Fig. 2. Predicted rearrangements and movement kinetics in a field of hypothetical `cells' uniformly expressing MIB (see Movie 1 at http://dev.biologists.org/supplemental/). (A-D) Time course of rearrangements of the cells (spheres) undergoing convergence and extension. The field halves in width and doubles in length over the period of A to D; the intermediate stages (B,C) represent the field at one- and two-thirds of completion of the round of MIB. The area and thickness of the field does not change, and MIB is constant with respect to cell position and time. (E,F) Close-up views near the field center (^*) at the beginning (E) and end (F) of the same sequence. See the text for description of the local cellular reorganizations. (G) The cellular flows resulting from intercalations occurring between times B and C. The most rapidly moving cells (longest lines) are those most distant from the center. (H,I) Linear gradients relate ML velocity with ML position (H, convergence) and AP velocity with AP position (I, extension). The red arrows indicate the directions and rates of cell movement (ML movement is inwards, AP movement is outwards) such that the gradient slopes are opposite in sign. (J,K) The field width decreases exponentially (J), and the field length increases exponentially (K). Cell position at a given time t can be predicted by the relationships x_t=x₀e^k_ct and y_t=y₀e^k_et.

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