On the nature of hereditable variation in cultured somatic cells.
About: This article is published in Cell.The article was published on 1976-01-01. It has received 459 citations till now. The article focuses on the topics: Somatic Cell Genetics.
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TL;DR: It is argued that this variation in plant cell culture itself generates genetic variability (somaclonal variation) that may be employed to enhance the exchange required in sexual hybrids for the introgression of desirable alien genes into a crop species.
Abstract: It is concluded from a review of the literature that plant cell culture itself generates genetic variability (somaclonal variation). Extensive examples are discussed of such variation in culture subclones and in regenerated plants (somaclones). A number of possible mechanisms for the origin of this phenomenon are considered. It is argued that this variation already is proving to be of significance for plant improvement. In particular the phenomenon may be employed to enhance the exchange required in sexual hybrids for the introgression of desirable alien genes into a crop species. It may also be used to generate variants of a commercial cultivar in high frequency without hybridizing to other genotypes.
3,113 citations
TL;DR: It is proposed that epigenetic defects in germline cells due to loss of methylation can be repaired by recombination at meiosis but that some are transmitted to offspring.
Abstract: Evidence from many sources shows that the control of gene expression in higher organisms is related to the methylation of cytosine in DNA, and that the pattern of methylation is inherited. Loss of methylation, which can result from DNA damage, will lead to heritable abnormalities in gene expression, and these may be important in oncogenesis and aging. Transformed permanent lines often lose gene activity through de novo methylation. It is proposed that epigenetic defects in germline cells due to loss of methylation can be repaired by recombination at meiosis but that some are transmitted to offspring.
1,021 citations
TL;DR: Findings strongly suggest that the Na+/H+ antiport activity through regulation of intracellular pH plays a crucial role in growth control.
Abstract: A H+-suicide technique based on the reversibility of Na+/H+ antiport was developed for the selection of mutants deficient in this membrane-bound activity. The strategy was to use the Na+/H+ antiporter as a H+-vector killing device. Chinese hamster lung fibroblasts (CCL39) were loaded with LiCl and incubated in Na+-, Li+-free choline Cl saline solution (pH 5.5). Under these conditions, intracellular pH dropped in 5 min from 7.1 to 4.8, leading to a rapid loss of cell viability (less than 0.1% survival after 30 min). Cytoplasmic acidification and cell death were prevented by treatment with 5-N,N-dimethylamiloride, a potent inhibitor of Na+/H+ antiport. Of the H+-suicide resistant clones that survived two cycles of selection, 90% were found deficient in Na+/H+ antiport activity. One class of mutants (PS10, PS12) fully resistant to the H+-suicide test, does not acidify the cell interior in response to an outward-directed Li+ gradient and has no detectable amiloride-sensitive Na+ influx measured either in Li+- or H+-loaded cells. Growth of these fibroblast clones lacking Na+/H+ antiport was found to be pH conditional in HCO3(-)-free medium. Whereas wild-type cells can grow over a wide range of external pHs (6.6-8.2), PS mutants cannot grow at neutral and acidic pHs (pH less than 7.2); their optimal growth occurs at alkaline pH values (pH 8-8.3). These findings strongly suggest that the Na+/H+ antiport activity through regulation of intracellular pH plays a crucial role in growth control.
535 citations
Journal Article•
TL;DR: Studies of phenomena such as pleiotropic drug resistance are providing insights into how multiple levels of drug resistance occur and are yielding information on how certain types of drug resistant cells may be prevented or overcome.
Abstract: Drug resistance continues to be a major factor in limiting the effectiveness of cancer chemotherapy. Evidence from a variety of sources implicates a genetic basis for most drug-resistant phenotypes. Assuming a random spontaneous origin for these resistant cells, it is possible to develop mathematical and computer-based models of the drug treatment of tumors. These can provide a more intuitive understanding of the basis of treatment success or failure. This in turn may lead to the development of more rational and effective treatment protocols. Studies of phenomena such as pleiotropic drug resistance are providing insights into how multiple levels of drug resistance occur and are yielding information on how certain types of drug resistance may be prevented or overcome.
532 citations
Cites background from "On the nature of hereditable variat..."
...This is the basis of the fluctuation test of Luria and Delbruck, and the phenomenon has been observed repeatedly with mammalian tumor cells in vitro and in vivo (44, 65)....
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...cells and to a large number of antineoplastic agents (23,52,65)....
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References
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TL;DR: This work has demonstrated the first relationship between a specific enzyme defect and abnormal compulsive behavior in a neurological disease and the production of excessive uric acid in this disorder implies that the enzyme is involved in the normal regulation of purine biosynthesis.
Abstract: A sex-linked familial neurological disease consisting of cerebral palsy, mental retardation, choreoathetosis, and compulsive aggressive behavior is associated with a loss of an enzyme that participates in purine metabolism, namely, hypoxanthine-guanine phosphoribosyltransferase. The production of excessive uric acid in this disorder implies that the enzyme is involved in the normal regulation of purine biosynthesis. This is the first example of a relation between a specific enzyme defect and abnormal compulsive behavior. It is also the first enzyme defect in purine metabolism demonstrated in a neurological disease.
1,113 citations
TL;DR: Application of these techniques to chromosome delineation in large numbers of human subjects; determination of chromosomal sex in patients; spontaneuos and induced genetic changes in somatic mammalian cells in vivo and in vitro; comparison of metabolic differences between normal and cancerous cells and other problems have been indicated.
Abstract: A methodology designed to eliminate mitotic inhibitor action and involving use of pretested fetal calf serum and careful pH and temperature control has been described by which cells from normal human and animal tissue can be maintained in active growth for long periods in vitro without development of aneuploidy. By means of this procedure, it is possible reliably to establish cell cultures from minute skin biopsies which can be taken from any individual. Clones of mammalian cells with chromosomal markers have been isolated by this means from x-irradiated non-irradiated cell cultures. Application of these techniques to chromosome delineation in large numbers of human subjects; determination of chromosomal sex in patients; spontaneuos and induced genetic changes in somatic mammalian cells in vivo and in vitro; comparison of metabolic differences between normal and cancerous cells and other problems have been indicated.
942 citations
TL;DR: The CHR lines were also cross resistant to other drugs such as actinomycin D, vinblastine and Colcemid; furthermore, the degree of cross resistance was positively correlated with thedegree of colchicine resistance.
Abstract: Colchicine resistant (CHR) lines of stable phenotype have been isolated from cultured Chinese hamster (CHO) cells. Successive single-step selections for increasing resistance were performed by isolating resistant colonies at each step. Two complementary assays involving [3H] colchicine uptake by whole cells and binding of [3H] colchicine by cytoplasmic extracts were developed to test for altered permeability and altered intracellular target protein, respectively. All clones isolated appeared to have decreased permeability to the drug while their colchicine-binding ability was not reduced. The amount of reduction in colchicine uptake correlated strongly with cellular resistance. The CHR lines were also cross resistant to other drugs such as actinomycin D, vinblastine and Colcemid; furthermore, the degree of cross resistance was positively correlated with the degree of colchicine resistance. The non-ionic detergent Tween 80 potentiated the cytotoxic action of colchicine on mutant cells as well as its rate of uptake into whole cells.
678 citations
TL;DR: Cell-cell hybridization experiments utilizing OUA R and wild-type CHO cells indicate that resistance to ouabain behaves as a codominant trait, and that this marker can be useful for selection of somatic cell hybrids.
387 citations
TL;DR: At least 8 different phenotypes have been identified on the basis of this analysis, and complementation between 2 of them has been demonstrated.
275 citations