The Drosophila neuromuscular junction is a beautiful and yet powerful model synapse for in vivo studies of development, physiology, cell biology and plasticity. This illustration by Saskia Van Vactor shows a field of ventral longitudinal body wall muscles in red, as if stained with phalloidin to highlight filamentous actin, the main protein building block of muscle. Against this background, several branches of intersegmental nerve extend across its targets to elaborate a stereotyped pattern of excitatory presynaptic boutons, shown in green as if stained for a neuronal marker to highlight the motor axon terminals. Presynaptic boutons contain release sites for glutamate, a neurotransmitter, called active zones. Release of neurotransmitters at active zones allows the presynaptic neuron to communicate with the postsynaptic neuron, ultimately leading to contraction of the desired muscle. The boutons depicted here represent the third instar stage of larval development, which occurs before the larva progresses into a pupa to begin metamorphosis into an adult fly.
Contributed by David Van Vactor, PhD.