The DNA content of Chinese hamster meiotic metaphase chromosomes

1989 ◽  
Vol 50 (2-3) ◽  
pp. 125-126 ◽  
Author(s):  
A.T. Sumner
Keyword(s):  
Dna Content ◽  
Chinese Hamster ◽  
Meiotic Metaphase ◽  
Metaphase Chromosomes

Chromosome-mediated gene transfer of hydroxyurea resistance and amplification of ribonucleotide reductase activity

1983 ◽  
Vol 3 (6) ◽  
pp. 1053-1061
Author(s):  
W H Lewis ◽  
P R Srinivasan
Keyword(s):  
Cell Line ◽  
Cell Lines ◽  
Ribonucleotide Reductase ◽  
Chinese Hamster ◽  
Fold Increase ◽  
Resistant Cell ◽  
Plating Efficiency ◽  
Wild Type Cell ◽  
Wild Type ◽  
Metaphase Chromosomes

Metaphase chromosomes purified from a hydroxyurea-resistant Chinese hamster cell line were able to transform recipient wild-type cells to hydroxyurea resistance at a frequency of 10(-6). Approximately 60% of the resulting transformant clones gradually lost hydroxyurea resistance when cultivated for prolonged periods in the absence of drug. One transformant was subjected to serial selection in higher concentrations of hydroxyurea. The five cell lines generated exhibited increasing relative plating efficiency in the presence of the drug and a corresponding elevation in their cellular content of ribonucleotide reductase. The most resistant cell line had a 163-fold increase in relative plating efficiency and a 120-fold increase in enzyme activity when compared with the wild-type cell line. The highly hydroxyurea-resistant cell lines had strong electron paramagnetic resonance signals characteristic of an elevated level of the free radical present in the M2 subunit of ribonucleotide reductase. Two-dimensional electrophoresis of cell-free extracts from one of the resistant cell lines indicated that a 53,000-dalton protein was present in greatly elevated quantities when compared with the wild-type cell line. These data suggest that the hydroxyurea-resistant cell lines may contain an amplification of the gene for the M2 subunit of ribonucleotide reductase.

Experiments on blocking and unblocking of first meiotic metaphase in eggs of the parthenogenetic stick insect Carausius morosus Br. (Phasmida, Insecta)

Development ◽  
1976 ◽  
Vol 36 (2) ◽  
pp. 383-394
Author(s):  
L. P. Pijnacker ◽  
M. A. Ferwerda
Keyword(s):  
Interphase Nucleus ◽  
Stick Insect ◽  
Meiotic Metaphase ◽  
Anterior Region ◽  
Egg Cell ◽  
Metaphase Chromosomes ◽  
Carausius Morosus ◽  
Cytoplasmic Factors ◽  
Activating Agent ◽  
Nuclear Behaviour

The eggs of the parthenogenetic stick insect Carausius morosus, which remain arrested in first meiotic metaphase until oviposition, must be activated in order to develop. The activating agent is oxygen from the air, which enters the egg cell through the micropyle. An exposure shorter than one minute is sufficient to release the blockage. In non-activated (micropyle-less) eggs the first metaphase chromosomes either degenerate or change into an interphase nucleus. This nucleus polyploidizes by endoreduplication, and then either degenerates or multiplies by amitosis. Similarly more generations of nuclei may arise resulting in a chaotic development. These nuclei survive better in the anterior region of the egg. The question of whether the cytoplasmic factors which control nuclear behaviour, also operate in eggs of C. morosus is discussed.

scholarly journals CONTRAST BETWEEN THE ENVIRONMENTAL pH DEPENDENCIES OF PROPHASING AND NUCLEAR MEMBRANE FORMATION IN INTERPHASE-METAPHASE CELLS

1973 ◽  
Vol 58 (3) ◽  
pp. 608-617 ◽  
Author(s):  
Yoshitaka Obara ◽  
Hiroshi Yoshida ◽  
Lee S. Chai ◽  
Herbert Weinfeld ◽  
Avery A. Sandberg
Keyword(s):  
Structural Changes ◽  
Chinese Hamster ◽  
Binucleate Cell ◽  
M Cells ◽  
M Cell ◽  
Metaphase Chromosomes ◽  
Membrane Formation ◽  
Interphase Cell ◽  
Double Membrane ◽  
Mononucleate Cell

In Chinese hamster Don cells, fusion of an interphase cell with a metaphase cell resulted either in prophasing of the interphase nucleus, including loss of the nuclear envelope (NE), or in the formation of a double membrane around the metaphase chromosomes. Only one of these phenomena occurred in a given interphase-metaphase (I–M) binucleate cell. At pH 7.4, there was about an equal probability that either event could occur amongst the population of I–M cells. The effect of pH changes in the medium containing the fused cells was examined. At pH 6.6, prophasing was the predominant event; at pH 8.0, membrane formation predominated. It was found that the rate of progression of a mononucleate cell from G2 to metaphase was appreciably faster at pH 6.6 than at pH 8.0. Conversely, the progression from metaphase to G1 was faster at pH 8.0 than at pH 6.6. These results with the mononucleate cells strengthen the hypothesis that structural changes in I–M cells are reflections of normal mitotic phenomena. Additional evidence for this hypothesis was produced by electron microscope examination after direct fixation in chrom-osmium. The double membrane around the chromosomes of the I–M cell was indistinguishable from the normal NE. The results obtained by varying the pH of the medium containing the fused cells provide an indication that disruption or formation of the NE of Don cells depends on the balance reached between disruptive and formative processes.

scholarly journals Polyploid Formation via Chromosome Duplication Induced by CTP:Phosphocholine Cytidylyltransferase Deficiency and Bcl-2 Overexpression: Identification of Two Novel Endogenous Factors

2005 ◽  
Vol 53 (6) ◽  
pp. 725-733 ◽  
Author(s):  
You-Jun Shen ◽  
Cynthia J. DeLong ◽  
Francois Tercé ◽  
Timothy Kute ◽  
Mark C. Willingham ◽  
...  
Keyword(s):  
Dna Content ◽  
Chinese Hamster ◽  
B Cell Lymphoma ◽  
Negative Regulator ◽  
Ovary Cell ◽  
Endogenous Factors ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Polyploid Formation ◽  
Cellular Dna ◽  
Diploid Cells

Polyploidy is a profound phenotype found in tumors and its mechanism is unknown. We report here that when B-cell lymphoma gene-2 (Bcl-2) was overexpressed in a Chinese hamster ovary cell line that was deficient in CTP:phosphocholine cytidylyltransferase (CT), cellular DNA content doubled. The higher DNA content was due to a permanent conversion from diploid cells to tetraploid cells. The mechanism of polyploid formation could be attributed to the duplication of 18 parental chromosomes. The rate of conversion from diploid to tetraploid was Bcl-2 dose dependent. The diploid genome was not affected by Bcl-2 expression or by CT deficiency alone. Endogenous CT or expression of recombinant rat liver CTα prior to Bcl-2 expression prevented the formation of polyploid cells. This conversion was irreversible even when both initiating factors were removed. In this study, we have identified Bcl-2 as a positive regulator and CTα as a negative regulator of polyploid formation.

The Influence of Formamide on Thermal Denaturation Profiles of DNA and Metaphase Chromosomes in Suspension

2000 ◽  
Vol 55 (9-10) ◽  
pp. 737-746 ◽  
Author(s):  
Joachim Rauch ◽  
Dietmar Wolf ◽  
Michael Hausmann ◽  
Christoph Cremer
Keyword(s):  
Melting Point ◽  
Metaphase Chromosome ◽  
Thermal Denaturation ◽  
Chinese Hamster ◽  
Maximum Temperature ◽  
Metaphase Chromosomes ◽  
Culture Cells ◽  
Optical Sensitivity ◽  
Conformation Changes ◽  
Dna Solutions

Abstract Systematic photometric studies are presented to analyze the thermal denaturation behaviour with and without formamide of metaphase chromosome suspensions in comparison to DNA solutions. Temperature dependent hyperchromicity measurements at 256 nm and 313 nm were performed using an appropriately designed computer-controlled photometer device. Due to an upright optical axis, this allowed absorbance measurements with negligible sedimentation effects not only for solutions of pure DNA, but also for particle suspensions of isolated metaphase chromosomes. This device has a temperature resolution of ± 0.5 °C and an optical sensitivity of 10-3 to 10-4 optical density. For calf thymus DNA the reduction of the melting point with the increase of formamide in the solution was measured at pH 7.0 and pH 3.2. The good correlation of the theoretical approximation to experimental data indicated the suitability of the apparatus to quantitatively describe DNA conformation changes induced by thermal denaturation. For metaphase chromosome preparations of Chinese hamster culture cells, absorbance changes were measured between 20 °C and 95 °C with a temperature gradient of 1 °C/min. These measurements were performed at pH 7.0 and at pH 3.2. The denaturation profiles (= first derivative of the absorbance curve) resulted in a highly variable peak pattern at 256 nm and 313 nm indicating complex conformation changes. A statistical evaluation of the temperature values of the peak maxima resulted in temperature ranges typical for chromosomal conformation changes during thermal treatment. Especially the range of highest temperature values was independent from pH modifications. For pH 3.2 the influence of formamide on the denaturation behaviour of metaphase chromosome preparations was analyzed. In contrast to pure DNA solutions, a reduction of the “melting point” (i.e. the maximum temperature at which a conformation change takes place) was not found. However, the denaturation behaviour depended on the duration of formamide treatment before the measurement.

scholarly journals PROPHASING OF INTERPHASE NUCLEI AND INDUCTION OF NUCLEAR ENVELOPES AROUND METAPHASE CHROMOSOMES IN HELA AND CHINESE HAMSTER HOMO- AND HETEROKARYONS

1974 ◽  
Vol 62 (1) ◽  
pp. 104-113 ◽  
Author(s):  
Yoshitaka Obara ◽  
Lee S. Chai ◽  
Herbert Weinfeld ◽  
Avery A. Sandberg
Keyword(s):  
Nuclear Envelope ◽  
Hela Cells ◽  
Interphase Nucleus ◽  
Chinese Hamster ◽  
Binucleate Cell ◽  
Metaphase Chromosomes ◽  
Interphase Nuclei ◽  
Multinucleate Cells ◽  
Interphase Cells ◽  
Nuclear Envelope Formation

Fusing human HeLa metaphase cells with HeLa interphase cells resulted within 30 min in either of two phenomena in the resultant binucleate cell: either prophasing of the interphase nucleus or formation of a normal-appearing nuclear envelope around the metaphase chromosomes. The frequency of either occurrence was strongly dependent on environmental pH. At pH's of 6.6–8.0, prophasing predominated; at pH 8.5 nuclear envelope formation predominated. Additionally, the frequencies of the two events in multinucleate cells depended on the metaphase/interphase ratio. When the ratio was 0.33 nuclear envelope formation predominated; when it was 2.0 prophasing predominated. In their general features, the results with fused HeLa cells resembled those reported earlier with fused Chinese hamster Don cells. However, the results provided an indication that between pH 6.6 and 8.0 the HeLa metaphase cells possessed a much greater capacity than the Don metaphase cells to induce prophasing. Fusion of Don metaphase cells with HeLa interphase cells or of Don interphase cells with HeLa metaphase cells at pH 8.0 resulted in nuclear envelope formation or prophasing in each kind of heterokaryon. As in the homokaryons, the frequencies of the two events in the heterokaryons depended on the metaphase/interphase ratio. The statistics of prophasing and nuclear envelope formation in the homo- and heterokaryon populations were consistent with the notion that disruption or formation of the nuclear envelope depends on the balance attained between disruptive and formative processes.

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