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D V Markov

Publications and source records attributed to D V Markov.

At least 19 recordsLinked to original sources
PubMed1996

Localization of nucleic acids in hepatocyte nucleoli of rats upon D-galactosamine-induced block of transcription.

The precise localization of DNA and RNA within rat hepatocyte nucleoli during the process of D-galactosamine-induced nucleolar segregation has been studied by using sensitive methods for their detection: osmium-ammine staining and terminal deoxynucleotidyl transferase reaction for DNA, and immunoelectron microscopy with anti-RNA antibodies, RNase-gold, and autoradiography with tritiated orotic acid for RNA. The blocking of transcription was followed by the disappearance of intranucleolar condensed chromatin. Agglomerates of thin extended DNA filaments were found to change their location to the nucleolar periphery and to coalesce with each other. At the last stage of nucleolar segregation they were concentrated at the pole of the nucleolar fibrillar remnant while the rest of the nucleolus did not contain any DNA. No DNA was found in the dense fibrillar component of both intact and treated hepatocyte nucleoli. During the process of nucleolar segregation the bulk of the nucleolar RNA was found within the so-called spherical bodies. This RNA appeared to be synthesized shortly before or even after drug administration. The results obtained are in agreement with the hypothesis that the fibrillar centers are the site of nucleolar transcription. They also show that uncompleted molecules of pre-rRNA whose synthesis has been blocked are segregated from the rest of nucleolar RNA species into the spherical bodies.

Animals↗
PubMed1994

Spherical bodies and fibrillar centers in hepatic cell nucleoli of rats treated with D-galactosamine.

Inhibition of rDNA transcription leads to segregation of nucleolar components and accumulation of dense material of coarse fibrillogranular structure. Fibrillar centers are not always detectable. In the present study D-galactosamine was used to inhibit transcription in rat liver cells. Small dense microspherules detached from the dense fibrillar component, migrated to the nucleolar periphery, and coalesced into large spherical bodies. The latter represented a compartment of the granular component although there were some cytochemical differences. The spherical bodies detached from nucleoli and converted into clusters of interchromatin granules. The matrix substance of the spherical bodies formed filaments interconnecting the granules within the clusters. Nucleolar perichromatin-like granules were released continually from the periphery of spherical bodies before their detachment from nucleoli. The observations suggested that growth-arrested molecules of pre-rRNA synthesized in the initial stage of D-galactosamine action were stored in the nucleoplasm as interchromatin and perichromatin-like granules. The use of antimonate-osmium fixation demonstrated the presence of presumptive fibrillar centers of rapidly increasing density which coalesced with each other, migrating to the nucleolar periphery. At the final stage of nucleolar alterations a single presumptive fibrillar center occupied one of the poles of the nucleolar remnants.

Animals↗
PubMed1994

An alternative method for preparation of Schiff-like reagent from osmium-ammine complex for selective staining of DNA on thin Lowicryl sections.

Batches of osmium-ammine (OA) complex vary considerably in staining properties when used in a Feulgen-like reaction for selective staining of DNA-containing structures. An alternative procedure for preparation of Schiff-like reagent from OA complex is described. It is based on generation of H2SO3, respectively SO2, within the OA solution and ensures more favorable conditions for production of a Schiff-like stain than bubbling with SO2 does. The method is reproducible and yields high staining intensity. Data obtained suggest that the ability of OA complex to produce Feulgen-like staining is strongly influenced by variations in its chemical composition. Their unfavorable effect can be overcome by selecting suitable conditions for preparation of a Schiff-like reagent. Conditions for obtaining specific and sensitive Feulgen-like staining are determined.

Acrylic Resins↗
PubMed1986

Quantitative electron microscope autoradiography: application of multiple linear regression analysis.

A new method for the analysis of high resolution EM autoradiographs is described. It identifies labelled cell organelle profiles in sections on a strictly statistical basis and provides accurate estimates for their radioactivity without the need to make any assumptions about their size, shape and spatial arrangement. The radioactivity in interfacial membranes and transitional junctional regions between pairs of adjoining cell structures can be determined without any additional measurements. The uniformity of internal labelling of large cell organelles can be also assessed. Correcting for cross-fire does not need any predictive information from a frequency distribution function describing the image spread about a radioactive point source. Instead, the section area is subdivided into regions in such a way that each region with cross-fired silver grains over it includes also the sites of the radioactive disintegrations that have produced them. The method is based on the quantitative regression relationship between the number of developed silver grains overlying any given region and the size of the cell organelle profiles included. A transparent overlay screen bearing a regular array of circles and a point-counting procedure are applied to divide the section area into regions and to measure their area and the size of the cell organelle profiles. The least squares method is used for the simple and rapid calculation of specific activity estimates and exact standard errors to be attached to them. A modest computing facility and a standard library program are required. Simulation modelling and analysis of residuals were used to lend support to the validity of the method.

Animals↗
PubMed1983

Radioautographic study of the axonal transport of proteins into the sensory nerve endings of avian mechanoreceptors.

The axonal transport of proteins to the nerve endings of Herbst and Grandry sensory receptors has been investigated by electron-microscope radioautography. Soon after the injection of [3H]leucine into the trigeminal ganglia of young ducks, labeled proteins are conveyed along the suborbital sensory nerves to the sensory nerve endings at rates of at least 200-280 mm/day. Most of these rapidly transported proteins accumulate in areas containing vesicles of various kinds and along the axolemmal region. Later, the bulk of labeled proteins migrate along the axons at rates of about 15 mm/day and are distributed mainly to the mitochondria. A small portion of labeled material is transferred to the adjoining modified Schwann and specialized Grandry receptor cells. It is concluded that the transport of proteins from sensory ganglia to sensory nerve endings of mechanoreceptors is conveyed at fast and intermediate rates and is mainly used for the renewal of vesicles, axolemmal constituents and mitochondria.

Animals↗
PubMed1982

Electron microscopic localization of silver staining NOR-proteins in rat liver nucleoli upon D-galactosamine block of transcription.

The method for electron microscopy of the Ag-staining of NOR-specific proteins was adapted to tissue sections from solid organs. The distribution of the Ag-staining proteins in rat liver nucleoli after complete block of transcription caused by D-galactosamine was investigated. In control animals, the Ag-staining proteins are associated with the fibrillar components of nucleoli. After block of transcription, positive Ag-staining is observed in the condensed fibrillar components of segregated nucleoli and later in the derived dense nucleolar fibrillar remnants. The granular components and the spherical bodies in segregated nucleoli are negative. It is concluded that in interphase nucleoli the Ag-staining NOR proteins are associated with the fibrillar components and with the derived nucleolar fibrillar remnants. The positive Ag-staining does not reflect the actual transcription of rRNA genes since it is present in both transcribed and non-transcribed r-chromatin.

Animals↗
PubMed1978

Differentiation of malignant myoblasts in 7,12-dimethyl-benz(a)-anthracene-induced rhabdomyoblastomas. An electron microscopic study.

The differentiation of DMBA-induced rhabdomyoblastomas was studied during the early stages of tumour growth. Two cell populations were found to constitute the tumour tissue: small cells (SC) and long spindle-shaped cells (LSSC). The SC were the only tumor cells at the earliest detectable stage of tumour growth 10 weeks after intramuscular injection of DMBA. They had small heterochromatic nuclei with a compact nucleolus containing only fibrillar components. The cytoplasm was very rich in SER of tubular type, dense bodies and Golgi apparatus. Centrioles at all stages of the replicative cycle were very frequently observed. The cells did not fuse and showed no tendency to differentiate. The LSSC had large euchromatic nuclei with multiple irregular nucleoli containing both fibrillar and granular components. The cytoplasm had an abundant GER and well-developed Golgi apparatus. These cells formed 100 Angstrom thick cytofilaments the increase of which paralleled reduction of GER. The cells tended to fuse but did not form myofibrils. A rare variant of these cells neither possessed Golgi apparatus nor formed cytofilaments but accumulated dense protein substance in the cisternae of the GER. Myotubes with cross-striated myofibrils were but occasionally observed. The ultrastructural characteristics of both cell types revealed essential differences in the biosynthetic activity and the degree of differentiation. The SC were considered to belong to the myogenic cell line and to be most probably the malignant counterpart of proliferating satellite cells (presumptive myoblasts) and precursors of the LSSC. Morphologically and developmentally the LSSC bore close resemblance to normal myoblasts but the proliferative capacity of some of them seemed to be lost. The differentiation of the malignant myoblasts in the DMBA-induced rhabdomyoblastomas was similar to the early differentiation of the normal muscle tissue.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1976

Changes in the mitochondria in the initial part of the axon during regeneration.

The initial part of the axon including the axon hellock, the initial unmyelimated segment and the beginning of myelinated axon was studied electron microscopically during regeneration, 1--30 days following a crush lesion of the rat hypoglossal nerve. Large mitochondria reaching 1.1 mum in diameter, with abundant cristae and dense granules in the matrix were observed between days 3--21. They formed clusters in the initial myelinated segment of the axon. End-to-end contacts and ribosomes around them were very often visible. The large mitochondria exhibited strong succinate dehydrogenase and NAD - H2 diaphorase activities. The relationship between the appearance of large and active mitochondria in the initial part of the axon and the elevated axonal transport during regeneration of the peripheral nerve is also discussed.

Animals↗