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N Howell

Publications and source records attributed to N Howell.

107 records · Page 6Linked to original sources
PubMed1981

Genetic analysis of tumorigenesis. VIII. Suppression of SV40 transformation in cell hybrids and cytoplasmic transferants.

Intraspecies somatic cell hybrids of BALB/c mouse 3T3 and SV40-transformed embryonic fibroblast (SVT2) cells were analyzed for transformation-associated properties and their tumorigenic potential in nude mice. In confirmation of our earlier findings, hybrids expressing the viral T-antigen were not suppressed for the ability to clone in medium with 1% serum. In contrast, division rate in medium with 1% or 10% serum, anchorage independence, cytochalasin-sensitive growth control, and tumorigenicity were suppressed noncoordinately, and the extent of suppression varied from one hybrid to another. Suppression was not simply determined by the increased chromosome content of the hybrid cells, nor was suppression correlated with rearrangements of the integrated viral sequence (SAGER et al., 1981a, b). Similar results were found in cytoplasmic transferants expressing T-antigen. Four independent transferants and subclones derived from them varied in the extent of suppression of anchorage independence and tumorigenicity. In both hybrids and transferants, a low serum requirement for clonal growth apparently was determined solely by expression of SV40 T-antigen, but other transformation properties, as well as tumorigenicity, appeared to require multiple changes in the cellular genome for their expression. These changes must occur during or after viral integration, since they are not expressed in uninfected 3T3 cells.

Animals↗
PubMed1980

Cytoplasmic transfer of DNA containing simian virus 40 sequences into mouse 3T3 cells.

This paper describes the rare cytoplasmic transmission of defective simian virus 40 (SV40) viral DNA from enucleated cells (i.e., cytoplasts) of the SV40-transformed mouse cell line SVT2 (chloramphenicol-resistant) into cybrid cells formed by fusion of these cytoplasts with BALB/c 3T3 cells (thymidine kinase-deficient). The cybrids were selected in medium containing 1% serum, bromodeoxyuridine, and chloramphenicol. They were identified by their 3T3 chromosome content, by the instability of tumor (T)-antigen expression, by their transformed phenotype, and by their drug resistance. The yield of rare cybrids was about 5 x 10(-7) 0.1% of the yield on medium with 10% serum. The presence of the SV40 genome was detected by the expression of SV40-specific T antigen and confirmed (unpublished data) by hybridization of viral DNA probes with restriction enzyme fragments of nuclear DNAs from cybrid clones. Restriction site mapping (unpublished data) showed that at least 1 kilobase of host flanking DNA on each side of the SV40 DNA was included in the transferred segment. The transforming DNA was not stably integrated initially, as judged by cellular heterogeneity in T-antigen expression. Stable T-antigen-positive and negative subclones were recovered in 10% serum; instability could be retained for at least 30 doublings during growth in 1% serum. The instability is interpreted as evidence of non-integration or unstable integration of the transferred DNA into the host genome. The cytoplasmic transfer is interpreted as evidence that chromosomal fragments or intact chromosomes can be transferred rarely through the cytoplasm in cybrid crosses.

Animals↗
PubMed1979

Noncoordinate expression of SV40-induced transformation and tumorigenicity in mouse cell hybrids.

Somatic mouse cells hybrids formed by fusion of nontumorigenic 3T3 closely related SV40-transformed SVT2 cells were analyzed in a study designed to probe the genetic basis of the multiple phenotypic changes induced by SV40 transformation. These hybrids showed noncoordinate expression of the transformation phenotype. Although they cloned at high efficiency in medium with low serum and expressed the SV40 T-antigen of the SVT2 parent, hybrid cells grew poorly without anchorage and exhibited a cell and colony morphology intermediate between that of the parents. Tumorigenicity was assayed quantitatively by subcutaneous coinjection into athymic nude mice of serial dilutions of 10(2) to 10(5) hybrid cells with 10(7) lethally irradiated 3T3 cells. The results showed that 100--1000 times more hybrid cells had to be injected for tumor formation than were required with SVT2. These and other observations show that most 3T3/SVT2 hybrid cells are not tumorigenic but that each population contains a rare subset of tumorigenic cells.

Animals↗
PubMed1979

Cytoplasmic genetics of mammalian cells: conditional sensitivity to mitochondrial inhibitors and isolation of new mutant phenotypes.

We report here that glucose, as a carbon source, and pyruvate are required for the phenotypic expression of cytoplasmically transmitted chloramphenicol-resistance (CAP-R) mutations, recovery of CAP-R mutants, and continuous growth in the presence of oligomycin or antimycin. We assume that glucose supplies additional energy when mitochondrial respiration is diminished and that pyruvate provides intermediates when the Krebs cycle is inhibited. Thus, the requirement for pyruvate is fully satisfied by an exogenous source of purines, and partially by alpha-ketoglutarate or a pyrimidine source. Based upon these findings, we have obtained two types of mutations affecting mitochondrial function--oligomycin resistance and pyruvate-independent expression of chloramphenicol resistance. Both are cytoplasmically transmitted and provide new markers for a genetic analysis of mitochondrial biogenesis.

Animals↗
PubMed1978

Polyethylene-glycol-mediated cybrid formation: high-efficiency techniques and cybrid formation without enucleation.

Polyethylene glycol (PEG) can be used to promote the fusion of enucleated cytoplasts from chloramphenicol (CAP)-resistant mouse cells with intact cells, resulting in the formation of viable cybrids. The techniques are simple and highly efficient, yielding up to one viable cybrid per 20 intact cells fused. It also seems that PEG can be used to induce cybrid formation without the necessity of prior enucleation of the CAP-resistant cells.

Animals↗
PubMed1974

Genetic analyses of the polarity alleles in recombinants from mitochondrial genetic crosses.

A number of minority recombinant and parental types from a heterosexual cross were analyzed for the omega allele they carry. It was found that recombinant progeny can be omega(-), that minority parental types among the progeny can be omega(+) rather than omega(-), and, finally, that certain of the results suggest that the omega locus may not be at the proximal end of the mitochondrial genetic map (Bolotin et al., 1971; Grivell et al., 1973) but rather may lie between the [cap1-r/cap-s] and [ery1-r/ery-s] loci.

Alleles↗
PubMed1971

Mitochondrial biogenesis in Neurospora crassa. I. An ultrastructural and biochemical investigation of the effects of anaerobiosis and chloramphenicol inhibition.

The isolation of a new class of mutants permitting facultative anaerobiosis in Neurospora crassa is described. Backcross analyses to the obligate aerobe prototroph (An(-)) indicate single nuclear gene inheritance (An(-)/An(+)). An(+) and An(-) are indistinguishable in morphology and growth rates under aerobic conditions. Anaerobic growth requires nutritional supplements that are dispensable for aerobic growth. Conidiogenesis, conidial germination, and vegetative growth rate are suppressed by anaerobiosis. An(+) mutants produce substantial quantities of ethanol under anaerobic conditions. Anaerobiosis and chloramphenicol both affect mitochondrial enzyme activity and morphology. Chloramphenicol inhibition leads to reduction in cytochrome oxidase and swollen mitochondria with few cristae. Anaerobiosis leads to reduction in both cytochrome oxidase and malate dehydrogenase activities, enlarged mitochondria with fewer cristae, enlarged nuclei, and other alterations in cellular morphology. The fine structure of anaerobically grown cells changes with the time of anaerobic growth. We conclude that either inhibition of mitochondrial membrane synthesis or inhibition of respiration might lead to the observed alterations in mitochondria.

Aerobiosis↗
PubMedDate not supplied

Mitochondrial gene segregation in mammals: is the bottleneck always narrow?

The segregation of a heteroplasmic silent polymorphism in the mitochondrial ND6 gene has been followed in a human maternal lineage comprising eight individuals and spanning three generations. Heteroplasmy persisted in all eight maternally related family members. More importantly, the frequencies of the two alleles showed relatively little variation among individuals or between generations. In contrast to the findings in other mammalian lineages, the present results indicate relatively slow mitochondrial gene segregation. A narrow bottleneck in the number of mitochondrial DNA (mtDNA) molecules, which occurs at some stage of oogenesis, has been advanced to explain rapid mammalian mitochondrial gene segregation. It is suggested here that the segregation of mitochondrial genes may be more complex than initially envisaged, and that models need to be developed that account for both rapid and slow segregation. One possibility, which reconciles both physical and genetic studies of mammalian mtDNA, is that the unit of mitochondrial segregation is the organelle itself, each containing multiple mtDNA molecules.

Alleles↗
PubMedDate not supplied

Amplification of specific DNA sequences correlates with multi-drug resistance in Chinese hamster cells.

Mammalian cells selected for resistance to certain cytotoxic drugs frequently develop cross-resistance to a broad spectrum of other drugs unrelated in structure to the original selective agent. This phenomenon constitutes a major problem in cancer chemotherapy. Multi-drug resistance arises from decreased intracellular drug accumulation, apparently due to an alteration of the plasma membrane. The observation of double minute chromosomes or homogeneously staining regions in some of the multi-drug-resistant cell lines suggests that gene amplification underlies this phenomenon. We have used the technique of DNA renaturation in agarose gels to detect, compare and clone amplified DNA sequences in Adriamycin- and colchicine-resistant sublines of Chinese hamster cells. We show that both Adriamycin- and colchicine-resistant cells contain amplified DNA fragments, some of which are amplified in both of these independently derived cell lines. Furthermore, loss of the multi-drug resistance phenotype on growth in the absence of drugs correlates with the loss of amplified DNA. These results strongly suggest that the DNA sequences which are amplified in common in multi-drug-resistant cell lines include the gene(s) responsible for a common mechanism of multi-drug resistance in these cells. We have cloned one of the commonly amplified DNA fragments and show that the degree of amplification of this fragment in the cells correlates with the degree of their drug resistance.

Animals↗
PubMedDate not supplied

Accuracy or bias in nurses' ratings of patient compliance: a comparison of treatment modality.

OBJECTIVE: The study examined the accuracy of nurses' assessments of patient compliance and identified factors influencing these assessments, including possible biases. DESIGN: Nurses' assessments of compliance, lab serum levels of dietary compliance, and interdialytic weight gain (IWG) were collected and compared to each other. End-stage renal disease (ESRD) patients on peritoneal dialysis (PD) and hemodialysis (HD) were compared on these measures and their compliance. SETTING: The study was conducted at the tertiary care university hospital at Stony Brook. PATIENTS: Data were collected for 62 ESRD patients (38 male, 24 female; mean age 54 years). The sample consisted of 26 HD and 36 PD patients. INTERVENTIONS: Nurses rated patients' compliance with fluid restrictions (HD patients only) and overall dietary compliance, as well as individual indicators of compliance including protein, potassium, and phosphorus compliance on a 7-point rating scale. Interdialytic weight gain, dietary (serum BUN and K levels), and medication compliance were recorded from charts for a 3-month period for each patient. MAIN OUTCOME MEASURES: The main outcome measures were the correlations between nurses' ratings of compliance and medical compliance data and the regression coefficients, which indicate the relative importance of each of the factors that nurses use to make their compliance ratings. RESULTS: Nurses' ratings for patients in both treatment modalities were highly correlated with the medical data for measures of fluid (r = 0.66, p < 0.001), potassium (r = 0.36, p < 0.01), and phosphorus (r = 0.36, p < 0.01). A regression analysis indicates that potassium (beta = 0.48, p < 0.001), phosphorus (beta = 0.19, p < 0.05), and protein (beta = 0.31, p < 0.01) all significantly contributed to nurses' assessments of patients' overall compliance. However, nurses' ratings of education levels for patients in both treatment modalities were not associated with phosphorus (r = 0.07, p < 0.61), protein (r = 0.18, p < 0.23), or potassium (r = 0.03, p < 0.85) measures. Finally, regressions revealed that nurses used personal knowledge of the patients when rating noncompliant patients (beta = 0.49, p < 0.05) but not when rating compliant patients (beta = 0.05, p < 0.75). CONCLUSIONS: Nurses rely heavily on medical records to rate patients' compliance and to make accurate assessments. Nurses also use several individual indicators (lab values and IWG) to rate overall dietary compliance, suggesting a thorough assessment. While assessments are not biased by personal factors such as nurses' perceptions of patients' education levels, nurses do rely on personal knowledge when rating noncompliant patients.

Adult↗