Fig. 4. Timing of extension by CaP axons on the common pathway in control and antisense sema3a1 morphants. Three steps of axonal development, initial projection (A), extension along the common pathway (B) and pausing at the horizontal myoseptum (C), were assayed in living nrp1a:gfp transgenic embryos. (A) Time of axonal projection was comparable between control morphants/uninjected embryos and antisense morphants (F-test and t-test). Time when the axon was initially projected occurred within a window ±1 hour from the time measured from mAb Znp1-labeled CaPs (see Fig. 1C) in uninjected embryos/control morphants and antisense morphants. (B) The duration for extension by CaP axons along the common pathway from the cell body to the horizontal myoseptum was generally similar, but more dispersed in antisense morphants than in controls (P<0.003, F-test). Asterisks indicate three cases in which the time required to reach the horizontal myoseptum was significant longer compared with control CaPs. (C) A significant number of CaP axons failed to stop and pause at the horizontal myoseptum in antisense morphants (P<0.0002, Fisher's exact probability test). White dots in the upper part of each panel indicate CaP axons in control sema3a1 morphants and black dots indicate axons in uninjected embryos.