Figure 1

Axon morphology of sensory neurons in wild-type Drosophila embryo. (a) Diagram of the pathways and substrates followed by sensory axons in the Drosophila embryo. Only a subset of the sensory neurons in each of the dorsal (blue), lateral (green), ventral' and ventral clusters (purple) has been represented. The relative positions of the lch5-5, dbd and v'ch1 neurons are shown, together with their schematic axonal projections in the CNS. Major axon tracts in the CNS, the anterior commissure (AC), the posterior commissure (PC) and longitudinal connectives (LC) are shaded light grey. Motor axons (MNs, orange) originate within the CNS (dashed lines) and project into the periphery within the segmental (SN) or intersegmental (ISN) nerves. Tracheal branches, including the dorsal trunk (DT), transverse commissure (TC) and spiracular branch (SB) are shown in grey. (b-d) Central projections of lch5-5 (b), v'ch1 (c; two neurons in adjacent hemisegments filled) and dbd (d) axons in early stage 17 wild-type embryos, revealed by juxtacellular DiI labeling. All preparations were photo-converted, yielding a brown diaminobenzidine reaction product in the sensory axon and imaged with DIC optics to reveal axon tracts in the CNS. The bar in each diagram shows the medial-lateral extent of the LC, which is approximately 10 μm wide at this stage. lch5-5 and v'ch1 both project anteriorly in the middle of the LC, while the dbd axon has a bifurcating terminal projection located at the medial edge of the LC.