Figure 3. Cells exhibit pathfinding behavior on EV trails.

A. Left: Fluorescence maximum intensity images taken from a time lapse recording of Dictyostelium discoideum aca⁻ cells expressing ACA-YFP moving towards an aggregate of cells. Cell outline traces depicting the relative position of 4 cells is presented as a time evolution of outlines from lighter to darker colors for each cell. The secreted ACA-YFP-containing vesicles are depicted in gray. Right: Plot showing the correlation between the distance of a cell to its nearest vesicle and the angle θ between the cell direction of motion and the direction vector to the nearest vesicle. In this context, the closer a cell is to a vesicle, the higher the chemotactic response of the cells, which is measured by smaller angles of deviation. Reproduced under the term of the Creative Commons CC BY-NC-SA 4.0 license (Kriebel et al., 2018). Copyright © 2018, Rockefeller University Press. B. Left: Fluorescence time series images of HT1080 fibrosarcoma cells co-expressing pHluo_M153R-CD63 (exosome label) and mCherry-CAAX (plasma membrane label), showing leader-follower cell migration behavior in 3D collagen gels. Exosome trails (arrowheads) deposited behind migrating leader cells promote directional migration of follower cells (arrows). Right: Scatter plot with median and quartile range showing pathfinding index quantitated by the cosine value of the angle θ between the cell direction of motion and the nearest exosome trail. Note that migration towards exosome trails yields positive cosine θ values, with perfect migration along an exosome trail yielding a cosine θ = 1, whereas migration away from exosome trails yields negative cosine θ values, with a maximum possible value of −1. Reproduced under the term of the Creative Commons CC BY 4.0 license (Sung et al., 2020). Copyright © 2020, Springer Nature.