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Figure 7. N-Cadherin Is Required for CIL(A–J) Collision assays between control (A–E) and NCD2-treated NC cells (F–J). Velocity (D–I) and acceleration (I–J) vectors for control (D and E) and NCD2-treated cells (I–J). Note the clear change in direction of migration upon collision in control cells (p < 0.005, n = 10) is lost in NCD2-treated cells (n = 10).(K–O) Invasion assays between control NC cells explants ([K and L], n = 36) and NCD2-treated explants (M and N, n = 47). Control explants do not invade each other (L and O), whereas N-cadherin inhibition allows NC cells to invade each other (O).(P–R) Model for Xenopus NC cells collective chemotaxis. The color gradient in the cytoplasm represents the levels and distribution of Rac1 (red) and RhoA (blue, after Carmona-Fontaine et al., 2008; Matthews et al., 2008) activities. The different thicknesses and directions of the arrows indicate the relative stabilities and orientation of protrusions, respectively. N-cadherin is represented as a green bar. Nuclei are shown as gray circles and the external gradient of Sdf1 as shades of green. (P) NC cells clusters exhibit radial symmetry where all outer cells are polarized with protrusions toward the free edge and inner cells are not polarized. When exposed to a gradient of Sdf1, protrusions at the front are further stabilized and the initial radial organization is broken leading to directional migration. (Q) If cell interactions are prevented (N-cadherin inhibition, cell dissociation), Rac1 distribution no longer matches cell-cell interactions and global levels are lowered thus inducing protrusions instability, loss of coordination among the cells, and the loss of directional migration. (R) Representation of the NC cells migration in vivo where NC cells are maintained on migratory routes by inhibitory cues (shades of purple) and attracted ventrally by chemotaxis to Sdf1. Protrusions can be seen at the border of the group and in between the cells only when gaps are generated. The NC cells population gets looser as migration proceeds ventrally and progressively breaks away as single cells. Error bars show standard deviation. See also Movie S10. Image published in: Theveneau E et al. (2010) © 2010 ELL & Excerpta Medica. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution license Larger Image Printer Friendly View

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