Fig. 4. Persistent MT growth confirmed by long CLIP-170 tracks. GFP-CLIP-170 movement was analyzed by time-lapse microscopy. Images were acquired every 3 seconds. (A) Three next-nearest frames are shown, displaying radial organization and movement of CLIP-170 patches. Tips of four CLIP-170 patches are indicated over time by arrowheads. Numbers in the upper left corner indicate time in seconds; bar, 5 µm. Diagram shows 25 CLIP-170 tracks over a 90 second period of which four tracks (1-4) correspond to CLIP patches indicated by arrowheads on the images. Many tracks are long indicating continuous MT growth; radial pattern of tracks permits identification of the centrosome region (dashed circle) as the point from which the tracks originate. The centrosome is indicated as two dots in the diagram. (B) Histogram of the length distribution of CLIP-170 tracks. Mean length, 17.3±4.8 µm (n=78). (C) Histogram of length distribution of CLIP tracks normalized against the distance between the centrosome and plasma membrane. The histogram shows that the majority of MTs born at the centrosome grow persistently to 85% of the cell radius.