Anterograde trains are converted to retrograde trains while remaining on the same track. (A and B) IFT trafficking was analyzed in the GFP::IFT52-expressing cell line. The tip of the flagellum was bleached, and the arrival of new anterograde trains was monitored (see corresponding Video 10). For technical reasons, the bleaching event could not be recorded, and only the recovery phase can be presented. (A) Still images corresponding with the indicated times from Video 10. The thin green and magenta lines indicate the left and right sides of the axoneme, respectively. At 11 s, two anterograde trains were marked with a green (left side) or a magenta (right side) line, and the corresponding arrows indicate their direction. At 13 s, the left anterograde train converted to two retrograde ones that remained on the same left side of the flagellum. A second anterograde train arrived on the right side. At 14 s, the first left retrograde train left the field of view, and the second one progressed toward the base of the flagellum. The first anterograde train of the right side converted to a retrograde one that also remained on the right side. At 18 s, all retrograde trains on the left side were not in the field of view anymore as well as the first one on the right side. A new retrograde train was present on the right side and issued from the second anterograde train. Once again, conversion took place on the same side of the axoneme. (B) Kymograph analysis for the indicated left and right sides of the flagellum. The original kymograph is shown on the left of each panel, and the three annotated trains described above are marked in color.