Living vegetative D, discoideum amoebae were studied to determine whether their filopodia respond to folic acid, a chemoattractant for these cells. Exponentially growing amoebae (ca. 10 micron diameter) exhibit 5-30 micron long filopodia; at stationary phase, aggregation competent amoebae have numerous multibranched filopodia up to 100 micron long. Folic acid was observed to stimulate production, elongation, and branching of filopodia with its effects progressively changing as the amoebae approach aggregation. Filopodial construction was also found to be dependent upon Mg2+ levels. The significance of these results is discussed with respect to progressive changes within the vegetative phase as well as to the mechanisms of amoeboid movement, pseudopodial activity, and chemotaxis.
Living vegetative amoebae of NC-4H Dictyostelium discoideum were studied to determine if a variety of pteridines had any effect on the filopodia. We observed that production, elongation, and branching of these filopodia were stimulated by pteridines that are chemoattractants for cells of this strain. This stimulation occurs at chemotactically effective concentrations and is observed before motility is evident. A relationship between filopodia and chemoattractant signal processing is discussed.
A convenient, sensitive, quantitative assay for the measurement of chemotaxis of populations of D. discoideum vegetative amoebae is presented. A strategy for determining the boundary of the bulk of a population of migrating amoebae was devised and is described. This assay employs a dynamic gradient and is independent of deaminase activity. Measurements of chemoattractant capabilities of various pteridines, folates, and mixtures of folate fragments are reported. 2-Amino 4-quinazolinone, a pterin analog without the pyrazine ring nitrogens, is chemotactic. Lumazine, deaminated pterin, inhibits chemotaxis towards pterin but not towards folic acid. Deaminofolic acid is a chemoattractant as are mixtures of lumazine plus aminobenzoylglutamic acid or deaminopteroic acid plus various amino acids. Separately, the components of these mixtures exhibit no ability to stimulate chemotaxis. These mixtures are of fragments that together comprise most of the folate structure. Our results are in accord with separate receptors for pterin vs. folic acid and with a high stringency for pterin reception but a relative tolerance for folate reception. The possibility of using such mixtures to investigate the requirements of various parts of the folate structure for competent signalling is discussed.
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