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Fig. 8. Schematic of the neural crest cell streams and different forms of contact
between two neural crest cells, which lead to directional movement. (A)
Tracking a lead cell. Two neural crest cells (1 and 2) within a migratory
stream may have short filopodia around the circumference of the cell. The
contact is initiated when one of the cells (1) extends a filopodium in the
direction of the other cell (2) and makes contact. The filopodium from the
trailing cell then tracks the position (back end) of the downstream cell as
the rest of the trailing cell body follows. (B) Contact, retraction, forward
movement. Two migrating neural crest cells within a stream may come into
contact with each other when a filopodium of the trailing cell (1) extends and
contacts a downstream cell (2). The filopodium retracts and then the trailing
cell moves forward to a new position (1') near the location of the contact as
the downstream cell (2) moves away. (C) Tethered contact. Two neighboring
cells (1 and 2) may begin to move apart from each other. As the cells move
apart, or, as shown here, one of the cells (2) moves away, the cells maintain
a filopodial connection. As the length of the filopodium grows, it breaks at
an arbitrary point, leaving fragments in the extracellular matrix. The
trailing cell (1) may stay in its location or move in the direction of the
former neighboring cell (2). (D) Our previous view of neural crest cells
within migratory streams (for example, the stream forming adjacent to r4)
based on DiI cell labeling revealing round neural crest cells with short
filopodia. (E) Our working model of neural crest cells within migratory
streams based on imaging of cells with fusion protein expressing constructs
targeted to the plasma membrane and cytoskeletal elements to reveal multiple
cell-cell connections with short and long filopodia.
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