Fig. 5. POC axon dynamics with respect to the midline. Quantitative analysis of axon growth rates reveals a difference in axon behavior around the midline not readily apparent from direct observation of timelapse experiments. (A,B) Representative plots of distance from the midline along the POC trajectory versus time for leader (A) and follower (B) axons. Leader axons spend longer time within ±10µm of midline (broken black line in A-C), while the growth of later axons does not slow down in this region. (C) Average behavior of leader (n=16) and follower (n=24) axons at the midline. Leader and follower axon plots were centered on the timepoint when each axon crossed the midline. The average plot shows a more than twofold difference between the time leader and follower axons stay at the midline. Individual plots of all axons from the left vrc were reflected around the x-axis. (D) Average growth rates±s.e.m. for leader (pink) and follower (blue) axons with respect to the midline and outside midline region. Leading axons grow significantly more slowly at the midline compared with their average growth rate away from midline and compared with follower axons at the midline (P<0.001, Student's t-test corrected for multiple comparison).

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