Fig. 3. Time-lapse observation of YFP-labeled olfactory axons in living embryos. Dynamic axon behaviors in representative ast/+;omp:yfp/+ (A-E) and ast/ast;omp:yfp/+ (F-J) embryos are shown. YFP expression under the control of the OMP promoter is observed in unipolar neurons (closed arrowheads in A,F), as well as in OSNs (open arrowheads in A,F). In the ast homozygote, several axons misroute ventromedially soon after exiting the olfactory placode at 1.5 dpf (short arrows in G). These misrouted axons form two fascicles at 2 dpf (short arrows in H), and further extend posteriorly to reach the diencephalon at 3 dpf (short arrows in I,J). A single aberrant fascicle that directly misprojects to the diencephalon is marked by the long arrows in G-J. Note that the YFP-labeled lateral glomeruli observed in the ast heterozygote (thick arrows in D) are not present in the homozygote (I). A-D,F-I, frontal views; E,J, dorsal views. Scale bar: 100 µm.