PubMed Health⌕ Search

Biomedical subjects

D Mager

Publications and source records attributed to D Mager.

27 records · Page 2Linked to original sources
PubMed1986

Normal dosage of the insulin and insulin-like growth factor II genes in patients with the Beckwith-Wiedemann syndrome.

Several patients in whom the Beckwith-Wiedemann syndrome (BWS) is associated with duplication of chromosomal region 11p15 have recently been observed. The genes encoding insulin and insulin-like growth factor II (IGF-II), proteins that affect cellular growth and pancreatic function, have been mapped to 11p15, and their increased expression might, thus, account for the physical features of BWS. To determine whether BWS is frequently associated with small duplications of 11p15, we performed dosage analyses of the insulin and IGF-II genes in somatic DNAs of seven patients with BWS. In each case, we observed apparent diploid representation of these genes. These data suggest that BWS is not frequently associated with small duplications of 11p15 material that embed the insulin and IGF-II genes.

Beckwith-Wiedemann Syndrome↗
PubMed1981

Clonal analysis of early and late stages of erythroleukemia induced by molecular clones of integrated spleen focus-forming virus.

The integrated proviral DNA of the polycythemia-inducing isolate of Friend spleen focus-forming virus (SFFVp) has been identified in rat cell clones nonproductively infected with this replication-defective erythroleukemia virus and cloned in phage lambda vectors. These lambda SFFVp recombinants, lambda SFFVp502 and lambda SFFVp542, contain endonuclease EcoRI inserts of size 7.4 and 8.2 kilobases, respectively, and include full copies of the SFFVp genome, along with host flanking sequences. Infectivity of the cloned SFFVp genomes was tested by a two-step DNA transfer procedure involving transfection of the cloned DNA into 3T3 mouse fibroblasts or cotransfer of the cloned DNA into thymidine kinase-deficient 3T3 cells together with the cloned thymidine kinase gene of herpes simplex virus, followed by rescue of the transferred DNA by superinfection with a helper virus. Inoculation of the rescued virus into adult mice resulted in the appearance of spleen foci, rapid splenomegaly, and polycythemia. Early after infection, spleen cell populations contained large numbers of cells capable of forming small erythroid colonies in vitro (CFU-E) in the absence of erythropoietin. Late after infection, these mice contained cells capable of forming macroscopic colonies (CFU-FV) in vitro. These data indicate that molecular clones of SFFVp, in conjunction with a helper virus, induce the appearance of hemopoietic colony-forming cells characteristic of both the early and late stages of Friend leukemia.

Animals↗
PubMed1981

Clonal analysis of the late stages of erythroleukemia induced by two distinct strains of Friend leukemia virus.

We observed striking differences between the tumorigenic colony-forming cells present in the spleens of mice late after infection with the anemia-inducing strain of Friend leukemia virus (strain FV-A) and those present after infection with the polycythemia-inducing strain (strain FV-P). Cells within primary colonies derived from FV-A- and FV-P-transformed cells (CFU-FV-A and CFU-FV-P, respectively) contained hemoglobin and spectrin, indicating that the CFU-FV-A and CFU-FV-P were transformed erythroid progenitor cells. The proportion of cells containing hemoglobin was relatively high (> 25%) in newly isolated cell lines derived from CFU-FV-P colonies, whereas cell lines derived from CFU-FV-A colonies had only low levels (0 to 2%) of hemoglobin-containing cells. A high proportion of the cell lines derived from CFU-FV-A colonies responded to pure erythropoietin and accumulated spectrin and hemoglobin, whereas the cell lines derived from CFU-FV-P colonies did not. A cytogenetic analysis indicated that primary CFU-FV-P colony cells were diploid, whereas chromosomal aberrations were observed in the immediate progeny of CFU-FV-A. The presence of unique chromosomal markers in the majority of the cells within individual colonies derived from CFU-FV-A suggested that these colonies originated from single cells. Finally, leukemic progenitor cells transformed by strain FV-A appeared to have an extensive capacity to self-renew (i.e., form secondary colonies in methylcellulose), whereas a significant proportion of the corresponding cells transformed by strain FV-P did not. In addition, the self-renewal capacity of both CFU-FV-A and CFU-FV-P increased as the disease progressed. From these observations, we propose a model for the multistage nature of Friend disease; this model involves clonal evolution and expansion from a differentiating population with limited proliferative capacity to a population with a high capacity for self-renewal and proliferation.

Animals↗
PubMed1980

Friend leukaemia virus-transformed cells, unlike normal stem cells, form spleen colonies in Sl/sld mice.

Neoplastic cells are characterized by partial or total autonomy from the interactions that regulate the behaviour of normal cells in the intact animal. Despite the role of the host cellular environment in governing the proliferation and differentiation of both normal and malignant cells, little is known about these host factors. The characterization of host genes that influence both normal cellular processes, as well as susceptibility to tumour induction, is one approach to identifying such factors. Mice carrying two recessive mutations at the steel (Sl) locus have an environmental defect that affects both normal haematopoietic stem cell function as well as susceptibility to Friend leukaemia virus. In this study, we have used Sl/sld mice to examine whether malignant transformation by this RNA tumour virus results in a population of cells capable of proliferating even in the defective cellular microenvironment of Sl/sld mice. We report here that late after infection, the leukaemic spleens of Friend virus-infected mice contain cells which, unlike normal haematopoietic stem cells, are able to form macroscopic spleen colonies in irradiated mice of genotype Sl/Sld. This observation forms the basis for the first in vivo colony assay for leukaemic cells transformed by Friend virus.

Animals↗
PubMed1980

Phorbol ester tumor promoters block the transition from the early to the heme-dependent late program of Friend cell differentiation.

In this study, the mechanism of inhibition of differentiation of Friend erythroleukemia cells by the phorbol ester tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), has been examined. These studies indicate that some early events associated with Friend cell differentiation, including an early change in 86Rb+ transport and a decrease in cell volume, still occur in the presence of TPA. However, several late events in the program of Friend cell differentiation, including the induction of heme synthesis and the loss of proliferative capacity, are inhibited by TPA. These effects of TPA can be reversed by hemin, which alone does not induce Friend cells to differentiate. The addition of hemin to cultures grown in the presence of inducer plus TPA for several days results in the rapid restoration of hemoglobin synthesis, and also causes a parallel decrease in colony-forming ability. These results suggest that tumor promoters may inhibit only heme-dependent events, rather than the entire program of Friend cell differentiation.

Animals↗
PubMed1979

The role of heme in the regulation of the late program of Friend cell erythroid differentiation.

The addition of a chemical inducer, such as dimethylsulfoxide (DMSO), to cultures of mouse Friend erythroleukemic cells results in the induction of a number of late erythroid events, including the accumulation of globin mRNA, the inducation of hemoglobin synthesis, the appearance of erythrocyte membrane antigens (EMA), and the cessation of cell division. The experiments presented in this study demonstrate that heme is necessary but not sufficient for the loss of proliferative capacity associated with DMSO-induced Friend cell differentiation, whereas the accumulation of globin mRNA and EMA can occur in the absence of heme synthesis or heme itself. These conclusions were reached by selectively inhibiting heme synthesis in DMSO-treated cells in two independent ways: (i) Inducible cells were treated with 3-amino-1,2,4-triazole (AT), a drug which inhibits the induction of heme synthesis in Friend cells in a dose-dependent manner. Treatment of inducible Friend cells with 1.5% DMSO for five days caused the plating efficiency in methyl cellulose to decrease to 1% of that in untreated cultures. However, treatment of the cells with DMSO plus AT almost totally prevented this decrease in plating efficiency. The addition of exogenous hemin, which alone had no significant effect on plating efficiency, largely reversed the effect of AT in DMSO-treated cells, reducing the plating efficiency to below 5%. In contrast to the marked effects of AT on the proliferative capacity of differentiating Friend cells, the levels of globin mRNA and EMA were only partially decreased in cells treated with DMSO plus AT, compared to cells treated with DMSO alone. (ii) The relationship between heme synthesis, terminal cell division, and the induction of globin mRNA was investigated further through the use of non-inducible Friend cell variant clones. One such non-inducible clone, M18, appears to be a phenotypic analog of inducible cells treated with DMSO plus AT. Clone M18 did not accumulate heme or hemoglobin, as detected by benzidine staining, nor lose its proliferative capacity in response to DMSO. However, globin mRNA was induced by DMSO in this clone. Treatment of clone M18 with DMSO plus hemin overcame the block in hemoglobin accumulation suggesting that M18 has a defect in the induction of heme biosynthesis. In addition, exposure of M18 cells to DMSO plus hemin caused a gradual decrease in plating efficiency which was not due to non-specific toxicity. Prior incubation of M18 cells in DMSO for three to five days was necessary before hemin caused a rapid loss of proliferative capacity. Thus, these results, in agreement with the AT studies on inducible Friend cells and previous studies on the induction of EMA in clone M18, indicate that there may be both heme-dependent and heme-independent events in the program of Friend cell differentiation.

Amitrole↗
PubMed1978

Early transport changes during erythroid differentiation of Friend leukemic cells.

Early transport changes occurring during Friend erythroleukemic cell differentiation are reported. A decrease in the rate of 86Rb transport was observed beginning approximately five hours after stimulation with 1.5% dimethylsulfoxide (DMSO), a potent inducer of Friend cell differentiation. By 12 to 14 hours after DMSO addition, the transport rate had stabilized at close to 60% of control level. This decrease in the rate of 86Rb transport preceded a previously reported decrease in cell volume. Other chemical inducers of Friend cells, such as hypoxanthine and ouabain, also caused early decreases in 86Rb influx. In contrast, xanthine, which does not induce Friend cell differentiation, also did not affect 86Rb influx. The transport of two amino acid analogues, alpha-aminoisobutyric acid and 2-aminobicyclo [2,2,1]-heptane-2-carboxylic acid, which differ in their mode of uptake, was also measured following induction by DMSO. The transport rates of both compounds decreased after a 12-hour exposure to DMSO. In contrast, the uptake of 3H-colchicine, a drug which diffuses passively across the cell membrane, was not significantly affected. Studies with several variant cell lines which do not synthesize hemoglobin in response to DMSO indicate that these non-inducible cells can be divided into two classes--those that demonstrate early changes in transport very similar to the changes observed in inducible cell lines and those which exhibit only small changes in transport. Results obtained using a revertant clone have helped to distinguish between those transport changes which are associated with the induction of hemoglobin synthesis and those which are not. In addition, these early transport changes may be useful in defining the stage in the differentiation process at which a particular variant line is blocked.

Amino Acids↗
PubMed1978

The program of Friend cell erythroid differentiation: early changes in Na+/K+ ATPase function.

Treatment of Friend erythroleukemia cells with several different chemical agents causes an early decrease in the 86Rb+ influx mediated by Na+/K+ adenosine triphosphatase (ATPase). These agents, which induce Friend cells to differentiate, include dimethylsulfoxide (DMSO), ouabain, hypoxanthine, and actinomycin D. The magnitude of the early decrease in 86Rb+ influx correlates with the proportion of cells in cultures of inducible Friend cell clones which later go on to synthesize hemoglobin. Compounds which do not incude differentiation in these cells, such as xanthine, exogenous hematin, and erythropoietin, do not cause a change in 86Rb+ influx. A change in the intracellular K+ ion concentration does not occur during induction by DMSO because, although there is a decrease in K+ content per cell soon after induction, there is a parallel decrease in cell volume. These results and previous observations from this laboratory are discussed in terms of the posible involvement of the Na+/K+ ATPase in Friend cell differentiation.

Animals↗