Fig. 3. (A) MT treadmilling: Most MTs ( 80%) in the discoid fragment (radius 20 µm) with a pigment aggregate at the center have their minus ends in the aggregate, and plus ends at the periphery. MTs are in this state for 40 minutes. About 10% of the MTs have their minus ends in the aggregate with their plus ends growing toward the fragment boundary. The plus ends of another 10% of MTs are stalled at the boundary, while the corresponding minus ends shorten. MTs are in each of these states for 5 minutes. Rare MTs (1%) treadmill. (B) The evolution of MTs throughout aggregation and aster formation (stimulus at 4 time units). (Top) Computed total length of MT polymer before and after stimulation of dynein motors. The total length of MT polymer increases by a factor of 3 during aggregation and MT aster formation (from before stimulus until steady state). (Bottom) Percentages of MTs, with minus ends anchored in the pigment aggregate and plus ends at the periphery (solid), with minus ends anchored and plus ends growing (dashed), with minus ends shortening and plus ends at the periphery (dot-dashed), and treadmilling (dotted), agree well with the corresponding observed percentages.