Figure 6.

The Deviation of ERK Activity from the Average Regulates Motility in the CD4-SP Subset

(A) The relationship between the absolute value of the FRET/CFP ratio and the speed (μm/min) in each subset of thymocytes. The gray dashed line represents the average value of ERK activity in DP thymocytes. Data represent the analysis of samples from three individual mice: n = 37 tracks (DP); n = 21 tracks (CD4-SP); n = 17 tracks (CD8-SP). See also Table S1. The relationship between pairs of variables was analyzed using the Pearson correlation analysis.

(B) Representative time-lapse analysis of two CD4-SP cells. ERK activity (black line) and the speed (μm/min) (black dashed line) are shown on the line plot (top) and the deviation of ERK activity (Z_ERK) and that of speed (Z_SPEED) are shown on the bar plot (bottom). The color of the bar represents the relative deviation of the ERK activity from the average, and the length of the bar represents the relative deviation of the speed.

(C) The relationship between Z_ERK and Z_SPEED in each subset of thymocytes analyzed in (A). The relationship between pairs of variables was analyzed using the Pearson correlation analysis.

(D) Schematic model of the relationship between ERK activity dynamics and thymocyte motility. At the single-cell level, CD4-SP cells respond to the deviation from the set point for ERK activity, whereas other subsets respond to the strength of ERK activity. Thus, CD4-SP cells are more sensitive to the physiological range of ERK activity dynamics than the other subsets.