Analysis of Postsynaptic Morphology During Neuromuscular Synaptogenesis in Drosophila Melanogaster

Abstract

The successful construction of a functional neuronetwork requires that precise connections be made between vast numbers of individual cells. Pre- and postsynaptic cells use a variety of molecular cues to recognize one another. Changes in presynaptic cell morphology during encounters with these environmental cues has been well-documented, while postsynaptic cells have traditionally been regarded as passive targets. I have examined the morphology of postsynaptic cells (muscles) in the Drosophila embryonic neuromuscular system during the period of axon pathfinding and synaptic targeting. Embryonic Drosophila muscle cells extend numerous actin-based microprocesses (myopodia) during these stages of development. While the initial extension of myopodia appears random, their spatial distribution shifts progressively until most myopodia have retracted, leaving a "cluster" of stabilized myopodia on the muscle surface. The clustered myopodia intermingle extensively with motoneuron growth cones. Myopodia clustering, but not their initial appearance, is dependent on the presence of motoneurons. When the rate of synaptic targeting at an identified muscle is lowered, myopodia clustering at the same muscle is also observed less frequently. This suggests that myopodia behavior results from the specific molecular interactions between synaptic partners. The data indicate a dynamic role for postsynaptic cells during the events of synaptic target recognition.