Figure 2—figure supplement 2.

Our transplantation procedure leads to random variation in the number and position of sensor cells in host embryos. We therefore investigated whether clustering (i.e. variation in the number of nearby sensor cells) affects the behavior of each sensor. The data presented in this figure derive from the Mvg1 to MZoep sensor cell experiment of main text Figure 2B. (A) Definition of neighboring cells. For each sensor cell (center of dashed circle), sensor cells within a 30 ?m radius (area within dashed circle) are counted as neighbors. (B) Illustration of pSmad2 staining residual using main text Figure 2B. We define the pSmad2 staining residual for each sensor as the difference between its observed staining intensity and the expected intensity given its distance from the Nodal source. In this illustration, the residual for the highlighted sensor cell (large red point) is the vertical distance (arrow) to the sliding window average of all sensor cells (red curve). Host cell staining intensities are depicted as blue points. (C) Neighbor number does not influence pSmad2 staining residual. Scatter plot of the number of sensor cells within a 30 ?m radius against pSmad2 staining residual. Each point represents a sensor cell, and the figure pools sensors from 10 host embryos. The least-squares linear fit is plotted (red line, R2 = 0.003). If Nodal sensitivity increased or decreased with the number of nearby sensors, the plot would show an increasing or decreasing trend, respectively. (D) Sensor behavior is independent of total number of transplanted cells. The total number sensors transplanted into each MZoep host embryo is scattered against the average pSmad2 staining residual for all sensors in that embryo. The least-squares linear fit is plotted (red line, R2 = 0.009). If Nodal sensitivity increased or decreased with the total number of transplanted cells, the plot would show a clear positive or negative trend, respectively.