MT dynamics in fibroblast cells.
(A) Distribution of EB1 labeled microtubule tips (spots) in a fibroblast cell. The inset shows a zoomed part of the cell margin. (B) The fraction nf of active plus ends versus d, the relative position of MT tip between the cell interior and margin. The solid line indicates the best fit to an exponential growth with k = 4.36 ± 0.37. The imaging frequency is 1 frame/s and the total observation time is 850 s. (C) The number of rescue Nr and catastrophe Nc events (per 100 growing tips) versus d. The dashed and dotted lines denote exponential fits with constants 9.06 ± 0.66 and 6.81 ± 1.61, respectively. (D) Frequency histogram of the excursion length of polymerization (i.e. the run length in the growth phase) in the cell interior (d < 0.8, left) and near the cell margin (d > 0.8, right). (E) Temporal evolution of the position of a few typical plus-end tips that reach the cell margin. The dashed lines are obtained from the three-parameter fit, as explained in the text. (F) The growth velocity vg versus d. (G) Frequency histogram of the growth velocity in the cell interior (left) and near the cell margin (right). The inset shows the corresponding mean values (P ≤ 0.01, t test). (H) Scattered data points showing the excursion time of polymerization near the cell margin, τm, versus the growth velocity, vg. The solid line indicates the best linear fit.