation of the fibrous capsular component (PMM and membranous structures) is discussed.

Animals↗
PubMed1975

[Nuclear structures in the late oogenesis of the common frog. I. Light microscopic observations].

The dynamics of the Rana temporaria karyosphere formation throughout different seasons was studied in addition to morphological changes in the karyosphere components with and without hormonal stimulation of oocyte maturation in vitro. Towards the end of summer, the nuclear structure (lampbrush chromosomes and multiple nucleoli) were shown to assemble in the centre of the nucleus forming a karyosphere. The completely formed karyosphere (up to 150--200 mu in diameter) is observed during autumn and winter to consist of the central chromosome part and a surrounding capsule. The capsule consists of numerous nucleoli and a distinct fibrous component. Filaments penetrating the whole nucleolar zone of the capsule are tightly packed around the chromosomes, thus forming the inner fibrous zone of the capsule, separating the chromosomes from the nucleoli. On the periphery of the karyosphere, threads attached to the nucleoli are clearly seen. This pattern of the karyosphere construction is conserved through winter till spring. In winter, spherical nucleoli change into rings and necklaces. In spring, nucleoli become spherical again and lose their threads. In the period of oocyte maturation and disappearance of nuclear envelopes, numerous nucleoli fuse into a single conglomeration which later disappears. Only the inner fibrous zone is conserved which separates the chromosomes from the cytoplasm and yolk platelets. In this state, the karyosphere persists up to the first meiotic metaphase. The nature of the fibrous component of the karyosphere capsule, its origin and function are discussed.

Animals↗
PubMed1975

[Nuclear structures at late stages of Rana temporaria oogenesis. II. Autoradiographic data].

Seasonal dynamics of RNA synthesis in the nuclei of 3rd year vitellogenetic oocytes of Rana temporaria has been studied by autoradiography. The nucleoli and chromosomes exhibit the highest level of RNA synthesis in summer, when lampbrush chromosomes are well developed, and multiple nucleoli start moving away from the nuclear membrane. The weakening of RNA synthesis is observed in autumn, when the nuclear structures assemble in the centre of the nucleus to form the karyosphere. The synthesis level is the lowest in winter, and increases in spring. The karyosphere of Rana temporaria is involved in protein metabolism of oocytes. Possible reasons of the seasonal RNA synthesis dynamics by the oocyte nuclei are discussed.

Animals↗