Figure 3

Four identified types of tip cell-ECM interaction behavior.

I: “protrusion-related push”. II: “retraction-related push”. III: “pull”. IV: “release”. The shown vector fields were the results of tracing the beads in a 3D space with the method of DVC in⁵². The 3D outlines of the sprout and nucleus of each EC involved, in cyan and dark red, respectively, were built with their boundary contours extracted at the different depths using the open-source MATLAB software Sliceomatic⁵⁷. The arrows were plotted using the MATLAB code provided by⁵⁸. The “pull” type behavior was linked to a radial movement of beads in neighboring regions of a protruding lamellipodium with their directions of movement pointing toward the lamellipodium from all directions. The “release” type was particularly associated with a retracting lamellipodium, the surrounding beads of which moved radially away from it. For the “protrusion-related push”, the beads that were located above and very close to a protruding lamellipodium moved along with the protrusion. For the “retraction-related push,” the beads at the back of a retracting lamellipodium were pushed away approximately in direction of the lamellipodial retraction.