Fig. 4. Timelapse imaging of a wild-type gata2::GFP growth cones crossing the ventral forebrain and forming the POC. (A-D) Selected images of single time points from one 3 minute interval timelapse sequence showing a typical leading growth cone (pink arrows in A and B) from the vrc cluster navigating towards and past the midline, where it is joined by the growth cone from the opposite cluster (not visible in B because it is masked by fluorescence from more dorsal sections). Subsequently, later growth cones (blue arrows in B-D) also cross the midline and grow across the POC. The midline is indicated by a broken line; time is shown in minutes. Scale bar: 10 µm. (E) A typical distance from midline along the POC trajectory axon plot. Axon length at each time point is plotted as distance from midline along the POC trajectory. The leading growth cone is plotted in pink and a later (follower) axon is plotted in blue corresponding to the growth cones marked with pink and arrows in A-D. The axons shown here start from the right vrc (top of the plot) and cross over to the left vrc (bottom of the plot) as indicated in the schematic to the left of the graph. The two axons advance across the midline with different rates as indicated by the slope of each line (see pink and blue boxed regions). On the right, two microscope configurations show how the imaging was performed. The timelapse shown in A-D was obtained in the inverted configuration.