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Biomedical subjects

J Morrow

Publications and source records attributed to J Morrow.

At least 73 records · Page 4Linked to original sources
PubMed1984

Gene amplification as a mechanism of reversion at the HPRT locus in V79 Chinese hamster cells.

Spontaneous phenotypic revertants of hypoxanthine phosphoribosyl-transferase (HPRT) temperature-sensitive V79 Chinese hamster cells were selected by plating a temperature-sensitive mutant in HAT medium at 39 degrees C. The incidence of such revertants was approximately 2 X 10(-4) per cell. The majority of the revertants examined had increases of between three- and tenfold in their specific activity of the enzyme, and they were able to grow continuously in the presence of HAT medium at 39 degrees C. When the revertants were cultivated in the absence of HAT, they recovered their HAT-sensitive phenotype and their lowered level of HPRT. Three of the revertants were examined for their temperature inactivation profiles, and all were found to have profiles identical to the ts parent, and quite different from the V79 wild type. The kinetic properties of the cell lines were studied: the Km for both PRPP and hypoxanthine was significantly different in the temperature-sensitive cells but was not significantly altered in the revertants with respect to the ts mutants. A specific antibody to Chinese hamster brain HPRT was employed in immunoprecipitation experiments. By measuring the point at which the immunoprecipitation of the antibody to HPRT was overcome by increasing concentrations of cell supernatant, it was possible to estimate the relative amount of enzyme molecules in the cell lines. From these data, it could be concluded that the revertants overproduced an enzyme with the same immunological properties as the ts line. Southern blots of the Hind III restricted DNA from the ts mutant and two revertant cell lines were examined with an HPRT cDNA probe. This established that the HPRT gene was amplified twofold in one of the revertants, and threefold in the other. However, if the revertants were reintroduced into nonselective medium, the gene copy number declined to one. Finally, northern blots of RNA extracted from the various cell lines demonstrated that the HPRT mRNA was augmented 1.5-fold in one revertant and 1.4-fold in the other. Reintroduction into non-selective medium resulted in a decline in mRNA level for the second mutant, whereas the first mutant appeared to be stabilized. We conclude that gene amplification and concomitant amplification of messenger RNA and enzyme levels are mechanisms of phenotypic reversion at the HPRT locus in Chinese hamster cells.

Animals↗
PubMed1984

Bromodeoxyuridine resistance: thymidine transport and phosphorylation in Friend leukemia cells.

We have studied multiple step bromodeoxyuridine (BrdU) resistance in Friend leukemia cells. The mutation rate to 30 micrograms/ml resistance was 5.1 X 10(-5) per cell per generation, and to 100 micrograms/ml was 3.7 X 10(-7) per cell per generation. Resistant variants could not be obtained in a single step using BrdU concentrations higher than 100 micrograms/ml. Three clones isolated through multiple step selection were resistant to 640 micrograms/ml of BrdU and deficient in thymidine kinase, although their ability to transport radiolabeled thymidine was unimpaired relative to wild type. All three clones had low reversion frequencies, as judged by plating efficiencies in couterselective HAT medium. Two such revertant clones were isolated and tested for their forward mutation frequency in BrdU. No resistant clones were obtained when as many as 5 X 10(7) cells were tested. This observation argues against the hypothesis that the Friend cells possess two functional thymidine kinase loci and that the revertants represent a heterozygous condition. We conclude that the hypothesis of null mutations within a hemizygous or heterozygous thymidine kinase locus is sufficient to account for high-level BrdU resistance in Friend leukemia cells.

Animals↗
PubMed1984

Deviational salience: application to short stature and relation to perception of adolescent boys.

The concept of deviational salience attempts to explain an aspect of the relationship between self-perception and perception in general. When individuals perceive themselves as deviating from the perceived norm of a salient environmental stimulus, that stimulus becomes even more meaningful. Verification involved the influence of self-perception of own stature by 314 high school boys aged 15 to 18 yr., who were asked to rate 12 occupations in terms of prestige and physical stature. Analysis indicated that subjects, regardless of their self-perceptions, perceived stature to be a meaningful feature and stereotypically associated higher prestige occupations with taller stature. However, subjects who perceived themselves as short more closely associated the criterial variables than did those who perceived themselves as average and tall. No significant difference between those self-perceived as average and tall groups was ascertained, suggesting that the direction of the perceived deviation is critical.

Adolescent↗
PubMed1980

Puromycin resistance in Chinese hamster cells: genetic and biochemical studies of partially resistant, unstable clones.

Resistance to 10 microgram/ml of puromycin has been analyzed in V79 Chinese hamster cells. Clones that were isolated in 10 microgram/ml of puromycin and subsequently cultivated in its absence consistently lost their resistance. One clone was analyzed in detail by recloning in the presence and absence of puromycin, and it was found that non-puromycin cultivated subclones also lost their resistance and regained inhibition profiles similar to the V79 parent. Reconstruction experiments between sensitive and resistant cells demonstrated that the yield of mutants was not affected by metabolic cooperation. The mutation rate was calculated to be 1 x 10(-7) per cell generation, and was the same within the limits of statistical error in a colchicine-produced polyploid derivative of the V79 line. Although a number of resistant clones were found to have polyploid karyotypes, the polyploid V79 lines was not more resistant to puromycin, nor did it possess a higher frequency of puromycin resistant cells. Studies employing radiolabeled puromycin established that resistance was due to a lowered uptake of puromycin and that an inverse relationship existed between resistance level and uptake rate.

Animals↗
PubMed1980

Thymidine resistance in Chinese hamster V79 cells in vitro.

Thymidine resistance in V79 Chinese hamster cells has been investigated. Phenotypically stable variant resistant lines occurred at a high frequency, and the mutation rate (2.67 x 10(-3) per cell per generation) to 400 micrograms/ml thymidine resistance as measured by the standard Luria--Delbrück fluctuation analysis was extremely high. Populations of cells maintained for extended periods in F-10 medium spontaneously increased in resistance, possibly as a result of selective pressures due to the thymidine present in F-10 medium since this change was not observed in Dulbecco's medium. The degree of resistance for a given variant was correlated with the amount of thymidine employed in its selection. Metabolic cooperation, resulting in the suppression of the resistant phenotype, was demonstrated in artificial mixtures of sensitive and resistant clonal lines. Clones isolated in high levels of thymidine possessed lowered uptake of [3H]thymidine and the depression in uptake was related to the level of resistance of the particular clone. Although thymidine kinase specific activity levels were slightly depressed in variant cell lines, growth rate and uridine uptake were unaffected. We conclude that thymidine resistance is due to a genetically controlled depression of external thymidine uptake.

Animals↗
PubMed1979

The requirement of DNA synthesis for the induction of alkaline phosphatase by bromodeoxyuridine in a derivative of the HeLa cell line.

Non-lethal concentrations of bromodeoxyuridine induce a 2- to 5-fold increase in the specific activity of alkaline phosphatase in a HeLa subclone, S3G. Experiments employing 10-hour pulses of BRdU showed that 48 hours were required before induction commenced, and that maximal induction was attained by 96 hours. Under conditions in which DNA synthesis was prevented with hydroxyurea induction did not occur. Upon removal of hydroxyurea both DNA synthesis and induction were rapidly reestablished. Furthermore, experiments employing radiolabelled BRdU demonstrated that the kinetics of the induction process paralleled the incorporation of the analogue into cellular DNA. These results indicate that DNA synthesis, or some process intimately linked to DNA synthesis, is required for the induction of alkaline phosphatase, and suggest that the mode of the induction may be through the incorporation of the analogue into cellular DNA.

Alkaline Phosphatase↗
PubMed1979

An evaluation of some theories of the mechanism of aging.

Two theories of aging are considered in this review. Although there exists substantial experimental evidence in support of the somatic mutation and error catastrophe hypotheses, several experiments have been published which are extremely difficult to reconcile with these models, at least in their simplest forms. These include the observation that biochemical and morphological degenerative changes observed in fibroblasts aged in vitro do not resemble alterations observed in cells obtained from aged donors, and the fact that tissues transplanted serially through different hosts do not decline in vigor in the manner predicted by the somatic mutation theory. Although biochemical and mutational alterations appear to accumulate in fibroblasts aged in vitro (in support of the error catastrophe model), there are substantial problems with the interpretation of such experiments, and some observations (such as the lack of increase in translational error in hemoglboin synthesis as a function of age) seem to argue directly against the error catastrophe theory. Some alternative theoretical and experimental possibilities are discussed, including the concept of programmed aging as the cause of senescence.

Age Factors↗
PubMed1979

Ototoxicity in neonates treated with gentamicin and kanamycin: results of a four-year controlled follow-up study.

This article reports the results of a four-year follow-up study initiated in 1970 on the long-term effects of gentamicin and kanamycin use in newborn infants. Audiometric, vestibular, and psychometric evaluations were performed on gentamicin-treated, kanamycin-treated, and untreated, matched control infants and children. No substantial sensorineural hearing loss or vestibular dysfunction was identified in these patients that could be attributed to aminoglycoside therapy. Performances on the Illinois Test of Psycholinguistic Abilities, Beery Test of Visual Motor Integration, the Peabody Picture Vocabulary Test, and on fine and gross motor examinations were comparable for the three study groups.

Audiometry↗
PubMed1978

Spontaneous mutation rate to thioguanine resistance is decreased in polyploid hamster cells.

The mutation rate to thioguanine resistance was 3.11 X 10(-6) in a near diploid V79 hamster cell line and 7.58 X 10(-8) in a near tetraploid derivative produced with colchicine. The specific activities of glucose-6-phosphate dehydrogenase and phosphoglycerate kinase of the tetraploid line were greater than that of the diploid which suggests that twice the number of active X chromosomes were present in the tetraploid. These results are compatible with the hypothesis that spontaneous variants resistant to thioguanine arise through mutation and chromosomal segregation, as has been suggested for induced mutations in tetraploid hamster cells.

Cell Line↗
PubMed1976

Bromodeoxyuridine induced variations in the level of alkaline phosphatase in several human heteroploid cell lines.

The level of alkaline phosphatase in a number of established cell lines of human origin can be modified by exposure to non-lethal concentrations of bromodeoxyuridine (BRdU). In the several cell lines examined an inverse relationship between amount of induction and constitutive level of the enzyme was observed. Thus, the H.Ep 2 line, which had the highest basal level of enzyme, was reversibly repressed following exposure to the drug, whereas other cell lines with relatively low constitutive enzyme levels were induced to a maximum of 10-fold following exposure. Initiation of induction required from 24 to 48 hours, and as short an exposure ("pulse") as five hours was sufficient to produce induction. Exposure to visible light had no effect upon the repression of alkaline phosphatase in H.Ep 2 by BRdU. Induction did not occur in non-dividing, serum starved cells. The time course of induction by BRdU and hydrocortisone was similar, and simultaneous exposure of the cells to both agents resulted in no greater induction than that observed with either drug alone. Experiments utilizing mitomycin C yielded significant induction in the presence of this agent alone, and somewhat less induction when both mitomycin C and BRdU were added simultaneously. These results suggest that DNA synthesis is required for BRdU were added simultaneously. These results suggest that DNA synthesis is required for BRdU-mediated induction of alkaline phosphatase.

Alkaline Phosphatase↗
PubMed1976

Purine uptake by azaguanine-resistant Chinese hamster cells.

In this study the resistance of a number of lines of Chinese hamster ovary cells to azaguanine is examined. Those which are drug resistant by virtue of a deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT) fail to take up any exogenous hypoxanthine or azaguanine. A second class of drug resistant cells which grow in the reverse selective HAT medium and have levels of HPRT in the range of the wild type parent line take up these purines at lower rates than the nonresistant cells and incorporate smaller amounts of them into trichloracetic acidinsoluble constituents. The results suggest that their basis for resistance resides in lowered incorporation of azaguanine into DNA and RNA, possibly due to a mofified HPRT molecule which accepts hypoxanthine, but not azaguanine as a substrate.

Amino Acids↗
PubMed1976

Mutagenesis studies on cultured mammalian cells. The sensitivity of the asparagine-requiring phenotype to several chemical agents.

The effect of several chemical agents on the mutation frequency from asparagine dependence to asparagine independence has been studied in Jensen sarcoma cells. It was found that ethylmethanesulfonate brought about a dramatic exponential increase, while nitrosoguanidine was not lighly effective as a mutagen, causing only a modest increase in mutation frequency, and quinacrine HCl was ineffective. The results presented here are compared with those obtained in other systems and with our previous work on the effects of UV on mutation induction in the asparagine system. They suggest that the basis of the asparagine requirement of mammalian cell lines resides in a specific genetic alteration in nuclear DNA which is corrected by the mutagenic action of the agents tested here.

Asparagine↗
PubMed1975

On the relationship between spontaneous mutation rates in vivo and in vitro.

Recent estimates of spontaneous mutation rates in man, in which previous sources of bias are corrected, indicate that the average is about 3 x 10(-7) per locus per generation, a much lower figure than is generally accepted. Assuming 100 to 1000 cell divisions between each gametic union, this information predicts that cellular mutation rats should be in the order of 10(-9) per locus per generation. Since none of the mutation rates measured in cultured cells are this low (average for seven characters equals 7 x 10(-7)), the size of mutation rates in cultured cells cannot be used to substantiate the claim of epigenetic inheritance. Furthermore, this information suggests that in multicellular organisms the germinal tissue is sequestered from mutagenic insult or subjected to selection against mutational damage so as to keep the genetic load of a species at a tolerable level. Alternatively, cell culture environments may present an extremely abnormal situation to somatic cells, thus elevating the mutation rate.

Cells, Cultured↗
PubMed1975

Prostate carcinoma: measures to improve therapeutic response and prevent complications.

Between 1965 and 1973, 80 patients with prostatic carcinoma were treated with definitive supervoltage irradiation; 35 patients received adjuvant estrogens. A favorable tumor response was uniformly observed in patients with less advanced tumors who received a minimum of 6,000 rads tumor dose and adjuvant estrogens. Radiation complications were frequent and severe in patients with locally advanced tumors who had antecedent lower urinary tract surgery and received a minimum of 7,000 rads tumor dose. Complications were less frequent in patients who received adjuvant estrogens, and complications were uncommon and mild in patients who received less than 7,000 rads.

Adenocarcinoma↗