Figure 6.
Invasion of the tip is facilitated by directional cell movement, which is redirected during tip bifurcation. (A) Correlation of leading edge velocities of elongating branches with the average velocity of tip cell tracks (n = 9, four experiments). (B) Cell displacement vectors color-coded based on their angle (inferno LUT, black = 0/360°, yellow = 180°) to the displacement vector of the leading edge of the elongating branch (green). Parallel cell movement corresponds to angles closer to 0/360 degrees, while antiparallel movement correspond to angles closer to 180 degrees. In addition, Rose diagrams are shown to further illustrate left- and right-sided angles in the 360° range for tracks within the tip and duct. (C and D) From the aggregated data of nine different elongating branches (four experiments), we merged left- and right-sided angles to the range of 0–180 degrees (parallel movement = 0°, antiparallel movement = 180°) and show rose diagrams of the angles of tip cell displacement vectors (contained within the area where M/G2/S cells were visibly enriched; C) and duct cell displacement vectors (D) against the displacement vector of the leading edge as a reference (ntip = 600, nduct = 1,814). (E–G) Cell displacement vectors that were created before bifurcation (E), during tip widening (F), and after cleft formation (G), color-coded based on their angle (inferno LUT, black = 0/360°, yellow = 180°) to the reference vector (green) running from the center of the neck to the leading edge/future cleft (green arrow). To assess the degree of asymmetric cell movement, we also show rose diagrams that distinguish between left- and right-sided angles of the displacement vectors in the 360° range for tracks within the bifurcating tip (boundary defined based on curvature of the neck). (H–J) From the aggregated data of 10 different bifurcations (seven experiments), we merged left- and right-sided angles to the range of 0–180 degrees and show rose diagrams of the angles of tip cell displacement vectors relative to the reference vector, depending on whether they started and ended before bifurcation (n = 214; H), during tip widening (n = 475; I) and after the cleft first became visible (n = 2,214; J). (K) Examples of cell displacement vectors from different bifurcations during cleft formation, showing variable patterns of directional cell movement with rose diagrams to distinguish between left- and right-sided angles in the 360° range (inferno LUT, black = 0/360°, yellow = 180°) within the bifurcating tips (boundary defined based on neck curvature). Correlation between variables in A was assessed with the Pearson coefficient (R) and P value for the linear correlation given. Uniformity of angles was tested with the Rayleigh test and statistical significance between groups was assessed with the Watson's Two-Sample Test of Homogeneity; *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001.

Invasion of the tip is facilitated by directional cell movement, which is redirected during tip bifurcation. (A) Correlation of leading edge velocities of elongating branches with the average velocity of tip cell tracks (n = 9, four experiments). (B) Cell displacement vectors color-coded based on their angle (inferno LUT, black = 0/360°, yellow = 180°) to the displacement vector of the leading edge of the elongating branch (green). Parallel cell movement corresponds to angles closer to 0/360 degrees, while antiparallel movement correspond to angles closer to 180 degrees. In addition, Rose diagrams are shown to further illustrate left- and right-sided angles in the 360° range for tracks within the tip and duct. (C and D) From the aggregated data of nine different elongating branches (four experiments), we merged left- and right-sided angles to the range of 0–180 degrees (parallel movement = 0°, antiparallel movement = 180°) and show rose diagrams of the angles of tip cell displacement vectors (contained within the area where M/G2/S cells were visibly enriched; C) and duct cell displacement vectors (D) against the displacement vector of the leading edge as a reference (ntip = 600, nduct = 1,814). (E–G) Cell displacement vectors that were created before bifurcation (E), during tip widening (F), and after cleft formation (G), color-coded based on their angle (inferno LUT, black = 0/360°, yellow = 180°) to the reference vector (green) running from the center of the neck to the leading edge/future cleft (green arrow). To assess the degree of asymmetric cell movement, we also show rose diagrams that distinguish between left- and right-sided angles of the displacement vectors in the 360° range for tracks within the bifurcating tip (boundary defined based on curvature of the neck). (H–J) From the aggregated data of 10 different bifurcations (seven experiments), we merged left- and right-sided angles to the range of 0–180 degrees and show rose diagrams of the angles of tip cell displacement vectors relative to the reference vector, depending on whether they started and ended before bifurcation (n = 214; H), during tip widening (n = 475; I) and after the cleft first became visible (n = 2,214; J). (K) Examples of cell displacement vectors from different bifurcations during cleft formation, showing variable patterns of directional cell movement with rose diagrams to distinguish between left- and right-sided angles in the 360° range (inferno LUT, black = 0/360°, yellow = 180°) within the bifurcating tips (boundary defined based on neck curvature). Correlation between variables in A was assessed with the Pearson coefficient (R) and P value for the linear correlation given. Uniformity of angles was tested with the Rayleigh test and statistical significance between groups was assessed with the Watson's Two-Sample Test of Homogeneity; *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001.

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