Precision and plasticity during Drosophila neuromuscular development

Abstract

Synaptogenesis can be analyzed in a simple array of motoneurons and muscle fibers of the embryos and larvae of Drosophila melanogaster. Each abdominal hemisegment contains a stereotypic array of 30 muscle fibers. During middle to late embryogenesis, motoneurons exit the central nervous system to make precise synaptic connections with specific muscle fibers. Target recognition has been tested using both genetic and microsurgical manipulations, which indicate that motoneurons actively recognize specific muscle fibers. The molecular basis of target recognition has been examined by screens for mutations that disrupt both guidance events and correct innervation. In addition, the motoneurons and muscle fibers both express an array of putative cell adhesion molecules whose functions may contribute to normal connectivity. Postsynaptic specializations, including glutamate receptor distribution, depend on innervation and neural activity. The neuromuscular system is not "hardwired," as motoneurons are capable of altering both their branch arborizations and connectivity in response to local denervation and blockade of synaptic function. Collectively, these studies show that the Drosophila motor innervation is a powerful model system for testing at the cellular and molecular level the mechanisms that govern synaptic development.

Development and plasticity of the Drosophila larval neuromuscular junction

“…In early embryonic development, motor neurons form ectopic contacts on nontarget muscles. These misplaced synapses are then eliminated in late‐stage embryos by an activity‐dependent process . An additional form of refinement occurs after embryogenesis at the level of synaptic gain control once the motor neurons have reached their appropriate muscle targets.…”

Blockade of the central generator of locomotor rhythm by noncompetitive NMDA receptor antagonists in Drosophila larvae

“…L-Glutamate has long been known to be involved in excitatory neurotransmission at the neuromuscular junction (NMJ) in arthropods (Gerschenfeld, 1973) and Drosophila (Jan and Jan, 1976b;Johansen et al, 1989). The physiology and development of the glutamatergic NMJ in Drosophila late embryos and larvae have been extensively characterized (McLarnon and Quastel, 1988;Delgado et al, 1989;Broadie and Bate, 1993;Keshishian et al, 1993;Keshishian et al, 1994;Kidokoro and Nishikawa, 1994). In the ventral ganglia (segments A1-A7), about 34 motoneurons per hemisegment were identified using an antibody to glutamate and retrograde labeling methods (Sink and Whitington, 1991;Landgraf et al, 1997) that innervate in a stereotyped pattern 30 muscles per hemisegment (Keshishian et al, 1994;Bate et al, 1999).…”

Motor nerve terminals on abdominal muscles in larval flesh flies, Sarcophaga bullata: Comparisons with Drosophila

“…The major ventral longitudinal muscles (muscles 6 and 7) are innervated by two motor axons differing in morphology and physiology (Jan and Jan, 1976a;Atwood et al, 1993;Kurdyak et al, 1994). The motor axon designated as Axon 2 (derived from motor neuron 6/7b: Keshishian et al, 1993Keshishian et al, , 1994 has smaller terminal varicosities with fewer synapses and dense bodies, fewer mitochondria, and a less elaborate subsynaptic reticulum than the accompanying axon (Axon 1, derived from motor neuron RP3). The two types of terminal associated with these two axons have been designated Type Is (''small'') and Type Ib (''big''), respectively (Atwood et al, 1993).…”