摘要:

AbstractTwo isogenic acyclic strains ofParamecium multimicronucleatum, syngen 2, expressing mating types III and IV, and a cycler strain, which displays circadian alternation of the two mating types, were treated with proteolytic enzymes, or the inhibitors actinomycin D or puromycin at various stages of the mating reactive period induced by food depletion. Reactivity of acyclic animals was sensitive to proteolytic enzymes, and to both inhibitors before or after the onset of reactivity, suggesting that reactivity is attained and maintained via continuous RNA and protein synthesis, and that protein integrity is essential to the activity of the type‐specific substances. A new cell cycle was not necessary for recovery from a block in reactivity.Type III animals were consistently more sensitive to inhibition by puromyin, and required longer recovery periods after all treatments except actinomycin D given after the development of reactivity. Possible explanations of these observations are considered.The daily type changes seen in cycler animals seemed to occur by replacement of one mating type substance with the other. Type‐switching was neither prevented nor displaced by exposure to actinomycin D or puromycin during a period before or including a type change, even though reactivity was reduced by more than 95%, suggesting that type‐switching is not directly associated with transcription or translation of the type‐specifi

ISSN:0021-9541    

DOI:10.1002/jcp.1040790102

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

年代:1972

数据来源: WILEY

摘要:

AbstractXenopusembryo cells and HeLa cells were investigated under various conditions to test for coordinate synthesis of high molecular weight (28S and 18S) and low molecular weight (5S) rRNA.Xenopusembryos initiate 28S and 18S rRNA synthesis at gastrulation (Brown and Littna, '64); we found that 5S rRNA synthesis is coordinately initiated with the 28S and 18S rRNAs at the same time in development. DissociatedXenopusblastula cells were culturedin vitrofor several hours to condition the medium; post‐gastrula cells were then grown in the conditioned medium to test for the existence of an inhibitor of rRNA synthesis. No inhibitor was detected.Low doses of actinomycin D profoundly inhibit the synthesis of 28S and 18S rRNA in HeLa cells, while 5S rRNA synthesis is less affected by this treatment. Therefore, actinomycin D does not produce a coordinate inhibition of all rRNA species. Similar effects of the antibiotic were found in cultured amphibian cells. Synchronized HeLa cells reinitiating RNA synthesis following mitosis also respond to actinomycin D in a non‐coordinate man

ISSN:0021-9541    

DOI:10.1002/jcp.1040790103

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

年代:1972

数据来源: WILEY

摘要:

AbstractMarmosets are unique in that they are “always” blood cell chimeras. When the nucleated cells from the bone marrow and from the peripheral blood of marmosets were incubated in the appropriate culture fluid they were shown capable of extensive proliferationin vitro. Two patterns of cellular proliferation, adherent and nonadherent, occurred in the same culture vessel. Repeated passage of nonadherent cells in RPMI 1640 medium supplemented with calf serum resulted in relatively long‐term fluid bulk cultures showing myelocytic differentiation and megakaryocytic maturation. As myelocytic maturation became the predominant feature of cultures mitoses of the precursors diminished. About half of 41 marrow‐derived cultures underwent extensive proliferation lasting about two months, as evidenced by an increasing cellularity and the presence of dividing cells. Such active growth occurred in one culture for over 120 days. The natural blood‐cell chimerism of marmosets was demonstratedin vitroby cytogenetic analyses of metaphases from four relatively long term marrow cultures. The ratios of male and female cells remained either relatively stable or changed slowly with time in culture. Cells having both diploid and polyploid number of chromosomes were identified male or female, suggesting chimerism in myelocytic and megakaryocytic series. Marmoset lymph node and spleen cells proliferated as lymphoid cultures for various lengths of time up to five weeks but these cells did not differentiate into hemic cell lines. Attempts to culture human and rodent hemic tissue by the procedure used on marmoset tissue were uns

ISSN:0021-9541    

DOI:10.1002/jcp.1040790104

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

年代:1972

数据来源: WILEY

摘要:

AbstractEffects of ionizing radiation and of sulfhydryl reagents on the45Ca binding of red cell membranes were studied. Corresponding effects of these agents on potassium leak from intact red cells were also determined. Essentially all the45Ca associated with the ghosts appeared to be bound. Calcium binding could be described by assuming two independent groups of binding sites with dissociation constants of about 6 × 10−4m and 2 × 10−4m. The total binding capacity was about 2.5 × 10−4moles/g ghost protein. Membrane calcium was decreased by radiation and by the two sulfhydryl reagents, p‐chloromercuribenzoate (PCMB) and N‐ethyl maleimide (NEM). The tightly bound calcium fraction appeared to be most affected by these agents. Changes in potassium leak evoked by varying doses of agents appeared to parallel effects on membrane calcium. These investigations suggest that the increased cation permeability observed after exposure or red cells to radiation or sulfhydryl reagents may be related to alterations in the calcium‐binding properties of the

ISSN:0021-9541    

DOI:10.1002/jcp.1040790105

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

年代:1972

数据来源: WILEY

摘要:

AbstractLivers from five‐day chick embryos maintained as organ cultures on Eagle's minimum essential medium (MEM) develop an ultrastructure similar to more mature liver cells, except for glycogen deposits and the smooth endoplasmic reticulum (SER) normally associated with such deposits. The enzymes, glycogen synthetase and glycogen phosphorylase, failed to develop in these cells. The addition of zinc‐free insulin (insulin‐HCl) to MEM promoted the development of small amounts of SER in the cultured cells, as well as an increase in both glycogen synthetase and phosphorylase activities. The addition of zinc‐insulin also stimulated an increase in the activities of both enzymes, and promoted the development of greater amounts of SER and the deposition of glycogen, as well. In addition, both forms of insulin not only prevented the fall of total tissue protein which occurs during organ culture on MEM, but also stimulated net protein synthesis in the explanted liver (Benzo and de la Hab

ISSN:0021-9541    

DOI:10.1002/jcp.1040790106

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe mitochondrial‐plus‐lysosomal fraction of rabbit lung parenchyma was studied by equilibrium density centrifugation in continuous sucrose density gradients (specific gravity 1.035 to 1.250). High concentrations of lysosomal marker enzymes were found both in a broad band at density 1.15–1.18, a density typical for lysosomes, and in a band at density 1.06–1.07. This light density band also had the highest specific activity of phospholipid, which thin layer and gas‐liquid chromatography showed to be primarily lecithin with a high content of palmitic acid residues. Electron microscopy of material from the light density band showed a homogeneous array of particles which bear a strong resemblance to the inclusion bodies of the type II alveolar epithelial cell as seen in electron micrographs of rabbit lung tissue sections. These data suggest that the light density band is an isolation of intact type II alveolar epithelial cell inclusion bodies, which previous studies have implicated as the storage site of the phospholipid moiety of pulmonary s

ISSN:0021-9541    

DOI:10.1002/jcp.1040790107

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe effect of extracellular Pi and arsenate on Pi‐transport in Ehrlich ascites tumor cells has been studied. Pi‐transport can be described by Michaelis‐Menten kinetics; the maximal flux equal to 44 mmoles (kg cell water)−1hour−1and Kmequal to 3.3 × 10−4M. Arsenate is a competitive inhibitor of Pi‐transport with an inhibition constant (Ki) equal to 2.41 × 10−3M.The data support the hypothesis that cellular Pi is regulated by the cell membrane through the mediation of

ISSN:0021-9541    

DOI:10.1002/jcp.1040790108

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

年代:1972

数据来源: WILEY

摘要:

AbstractSuspension cultures of L‐929 fibroblasts grown to densities of 6 to 10 × 106cells/ml through daily centrifugation and resuspension in fresh media, have been maintained for periods up to five months without change in viability or cell size. DNA synthesis and mitosis in these cultures is limited to 5% of the cells per day, a fraction very nearly equal to the fraction of cells rendered nonviable, most likely during the manipulations associated with medium renewal. The kinetics of the flow of cells into the S and M periods following (a) renewal of the medium and (b) dilution of the high density cultures, suggest that the large majority of the cells are in a G0or early G1phase, resuming growth readily in response to decreased cell density. This is further indicated by the sequence of the marked shifts occurring in the cell volume distribution spectrum of the high density cultures after dilution. Long term, steady state regulation of growth with retention of intact viability was thus demonstrated in the case of a long established aneuploid cell line. The fact that this occurs in suspension but not in attached cultures, supports the concept that impairment of growth control in such cells affects predominantly regulatory mechanisms located at the cell surface rather than those concerned with intracellular synthesis and metaboli

ISSN:0021-9541    

DOI:10.1002/jcp.1040790109

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

年代:1972

数据来源: WILEY

摘要:

AbstractTreatment of polymorphonuclear leukocytes with sialidase release about one‐half of the total sialic acid of the cells. Such treatment affects neither phagocytic ingestion nor glycolysis. These results are in contrast to earlier data in the literature that indicate suppression of both functions mentioned upon desialation of these cells. The presence of an inhibitor of glycolysis that contaminated the crude enzyme previously used is suggeste

ISSN:0021-9541    

DOI:10.1002/jcp.1040790110

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

年代:1972

数据来源: WILEY

摘要:

AbstractThe lipid composition of a highly purified preparation of rat skeletal muscle sarcoplasmic reticulum was studied. These membranes contain per mg of protein 0.50 ± 0.02 μmoles of phosphatidylcholine, 0.13 ± 0.02 μmoles of phosphatidylethanolamine and 0.07 ± 0.02 μmoles ofphosphatidylinositol. These three components account for 97.3% of total lipid phosphorus. Unlike other mammalian membranes so far studied, this preparation contains neither sphingomyelin nor phosphatidylserine. Neural lipids were also measured and it is concluded that neither cholesterol nor other neutral lipids are components of the membranes studied. The results of this study indicate therefore that the lipid profile of sarcotubular membranes is relatively simple compared with most other memb

ISSN:0021-9541    

DOI:10.1002/jcp.1040790111

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

年代:1972

数据来源: WILEY