Abstract
Glia are integral participants in synaptic physiology, remodeling and maturation from blowflies to humans, yet how glial structure is coordinated with synaptic growth is unknown. To investigate the dynamics of glial development at the Drosophila larval neuromuscular junction (NMJ), we developed a live imaging system to establish the relationship between glia, neuronal boutons, and the muscle subsynaptic reticulum. Using this system we observed processes from two classes of peripheral glia present at the NMJ. Processes from the subperineurial glia formed a blood-nerve barrier around the axon proximal to the first bouton. Processes from the perineurial glial extended beyond the end of the blood-nerve barrier into the NMJ where they contacted synapses and extended across non-synaptic muscle. Growth of the glial processes was coordinated with NMJ growth and synaptic activity. Increasing synaptic size through elevated temperature or the highwire mutation increased the extent of glial processes at the NMJ and conversely blocking synaptic activity and size decreased the presence and size of glial processes. We found that elevated temperature was required during embryogenesis in order to increase glial expansion at the nmj. Therefore, in our live imaging system, glial processes at the NMJ are likely indirectly regulated by synaptic changes to ensure the coordinated growth of all components of the tripartite larval NMJ.
Highlights
Glia are integral parts of synapses in the CNS and PNS of most animals, and regulate many aspects of synaptic development and function
Of the three glial classes found in the peripheral nerve, we found glial processes from both the perineurial and subperineurial glia at the neuromuscular junction (NMJ)
Using the living imaging system developed to visualize all three components present at the neuromuscular junction, we tested the developmental regulation of glial processes in concert with synaptic expansion
Summary
Glia are integral parts of synapses in the CNS and PNS of most animals, and regulate many aspects of synaptic development and function. Coordination of glial growth and development with neuronal synapses is not well understood. The Drosophila larval NMJ grows dramatically, and motor synaptic strength adjusts to match muscle input resistance of the growing muscle cells [12,13]. Increased motor activity as in Shaker, ether-a-go-go (Sh, eag) mutants [14,15] and larvae reared at high temperatures (30uC) [16] results in increased motor neuron branching and bouton number. Disinhibition of motor neuron growth and synapse formation, as occurs in highwire mutations, results in hyper-expanded neuronal branches and less defined boutons. The conditions and mechanisms that control growth of the pre- and post-synaptic NMJ components have been extensively studied [19], but much less is know about what controls the presence and growth of glial processes to match synaptic growth
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