Biomaterial Database

Molecular structure and evolution of double-minute chromosomes in methotrexate-resistant cultured mouse cells. 1992

P J Hahn, and B Nevaldine, and J A Longo

Department of Radiology, State University of New York Health Science Center, Syracuse 13210.

To determine whether microscopically visible double-minute chromosomes (DMs) are derived from submicroscopic precursors, we monitored the amplification of the dihydrofolate reductase (DHFR) gene in 10 independent isolates of methotrexate (MTX)-resistant mouse cells. At every other doubling in MTX concentration, the cells were examined both microscopically, to detect the presence of microscopically visible DMs, and by pulsed-field gel electrophoresis and hybridization to a DHFR-specific probe, to detect submicroscopic DMs. One of the cloned MTX-resistant isolates was examined in detail and was shown to originally contain amplified DHFR genes on circular DMs measuring 1 and 3 Mb in size; additionally, metaphase chromosome preparations from this cloned isolate were examined and were shown to contain microscopically visible DMs too large to enter a pulsed-field gel. During stepwise selection for increasing levels of MTX, the smaller DMs (not microscopically visible) were shown to be preferentially amplified, whereas the larger (microscopically visible) ones decreased in relative numbers. Rare-cutting NotI digestion patterns of total genomic DNA that includes the DMs containing the DHFR gene suggest that the DMs increase in copy number without any further significant rearrangements. We saw no evidence from any of the 10 isolates to suggest that microscopically visible DMs are formed from smaller submicroscopic precursors.

UI	MeSH Term	Description	Entries
D008727	Methotrexate	An antineoplastic antimetabolite with immunosuppressant properties. It is an inhibitor of TETRAHYDROFOLATE DEHYDROGENASE and prevents the formation of tetrahydrofolate, necessary for synthesis of thymidylate, an essential component of DNA.	Amethopterin,Methotrexate Hydrate,Methotrexate Sodium,Methotrexate, (D)-Isomer,Methotrexate, (DL)-Isomer,Methotrexate, Dicesium Salt,Methotrexate, Disodium Salt,Methotrexate, Sodium Salt,Mexate,Dicesium Salt Methotrexate,Hydrate, Methotrexate,Sodium, Methotrexate
D002478	Cells, Cultured	Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.	Cultured Cells,Cell, Cultured,Cultured Cell
D002869	Chromosome Aberrations	Abnormal number or structure of chromosomes. Chromosome aberrations may result in CHROMOSOME DISORDERS.	Autosome Abnormalities,Cytogenetic Aberrations,Abnormalities, Autosome,Abnormalities, Chromosomal,Abnormalities, Chromosome,Chromosomal Aberrations,Chromosome Abnormalities,Cytogenetic Abnormalities,Aberration, Chromosomal,Aberration, Chromosome,Aberration, Cytogenetic,Aberrations, Chromosomal,Aberrations, Chromosome,Aberrations, Cytogenetic,Abnormalities, Cytogenetic,Abnormality, Autosome,Abnormality, Chromosomal,Abnormality, Chromosome,Abnormality, Cytogenetic,Autosome Abnormality,Chromosomal Aberration,Chromosomal Abnormalities,Chromosomal Abnormality,Chromosome Aberration,Chromosome Abnormality,Cytogenetic Aberration,Cytogenetic Abnormality
D002875	Chromosomes	In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)	Chromosome
D004351	Drug Resistance	Diminished or failed response of an organism, disease or tissue to the intended effectiveness of a chemical or drug. It should be differentiated from DRUG TOLERANCE which is the progressive diminution of the susceptibility of a human or animal to the effects of a drug, as a result of continued administration.	Resistance, Drug
D005075	Biological Evolution	The process of cumulative change over successive generations through which organisms acquire their distinguishing morphological and physiological characteristics.	Evolution, Biological
D005784	Gene Amplification	A selective increase in the number of copies of a gene coding for a specific protein without a proportional increase in other genes. It occurs naturally via the excision of a copy of the repeating sequence from the chromosome and its extrachromosomal replication in a plasmid, or via the production of an RNA transcript of the entire repeating sequence of ribosomal RNA followed by the reverse transcription of the molecule to produce an additional copy of the original DNA sequence. Laboratory techniques have been introduced for inducing disproportional replication by unequal crossing over, uptake of DNA from lysed cells, or generation of extrachromosomal sequences from rolling circle replication.	Amplification, Gene
D000220	Adaptation, Biological	Changes in biological features that help an organism cope with its ENVIRONMENT. These changes include physiological (ADAPTATION, PHYSIOLOGICAL), phenotypic and genetic changes.	Adaptation, Biologic,Biological Adaptation,Biologic Adaptation
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013762	Tetrahydrofolate Dehydrogenase	An enzyme of the oxidoreductase class that catalyzes the reaction 7,8-dihyrofolate and NADPH to yield 5,6,7,8-tetrahydrofolate and NADPH+, producing reduced folate for amino acid metabolism, purine ring synthesis, and the formation of deoxythymidine monophosphate. Methotrexate and other folic acid antagonists used as chemotherapeutic drugs act by inhibiting this enzyme. (Dorland, 27th ed) EC 1.5.1.3.	Dihydrofolate Dehydrogenase,Dihydrofolate Reductase,Folic Acid Reductase,Acid Reductase, Folic,Dehydrogenase, Dihydrofolate,Dehydrogenase, Tetrahydrofolate,Reductase, Dihydrofolate,Reductase, Folic Acid