Showing papers on "Metaphase published in 1979"
TL;DR: A model in which the nucleoprotein fiber is folded into loops which are arranged in the Chromatid in radial fashion, in such a way that their bases become the central axis of the chromatid is discussed.
530 citations
TL;DR: It is concluded that calmodulin is more closely associated with the kinetichore-to-pole microtubules than other components of the mitotic apparatus.
Abstract: Indirect immunofluorescence was used to determine the distribution of calmodulin in the mitotic apparatus of rat kangaroo PtK2 and Chinese hamster ovary (CHO) cells. The distribution of calmodulin in PtK2 cells was compared to the distribution of tubulin, also as revealed by indirect immunofluorescence. During mitosis, calmodulin was found to be a dynamic component of the mitotic apparatus. Calmodulin first appeared in association with the forming mitotic apparatus during midprophase. In metaphase and anaphase, calmodulin was found between the spindle poles and the chromosomes. While tubulin was found in the interzonal region throughout anaphase, calmodulin appeared in the interzone region only at late anaphase. The interzonal calmodulin of late anaphase condensed during telophase into two small regions, one on each side of the midbody. Calmodulin was not detected in the cleavage furrow. In view of the differences in the localization of calmodulin, tubulin, and actin in the mitotic apparatus, experiments were designed to determine the effects of various antimitotic drugs on calmodulin localization. Cytochalasin B, an inhibitor of actin microfilaments, had no apparent effect on calmodulin or tubulin localization in the mitotic apparatus of CHO cells. Microtubule inhibitors, such as colcemid and N2O, altered the appearance of tubulin- and calmodulin-specific fluorescence in mitotic CHO cells. Cold temperature (0 degrees C) altered tubulin-specific fluorescence of metaphase PtK2 cells but did not alter calmodulin-specific fluorescence. From these studies, it is concluded that calmodulin is more closely associated with the kinetichore-to-pole microtubules than other components of the mitotic apparatus.
180 citations
TL;DR: Isolated mammalian chromosomes have been quantitatively classified by high resolution flow cytometry and chromosome to chromosome variations in HO and CA3 staining are attributed to variations in chromosomal base composition.
Abstract: Isolated mammalian chromosomes have been quantitatively classified by high resolution flow cytometry. Chinese hamster chromosomes stained with 33258 Hoechst and excited in the UV showed a fluorescence distribution in which the 14 types of Chinese hamster chromosomes were resolved into 16 groups seen as distinct peaks in the distributions. Chinese hamster chromosomes were also stained with both 33258 Hoechst (HO) and chromomycin A3 (CA3); the two dye contents were measured by selective excitation in the UV and at 458 nm in a dual beam flow cytometer. The resulting two parameter distribution (HO versus CA3) showed 10 chromosome groups1. Human strain LLL 761 chromosomes stained with HO and excited in the UV showed a fluorescence distribution in which the 23 types of human chromosomes were resolved into 12 groups. Human chromosomes stained with both HO and CA3 and measured in the dual beam flow cytometer produced two parameter fluorescence distributions which showed 20 groups. The chromosomes associated with each group were determined by quinacrine banding analysis of sorted chromosomes and by DNA cytophotometry of preidentified metaphase chromosomes. The relative HO and CA3 stain content and frequency of occurrence of chromosomes in each group were determined from the fluorescence distributions and compared to the results from DNA cytophotometry. The chromosome to chromosome variations in HO and CA3 staining are attributed to variations in chromosomal base composition.
136 citations
TL;DR: The 24 human chromosome types of normal diploid fibroblast cell strain were classified into 15 groups by high-resolution flow cytometry on the basis of 33258 Hoechst fluorescence and the average purity for the 12 sorted fractions was 78%.
Abstract: The 24 human chromosome types of normal diploid fibroblast cell strain were classified into 15 groups by high-resolution flow cytometry on the basis of 33258 Hoechst fluorescence. Chromosomes associated with each group were flow sorted onto microscope slides and identified by quinacrine banding analysis. DNA cytophotometry of metaphase chromosomes from the same cell strain supported and extended this identification. Four of the groups purified were due to chromosomes of a single type--namely, chromosomes 5, 6, 13, and 17. Eight additional groups were also separated and found to contain the following chromosomes: 1 and 2; 3 and 4; 7, 8, and X; 9--12; 14 and 15; 16 and 18; 20 and Y; and 19, 21, and 22. The average purity for the 12 sorted fractions was 78%.
128 citations
TL;DR: The findings support the following ideas on the arrangement of interphase chromosome: (1) Decondensed interphase chromosomes may occupy rather compact territories and (2) Chromosomes do not necessarily exhibit a close and permanent association with their respective homologues.
123 citations
TL;DR: The results reported here suggest that actin is involved in the condensation of Xenopus chromosomes.
Abstract: The role of contractile proteins in the structural organisation of the interphase nucleus and of metaphase chromosomes is largely unknown. Actin has been found in interphase nuclei of different species, especially in association with condensed chromatin. In the germinal vesicle (nucleus) of Xenopus oocytes, actin has been localised in the nuclear gel supporting the chromosomes and the extrachromosomal nucleoli. It has been reported that the premeiotic lampbrush chromosomes in these germinal vesicles are positively stained for actin and tubulin by the immunoperoxidase technique. Moreover, the longitudinal contraction of these chromosomes is ATP dependent. Therefore it has been suggested that actin participates in the structural organisation of the highly specialised lampbrush chromosomes. However, actin is not a major component of the metaphase chromosome scaffold. The results reported here suggest that actin is involved in the condensation of Xenopus chromosomes.
115 citations
TL;DR: This work demonstrates that spindle microtubules are involved in the mechanisms that control the time when the cell will initiate anaphase, finish mitosis, and start the next cell cycle.
Abstract: Sea urchin eggs are used to investigate the involvement of spindle microtubules in the mechanisms that control the timing of cell cycle events. Eggs are treated for 4 min with Colcemid at prophase of the first mitosis. No microtubules are assembled for at least 3 h, and the eggs do not divide. These eggs show repeated cycles of nuclear envelope breakdown (NEB) and nuclear envelope reformation (NER). Mitosis (NEB to NER) is twice as long in Colcemid-treated eggs as in the untreated controls. Interphase (NER to NEB) is the same in both. Thus, each cycle is prolonged entirely in mitosis. The chromosomes of treated eggs condense and eventually split into separate chromatids which do not move apart. This "canaphase" splitting is substantially delayed relative to anaphase onset in the control eggs. Treated eggs are irradiated after NEB with 366-nm light to inactivate the Colcemid. This allows the eggs to assemble normal spindles and divide. Up to 14 min after NEB, delays in the start of microtubule assembly give equal delays in anaphase onset, cleavage, and the events of the following cell cycle. Regardless of the delay, anaphase follows irradiation by the normal prometaphase duration. The quantity of spindle microtubules also influences the timing of mitotic events. Short Colcemid treatments administered in prophase of second division cause eggs to assemble small spindles. One blastomere is irradiated after NEB to provide a control cell with a normal-sized spindle. Cells with diminished spindles always initiate anaphase later than their controls. Telophase events are correspondingly delayed. This work demonstrates that spindle microtubules are involved in the mechanisms that control the time when the cell will initiate anaphase, finish mitosis, and start the next cell cycle.
113 citations
TL;DR: The differing rates of assembly and disassembly of each end of a microtubule suggest that a difference in polarity of growth off nucleating sites could serve as one basis for regulating the polymerization of different groups of microtubules in the same cell.
Abstract: We describe here the continuous observations of the polymerization of individual microtubules in vitro by darkfield microscopy. In homogeneous preparations we verify that polymerization can occur onto both ends of microtubules. The assembly of microtubules is polar, with one end growing at three times the rate of the other. The differential rate of elongation can be used to determine the polarity of growth off cellular nucleating centers. We show that the microtubules grow off the proximal end of ciliary axonemes at a growth rate equal to that of the slow growing end of free microtubules, while growth off the distal end proceeds at the same rate as the fast growing end. Applying this technique to microtubule growth from metaphase chromosomes isolated from HeLa and CHO cells, we demonstrate that chromosomes initiate polymerization with the fast growing end facing away from the chromosome nucleation site. The opposite ends of free microtubules show different sensitivities to microtubule depolymerizing agents such as low temperature, Ca++ or colchicine as measured directly by darkfield microscopy. The differing rates of assembly and disassembly of each end of a microtubule suggest that a difference in polarity of growth off nucleating sites could serve as one basis for regulating the polymerization of different groups of microtubules in the same cell.
112 citations
TL;DR: The conclusion has been drawn that the bulk of attachment sites of DNP fibrils to axial chromosomal structures remains unchanged during the cell cycle.
Abstract: The fragments of DNA attached to protein skeleton of interphase nuclei or metaphase chromosomes were obtained Both the method involving restriction endonuclease treatment/1,2/and a novel procedure based on mild staphylococcal nuclease digestion were used In the latter case, DNA fragments remaining bound to nuclei or chromosomes are not enriched in satellite but only in abundant middle repetitive DNA The shorter the fragments of attached DNA, the higher the content of middle repetitive DNA in the fraction It has a slightly higher density in a CsCl gradient comparing to the main DNA The yield of attached DNA, its distribution in a CsCl density gradient, and its renaturation properties are essentially the same for interphase and metaphase chromosomes The average size of DNA loops was found to be equal to approximately 60 kb for both metaphase chromosomes and interphase nuclei The conclusion has been drawn that the bulk of attachment sites of DNP fibrils to axial chromosomal structures remains unchanged during the cell cycle
98 citations
TL;DR: Metaphase chromosomes with high molecular weight DNA were isolated from Chinese hamster ovary cells in a neutral buffer containing polyamines and chelators, providing useful material for studies of the structure and biochemistry of individual chromosomes.
Abstract: Metaphase chromosomes with high molecular weight DNA were isolated from Chinese hamster ovary (CHO) cells in a neutral buffer containing polyamines and chelators. The individual, unfixed chromosomes retained their centromeric and secondary constrictions, distinct sister chromatids, and complex banding patterns. The DNA from these chromosomes was 100-fold larger (2 x 10(8) daltons) than DNA from chromosomes isolated by other procedures. These characteristics indicate preservation during isolation of considerable native structure. In contrast to chromosomes produced by other methods, these chromosomes were stable in storage and did not aggregate, thus providing useful material for studies of the structure and biochemistry of individual chromosomes.
94 citations
TL;DR: The findings show that certain necessary conditions for a sliding filament model of anaphase spindle elongation are met, and there is evidence for a specific interaction between antiparallel MTs.
Abstract: During the transition from prometaphase to metaphase, the cross-sectional area of the central spindle of Diatoma decreases by a factor of nearly two, both at the poles and at the region of overlapping microtubules (MTs) near the spindle equator. The density of spindle MT packing stays approximately constant throughout mitosis. Optical diffraction analysis of electron micrographs shows that the packing of the MTs at the poles at all stages of mitosis is similar to that expected for a two-dimensional liquid. Analysis of the region of overlap reveals more packing regularity: during prometaphase, a square packing emerges that displays sufficient organization by late metaphase to generate five orders of diffraction; during anaphase the packing in the overlap region shifts to hexagonal; at telophase, it returns to square. From the data provided by serial section reconstructions of the central spindle, it is possible to identify the polarity of almost every spindle MT, that is, to identify one pole with which the MT is associated. Near neighbor analyses of MTs in cross sections of the overlap region show that MTs prefer antiparallel near neighbors. These near neighbors are most often found at a spacing of approximately 40 nm center-to-center, while parallel near neighbors in the zone of overlap are spaced essentially at random. These results are evidence for a specific interaction between antiparallel MTs. In some sections definite bridges between MTs can be seen. Our findings show that certain necessary conditions for a sliding filament model of anaphase spindle elongation are met.
TL;DR: The results suggest that DNA in condensed chromatin of quiescent lymphocytes is more sensitive to acid-denaturation than DNA in dispersed Chromatin of the cycling interphase cells.
Abstract: quiescent nonstimulated lymphocytes as compared with interphase lymphocytes that have entered the cell cycle after stimulation by mitogens. The difference is seen after cell treatment with buffers at pH 1.5 (1.3-1.9 range) followed by staining with acridine orange at pH 2.6 (2.3-2.9). Under these conditions the red metachromatic fluorescence of the acridine orange-DNA complex is higher in quiescent cells than in the cycling lymphocytes while the orthochromatic green fluorescence is higher in the cycling, interphase cells. The results suggest that DNA in condensed chromatin of quiescent lymphocytes (as in metaphase chromosomes) is more sensitive to acid-denaturation than DNA in dispersed chromatin of the cycling interphase cells. The phenomenon is used for flow cytometric differentiation between G0 and G1 cells and between G2 and M cells. In contrast to normal lymphocytes the method applied to neoplastic cells indicates the presence of cell subpopulations with condensed chromatin but with DNA content characteristic not only of G but
TL;DR: It is discussed that these filaments may function in transport of organelles and structural proteins, and provide the daughter cells with topological information about placement and assembly of these elements within the microtrabecular lattice.
Abstract: By indirect immunofluorescence the behavior of the 10-nm filaments was studied at various stages of mitosis in guinea pig vascular endothelial cells. Interphase cells contain a ring of 10-nm filaments that encircles the nucleus and is maintained in a plane parallel to the substrate. During prophase and metaphase the cells round up and the 10-nm filament ring becomes wavy though still a closed structure. As anaphase progresses the ring then elongates into a rectangle that contains the spindle apparatus and chromosomes. In late telophase, cytokinesis cleaves the 10-nm filaments into crescents at the site of the contractile ring. These crescents then close into rings in the daughter cells. If cytokinesis is inhibited with 5 microgram of cytochalasin B per ml, then cleavage of the 10-nm filaments is blocked and the daughter nuclei remain surrounded by the parent ring. At no point during mitosis does the array of 10-nm filaments undergo major disassembly. These results indicate that, in contrast to the other major cytoplasmic structures, ventral microfilament bundles and cytoplasmic microtubules, which disassemble and reassemble during mitosis, 10-nm filaments remain intact throughout this process. The possibility is discussed that these filaments may function in transport of organelles and structural proteins, and provide the daughter cells with topological information about placement and assembly of these elements within the microtrabecular lattice.
TL;DR: Isolated Chinese hamster metaphase chromosomes were resuspended in 4 M ammonium acetate and spread on a surface of distilled water and shown to be very similar to nuclear nonhistone proteins except for the presence of more actin and tubulin.
Abstract: Isolated Chinese hamster metaphase chromosomes were resuspended in 4 M ammonium acetate and spread on a surface of distilled water or 0.15 to 0.5 M ammonium acetate. The DNA was released in the form of a regular series of rosettes connected by interrossette DNA. The mean length of the rosette DNA was 14 μm, similar to the mean length of 10 μm for chromomere DNA of Drosophila polytene chromosomes. The mean interrosette DNA was 4.2 μm. SDS gel electrophoresis of the chromosomal nonhistone proteins showed them to be very similar to nuclear nonhistone proteins except for the presence of more actin and tubulin. Nuclear matrix proteins were present in the chromosomes and may play a role in forming the rosettes. Evidence that the rosette pattern is artifactual versus the possibility that it represents a real organizational substructure of the chromosomes is reviewed.
TL;DR: It is found that at prometaphase, when the nuclear envelope is dissassembling, the spindle is constructed from two sets of polar microtubules (MTs) that interdigitate to form a zone of overlap.
Abstract: Central mitotic spindles in Diatoma vulgare have been investigated using serial sections and electron microscopy. Spindles at both early stages (before metaphase) and later stages of mitosis (metaphase to telophase) have been analyzed. We have used computer graphics technology to facilitate the analysis and to produce stereo images of the central spindle reconstructed in three dimensions. We find that at prometaphase, when the nuclear envelope is dissassembling, the spindle is constructed from two sets of polar microtubules (MTs) that interdigitate to form a zone of overlap. As the chromosomes become organized into the metaphase configuration, the polar MTs, the spindle, and the zone of overlap all elongate, while the number of MTs in the central spindle decreases from greater than 700 to approximately 250. Most of the tubules lost are short ones that reside near the spindle poles. The previously described decrease in the length of the zone of overlap during anaphase central spindle elongation is clearly demonstrated in stereo images. In addition, we have used our three-dimensional data to determine the lengths of the spindle MTs at various times during mitotis. The distribution of lengths is bimodal during prometaphase, but the short tubules disappear and the long tubules elongate as mitosis proceeds. The distributions of MT lengths are compared to the length distributions of MTs polymerized in vitro, and a model is presented to account for our findings about both MT length changes and microtubule movements.
TL;DR: It is concluded that there is no positive correlation between microtubule numbers at the egg equator and the timing of cleavage stimulation, and coordination between karyokinesis and cell cleavage is achieved by some process other than the simple numerical increase of microtubules at the equatorial cortex.
TL;DR: The Ag-stain, however, seems insensitive to low rates of rRNA synthesis and obviously follows a threshold reaction, and the frequency of Ag-positive chromosomes involved in satellite associations in interphase does not differ from that in metaphase.
TL;DR: These experiments confirm the earlier assignment of the endogenous viral sequence related to Rous-associated virus-0 to a separate (and larger) chromosome than the cellular sequencerelated to the transforming gene of avian sarcoma virus (cellular sarc), although it now appears that cellular sarc is on a small macrochromosome, rather than on a micro Chromosome.
Abstract: Chicken metaphase chromosomes were partially purified by rate zonal centrifugation, and DNA was prepared from each of the fractions of the sucrose gradient. The DNA was digested with various restriction enzymes and subjected to electrophoresis in agarose gels. The DNA was transferred to nitrocellulose filters (as described by Southern), and the filters were hybridized with cDNA probes. Four globin genes alpha A, alpha D, beta, and rho or epsilon are located on at least two chromosomes, and three of the estrogen-inducible genes of the hen oviduct--ovalbumin, ovomucoid, and transferrin--are on three different chromosomes. These experiments also confirm our earlier assignment of the endogenous viral sequence related to Rous-associated virus-0 to a separate (and larger) chromosome than the cellular sequence related to the transforming gene of avian sarcoma virus (cellular sarc), although it now appears that cellular sarc is on a small macrochromosome, rather than on a microchromosome.
TL;DR: The possibility of relatively increased macropinocytosis in late telophase was compatible with the finding of an increase in the number and volume of colloid droplets at this time to three times the amount found in any other portion of the mitotic cycle.
TL;DR: In situ hybridization to metaphase chromosomes shows that the hepatoma cells have a 10 fold increase in DNA coding for 18S and 28S ribosomal RNA, 90% of it located in the differentially stained regions, and no change in the number of genes coding for 5S RNA.
Abstract: An H4-IIE-C3 hepatoma cell line derived from an ACI rat has been shown to have differentially stained regions attached to the short arms of chromosomes 3, 11 and 13 and the long arm of an unidentified small chromosome. There is cell to cell variability in the number and size of the differentially stained regions, which contain, on the average, about 5% of the total DNA. A series of secondary constrictions occur at intervals along the length of each differentially stained region. These stain with silver by the Ag-AS method, indicating that the differentially stained regions contain sites of active 45S ribosomal precursor RNA transcription. In situ hybridization to metaphase chromosomes shows that the hepatoma cells have a 10 fold increase in DNA coding for 18S and 28S ribosomal RNA, 90% of it located in the differentially stained regions, and no change in the number of genes coding for 5S RNA. These results have been confirmed by filter disc hybridization.
TL;DR: The hypothesis that the birefringent chromosomal fibers anchor the chromosomes to the spindle and transmit the force for anaphase chromosome movement is supported.
Abstract: The degree of mechanical coupling of chromosomes to the spindles of Nephrotoma and Trimeratropis primary spermatocytes varies with the stage of meiosis and the birefringent retardation of the chromosomal fibers. In early prometaphase, before birefringent chromosomal fibers have formed, a bivalent can be displaced toward a spindle pole by a single, continuous pull with a microneedle. Resistance to poleward displacement increases with increased development of the chromosomal fibers, reaching a maximum at metaphase. At this stage kinetochores cannot be displaced greater than 1 micrometer toward either spindle pole, even by a force which is sufficient to displace the entire spindle within the cell. The abolition of birefringence with either colcemid or vinblastine results in the loss of chromosome-spindle attachment. In the absence of birefringent fibers a chromosome can be displaced anywhere within the cell. The photochemical inactivation of colcemid by irradiation with 366-nm light results in the reformation of birefringent chromosomal fibers and the concomitant re-establishment of chromosome attachment to the spindle. These results support the hypothesis that the birefringent chromosomal fibers anchor the chromosomes to the spindle and transmit the force for anaphase chromosome movement.
TL;DR: It is argued that spindle structure is not disrupted by the procedures, and therefore that the arrangements of actin-containing filaments are not artifacts of the glycerination procedures.
Abstract: We have studied the arrangements of actin-containing filaments in 13 bundles of kinetochore microtubules in glycerinated, heavy meromyosin-treated Haemanthus endosperm cells: 7 bundles were in a cell at anaphase, and 6 were in a cell at metaphase. Actin-containing filaments were present in each of the 13 bundles of kinetochore microtubules: they were in amongst the microtubules in the bundle and seemed to be associated with the microtubules. Actin-containing filaments in each bundle seemed to terminate at the kinetochores. Actin-containing filaments associated with the kinetochore microtubules were of consistent polarity (the arrowheads pointed towards the kinetochores) whereas those associated with other microtubles and those not associated with microtubules did not have consistent polarity (some pointed towards the spindle pole, others pointed away from it). Roughly, there were as many individual stretches of actin-containing filaments identified per bundle of kinetochore microtubules as there were microtubules which terminated at the kinetochore. These data suggest that actin-containing filaments in spindles have a functional role. We used 2 glycerination procedures in our studies (one for each cell), and neither seemed to disrupt the basic microtubule arrangements: the arrangements of spindle microtubules seen after glycerination of Haemanthus endosperm were identical to those described previously by others in non-glycerinated glutaraldehyde-fixed Haemanthus endosperm. Thus we argue that spindle structure is not disrupted by the procedures, and therefore that the arrangements of actin-containing filaments are not artifacts of the glycerination procedures. The only difference between microtubules in glycerinated cells and microtubules in untreated cells is that there seem to be fewer in the glycerinated cells. The possible role of actin-containing filaments in the spindle is discussed.
Journal Article•
TL;DR: The mitotic cells from an asynchronous population of Chinese hamster ovary cells exposed to 41.5° for 7 hr were examined by light and electron microscopy to determine if there were any morphological abnormalities related to cell death or lengthening of metaphase induced by hyperthermia.
Abstract: The mitotic cells from an asynchronous population of Chinese hamster ovary cells exposed to 415° for 7 hr were examined by light and electron microscopy to determine if there were any morphological abnormalities related to cell death or lengthening of metaphase induced by hyperthermia All components of the mitotic apparatus were formed during exposure to heat, and the mitotic apparatus was functional as demonstrated by eventual cell division However, heat caused the nuclear envelope to reform precociously around the chromosomes except in the region of the kinetochores, and the nuclear envelope remained associated with the chromatids during segregation The precocious reformation of the nuclear envelope may be responsible for the lengthening of metaphase Cells undergoing mitosis during the heat treatment possessed large evaginations of the plasma membrane, and the ubiquitous cortical microfilaments were absent in the region of these evaginations Possibly related to the membrane damage were osmotic changes resulting in swollen mitochondria observed in heated cells entering mitosis Since hyperthermic damage to the plasma membrane-microfilament complex was not observed in interphase cells or in cells completing division but was morphologically expressed during mitosis, the thermal lability of the plasma membrane must increase as the cells enter mitosis
TL;DR: A precise schematic representation of the number, height, position, and staining intensity of the Giemsa bands of late prophase, prometaphase, early metaphase, and mid-metaphase chromosomes 6–22, X, and Y is presented.
Abstract: A precise schematic representation of the number, height, position, and staining intensity of the Giemsa bands of late prophase, prometaphase, early metaphase, and mid-metaphase chromosomes 6--22, X, and Y is presented. Late prophase chromosomes were found to have 2--2 1/2 times the length and 3--3 1/2 times the number of bands previously observed in mid-metaphase, whereas prometaphases and early metaphases were intermediate in length and number of bands. In this work, the maximum number of bands observed per haploid set in late prophase was 1353, while more than 350 were generally found in mid-metaphase.
TL;DR: The growth, movements, and orientations of centrioles and the behavior of pericentriolar material during mitosis in vivo was studied at the ultrastructural level in stimulated rat thyroid epithelial cells.
TL;DR: The data suggest that these nucleolus-like ‘blobs’ contain nucleolar material which, following mitosis, has been enclosed in micronuclei which do not contain nucleoli, and no evidence was found for the activation of latent NORs not expressed in mononucleate cells.
TL;DR: The results are interpreted as indicating that CSF does not directly bring about chromosomes condensation, but arrests the cell cycle at metaphase and stabilizes the cytoplasmic conditions of metaphase which, in turn, induce chromosome condensation in foreign nuclei as well as spindle and aster formation.
TL;DR: Mitosis in the imperfect yeast-like basidiomyceteBullera alba was studied by comparative light and electron microscopy and was deemed closest to the heterobasidiomyCete yeasts.
Abstract: Mitosis in the imperfect yeast-like basidiomyceteBullera alba was studied by comparative light and electron microscopy. During mitosis the chromatin containing part of the nucleus moved into the progeny cell, and the nucleolus containing part of the nucleus remained in the parent cell. The two portions of the nucleus then separated and the nucleolar part degenerated. Metaphase and anaphase took place in the progeny cell. Subsequently one mass of chromatin returned to the parent cell, and two new nuclei were formed. The study concentrated on the nuclear envelope, nucleolus, spindle pole body, chromatin, spindle, and cytoplasmic microtubules. Mitosis inB. alba was compared with reports of mitosis in other basidiomycetes, theUredinales, and theAscomycotina and was deemed closest to the heterobasidiomycete yeasts. Histochemical evidence for the presence of lipid, glycogen, and polyphosphate in the cytoplasm was presented.
TL;DR: It is concluded that in man, reflected by the difference in frequencies of silver staining NORs between young and aged persons, a rather extensive loss of ribosomal RNA-gene activity may occur during aging.
TL;DR: Microfluorometric measurements were used to document the occurrence of energy transfer between quinacrine or 33258 Hoechst as energy donor and ethidium or 7-aminoactinomycin D as acceptor when used jointly to stain cytologic preparations of human metaphase chromosomes.
Abstract: If two fluorescent dyes with different binding or fluorescence specificities are used simultaneously to stain DNA or chromosomes, the ratio of their fluorescent signals can provide information about base composition or base analogue substitution. Energy transfer between such dye pairs, possible if the fluorescence spectrum of one overlaps the absorption spectrum of the other, can modify observed fluorescence. Microfluorometric measurements were used to document the occurrence of energy transfer between quinacrine or 33258 Hoechst as energy donor and ethidium or 7-aminoactinomycin D as acceptor when used jointly to stain cytologic preparations of human metaphase chromosomes. Use of 7-aminoactinomycin D, a dye with G-C binding specificity, as energy acceptor permitted the identification of human chromosome regions presumptively enriched for clusters of A-T base pairs, based on the resistance of A-T specific fluorescence, from quinacrine or 33258 Hoechst, to energy transfer dependent quenching. The results provide information about basic structural features of metaphase chromosomes, and the associated methodology may prove useful in accentuating specific fluorescent polymorphic chromosome regions.