Analysis of Optical Density Wave Propagation and Cell Movement during Mound Formation in Dictyostelium discoideum

Waves of chemotactic movement during the early phase of aggregation in Dictyostelium discoideum were analyzed by digital image processing in a manner that immediately shows the following parameters: wave propagation velocity, period length, wave amplitude und wave shape. We have characterized the aggregation of AX-2 and the streamer F mutant NP 377 in terms of these parameters and investigated the influence of caffeine and ammonia. It was found that during normal aggregation oscillation frequency increases while at the same time wave propagation velocity decreases. Caffeine, a known inhibitor of cyclic AMP relay, reduces oscillation frequency and wave propagation velocity in a dose-dependent manner but most notably leads to the appearance of bimodal (harmonic) oscillations. These bimodal waves are also found in streamer F mutants without caffeine during early aggregation. The effect of caffeine is interpreted as an increase in the average chemotactic deadaptation time due to elevated cyclic GMP levels after a cyclic AMP stimulus. This increased deadaptation time results in some cells responding to every chemotactic signal, while others respond only to every second signal, leading to mixed population behavior and hence biphasic optical density waves. Ammonia has no significant influence on oscillation frequency and wave propagation velocity but shows a clear increase in the amplitude of the optical density waves. This may indicate a more vigorous chemotactic response by individual cells or a better synchronization of the responding cell populations due to shortened chemotactic deadaptation times.

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Propagating chemoattractant waves coordinate periodic cell movement inDictyosteliumslugs

Development ◽

10.1242/dev.128.22.4535 ◽

2001 ◽

Vol 128 (22) ◽

pp. 4535-4543 ◽

Cited By ~ 3

Author(s):

Dirk Dormann ◽

Cornelis J. Weijer

Keyword(s):

Wave Propagation ◽

Optical Density ◽

Cell Movement ◽

Camp Phosphodiesterase ◽

Periodic Cell ◽

Propagating Waves ◽

On Line ◽

Camp Receptor ◽

The Waves ◽

Slug Movement

Migration and behaviour of Dictyostelium slugs results from coordinated movement of its constituent cells. It has been proposed that cell movement is controlled by propagating waves of cAMP as during aggregation and in the mound. We report the existence of optical density waves in slugs; they are initiated in the tip and propagate backwards. The waves reflect periodic cell movement and are mediated by cAMP, as injection of cAMP or cAMP phosphodiesterase disrupts wave propagation and results in effects on cell movement and, therefore, slug migration. Inhibiting the function of the cAMP receptor cAR1 blocks wave propagation, showing that the signal is mediated by cAR1. Wave initiation is strictly dependent on the tip; in decapitated slugs no new waves are initiated and slug movement stops until a new tip regenerates. Isolated tips continue to migrate while producing waves. We conclude from these observations that the tip acts as a pacemaker for cAMP waves that coordinate cell movement in slugs.Movies available on-line

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In situ measurements of external pH and optical density oscillations in Dictyostelium discoideum aggregates.

The Journal of Cell Biology ◽

10.1083/jcb.102.5.1623 ◽

1986 ◽

Vol 102 (5) ◽

pp. 1623-1629 ◽

Cited By ~ 11

Author(s):

K Gottmann ◽

C J Weijer

Keyword(s):

Wave Propagation ◽

Dictyostelium Discoideum ◽

Optical Density ◽

In Situ Measurements ◽

Extracellular Ph ◽

Harmonic Oscillations ◽

Density Measurements ◽

External Ph

In situ measurements of extracellular pH by means of microelectrodes and in situ measurements of optical density were performed on aggregating cells of Dictyostelium discoideum. Early aggregation stage AX2 cells showed sinusoidal pH oscillations, which could be inhibited by the specific relay inhibitor caffeine, indicating that they were coupled to cAMP oscillations. Sometimes biphasic pH oscillations were found, which can be explained by the superposition of two harmonic pH oscillations. These harmonic oscillations might arise by gating of the cAMP signal; a part of the cells respond to every cAMP signal and another subpopulation to every second cAMP pulse. Late aggregation-stage cells showed complex changes of the extracellular pH, which could be inhibited by caffeine. Optical density measurements of wave propagation in aggregation streams of HG220 also revealed gating behavior. In addition to sinusoidal optical density oscillations, biphasic and still more complex oscillations were observed.

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Cell movement within aggregates of the slime mould Dictyostelium discoideum revealed by surface markers

Development ◽

10.1242/dev.13.1.97 ◽

1965 ◽

Vol 13 (1) ◽

pp. 97-117

Author(s):

B. M. Shaffer

Keyword(s):

Dictyostelium Discoideum ◽

Cell Movement ◽

Surface Markers ◽

Slime Mould ◽

Culture Plate ◽

Multicellular Organisms

Earlier workers examined the behaviour of foreign particles placed as markers on aggregates of D. discoideum that were migrating over the surface of the culture plate (Bonner, 1959; Francis, 1959, 1962). Comparable observations, made on aggregates in other conditions and at other stages, have now provided further information about the movement of individual cells within the aggregates. Before reporting them, the course of development must be described in some detail. During aggregation on an ordinary culture plate, D. discoideum amoebae crawl towards centres, in which they pack themselves together, forming rounded aggregates of no fixed shape. Papillae develop on the side of the aggregates away from the agar, and by extension, roughly perpendicular to the substratum, transform them into cylindrical multicellular organisms with tapered tips (Text-fig. 1, A—E). Such an organism, which contains from a dozen to a few hundred thousand cells, has been named a grex (Shaffer, 1962) because ‘aggregation’ is derived from the Latin aggregare, to form a grex.

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Independent control of locomotion and orientation during Dictyostelium discoideum chemotaxis

Journal of Cell Science ◽

10.1242/jcs.102.4.763 ◽

1992 ◽

Vol 102 (4) ◽

pp. 763-768

Author(s):

B. Van Duijn ◽

P.J. Van Haastert

Keyword(s):

Dictyostelium Discoideum ◽

High Voltage ◽

Cell Movement ◽

Cell Length ◽

Independent Control ◽

Motile Cells ◽

Two Component ◽

Extracellular Camp

Chemotaxis is cell movement in the direction of a chemical and is composed of two component: movement and directionality. The directionality of eukaryotic chemotaxis is probably derived from orientation: the detection of the spacial gradient of chemoattractant over the cell length. Chemotaxis was investigated in eukaryotic Dictyostelium discoideum cells that were permeabilized by high-voltage discharges. These permeable cells respond chemotactically to extracellular cAMP. However, locomotion is impaired if the Ca2+ concentration is clamped at submicromolar concentrations; interestingly, these non-motile cells still form pseudopodia and elongate in the direction of the cAMP gradient. These results imply that locomotion and orientation during Dictyostelium chemotaxis are independently regulated.

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