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. 2019 Feb 4;8:e42692. doi: 10.7554/eLife.42692

Figure 1. Sequential defasciculation and branching of developing Drosophila adult leg motor neurons.

(A) Development of Drosophila adult leg motor neurons across six distinct time points during pupariation – Late L3 (96 hr AEL/0 hr APF), Early Pupa (10 hr APF), Mid Pupa (20 hr and 25 hr APF), Late Pupa (45 hr APF) and Adult (120 hr APF). Left Column: Schematic representation of Drosophila larval to adult stages denoting the locations of adult leg MN cell bodies and dendrites (green) in the CNS (gray) along with axons (green) targeting ipsilateral legs (T1 - forelegs, T2 - midlegs and T3 - hindlegs). Middle Column: Schematic representation of the developing T1 leg denoting the locations of muscle precursors (magenta) and leg MN axons (green). Locations of muscles within the four leg segments (Coxa, Trochanter, Femur and Tibia) are denoted from 20 hr APF onwards. Right Column: Leg MN axons in the developing T1 leg labeled by VGlut-QF >10XUAS-6XGFP (green) and stained for Mef2 (magenta) to label muscle precursors. Mature MNs and muscles in the Adult T1 leg are labeled using OK371-Gal4 > 20XUAS-6XGFP and Mef2-QF > 10XQUAS-6XmCherry respectively. (scale Bar: 50 μm) (B) Snapshots from a time-lapse series of developing LinA/15 leg MNs expressing myr::GFP at 25 hr APF (B); before extension) and 35 hr APF (B’); after extension) (see also Video 1). Arrows denote distinct axon bundles within the Ti-ltm-targeting bundle. Axon bundles are labeled according to muscle targeting – Ti-ltm: Tibia-long tendon muscle, Tadm: Tarsal depressor muscle, Talm: Tarsal levator muscle. (scale Bar: 50 μm) (C–E) Confocal images of LinA/15 Ti-ltm-targeting leg MN axons expressing myr::GFP (green) and muscles stained for Mef2 (magenta) at 25 hr APF (C–C’), 35 hr (D–D’) and 45 hr APF (E–E’). Arrows point to defasciculating tertiary bundles and arrowheads (E–E’) point to terminal axon branches. (scale Bar: 50 μm).

Figure 1.

Figure 1—figure supplement 1. Sequential defasciculation and branching of developing Drosophila adult leg motor neurons.

Figure 1—figure supplement 1.

(A, A’) Maximum projection confocal images of a T1 leg disc denoting the terminal position (white arrowhead) of LinA/15 leg MNs expressing myr::GFP (green; generated by lineage tracing) and all MNs labeled with VGlut-QF >10XQUAS-6XmCherry (red). Note that VGlut+ axons extend beyond the leg disc, while the LinA/15 MNs are within this same fascicle but stop in the middle of the leg disc (arrowhead). Muscle precursors in the leg disc are identified by Mef2 expression (blue). (B) Maximum projection confocal image of the glutamatergic axon bundle labeled with VGlut-QF >10XQUAS-6XGFP (red), comprising of adult leg and larval body wall MNs, passing through the T1 leg disc and innervating mature larval body wall muscles. Muscle precursors in the leg disc and mature body wall muscles are identified by Mef2 expression (blue). (scale bar: 50 μm). (C–E) Maximum projection confocal images of LinA/15 leg MNs expressing myr::GFP (green) targeting Tibia muscles, labeled by staining against Mef2 (magenta), at 45 hr APF (C) and leg MNs alone at 45 hr APF (C’), 60 hr APF (D) and in the adult (E). White arrows denote distinct axon bundles within the Ti-ltm-targeting bundle and colored arrowheads represent examples of secondary branches whose stereotyped morphologies are retained between 45–60 hr APF. (scale Bar: 50 μm).