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Jones, Alick R.; Jahn, Theodore L.; Fonseca, James R.
doi: 10.1002/jcp.1040750102pmid: 4984851
10.1002/jcp.1040750102.abs The contraction of Stentor and Blepharisma, in response to mechanical and electrical stimulation and of Spirostomum in response to mechanical stimulation is described. All three species respond to electrical stimulation by contraction of the cytoplasm, beginning at the anodal end regardless of orientation of the animal. The differences in contractile ability and shapes during contraction are discussed in relation to body form and microanatomy. Stentor and Spirostomum also respond to mechanical stimulation. Dropping a weight on the slide causes contraction of the whole body of Spirostomum, but not of Stentor. Stimulation of the oral region of Stentor by means of a vibrating needle causes a contraction of the entire body, but this sensitivity is limited to the oral region. Blepharisma does not respond to mechanical stimulation. Spirostomum and Stentor undergo rapid spontaneous contractions, but Blepharisma does not contract spontaneously.
Jones, Alick R.; Jahn, Theodore L.; Fonseca, James R.
doi: 10.1002/jcp.1040750103pmid: 4984852
10.1002/jcp.1040750103.abs The contraction and relaxation of Vorticella difficilis, V. campanula and Carchesium sp. were studied by high speed cinematography. In Vorticella it was shown that coiling of the stalk usually started near the zooid and spread downwards; the point of initiation bore no relation to the position of the stimulating electrodes. Contraction took about 5 msec to complete, and the fully contracted animals were 29 ± 3.9% of their original lengths. The zooids were 66 ± 5.0% and the stalks 14 ± 6.0% of their original lengths (V. difficilis). The shortening of the stalk was mostly in the form of coiling. Measurement of the myoneme length demonstrated that its real shortening was less than 10%. Thus the contraction is virtually isometric, producing a helical deformation of the stalk. As the stalk contracts it takes the form of a steeply pitched helix. This change in shape should produce rotational forces on the zooid (torque). Physical models of similar proportions produced about 1.5 revolutions of torque for similar changes in pitch. However during contraction no turning of the zooid was detected, though rotation did occur after the completion of contraction. In Carchesium the contraction is not so isometric, the myoneme apparently shortening by 20%. While the coiled shape of the contracted Vorticella stalk can be explained by its acentric structures, the stalk of Carchesium is much more symmetrical in cross‐section, demonstrating that a high acentricity is not necessary for helical coiling. In all three species there seems to be some separation of the control of zooid and stalk contraction.
doi: 10.1002/jcp.1040750104pmid: 4392119
10.1002/jcp.1040750104.abs Direct measurements of the methylation of newly‐synthesized DNA were made in cultures of a clonal mouse adrenal cortex cell line, Y129OS3, by (1) following the incorporation of radioactivity from methionine‐(methyl)‐C14 into a segment of DNA which had been density‐labeled with bromouracil and (2) labeling DNA cytosine with C14‐deoxycytidine and then following the appearance of radioactivity in DNA 5‐methylcytosine. The results establish that during exponential growth the DNA of this cell line is methylated entirely within a few minutes of its synthesis. Using the second technique described above accurate, sensitive measurements of DNA methylation levels can be made by comparing radioactivity in 5‐methylcytosine to radioactivity in cytosine plus 5‐methylcytosine. In this cell line 5‐methylcytosine accounts for 4.3 ± 0.2% of the DNA cytosine. Some apparent contradictions between these results and those of other workers are discussed.
doi: 10.1002/jcp.1040750105pmid: 5461456
10.1002/jcp.1040750105.abs The stability of glandular epithelial cells has been investigated utilizing the techniques of cell culture. Embryonic chick thyroid was chosen as a representative cell type and methods were developed for the successful clonal culture of thyroid follicular cells. Thyroid cells were found to be morphologically and functionally stable while undergoing rapid division in both dense (monolayer) and dilute (clonal) cell culture. Differentiated features were retained for a minimum of 32 days of primary clonal culture (approximately 17 generations under clonal conditions). During the culture period, the cells retained their epithelial morphology, retained their cytoplasmic rough endoplasmic reticulum, and continued to produce chromatographically detectable thyroid hormones. Hormone production in culture was a specific thyroid characteristic since control cultures of embryonic heart and liver did not contain the hormones.
Hill, Helene Z.; Puck, Theodore T.
doi: 10.1002/jcp.1040750106pmid: 5418108
10.1002/jcp.1040750106.abs The method for simultaneous measurement of the first two sequential enzymes of galactose metabolism of red cells has been extended to include the third step of the chain, epimerization of uridine diphosphogalactose to uridine diphosphoglucose. The method is rapid and precise and is applicable to a variety of genetic‐biochemical problems.
doi: 10.1002/jcp.1040750107pmid: 5461457
10.1002/jcp.1040750107.abs The kinetics of cell division and movement in four epithelial‐like cell lines, grown in continuously perfused culture medium, were studied by time‐lapse cinemicrography. One line exhibited “contact regulation of cell division,” so that the rate of mitosis per cell decreased steadily as population density increased. In the other three lines mitosis was not controlled as a function of population density until the cells became very crowded. An explanation for this difference was sought in terms of the hypothesis that the rate of division depends on the area of the cell membrane. Cells of the contact‐regulated line flattened uniformly on the substrate. Their motility was restrained by adhesion between their borders. As they crowded together, contact inhibition of cell overlap caused a steady decrease in average surface area per cell. All three of the non‐controlled lines also had contact inhibition of overlap. Cells of two of them flattened on the substrate; but these cells had little mutual adhesion and were highly motile, so that they continually changed their shapes. The areas of their cell membranes were therefore not subject to a restraint that could control the rate of division. Cells of the fourth line remained rounded or only slightly flattened during culture growth, so that no change in cell membrane area occurred that could change the rate of division.
doi: 10.1002/jcp.1040750108pmid: 5461458
10.1002/jcp.1040750108.abs Nutritional factors were evaluated for effects on growth of mouse fibroblast cells in suspension in a chemically defined medium. Quantitative requirements for each of the essential amino acids, choline, inorganic phosphate, iron, and zinc were established. An improved chemically defined medium was formulated on the basis of the findings yielding populations of L cells in excess of 5 × 106 per ml without nutrient replenishment. When spent medium was replaced periodically, yields approaching 30 × 106 cells per ml were attained. The efficiency of utilization of most amino acids in the new medium appears to be 2‐ to 3‐fold better than results reported by others.
Hare, Theodore A.; Schmidt, Robert R.
doi: 10.1002/jcp.1040750109pmid: 5418109
10.1002/jcp.1040750109.abs The levels of free‐, peptide‐, and protein‐amino acids were measured during the synchronous growth and division cycle of a thermophilic strain of Chlorella pyrenoidosa. Most of the protein amino acids exhibited little periodism (as % of total cellular‐N); however, the free‐ and peptide‐amino acids showed a variety of dramatic changes in level during the cell cycle. Fractionation of the acid‐soluble peptides by Sephadex gel‐filtration showed that an average of only 2.8% of the peptide amino acids were associated with peptides of high molecular weight (> 5000), while approximately 75% of the peptide amino acids were components of low molecular weight peptides (< 700). The low molecular weight peptides were predominately made up of relatively few amino acids (i.e., alanine, glutamate, lysine, glycine and arginine accounted for approximately 92% of the low molecular weight peptide amino acids). Several experiments revealed that nucleotide‐peptides do not contribute significantly to the pool of acid‐soluble peptides during the cell cycle of this organism.
doi: 10.1002/jcp.1040750110pmid: 5418110
10.1002/jcp.1040750110.abs A kinetic model of adenine and glucose incorporation into log phase yeast cells has been developed, and experimental tests of certain predictions of the model validate it. The cellular pool of purine nucleotides is 6 × 10−3 μmoles per 107 cells, the turnover time of this pool is 21.8 minutes, and the rate of incorporation into nucleic acids is 4.86 × 10−2 μmoles per hour per 107 cells. Corresponding figures for glucose are given. The model should be useful in other kinetic studies and the method of applying it is explained.
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