摘要:

AbstractThe macromolecular reguirements for the initiation and maintenance of macronuclear DNA replication were studied in heat synchronizedTetrahymena pyriformisGL‐C. Previous work had established that macronuclear S periods could occur in a consecutive fashion without intervening cell divisions during a multiple heat shock treatment, as well as immediately following the synchronized cell divisions. Cycloheximide treatment prior to or during the S period which follows the first synchronized cell division resulted in abolition of the initiation of DNA synthesis or an almost immediate cessation of DNA synthesis in progress. Temporary inhibition of DNA synthesis occurred when cycloheximide was added late in the S period. Treatment with actinomycin D was found to block the initiation of DNA synthesis but did not appreciably affect the continuation of the S period. It was concluded that RNA synthesis was required for the initiation but not the maintenance of DNA replication, whereas protein synthesis was necessary for both processes.The dependency of the initiation of an S period on prior RNA and protein synthesis was also shown to exist when a second consecutive S period was initiated without a preceding cell division. Treatment with actinomycin or cycloheximide prior to a supernumerary S period during a multiple heat shock treatment completely abolished the initiation of DNA synthesis. InT. pyriformisthe synthesis of RNA and protein related to the initiation of the S period is tightly coupled to each cycle of DNA replicatio

ISSN:0021-9541    

DOI:10.1002/jcp.1040830102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractA single hematocytoblast in the yolk sac of the chick embryo has been shown previously to give rise on the average to a clone of 128 erythrocytes. Furthermore, in any given generation the erythroid cell synthesizes a characteristic amount of hemoglobin (Hb). In these experiments day 4 embryos were treated with FUdR for 12 hours, and then reversed with thymidine. We have monitored both the passage of these erythroblasts through the cell cycle, and the effect of this perturbation on the Hb content of single cells. As a result of this disruption the amount of Hb synthesized in a given generation can be varied, but the final amount of Hb/cell in the mature erythrocyte is the same as in the untreated controls. Apparently the total amount of the Hb/cell does not in itself influence the passage of the cell through the cycle. The coefficients of variation of the Hb values in the mature erythrocytes from both normal an perturbed embryos are similar.

ISSN:0021-9541    

DOI:10.1002/jcp.1040830103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractIntranuclear Na, K and Mg concentrations were determined in cells of salivary glands incubated for 1hin selected NaCl/KCl/MgCl2media. By variation of the external milieu beyond “physiological” limits the intranuclear electrolytes can be shifted between ca 100 and 280 mM [K]i, between ca 8 and 100 mM [Na]iand between ca 5 and 75 mM [Mg]i. No significant competition or interactions of the 3 ionic species are apparent. The relationships [K]e: [K]iand [Na]e: [Na]ican best be described by a positive and linear, that between [Mg]e: [Mg]iby a negative and exponential function. Regression parameters are given which permit a computation of intranuclear [Na], [K]and [Mg] as induced by NaCl/KCl/MgCl2in any binary or triple combination that is tolerated by the explanted gland without visible dam

ISSN:0021-9541    

DOI:10.1002/jcp.1040830104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe relationship between alkaline phosphatase activity and cell growth has been studied in hamster cells transformed by different carcinogens. About 90% of normal hamster embryo cells were constitutively positive for alkaline phosphatase activity (AP+). However, there were no AP+cells in cell lines transformed after treatment with the chemical carcinogens dimethylnitrosamine or 4‐nitro‐quinoline‐N‐oxide and 0.02% and 4% AP+cells in cell lines transformed by polyoma virus or Simian virus 40. The glucocorticoid hormone, prednisolone, induced alkaline phosphatase activity in 12% and 44% of the enzyme‐negative (AP−) cells in cell lines transformed by polyoma or Simian virus 40, but this hormone did not induce alkaline phosphatase activity in AP−cells from cell lines transformed after treatment with the chemical carcinogens. Treatment of polyoma transformed AP−cells with the mutagen N‐methyl‐N′‐nitro‐N‐nitro‐soguanidine produced AP+cells, whereas no AP+cells were found after mutagen treatment of AP−cells from the chemically transformed cell lines. Studies on spontaneous segregation in the polyoma transformed cell line has shown that AP+cells segregated AP−cells both in vitro and in vivo, although no spontaneous segregation was observed from AP−to AP+cells.AP+cells, compared to AP−cells, showed a decrease in DNA synthesis, cell multiplication, the ability to form colonies in soft agar and tumorogenicity in animals. AP−cells induced for alkaline phosphatase activity by prednisolone, showed the same growth properties in vitro as uninduced AP−cells. The decreased cell growth found in AP+cells which were constitutive for alkaline phosphatase activity was therefore not found in the hormone induced AP−cells. The results indicate that constitutive alkaline phosphatase activity appears to be related to the regulation of cell growth and that AP−c

ISSN:0021-9541    

DOI:10.1002/jcp.1040830105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractMouse bone marrow forms colonies of granulocytes and monocytic phagocytes when cultured in the presence of human plasma, urine or “feeder layers” prepared from human leukocytes. By contrast, human marrow produces colonies in the presence of leukocyte feeder layers but not in the presence of plasma or urine. It has been tacitly assumed that the response of mouse marrow to human blood leukocyte feeder layers is a measure of physiological substances released by those leukocytes which might control human granulopoiesis. This assumption however, has never been put to the test by comparing the response of mouse and human marrow to stimulation by leukocytes from the same individual. This has been done in the present study by using leukocytes from normal and leukemic subjects. Different human marrows responded similarly to stimulation by the same normal feeder layers, but there was no quantitative or qualitative correlation between the response of human and mouse marrows. Feeder layers from patients with acute granulocytic leukemia did not stimulate colony growth in normal human marrow but were as potent in stimulating mouse marrow colony growth as were feeder layers of normal leukocytes.We conclude that different factors may stimulate human and mouse marrows and that assays of granulopoietic factors of human origin should in future be carried out in human rather than mouse marr

ISSN:0021-9541    

DOI:10.1002/jcp.1040830106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThis paper reports the isolation of a phenotypically stable line of Chinese hamster ovary cells which exhibits a temperature dependent alteration in the transport of some purines. The alteration manifests itself for the uptake of guanine, hypoxanthine, azaguanine and guanosine but not for adenine, adenosine or thymidine. Studies with crude cell extracts suggest that, at the temperature the alteration is being expressed, the HGPRT activity is within the normal range. In cell‐cell hybridization studies the alteration behaves as a recessive genetic trai

ISSN:0021-9541    

DOI:10.1002/jcp.1040830107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractEnzymatic activities involved in the transformations of uridine nucleotides by intact erythrocytes and their subfractions have been studied and the following enzymatic activities have been identified: UTPase, UDPase, UMPase and uridylate kinase.UTPase activity was present exclusively in the stromal fraction while UMPase and uridylate kinase activities were specific in the soluble fraction. UDPase was present in both the stromal and soluble fractions.This compartmentation in erythrocytes differs from that reported for the enzymes involved in adenine nucleotides transformations. Due to its sensitivity to Zn2+, uridylate kinase could be differentiated from adenylate kinase.

ISSN:0021-9541    

DOI:10.1002/jcp.1040830108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe pattern of changing activities of three lysosomal enzymes, N‐acetyl‐β‐D‐glucosaminidase, aryl sulfatase, and DNase II, and that of DNA polymerase was followed in homogenates of 3T3 cells during the logarithmic phase of growth and in stationary cultures. The change in activities of the polymerase and the lysosomal enzymes is antiparallel. DNA polymerase exhibits highest activity in growing cultures, and shows a three‐fold decline of the specific activity in stationary cultures. The lysosomal enzymes show a very marked increase in their specific activity after density saturation is reached, which can be prevented by the addition of cycloheximide. Colcemid added to logarithmically growing cultures also causes an increase in the specific activities of lysosom

ISSN:0021-9541    

DOI:10.1002/jcp.1040830109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractMammalian cell populations may be enriched for temperature‐sensitive (ts) mutants by the tritiated thymidine (3H‐TdR) suicide procedure (Thompson et al., '71). Such procedures were carried out on the near‐diploid Chinese hamster ovary (CHO) cell line and on a line made “tetraploid” by Colcemid treatment. Clones oftsmutants were obtained from the diploid line, but in spite of repeated attempts, notsmutants were isolated from the tetroploid line. The phenotypes of the new diploidtsmutants recovered were consistent with the particular selection regime

ISSN:0021-9541    

DOI:10.1002/jcp.1040830110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractDifferential centrifugation of homogenates of Harding‐Passey melanoma demonstrated that aryl sulfatase A and β‐glucuronidase sediment with particles (i.e., lysosomes) distinct from those particles bearing tyrosinase (i.e., melanosomes). The sedimentation curves for the lysosomal enzymes and tyrosinase, however, demonstrated that an adequate separation of these particle types could not be obtained by differential centrifugation. Isopycnic density gradient centrifugation was used to obtain the necessary resolution. The results of the density gradient studies demonstrated that lysosomes and melanosomes could be separated by this technique, as judged by enzyme distribution among the fractions recovered from the gradients and from electron microscopic examination of the melanosome fractions. It was further evident that the purified and washed melanosomes contained significant amounts of both acid hydrolase activities. Indeed 24% to 27% of the total acid hydrolase activities recovered from the density gradients were associated with the melanosome fractions. The acid hydrolases associated with the melanosomes could not be solubilized by treatment with 0.1% (v/v) Triton X‐100, nor by exposure to hypo‐osmotic shock. The melanoma lysosomes, however, did release most of both their hydrolase activities into soluble form after treatment with the same percentage of detergent. The lysosomes were, however, very resistant to rupture by exposure to hypo‐osmotic

ISSN:0021-9541    

DOI:10.1002/jcp.1040830111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY