Short- and long-term memory of moving amoeboid cells
Fig 8
Maintenance and adjustment of the polarity axis by pseudopods in the front.
a. angles between three pseudopods; a perfect inverse relationship implies that P1 and P3 are extended in a similar direction, irrespective of the direction of P2. The data were analyzed by linear and polynomial regression analysis, yielding y = -1.0027x, RSS = 4.07*105 and AICc1 = 4841 for linear regression with one parameter and y = 1.64*10−5*x3–1.0027x, RSS = 3.91*105 and AICc2 = 4832 for the polynomial fit with two parameters. The polynomial fit explains the data significantly better than the linear fit (P = 0.01). The quantity exp((AICc1 − AICc2)/2) = 90 indicates that the model with two parameters is 90 times as probable as the model with one parameter. The green area indicate the difference between the linear and polynomial fit, which reveals that P3 is not extended precisely in the direction of P1 if P2 is extended at a very large angle relative to P1; this difference (y = 1.64*10−5*x3) is indicated in panel c. Localization of active Rap1-GTP in a cell that extends a new pseudopod from the front at a large angle of 130 degrees to the left. The fluorescence intensity at the boundary is shown in panel d, showing that the midpoint of Rap1 activation changes by 22 degrees to the left. Panel e shows the change of midpoint of Rap activation as function of the change of pseudopod direction for 12 pseudopods as determined in panels c, d. the data points are mirror imaged; the red line shows the optimal polynomial fit with y = 0.89*10−5*x3. The results reveal that Rap1 is activated in the front half of the cell, and that this localization changes hardly thereby maintaining the direction of the polarity axis.