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C J Weijer

Publications and source records attributed to C J Weijer.

8 recordsLinked to original sources
PubMed1992

Three-dimensional scroll waves organize Dictyostelium slugs.

To test the hypothesis that periodic signals and chemotaxis direct later morphogenesis in Dictyostelium discoideum, we investigated cell behavior and cell movement in slugs. Trails of neutral red-stained prestalk and anterior-like cells were recorded by high-resolution digital image processing. Neutral red-stained anterior-like cells in the prespore zone of slugs move straight forward in the direction of slug migration and, furthermore, show coherent periodic cell movement. In contrast, cells in the prestalk zone move along completely different trajectories. Prestalk cells move perpendicular to the direction of slug migration; that is, they rotate around the tip. The cell movement data show that the chemotactic signal in the slug propagates as a three-dimensional scroll wave in the prestalk zone and as a planar wave in the prespore zone. The different behavior of prestalk and prespore cells is most likely caused by a difference in the oscillatory properties of the two cell types. We provide evidence that the slug stage of Dictyostelium behaves like an excitable system and that a (twisted) scroll wave organizes slug formation and migration.

Animals↗
PubMed1989

Expression of a cell surface antigen in Dictyostelium discoideum in relation to the cell cycle.

We have previously shown binding of a monoclonal antibody MUD 9 to the cell surface of Dictyostelium discoideum amoebae and slug cells. In the slug stage the prestalk region was predominantly labelled, while vegetative amoebae showed a great heterogeneity in binding. In the present paper it is shown that the heterogeneous label of vegetative amoebae is due to differences in MUD 9 binding by cells in different cell cycle phases. Cells were synchronized by dilution from stationary phase and the level of MUD 9 binding was determined. Synchrony was determined by investigating increase in cell number and changes in the volume distribution of the cells, and by estimating the number of cells in S phase by monitoring bromodeoxyuridine (BUdR) incorporation. Simultaneously the amount of MUD 9 binding was determined by quantitative microscopy and flow cytometry. The amount of MUD 9 label varies during the cell cycle. The highest amount of label is found on cells early in the cell cycle, i.e. S-phase. These results support the finding that the developmental fate of Dictyostelium discoideum cells depends among other things on the cell cycle position of the cells at the moment of starvation.

Antibodies, Monoclonal↗
PubMed1986

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

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.

Cell Aggregation↗
PubMed1985

Influence of cyclic AMP and hydrolysis products on cell type regulation in Dictyostelium discoideum.

We describe the effect of cyclic AMP on regulation of the proportion of prespore and prestalk cells in Dictyostelium discoideum. Prespore and prestalk cells from slugs were enriched on Percoll density gradients and allowed to regulate in suspension culture under 100% oxygen. The transition of prespore to prestalk cells is blocked by cAMP, while cAMP phosphodiesterase and caffeine cause a decrease in the number of prespore cells. This suggests that extracellular cAMP plays a role in cell type proportioning by inhibiting the conversion of prespore to prestalk cells. Low concentrations of cAMP prevent the conversion of prestalk to prespore cells; the same effect is seen with hydrolysis products of cAMP, 5 AMP, adenosine and also adenine. We suggest that, when low concentrations of cAMP are added to regulating cells, the cAMP itself is quickly broken down and the breakdown products thereafter inhibit the prestalk-to-prespore conversion. The relevance of these findings is discussed in the context of an non-positional double-negative feedback model for cell type homeostasis.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1984

A revision of the Dictyostelium discoideum cell cycle.

We have investigated the Dictyostelium discoideum cell cycle using fluorometric determinations of cellular and nuclear DNA contents in exponentially growing cultures and in synchronized cultures. Almost all cells are in G2 during both growth and development. There is no G1 period, S phase is less than 0.5 h, and G2 has an average length of 6.5 h in axenically grown cells. Mitochondrial DNA, which constitutes about half of the total DNA, is replicated throughout the cell cycle. There is no difference in the nuclear DNA contents of axenically grown and bacterially grown cells. Thus the long cell cycle in axenically grown cells is due to a lengthening of the G2 phase.

Cell Cycle↗
PubMed1984

Dependence of cell-type proportioning and sorting on cell cycle phase in Dictyostelium discoideum.

The relationship between the cell cycle phase of vegetative amoebae and prestalk and prespore differentiation in the slug stage were investigated in the slime mould Dictyostelium discoideum. Cells were synchronized by release from the stationary phase. Samples were taken at various times during the course of a synchronous cell doubling, fluorescently labelled and mixed with cells of random cell cycle phase from exponentially growing cultures. The fate of the fluorescently labelled cells was recorded at the slug stage. Cells early in the cycle exhibit strong prestalk sorting; cells taken later in the cycle exhibit strong prespore sorting. The period of prestalk sorting occurs immediately following mitosis and lasts about 1 h in a cell cycle of about 7 h duration. Accompanying the altered sorting behaviour is a marked changed in the prestalk-prespore proportions in slugs formed from synchronized populations of cells. Cells synchronized early in the cycle form slugs with 55% prespore cells; cells synchronized late in the cycle form slugs with 90% prespore. The results are discussed in terms of models for the formation of the prestalk-prespore pattern in slugs.

Cell Cycle↗
PubMed1978

Neural induction, a two-way process.

A quantitative analysis of Triturus alpestris recombinates of newly invaginated "caudal" archenteron roof with either competent gastrula ectoderm or non-competent neurula ectoderm has demonstrated that neuralisation evoked by the underlying archenteron roof affects, in its turn, the regional differentiation of the latter. It does so by enhancing its notochordal differentiation; so, neural induction is clearly a two-way process. Somite differentiation is not significantly different in the two series. This is especially remarkable since both series show positive correlations between the amounts of notochordal and somite structures. The explantation is that the correlation coefficients differ considerably in the two series. The possible reason for this is discussed. Moreover the recombinates with competent gastrula ectoderm demonstrate that the size of the neural structures is determined by the total mass of the axial mesoderm and not by that of the notochord or that of the somites separately.

Animals↗