scholarly journals Relationship of amplified dihydrofolate reductase genes to double minute chromosomes in unstably resistant mouse fibroblast cell lines.

1981 ◽  
Vol 1 (12) ◽  
pp. 1077-1083 ◽  
Author(s):  
P C Brown ◽  
S M Beverley ◽  
R T Schimke
Keyword(s):  
Dihydrofolate Reductase ◽  
Deoxyribonucleic Acid ◽  
Fibroblast Cell ◽  
Mouse Fibroblast ◽  
Gene Sequences ◽  
Resistant Mouse ◽  
Methotrexate Resistance ◽  
Double Minute ◽  
Relationship Of ◽  
Double Minute Chromosomes

Murine 3T6 selected in increasing concentrations of methotrexate were unstable with respect to dihydrofolate reductase overproduction and methotrexate resistance when they are cultured in the absence of methotrexate. An analysis of the karyotypes of these resistant cells revealed the presence of numerous double minute chromosomes. We observed essentially identical kinetics of loss of dihydrofolate reductase gene sequences in total deoxyribonucleic acid and in deoxyribonucleic acid from fractions enriched in double minute chromosomes and in the numbers of double minute chromosomes per cell during reversion to methotrexate sensitivity, and this suggested that unstably amplified gene sequences were localized on double minute chromosomes. This conclusion ws also supported by an analysis of cell populations sorted according to dihydrofolate reductase enzyme contents, in which relative gene amplification and double minute chromosome content were related proportionally.

Relationship of amplified dihydrofolate reductase genes to double minute chromosomes in unstably resistant mouse fibroblast cell lines

1981 ◽  
Vol 1 (12) ◽  
pp. 1077-1083
Author(s):  
P C Brown ◽  
S M Beverley ◽  
R T Schimke
Keyword(s):  
Dihydrofolate Reductase ◽  
Deoxyribonucleic Acid ◽  
Fibroblast Cell ◽  
Mouse Fibroblast ◽  
Gene Sequences ◽  
Resistant Mouse ◽  
Methotrexate Resistance ◽  
Double Minute ◽  
Relationship Of ◽  
Double Minute Chromosomes

Murine 3T6 selected in increasing concentrations of methotrexate were unstable with respect to dihydrofolate reductase overproduction and methotrexate resistance when they are cultured in the absence of methotrexate. An analysis of the karyotypes of these resistant cells revealed the presence of numerous double minute chromosomes. We observed essentially identical kinetics of loss of dihydrofolate reductase gene sequences in total deoxyribonucleic acid and in deoxyribonucleic acid from fractions enriched in double minute chromosomes and in the numbers of double minute chromosomes per cell during reversion to methotrexate sensitivity, and this suggested that unstably amplified gene sequences were localized on double minute chromosomes. This conclusion ws also supported by an analysis of cell populations sorted according to dihydrofolate reductase enzyme contents, in which relative gene amplification and double minute chromosome content were related proportionally.

Mathematical models of gene amplification with applications to cellular drug resistance and tumorigenicity.

Genetics ◽  
1990 ◽  
Vol 125 (3) ◽  
pp. 633-644
Author(s):  
M Kimmel ◽  
D E Axelrod
Keyword(s):  
Mathematical Models ◽  
Cell Lines ◽  
Gene Amplification ◽  
Dihydrofolate Reductase ◽  
Gene Copy Number ◽  
Gene Copy ◽  
Published Data ◽  
Reductase Gene ◽  
Double Minute ◽  
Double Minute Chromosomes

Abstract An increased number of copies of specific genes may offer an advantage to cells when they grow in restrictive conditions such as in the presence of toxic drugs, or in a tumor. Three mathematical models of gene amplification and deamplification are proposed to describe the kinetics of unstable phenotypes of cells with amplified genes. The models differ in details but all assume probabilistic mechanisms of increase and decrease in gene copy number per cell (gene amplification/deamplification). Analysis of the models indicates that a stable distribution of numbers of copies of genes per cell, observed experimentally, exists only if the probability of deamplification exceeds the probability of amplification. The models are fitted to published data on the loss of methotrexate resistance in cultured cell lines, due to the loss of amplified dihydrofolate reductase gene. For two mouse cell lines unstably resistant to methotrexate the probabilities of amplification and deamplification of the dihydrofolate reductase gene on double minute chromosomes are estimated to be approximately 2% and 10%, respectively. These probabilities are much higher than widely presumed. The models explain the gradual disappearance of the resistant phenotype when selective pressure is withdrawn, by postulating that the rate of deamplification exceeds the rate of amplification. Thus it is not necessary to invoke a growth advantage of nonresistant cells which has been the standard explanation. For another analogous process, the loss of double minute chromosomes containing the myc oncogene from SEWA tumor cells, the growth advantage model does seem to be superior to the amplification and deamplification model. In a more theoretical section of the paper, it is demonstrated that gene amplification/deamplification can result in reduction to homozygosity, such as is observed in some tumors. Other applications are discussed.

Localization of amplified MYC gene sequences to double minute chromosomes in acute myelogenous leukemia

1994 ◽  
Vol 9 (1) ◽  
pp. 62-67 ◽  
Author(s):  
Marilyn L. Slovak ◽  
Jennifer Pelkey Ho ◽  
Mark J. Pettenati ◽  
Aziz Khan ◽  
Daniel Douer ◽  
...  
Keyword(s):  
Acute Myelogenous Leukemia ◽  
Myelogenous Leukemia ◽  
Gene Sequences ◽  
Double Minute ◽  
Myc Gene ◽  
Acute Myelogenous ◽  
Double Minute Chromosomes

scholarly journals The Polyextreme Ecosystem, Salar de Huasco at the Chilean Altiplano of the Atacama Desert Houses Diverse Streptomyces spp. with Promising Pharmaceutical Potentials

Diversity ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 69 ◽  
Author(s):  
Carlos Cortés-Albayay ◽  
Johanna Silber ◽  
Johannes F. Imhoff ◽  
Juan A. Asenjo ◽  
Barbara Andrews ◽  
...  
Keyword(s):  
Phylogenetic Analyses ◽  
Atacama Desert ◽  
Fibroblast Cell ◽  
Mouse Fibroblast ◽  
Rrna Gene ◽  
Gene Sequences ◽  
The North ◽  
Streptomyces Spp ◽  
Chilean Altiplano ◽  
Bacteria And Fungi

Salar de Huasco at the Chilean Altiplano of the Atacama Desert is considered a polyextreme environment, where solar radiation, salinity and aridity are extremely high and occur simultaneously. In this study, a total of 76 bacterial isolates were discovered from soil samples collected at two different sites in the east shoreline of Salar de Huasco, including H0 (base camp next to freshwater stream in the north part) and H6 (saline soils in the south part). All isolated bacteria were preliminarily identified using some of their phenotypic and genotypic data into the genera Streptomyces (86%), Nocardiopsis (9%), Micromonospora (3%), Bacillus (1%), and Pseudomonas (1%). Streptomyces was found dominantly in both sites (H0 = 19 isolates and H6 = 46 isolates), while the other genera were found only in site H0 (11 isolates). Based on the genotypic and phylogenetic analyses using the 16S rRNA gene sequences of all Streptomyces isolates, 18% (12 isolates) revealed <98.7% identity of the gene sequences compared to those in the publicly available databases and were determined as highly possibly novel species. Further studies suggested that many Streptomyces isolates possess the nonribosomal peptide synthetases-coding gene, and some of which could inhibit growth of at least two test microbes (i.e., Gram-positive and Gram-negative bacteria and fungi) and showed also the cytotoxicity against hepatocellular carcinoma and or mouse fibroblast cell lines. The antimicrobial activity and cytotoxicity of these Streptomyces isolates were highly dependent upon the nutrients used for their cultivation. Moreover, the HPLC-UV-MS profiles of metabolites produced by the selected Streptomyces isolates unveiled apparent differences when compared to the public database of existing natural products. With our findings, the polyextreme environments like Salar de Huasco are promising sources for exploring novel and valuable bacteria with pharmaceutical potentials.

Loss and stabilization of amplified dihydrofolate reductase genes in mouse sarcoma S-180 cell lines

1981 ◽  
Vol 1 (12) ◽  
pp. 1084-1093
Author(s):  
R J Kaufman ◽  
P C Brown ◽  
R T Schimke
Keyword(s):  
Cell Line ◽  
Dihydrofolate Reductase ◽  
Stable State ◽  
Unequal Distribution ◽  
Continuous Growth ◽  
Daughter Cells ◽  
Reductase Gene ◽  
Double Minute ◽  
Multiple Copies ◽  
Double Minute Chromosomes

We studied the loss and stabilization of dihydrofolate reductase genes in clones of a methotrexate-resistant murine S-180 cell line. These cells contained multiple copies of the dihydrofolate reductase gene which were associated with double minute chromosomes. The growth rate of these cells in the absence of methotrexate was inversely related to the degree of gene amplification (number of double minute chromosomes). Cells could both gain and lose genes as a result of an unequal distribution of double minute chromosomes into daughter cells at mitosis. The loss of amplified dihydrofolate reductase genes during growth in the absence of methotrexate resulted from the continual generation of cells containing lower numbers of double minute chromosomes. Because of the growth advantage of these cells, they became dominant in the population. We also studied an unstably resistant S-180 cell line (clone) that, after 3 years of continuous growth in methotrexate, generated cells containing stably amplified dihydrofolate reductase genes. These genes were present on one or more chromosomes, and they were retained in a stable state.

scholarly journals Loss and stabilization of amplified dihydrofolate reductase genes in mouse sarcoma S-180 cell lines.

1981 ◽  
Vol 1 (12) ◽  
pp. 1084-1093 ◽  
Author(s):  
R J Kaufman ◽  
P C Brown ◽  
R T Schimke
Keyword(s):  
Cell Line ◽  
Dihydrofolate Reductase ◽  
Stable State ◽  
Unequal Distribution ◽  
Continuous Growth ◽  
Daughter Cells ◽  
Reductase Gene ◽  
Double Minute ◽  
Multiple Copies ◽  
Double Minute Chromosomes

We studied the loss and stabilization of dihydrofolate reductase genes in clones of a methotrexate-resistant murine S-180 cell line. These cells contained multiple copies of the dihydrofolate reductase gene which were associated with double minute chromosomes. The growth rate of these cells in the absence of methotrexate was inversely related to the degree of gene amplification (number of double minute chromosomes). Cells could both gain and lose genes as a result of an unequal distribution of double minute chromosomes into daughter cells at mitosis. The loss of amplified dihydrofolate reductase genes during growth in the absence of methotrexate resulted from the continual generation of cells containing lower numbers of double minute chromosomes. Because of the growth advantage of these cells, they became dominant in the population. We also studied an unstably resistant S-180 cell line (clone) that, after 3 years of continuous growth in methotrexate, generated cells containing stably amplified dihydrofolate reductase genes. These genes were present on one or more chromosomes, and they were retained in a stable state.

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