Typical features of embryonic neuromuscular junctions in Drosophila
Neuromuscular junctions of Drosophila embryos are potent models for work on synapse formation. They are easily accessible, can be monitored with single cell resolution, the involved muscles and motorneurons have been individually identified (>>> concept of identified neurons), and part of them is amenable to specific genetic manipulation. A) Drosophila muscles (green) represent single fibres which are named individually (black in white boxes) and innervated by reproducible nerve branches (blue). B) CNS and nerve pattern in a real specimen at late stage 17 stained with Drosophila N-CAM (Fas2; >>> spatial arrangement of motorneurons). C) Motorterminals have characteristic muscle-specific shapes: example shows the ventral muscle field (corresponding to red box in B) stained against presynaptic Synaptotagmin (Syt). D) Electron micrograph (EM) of single neuronal varicosity (N, blue; corresponding to red box in C) attached to the muscle (M, green) showing synaptic specialisations (arrow head and close up; >>> more on ultrastructure). E) Synaptic transmission at NMJs can be measured at different embryonic stages. Black arrow indicates anterior.

Sources: A) picture modified from Landgraf, M., Sánchez-Soriano, N., Technau, G. M., Urban, J. & Prokop, A. Charting the Drosophila neuropile: a strategy for the standardised characterisation of genetically amenable neurites. Dev. Biol. 260, 207–225 (2003); C,D) modified from Prokop, A. Integrating bits and pieces - synapse formation in Drosophila embryos. Cell Tissue Res. 297, 169-186 (1999); E) modified from Broadie, K. S. & Bate, M. Development of the embryonic neuromuscular synapse of Drosophila melanogaster. J. Neurosci. 13, 144-166 (1993).