Figure 8

Fig. 8. Relative contribution of plus and minus end pathways to MT turnover. The diagram shows dependence of the half time for MT turnover on the distance from the cell center for each of the plus and minus end pathways, considered separately. For the plus end pathway, the turnover half time rapidly increases with increasing distance from the margin. In contrast, for the minus end pathway the half time does not depend on the distance from the margin but is determined by the frequency of release of MTs from the centrosome. The relative impact of the two pathways depends on the position within the cell. For a model melanophore of radius, 70 µm, average length of MTs, 50 µm, diffusion coefficient, D = 7.5 µm2/min, drift coefficient, vd = 0.25 µm/min (corresponds to release frequency of 0.7% min-1 and minus end shortening speed of 10 µm/min), the point of equivalent impact of the two pathways is approximately 43 µm from the cell margin. The diagram indicates that turnover of the peripheral domains of MTs is determined primarily by the plus end pathway whereas turnover of the root domains of MTs near the centrosome is determined primarily by the minus end pathway.