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C D Town

Publications and source records attributed to C D Town.

33 records · Page 2Linked to original sources
PubMed1984

Differentiation of Dictyostelium discoideum in monolayer cultures and its modification by ionic conditions.

We have compared the pattern of enzyme expression in cyclic AMP-induced monolayer cultures of Dictyostelium discoideum with that found during normal development. We find that both the temporal and quantitative pattern of enzyme expression are initially similar in the two situations, although the developmental sequence is more protracted and terminal cell differentiation is delayed in the monolayer situation. We describe differentiation conditions that permit the expression of only one terminal phenotype, which may be useful for further biochemical studies. Enzyme accumulation patterns under these conditions indicate that UDP gal transferase is not required for stalk cell differentiation (i.e., it is a prespore enzyme). We have shown that, when cell monolayers are incubated with cAMP, the presence of a weak acid at low extracellular pH favors stalk-cell differentiation, while a weak base at high extracellular pH favors spore differentiation. Finally, we show that variations in the monovalent cation content of the buffer, or the addition of an ion transport inhibitor (scillaren), or an ionophore (valinomycin) all affect the ratio of stalk cells to spores. Taken together, these results suggest that intracellular H+ and/or other cations may play an important role in regulating differentiation of specific cell types in D. discoideum.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1981

Cell patterning in Dictyostelium.

We summarize studies on stalk and spore cell formation in D. discoideum cell monolayers, aimed at revealing factors involved in controlling the prestalk:prespore pattern in this organism. We propose that there are no cell interactions dependent on cell contact per se. Formation of mature stalk cells from isolated amoebae incubated in a buffered salts medium requires only cyclic AMP and a lipid-like factor (DIF) released by cells developing at high density. In addition, a variety of sporogenous mutants can form spores rapidly and efficiently when incubated at low density in tissue culture dishes containing a similar cyclic AMP and salts medium. In some cases spore formation is improved by the addition of one or other of a variety of protective agents such as bovine serum albumin. Wild-type amoebae at low density form prespore cells under the same conditions. We present some evidence that DIF is the activator of prestalk cell formation in a two-component patterning mechanism of the kind proposed by Wolpert et al. (Symp. Soc. exp. Biol. 25, 391-415 (1971)) and Gierer & Meinhardt (Kybernetik 12, 30-39 (1972)). We also provide data indicating that the role of inhibitor is played by ammonia, an idea first mooted by Sussman & Schindler (Differentiation 10, 1-5 (1978)).

Cell Adhesion↗
PubMed1971

DNA polymerase required for rapid repair of x-ray--induced DNA strand breaks in vivo.

A much higher yield of DNA single-strand breaks was obtained in the DNA polymerase-deficient mutant Escherichia coli K-12 pol A1 after a given dose of x-rays than had been found before in Escherichia coli. The increased yield of single-strand breaks was due to the absence of a rapid repair system, which had not been described in Escherichia coli K-12. This absence probably accounts for the x-ray sensitivity of the pol A1 mutant. The rapid repair system can be reversibly inhibited in pol+ cells.

Centrifugation, Density Gradient↗
PubMed1971

Production and repair of radiochemical damage in Escherichia coli deoxyribonucleic acid; its modification by culture conditions and relation to survival.

Late log-phase Escherichia coli B/r cells are 1.6 times more sensitive to killing by X rays than are stationary-phase cells when grown in Brain Heart Infusion (BHI) + glucose. The number of single-chain breaks formed per krad is the same for log- and stationary-phase cells. Stationary-phase cells show a somewhat greater ability to repair single-chain breaks (especially after high doses of X rays) than do log-phase cells. The rapidity and extent of postirradiation deoxyribonucleic acid (DNA) degradation are greater in log-phase cells than in stationary-phase cells. The enhanced viability exhibited by stationary-phase cells thus appears to correlate both with enhanced single-chain break repair and the reduced degradation of DNA. Cells grown to stationary phase in peptone medium (PO cells) are 3.4 times more sensitive to killing by X rays than cells grown to stationary phase in peptone medium supplemented with glucose and phosphate buffer (PG cells). The yield of single-strand breaks is the same for both types of cells (but the absolute yield is about two times higher than in the cells grown in BHI + glucose). The kinetics for the repair of single-chain breaks are the same for both types of cells for about 30 min. After this time period, further repair ceases in the PO cells but continues in the PG cells, provided that glucose is present in the medium. Postirradiation DNA degradation is both more rapid and more extensive in PO cells than in PG cells whether or not glucose is present in the postirradiation incubation medium. The survival of stationary-phase E. coli B/r grown in PO or PG medium is likewise unaffected by the presence of glucose in the plating medium, and thus correlates better with the lower DNA degradation seen in the PG cells than with the increased strand rejoining, since this latter process requires the presence of glucose.

Carbon Isotopes↗