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J B Rattner

Publications and source records attributed to J B Rattner.

At least 109 records · Page 6Linked to original sources
PubMed1978

Higher order structure in metaphase chromosomes. I. The 250 A fiber.

Metaphase chromosomes released from cells in the presence of Joklik's suspension media by vortex-mixing with 0.5 mm glass beads have been analyzed by electron microscopy. In these preparations the chromosomes are composed of series of loops (200-300 A in diameter) which are, in turn, composed of closely-apposed arrays of nucleosomes. Negative-staining of these preparations has allowed the identification of several distinct patterns within the loop which appear to arise from variations in nucleosome packing. Analogous patterns are also observed in chromatin fragments generated by brief micrococcal nuclease digestion. From these data we have deduced certain features of nucleosome-nucleosome interactions in higher-ordered chromatin fibers.

Animals↗
PubMed1978

Higher order structure in metaphase chromosomes. II. The relationship between the 250 A fiber, superbeads and beads-on-a-string.

The morphology of metaphase chromosome-derived chromatin fibers released from cells by non-ionic detergent cell lysis in the presence of divalent cations has been studied by electron microscopy. In these preparations the euchromatic arms appear as a series of loops, 200-300 A in diameter, which are composed of closely-apposed nucleosome arrays. The higher order fiber in chromosomes derived from detergent-lysed cells appears to be less stable than chromatin fibers obtained by mechanical cell lysis. The fiber breaks down into a series of non-uniform nucleosome aggregates (superbeads) and finally to chromatin in a beads-on-a-string morphology upon incubation at 31 degrees for 20 min. These observations allow us to suggest a relationship between uniform thick fibers, superbead-containing fibers, and beads-on-a-string chromatin within metaphase chromosomes.

Animals↗
PubMed1978

Selective digestion of mouse metaphase chromosomes.

Metaphase chromosomes prepared from colcemid-treated mouse L929 cells by non-ionic detergent lysis exhibit distinct heterochromatic centromere regions and associated kinetochores when viewed by whole mount electron microscopy. Deoxyribonuclease I treatment of these chromosomes results in the preferential digestion of the chromosomal arms leaving the centromeric heterochromatin and kinetochores apparently intact. Enrichment in centromere material after DNase I digestion was quantitated by examining the increase in 10,000 X g pellets of the 1.691 g/cc satellite DNA relative to main band DNA. This satellite species has been localized at the centromeres of mouse chromosomes by in situ hybridization. From our analysis it was determined that DNase I digestion results in a five to six-fold increase in centromeric material. In contrast to the effect of DNase I, micrococcal nuclease was found to be less selective in its action. Digestion with this enzyme solubilized both chromosome arms and centromeres leaving only a small amount of chromatin and intact kinetochores.

Animals↗
PubMed1978

Partial purification and characterization of the intercellular bridge from cultured mouse cells.

At the completion of mitosis, the two daughter cells are connected by a channel of membrane-bound cytoplasm, the intercellular bridge. This structure contains parallel arrays of spindle microtubules which are associated, at the bridge midline, with a metallophilic band called the midbody. In an effort to characterize midbody components, intercellular bridges were partially purified. The purification consisted of brief sonication of telophase populations of mouse L929 cells in order to shear intercellular bridges from daughter cells, digestion of chromatin by an excess of micrococcal nuclease, and differential centrifugation to enrich for intercellular bridges. Electron microscopy of these preparations substantiated the identity of the bulk of material as intercellular bridges. After solubilization with sodium dodecyl sulfate, the protein components of these preparations were iodinated with Na(125)I and separated by two-dimensional gel electrophoresis. From these analyses, the major polypeptide components of intercellular bridges appear to be tubulin, varying amounts of plasma membrane proteins, and a polypeptide with an apparent molecular weight of 42,000. Time-course studies reveal that this polypeptide is first detectable in a pelletable form approximately 30 min after cells are released from metaphase block, reaches maximal spot intensity in late telophase, and is no longer detectable in G1 populations. We interpret these data to suggest that the 42,000-dalton polypeptide is a component of the midbody.

Cells, Cultured↗
PubMed1977

The structure of mesokaryote chromosome.

Condensed and dispersed forms of the chromosomes of the dinoflagellate, Prorocentrum micans, deposited on grids by the microcentrifugation technique were studied by electron microscopy. In the normally condensed form, the chromosomes appear as banded rods surrounded by a peripheral cloud of partially dispersed fibers. Single fibers in these and in extensively dispersed preparations appear as smooth threads of uniform diameter (55-65 A). The chromosome fibers are contrasted by positive-group-specific stains indicating the presence of cationic moieties associated with the DNA. Occasionally Y-shaped chromosomes are seen; these may be replicating structures. These observations are in general agreement with studies of dinoflagellate chromosomes by other techniques, and provide support for the suggestion that these organisms possess a genome organization whose structure is typical of neither prokaryotes nor eukaryotes, and hence may be intermediate forms.

Animals↗
PubMed1977

The role of the centriolar region in animal cell mitosis. A laser microbeam study.

An argon ion laser microbeam (488 and 514 nm) was used to selectively irradiate one of the two centriolar regions of rat kangaroo Potorous tridactylis (PtK2) prophase cells in vitro. The cells were sensitized to the laser radiation by treatment with acridine orange (0.1-0.2 mug/ml). Ultrastructural examination of the irradiated centriolar regions demonstrated that the primary site of damage was the pericentriolar material. This result suggests that nucleic acid is present in the pericentriolar material. Behavioral and ultrastructural analysis demonstrated that cells with one damaged pericentriolar zone could undergo (a) nuclear membrane breakdown, (b) chromosome condensation, (c) metaphase plate formation, and (d) cytokinesis. However, the chromosomes neither separated nor exhibited any anaphase movements. Detailed ultrastructural analysis revealed the presence of kinetochore microtubules on both sides of chromosome mass and a lack of microtubules in the cytokinesis constriction. These results indicate that the pericentriolar material is important in spindle orgainization and essential for the formation of the interpolar microtubules.

Cell Line↗
PubMed1976

Centriole behavior in early mitosis of rat kangaroo cells (PTK2).

Behavior of the centriolar duplexes during early mitosis was investigated. In general, both duplexes are capable of migrating about the cell as a unit with little change in their center to center spacing prior to separation to form the spindle poles. This duplex separation may occur at any point within the mid-prophase-prometaphase period. If it is delayed to prometaphase, transitory monopolar spindles were observed.

Animals↗
PubMed1976

Dependence of centriole formation on protein synthesis.

Centriole formation was studied after inhibition of protein synthesis for various portions of the cell cycle. Synchronous populations of mitotic L929 (mouse) cells were plated into petri dishes and the course of procentriole formation was monitored by electron microscope analysis. The frequency with which procentrioles were seen in association with mature centrioles normally increased steadily in the interval from 4 to 12 h after mitosis. The formation of procentrioles was abruptly inhibited by the addition of cycloheximide at any time from mitosis until 12 h postmitosis (S phase). This suggested that the formation of procentrioles was dependent upon protein synthesis immediately before their appearance. Prophase-accociated elongation of procentrioles appeared to occur normally in cells treated with cycloheximide for up to 4 h before prophase, though the mitotic index in treated cultures decreased somewhat. Thus, protein synthesis did not appear to be essential for procentriolar elongation to the mature length.

Cell Division↗
PubMed1976

Distribution of microtubules during centriole separation in rat kangaroo (Potorous) cells.

The distribution of microtubule profiles during separation of the centriole duplexes in prophase of rat kangaroo cells (PTK2W) has been investigated by serial section reconstructions. Separation begins with a reduction of the interphase microtubular network which radiates from the region of the duplex to all parts of the cell. As duplexes separate, microtubular elements appear between the duplexes. However, most microtubular elements extend oblique to the axis of separation rather than aligned along the axis of separation. Few microtubules are seen extending directly between duplexes. Longer profiles are seen as separation continues. Prior to the completion of separation, microtubules coalesce to form a discrete band often juxtaposed on the nuclear membrane. Subsequently, the duplexes reach their final position and nuclear envelope dissolution is initiated.

Cell Line↗
PubMed1975

Electron microscopy of whole mount metaphase chromosomes.

Whole mount metaphase chromosomes, from cultured L cells, have been centrifuged onto grids and examined by electron microscopy. Compact and dispersed chromosome forms provide extensive ultrastructural information. Condensed chromosome arms appear as packed fibers with centromeric heterochromatin identifiable because it stains more intensely than the rest of the chromosome. Kinetochores are readily visible in these preparations. Under appropriate isolation conditions, it is possible to obtain mitotic spindles in which bundles of microtubules remain attached to kinetochores, suggesting that the kinetochores retain basic structural integrity throughout the isolation procedure. Dispersal of metaphase chromosomes by treatment with formalin and distilled water shows that these chromosomes are composed of a basic fiber that is normally highly condensed. This fiber is made up of regularly repeating 70-90 A diameter nucleoprotein granules separated from neighboring granules by a 20-40 A diameter fiber whose continuity is maintained by DNA. This structural arrangement is totally analagous to that reported for interphase chromatin from a variety of sources.

Animals↗
PubMed1973

Independence of centriole formation and DNA synthesis.

The temporal relationship between cell cycle events and centriole duplication was investigated electron microscopically in L cells synchronized by mechanically selecting mitotic cells. The two mature centrioles which each cell received at telophase migrated together from the side of the telophase nucleus distal to the stem body around to a region of the cytoplasm near the stem body and then into a groovelike indention in the early G(1) nucleus, where they were found throughout interphase. Procentrioles appeared in association with each mature centriole at times varying from 4 to 12 h after mitosis. Since S phase was found to begin on the average about 9 h after mitotic selection, it appeared that cells generated procentrioles late in G(1) or early in S. During prophase, the two centriolar duplexes migrated to opposite sides of the nucleus and the daughter centrioles elongated to the mature length. To ascertain whether any aspect of centriolar duplication was contingent upon nuclear DNA synthesis, arabinosyl cytosine was added to mitotic cells at a concentration which inhibited cellular DNA synthesis by more than 99%. Though cells were thus prevented from entering S phase, the course of procentriole formation was not detectibly affected. However, cells were inhibited from proceeding to the next mitosis, and the centriolar elongation and migration normally associated with prophase did not occur.

Cell Division↗