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cAMP receptor affinity controls wave dynamics, geometry and morphogenesis in Dictyostelium

¹ School of Life Sciences, Division of Cell and Developmental Biology, University of Dundee, Wellcome Trust Biocentre, Dow Street, Dundee, DD1 5EH, UK
² Department of Biological Chemistry, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA

View larger version (97K): [in a new window]   Fig. 1. Comparison of the darkfield wave patterns during early aggregation. The left column A-E shows the actual wave patterns of the different wild-type and mutant strains at the same scale (Bar, 10 mm). All images were enhanced by image subtraction. The according time-space plots are displayed in the right column, F-J. They all cover a period of 67 minutes (200 images), except for N272 (J) with 133 minutes (400 images) to show the disappearance of the waves. The vertical axis of the time-space plots corresponds to the time axis, time increases from the top to the bottom. (A,F) Wild-type strain Ax3 with spiral waves. (B,G) Parental strain DH1 with concentric waves. (C,H) cAR1 mutant with concentric waves. (D,I) cAR3 mutant with spiral waves. (E,J) N272 mutant with concentric waves.

View larger version (131K): [in a new window]   Fig. 2. Change from long period random waves to short period waves emitted by centres in cAR1/RI9. (A-D) Images of darkfield waves at successive stages of development. (E) Time-space plot of the experiment shown in (A-D) measured along the horizontal white line in D. (F) Change of optical density over time, read out along the white line shown in D. The black arrows in D,E indicate the position of a centre

View larger version (116K): [in a new window]   Fig. 3. Chemotactic response of cAR2/RI9 cells. (A) Positive response of aggregation-competent cells, 38 minutes after the cAMP-filled electrode (10-1 M cAMP) had been introduced. The cells have moved chemotactically towards the tip of the electrode and piled up. The outline of the tip in the cell mass is indicated in black. (B) The cAMP concentration in the electrode was 10-4 M, too low to be detected by the cAR2/RI9 cells. The cells remain evenly spread. The photograph was taken after about 38 minutes as well. Bar, 50 µm.

View larger version (77K): [in a new window]   Fig. 4. Optical density waves in mounds. Subtracted images of the mounds (A-D) reveal the wave pattern. Due to the image processing the wave fronts appear as black and white bands. Bar, 250 µm. In the schematic representations in the middle row (E-H), waves are shown as bold black lines and the direction of wave propagation is indicated by little arrows. Small circles represent the cores around which the spiral waves rotate, whereas the black dot in H marks the position from which concentric waves originated periodically. The outline of the mounds is indicated by a thin black line. The final phenotype after 24 hours is shown in the bottom row (I-L). (A,E,I) Parental strain DH1 with multi-armed spiral waves. (B,F,J) cAR1 mutant with single-armed spiral wave. (C,G,K) cAR3 mutant with complex wave patterns. (D,H,L) N272 mutant with concentric waves.

View larger version (84K): [in a new window]   Fig. 5. Multi-armed spirals in the cAR2 and cAR3 null strains. (A) Multi-armed spirals in a mound of the cAR2null strain. (B) Multi-armed spiral in a mound of the cAR3 null strain. (C,D) Schematic diagrams of the waves visible in A,B and an indication of their direction of propagation. Bar, 250 µm.

View larger version (50K): [in a new window]   Fig. 6. Frequency of darkfield waves measures in DH1, cAR1/RI9, cAR3/RI9 and N272/RI9 in at the aggregation and mound stage. Typical traces of the oscillations measured at one point in an aggregation field (left column) and in mounds (right column).

View larger version (30K): [in a new window]   Fig. 7. Frequency distribution of the period of optical density waves in early aggregation and in the mound stage. The data were divided into classes with a width of 40 seconds and normalised to account for the different number of measurements. (A) Period of darkfield waves during early aggregation. DH1 shows the shortest period, whereas all the other mutants are shifted towards the longer periods. (B) Period of waves in the mound stage. The periods are generally shorter in the mound stage, however the mutants still have longer periods.

View larger version (23K): [in a new window]   Fig. 8. Frequency distribution of wave velocities during early aggregation and in the mound stage. The data were divided into classes with a width of 25 µm/minute and normalised to account for the different number of measurements. (A) Distribution of the velocities of darkfield waves. The mutants show a similar distribution, whereas the parental strain DH1 is slightly shifted towards higher values. (B) Distribution of the velocities of optical density waves in the mound stage. The velocities of the four strains are essentially the same.

View larger version (73K): [in a new window]   Fig. 9. The frequency of wave initiation in the cAR1 affinity receptor mutants. Histogram showing the distribution of wave initiation periods and wave velocities of the mutant IIIb21 at the aggregation stage of development. The waves are concentric and the mutants do not fire successive wave from the same centre. Consequently, the cells do not aggregate. (A) Concentric darkfield wave initiated in random locations. (B) Time-space plot showing the disappearance of the waves after 6 hours. (C,D) Comparison of wave velocity and period between IIIb21 and N272.

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