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Showing papers on "Metaphase published in 1972"


Journal ArticleDOI
TL;DR: Results indicate that such chromosome regions are characterized chemically by an extremely high, if not exclusive, content of adenine and thymine.
Abstract: The pattern of intense fluorescence of interphase nuclei and metaphase chromosomes after staining with quinacrine is described in Samoaia leonensis. Autoradiographic analysis of interphase nuclei after pulse labeling with tritiated thymidine indicates that there is little or no overlap in the time of replication of the intensely fluorescing and weakly fluorescing regions. Autoradiographic analysis of metaphase figures after continuous labeling with tritiated thymidine shows that the intensely fluorescing regions are late replicating and establishes their order of replication. Autoradiographic analysis of interphase nuclei after pulse labeling with tritiated deoxycytidine and of metaphase figures after continuous labeling with this tracer show that there is little, if any, incorporation of deoxycytidine into those chromosome regions which fluoresce intensely after staining with quinacrine and quinacrine mustard. These results indicate that such chromosome regions are characterized chemically by an extremely high, if not exclusive, content of adenine and thymine.

120 citations


Journal ArticleDOI
TL;DR: It is concluded that myocardial cells can no longer be cited in support of the dogma, that differentiated cells do no divide, that there is a temporary competition between the two phenomena at the metaphase-anaphase stages.
Abstract: Ventricular heart cultures were prepared from newborn rats and examined in Rose chambers by high resolution, phase-contrast optics. Details of the procedure are given for obtaining a high yield of myocardial or endothelial cells. Photographic records were obtained of living cells by using photomicrography, cinematography, and high speed filming to document the cytological differences between endothelial and myocardial cells, details of mitosis in the two cell types, and patterns of contractility. Myocardial cells can be distinguished from endothelial cells in the living state by the following criteria; dense cytoplasm; giant and pleomorphic mitochondria or sarcosomes: presence of small, round nuclei; binucleation; one or two round, dense nucleoli; a specialized Golgi apparatus around the nucleus; myofobrils; intercalated discs; myopodia; small, cell size; failure of cell migration; spontaneous contractions; formation of synchronized networks; and flattened appearance with adhesion to other cells during mitosis. Contracting myocardial cells are shown to undergo mitosis. Contractions become weaker at metaphase and then cease at anaphase. Daughter cells may resume contractions. Organized myofibrils are generally not detected during the mitotic periods when contractions are minimal or absent. It is proposed that myofibrils undergo a transient disorganization during mid-mitosis and become reorganized in the daughter cell(s). It is suggested that there is a competition for energy at the time of spindle changes and chromosome movements, so that priority is given to the mitotic process rather than to myofibrillar contractions. Myofibrillogenesis is considered to be a relatively rapid process. The average mitotic time is 2.5 hr fore endothelial cells and 6.1 hr for myocardial cells. Failure of cytokinesis frequently occurs in dividing myocardial cells and results in the formation of binucleated cells. A sequence, is presented of a binucleated myocardial cell which undergoes an abormal multipolar mitosis, leading to polynucleation. Myocardial cells incorporate tritiated thymidine into nuclear DNA. The question of mitosis and differentiation of myocardial cells is reviewed. It is concluded that myocardial cells can no longer be cited in support of the dogma, that differentiated cells do no divide. However, these is a temporary competition between the two phenomena at the metaphase-anaphase stages.

114 citations


Journal ArticleDOI
TL;DR: Chinese hamster Don cells, synchronized by removing metaphase cells from an asynchronous population, were x-irradiated or fixed in different parts of the cell cycle.
Abstract: Chinese hamster Don cells, synchronized by removing metaphase cells from an asynchronous population, were x-irradiated or fixed in different parts of the cell cycle. Radiosensitivity, as measured b...

107 citations


Journal ArticleDOI
TL;DR: New postfixation procedures were developed specifically to preserve the fine-structure of the mitotic apparatus, which revealed a fibrillo-granular, extranuclear Spindle Pole Body at each pole of the intranuclear, microtubular spindles.
Abstract: Mitosis in Fusarium oxysporum Schlect. was studied by light and electron microscopy. The average times required for the stages of mitosis, as determined from measurements made on living nuclei, were as follows: prophase, 70 sec; metaphase, 120 sec; anaphase, 13 sec; and telophase, 125 sec, for a total of 5.5 min. New postfixation procedures were developed specifically to preserve the fine-structure of the mitotic apparatus. Electron microscopy of mitotic nuclei revealed a fibrillo-granular, extranuclear Spindle Pole Body (SPB) at each pole of the intranuclear, microtubular spindles. Metaphase chromosomes were attached to spindle microtubules via kinetochores, which were found near the spindle poles at telophase. The still-intact, original nuclear envelope constricted around the incipient daughter nuclei during telophase.

98 citations


Journal ArticleDOI
TL;DR: The phosphorylation is found in mitotic cells collected without use of a metaphase arrest agent and has a pronounced influence on the chemical extraction of lysine-rich histone during isolation of metaphase chromosomes.

91 citations


Journal ArticleDOI
04 Aug 1972-Nature
TL;DR: In amphibia, the cell cycle is completed in less than an hour at 180° C, and during early cleavage in Xenopus there is reportedly1 no G1 phase, and the G2 is either absent or very short.
Abstract: DURING maternal embryogenesis, the vertebrate egg is blocked in meiotic prophase. At ovulation it proceeds to the metaphase of the second meiotic division, which is complete after fertilization or an artificial stimulus. The first mitotic division occurs about three hours later, and is followed by a series of rapid mitoses without cell growth. In amphibia, the cell cycle is completed in less than an hour at 180° C. During early cleavage in Xenopus there is reportedly1 no G1 phase, and the G2 is either absent or very short.

81 citations


Journal ArticleDOI
P. E. Polani1
TL;DR: Techniques for obtaining differential Giemsa staining of the paracentromeric (p.c.) regions of male and female mouse meiotic chromosomes (centromeric heterochromatin) were explored and standard procedures developed and the possibility is discussed that the p.c. regions may be important for chromosome recognition and pairing, possibly on a quantitative basis.
Abstract: Techniques for obtaining differential Giemsa staining of the paracentromeric (p.c.) regions of male and female mouse meiotic chromosomes (centromeric heterochromatin) were explored and standard procedures developed for the different meiotic cells in the two sexes. The best result followed the use of heat at controlled pH in Sorensen's phosphate buffer or in Standard Saline Citrate (SSC) solutions. With these techniques, morphological features of the p.c. regions and their variation were studied in normal animals (CFLP strain) and in a strain (AKR) homozygous for a centric fusion [T(11; ?)-1 Ald] between chromosomes No. 6 and No. 15 (Miller et al., 1971). The Y chromosome was often found to show distinct p. c. staining at first and apparently at second meiotic metaphase, and the X and Y chromosomes were found to associate as bivalents by their long arms. Autosomal p.c. regions showed variation in size which might indicate differences between non-homologous chromosomes but a tendency to similarity between homologues. Differences were found between males and females in respect to proportions and variation of bivalents with single and double chiasmata. The relative positions of chiasmata were different in the two sexes. The presence of the centric fusion in the males did not seem to affect the pairing behaviour of the remaining autosomes or of those taking part in the centric fusion. The possibility is discussed that the p.c. regions, to which also other functions would seem to appertain, may be important for chromosome recognition and pairing, possibly on a quantitative basis.

80 citations


Journal ArticleDOI
TL;DR: Gametophyte germlings from unialgal cultures of Membranoptera platyphylla were examined with the electron microscope and the events of mitosis were observed in dividing cells near the thallus apex.
Abstract: SUMMARY Gametophyte germlings from unialgal cultures of Membranoptera platyphylla were examined with the electron microscope. The events of mitosis were observed in dividing cells near the thallus apex. In prophase the nucleus is spindle-shaped and surrounded by microtubules and a layer of endoplasmic reticulum. A unique organelle, the polar ring, is present at each pole; its junction is not clear. At metaphase the nuclear envelope is intact except for fenestrations at the poles. Spindle microtubules are attached to distinct kinetochores on the chromosomes and continuous pole-to-pole microtubules are present. The nucleolus has dispersed but, its granular components are still evident in the nucleoplasm. As the chromosomes separate, the nucleus elongates and finally constricts in the middle to produce 2 daughter nuclei.

77 citations


Journal ArticleDOI
TL;DR: During the first divisions of S. purpuratus an ATPase is found which shows in every cell cycle one activity peak in interphase and another one during metaphase, which cannot be prevented by colchicine or lithium but can be inhibited by a puromycin treatment which prevents the cells from entering mitosis.

76 citations


Journal ArticleDOI
TL;DR: In this paper, the authors showed that actin-like filaments were seen near regions where chromosomal spindle fibres are seen in living cells, and were oriented in the pole-to-pole direction.
Abstract: Decorated actin-like filaments were seen in spindles after crane fly spermatocytes were glycerinated and then treated with rabbit skeletal muscle heavy meromyosin (HMM). Both ATP and pyrophosphate inhibited the HMM reaction. In prometaphase, metaphase, and mid-anaphase cells, actin-like filaments were seen near regions where chromosomal spindle fibres are seen in living cells, and were oriented in the pole-to-pole direction. In the interzone of anaphase cells, actin-like filaments were not oriented in a preferential direction when they were not associated with the microtubules attached to the sex chromosomes. No filaments were seen in glycerinated spindles not treated with HMM. We discuss reasons why filaments might not be seen without prior HMM treatment, and we discuss the possible role of the actin-like filaments in the spindles. — Spindle microtubules often were not seen in cells treated with HMM. This depended on the stage of division: in prometaphase no microtubules were seen; in metaphase microtubules were seen, in apparently normal numbers; in mid-anaphase, microtubules between the autosomes and the poles were seen in reduced numbers, those associated with the equatorial sex-chromosomes were seen in apparently normal numbers, while those between the separating autosomal half-bivalents were not seen. Microtubules were not seen in glycerinated spindles not treated with HMM, suggesting that HMM in some way affects microtubule stability. The question of microtubule stability is briefly discussed.

76 citations


Journal ArticleDOI
TL;DR: Reciprocal crosses with the translation T163H as a marker chromosome at late prophase demonstrate that the group derived from the larger pronucleus and having less condensed chromosomes is of paternal origin.
Abstract: Chromosome counts of 338 mouse zygotes at late prophase and metaphase of the first cleavage division revealed 96.4% diploidy, 1.8% hypodiploidy, 1.2% triploidy, and 0.3% tetraploidy. One additional anomaly might have given rise to an embryo mosaic for maternal but not paternal genes. In zygotes collected without colchicine administration to the mother, one of ten anaphases had a lagging chromosome. Reciprocal crosses with the translation T163H as a marker chromosome at late prophase, when the male- and female-derived chromosome groups have not yet combined, demonstrate that the group derived from the larger pronucleus and having less condensed chromosomes is of paternal origin. T163H undergoes Mendelian segregation in female heterozygotes.


Journal ArticleDOI
TL;DR: The G-bands revealed by a heat renaturation method (ASG) were compared with those revealed by treatment with three proteolytic enzymes, and each autosomal pair can therefore be identified by its characteristic pattern.
Abstract: The C-band and G-band patterns of Microtus agrestis metaphase chromosomes are described. The C-band pattern reveals constitutive heterochromatin as uniformly intenselystained areas but cannot aid in identifying autosomal pairs. The G-bands revealed by a heat renaturation method (ASG) were compared with those revealed by treatment with three proteolytic enzymes. All procedures yield apparently the same specific pattern of crossbands on the autosomes, and each autosomal pair can therefore be identified by its characteristic pattern. The constitutive heterochromatin of the sex chromosomes stains uniformly with the heat renaturation method but is subdivided into regions with different staining intensities with each enzyme treatment. A G-band karyotype for Microtus agrestis metaphase chromosomes is presented.

Journal ArticleDOI
TL;DR: The findings indicate the existence in metaphase cells of factor(s) which are capable of initiating biochemical and morphological events in interphase nuclei intrinsic to the normal mitotic process.
Abstract: Fusion of an interphase cell with a metaphase cell results in profound changes in the interphase chromatin that have been called "chromosome pulverization" or "premature chromosome condensation" In addition to the usual light microscopy, the nature of the changes has been investigated in the present study with electron microscopy and biochemical techniques Metaphase and interphase cells were mixed and fused at 37°C by means of ultraviolet-inactivated Sendai virus. After cell fusion, morphological changes in interphase nuclei occurred only in binucleate cells which contained one intact set of metaphase chromosomes Irrespective of the nuclear stage at the time of cell fusion, the morphologic changes that occurred 5–20 min later simulated very closely a sequence of events that characterizes the normal G2-prophase transition. Radioautography revealed that, late in the process, substantial amounts of RNA and probably protein were transferred from the interphase nucleus into the cytoplasm of fused cells. Thus, the findings indicate the existence in metaphase cells of factor(s) which are capable of initiating biochemical and morphological events in interphase nuclei intrinsic to the normal mitotic process.

Journal ArticleDOI
TL;DR: The compound α,α,α-trifluoro-2,6-dinitro- N,N -dipropyl- p -toluidine (trifluralin) inhibited mitosis in onion and wheat root tips and showed that mitosis was being blocked at metaphase.
Abstract: The compound α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) inhibited mitosis in onion (Allium cepa L. ‘Yellow Globe’) and wheat (Triticum aestivum L. Thorn’) root tips. Photomicrographs showed that trifluralin affected mitosis in the same manner as colchicine. Arrested metaphases, c-pairs, micronuclei, amoeboid nuclei, and polyploidy were observed at various times after treatment. An increase in the percentage of arrested metaphases and a decrease in anaphase and telophase figures after 3 hr showed that mitosis was being blocked at metaphase. Prophase did not appear to be affected. Centrifugation of treated root tips displaced the chromosomes of arrested metaphases indicating that the spindle apparatus was disrupted.

Journal ArticleDOI
TL;DR: From 88 superovulated, mated CFI (Carworth) females, 2643 eggs were collected at two hourly intervals between 12 and 36 hours after administration of human chorionic gonadotrophin and then fixed, stained and examined as whole-mounts by light microscopy.
Abstract: From 88 superovulated, mated CFI (Carworth) females, 2643 eggs were collected at two hourly intervals between 12 and 36 hours after administration of human chorionic gonadotrophin and then fixed, stained and examined as whole-mounts by light microscopy. Mating and ovulation were essentially complete at 10 and 14 hours respectively. Metaphase II oocytes continued to decrease in number until 20 hours. Telophase II, a maximum at 16 hours (22% of all oocytes), was not seen after 20 hours. Pronuclei first appeared at 16 hours and at 24 hours, 87% of the ova were pronuclear. Metaphase of first cleavage, first detected at 28 hours, represented 17% of the ova at 32 hours. The first cleavage division occurred between 30 and 34 hours. The pronuclear chromatin network, which is always visible, is more diffuse in the larger, male pronucleus. During first cleavage prophase, the chromatin strands shorten and distinct chromosomes appear, those of male origin being less condensed. The two chromosome groups then combine to form first cleavage metaphase. Pronuclear fusion was not observed. Twenty-three per cent of the ova had not undergone first cleavage by 36 hours: 6% were at earlier stages and presumably arrested while 14% were fragmented or had degenerated metaphase II chromosomes. Anomalies of oocyte maturation and fertilization accounted for 1.6% of all ova.

Journal ArticleDOI
09 Jun 1972-Nature
TL;DR: THE AUTHORS have hybridized radioactive RNA specific for the production of haemoglobin with human metaphase chromosomes and the regions on the chromosomes which may contain the corresponding structural genes have been identified by autoradiography.
Abstract: WE have hybridized radioactive RNA specific for the production of haemoglobin with human metaphase chromosomes. The regions on the chromosomes which may contain the corresponding structural genes have been identified by autoradiography.

Journal ArticleDOI
TL;DR: The morphological change of kinetochores of spermatocytes can be asynchronous, as is especially conspicuous in the sex chromosomes in early and middle prometaphase as discussed by the authors.
Abstract: Longitudinal thin sections of preselected spermatocytes were studied with the electron microscope. The kinetochores of autosomes and sex chromosomes show a characteristic change of their form during the meiotic divisions. Just after nuclear membrane breakdown the kinetochore profiles have the form of circles, in early prometaphase they have flame shape, and in metaphase appear as straight zones. As early as prometaphase I two sister kinetochores are discernible in each kinetochore region of a dyad. In prometaphase the sister kinetochores of the sex chromosomes are connected with each other through condensation zones which are continuous with both kinetochores. A double line structure is often seen in kinetochores and condensation zones. The morphological change of kinetochores can be asynchronous, as is especially conspicuous in the sex chromosomes. —The mitotic apparatuses of Pales behave in hexylenglycol medium like mitotic apparatuses of marine eggs. Crystalloids (Fuge, 1970) and microfilament bundles (Bajer and Mole-Bajer, 1969) occur in mitotic apparatuses in early and middle prometaphase.

Journal ArticleDOI
TL;DR: The light and electron microscopic cytology of nuclear division in Vaucheria litorea Hofman ex C. Agardh is described, which shows that the interphase nucleus contains a prominent nucleolus and is associated with lipid droplets.
Abstract: The light and electron microscopic cytology of nuclear division in Vaucheria litorea Hofman ex C. Agardh is described. The interphase nucleus contains a prominent nucleolus and is associated with lipid droplets. The nucleus migrates through the coenocytic filament during all phases of division. During early prophase, the centrioles migrate to each pole, and the nucleolus fragments. At metaphase, the intra-nuclear spindles, which consist of continuous and chromosomal microtubules, are enclosed by a fully intact nuclear envelope. The nuclear membrane persists throughout the division. Chromosome separation is accomplished by lengthening of continuous microtubules at anaphase. Considerable elongation of continuous microtubules produces an extremely long interzonal spindle between the daughter nuclei which is ultimately separated at telophase by the invagination of the inner nuclear membrane and an electrondense area just within the abscission zone. Comparisons are made between Vaucheria and other organisms wi...


Journal ArticleDOI
TL;DR: It is demonstrated that specific antibodies against nuclear and nucleolar macromolecules could be important reagents for determination of the fates of certain macromolescules in eukaryotic cells.

Journal ArticleDOI
TL;DR: The satellite DNAs of D. ordii are non-randomly distributed within the chromosome and are responsible for the pattern of heterochromatin of metaphase chromosomes, which concludes that the shorter arms of chromosomes are largely if not entirely composed of satellite DNA.

Journal ArticleDOI
TL;DR: The Indian deer, Muntiacus muntjak, with its low number of individually identifiable chromosomes, is a suitable material for studies on the spatial interrelationships among metaphase chromosomes on the equatorial plate.
Abstract: The Indian deer, Muntiacus muntjak, with its low number of individually identifiable chromosomes (♂, 2n = 7), is a suitable material for studies on the spatial interrelationships among metaphase chromosomes on the equatorial plate. Cultured monolayers not subjected to colchicine or hypotonic treatments were analyzed in situ. The emphasis mainly was placed on determining the locations of the centromeres of the six large chromosomes, which usually occupied peripheral positions at the equator. The frequencies found of certain patterns of chromosome arrangement deviated significantly from what would be expected if these patterns were random. Cells in which homologs were next to each other were more frequent than expected. In configurations in which no homologous chromosomes occupied adjacent positions, symmetrical radial arrangements, based on homology or proximity in size, were favored. The position of the Y chromosome usually was close to the centromeric region of the X-autosome, which might be a consequence of a heterochromatic association or partial homology between the X and Y. Factors relevant to the chromosome arrangement on the equatorial plate may be somatic pairing, symmetrical spatial interrelationships between chromosomes based on homology or size, and heterochromatic association.

Journal ArticleDOI
TL;DR: A genotype of wheat deficient for a pair of chromosomes stabilizing chiasma frequency against extremes of temperature was investigated, and it was shown that the temperature-sensitive stage occurred in the premeiotic interphase.
Abstract: A genotype of wheat deficient for a pair of chromosomes stabilizing chiasma frequency against extremes of temperature was investigated to determine the position and duration of temperature sensitivity with respect to first metaphase of meiosis. Temperature changes over a critical range, followed by sequential sampling and measurement of chiasma frequency, showed a relatively short temperature-sensitive stage, the position and duration of which were dependent on the final temperature used. Comparison with meiotic timings made independently showed that the temperature-sensitive stage occurred in the premeiotic interphase. Euploid wheat was shown to have a stage in chiasma formation sensitive to high-temperature treatments at a similar time. Comparison with the work of others showed that the sensitive stage lay between the last premeiotic mitosis and the start of DNA synthesis. This modification of chromosome pairing at a much earlier stage than has been previously demonstrated is further evidence that the processes of chromosome pairing and crossing-over are probably more complex than formerly envisaged.

Journal ArticleDOI
TL;DR: The fine structure of mitosis in myocardial cells possessing myofibrils from embryonic chick hearts (4.5–6 days incubation age) is described and junctional complexes between dividing cells and adjacent resting cells persist.
Abstract: The fine structure of mitosis in myocardial cells possessing myofibrils from embryonic chick hearts (4.5–6 days incubation age) is described. In these cells during prophase, chromosomes appear, but the nuclear membrane, Golgi complexes, and Z bands mostly disappear. In metaphase, lipid droplets and large quantities of membranous cisternae localize around the centrioles, while sarcomeric lengths of myofibrils (largely without Z bands) are found disoriented in the periphery, mainly in the polar zones. In anaphase the cisternae collect near the chromosomes, as reconstruction of the nuclear membrane commences. An intact nuclear envelope and well-formed Golgi complexes characterize telophase, but Z bands still are not present. During all of the mitotic stages, junctional complexes between dividing cells and adjacent resting cells persist.

Journal ArticleDOI
TL;DR: It is concluded that this decrease in viability is caused by irreversible effects on theSpindle and/or centriolar components in metaphase cells located prior to the spindle activation marker.
Abstract: Chinese hamster mitotic cells (95% in mitosis with 85% in metaphase and 10% in anaphase) were shaken loose from monolayer asynchronous cultures and stored at 1°C for up to 28 hours. During this period, the mitotic index did not decrease and the cells remained cytologically normal. However, over a four-hour period, metaphase cells located within 1.8 minutes of anaphase, 10% of the metaphase population, were able to move into anaphase; this point of 1.8 minutes corresponds in time to that reported for the spindle activation marker. When the cells were warmed to 37°C, they were delayed in entering G1 and S (35 and 70 minutes, respectively, after a 4-hour treatment). This delay of 70 minutes was maintained for three cell cycles, during which a high degree of synchrony was maintained. Cold treatment for 12 hours produced delays into G1 and S of 50 and 110 minutes, respectively. A fraction of the metaphase cells (12 or 50% after treatments of 4 or 12 hours, respectively) evidenced chromosomal aggregation, were unable to complete cytokinesis, and appeared in the next division as tetraploid cells. These tetraploid cells were unable to survive and produce macroscopic colonies. It is concluded that this decrease in viability is caused by irreversible effects on the spindle and/or centriolar components in metaphase cells located prior to the spindle activation marker.

Journal ArticleDOI
TL;DR: The primordium of spindle microtubules, a somewhat electron opaque, amorphous structure with fibrous or granular elements, occurs in the center of early prophase, 20 to 30 minutes before metaphase as discussed by the authors.
Abstract: During intranuclear mitosis in plasmodia of Physarum polycephalum the primordium of spindle microtubules which is a somewhat electron opaque, amorphous structure with fibrous or granular elements, occurs in the center of early prophase, 20 to 30 minutes before metaphase. Then, the primordium seems to divide into two parts. Spindle microtubules develop radially from the primordia of spindle microtubules. These spindle microtubules increase in number and length during prophase. Spindle microtubules are completed in about five minutes before metaphase. The nuclear envelope remains intact during prophase, but after metaphase it breaks at the polar regions. The nuclear envelope of the daughter nucleus is re-formed from the original nuclear envelope.

Journal ArticleDOI
TL;DR: Colchicine, kinetin, and indole-3-acetic acid applied together cause end-to-end association of metaphase chromosomes and suggest that any step of the cell cycle is independently controlled both by specific balance of the growth regulators and by specific synthesis of the nucleic acids.
Abstract: A B S T R A C T The treatment of root tips of Allium carinatum, Allium cepa, and Allium flavum with colchicine, abscisic acid, kinetin, and indole-3-acetic acid, applied in appropriate concentrations, combinations, and durations, makes possible the selective blockade of the cell cycle in G1, G2, any mitotic stage, and between karyokinesis and cytokinesis. Moreover, treatment with abscisic acid followed by a recovery period stimulates polyploid nuclei in mature tissues to divide. Colchicine, kinetin, and indole-3-acetic acid applied together cause end-to-end association of metaphase chromosomes. These results together with earlier findings suggest that any step of the cell cycle is independently controlled both by specific balance of the growth regulators and by specific synthesis of the nucleic acids.

Journal ArticleDOI
TL;DR: If the proposed experiment requires an accumulation of arrested metaphases over a period longer than the average life span of an arrested metaphase there is a serious risk of under-estimating the metaphase index, and a simple method of assessing the magnitude of this risk is proposed.

Journal Article
TL;DR: Chromatid breakage can be used as a sensitive means of assessing cell cytotoxicity and neither the degree of inhibition of DNA synthesis nor the magnitude of unbalanced growth as determined by cell sizing produced by a variety of 1-β-d-arabinofuranosylcytosine dosages correlated with cell death.
Abstract: Summary 1-β-d-Arabinofuranosylcytosine-induced cell lethality as measured by survival fraction in a plating efficiency assay with the use of cultures of hamster fibroblasts correlates with the production of five or more chromatid breaks per metaphase. By contrast neither the degree of inhibition of DNA synthesis nor the magnitude of unbalanced growth as determined by cell sizing produced by a variety of 1-β-d-arabinofuranosylcytosine dosages correlated with cell death. Chromatid breakage can therefore be used as a sensitive means of assessing cell cytotoxicity.