Growth Cone Pathfinding and Neuromuscular Synaptogenesis in Drosophila Midline Mutants
Wolf, Brian David
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Permalink
https://hdl.handle.net/2142/86765
Description
Title
Growth Cone Pathfinding and Neuromuscular Synaptogenesis in Drosophila Midline Mutants
Author(s)
Wolf, Brian David
Issue Date
2000
Doctoral Committee Chair(s)
Chiba, Akira
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Language
eng
Abstract
The development of the nervous system involves a complex series of events that establish the intricate and precise neural network. Using the genetically manipulable Drosophila embryo and high resolution single cell analysis, I examined the function of commissureless, netrin, roundabout, and frazzled during neural development. Analysis of the individual axon pathways of RP3, V, and RP2 in wildtype and commissureless and roundabout mutants investigated how abnormal midline decisions affect subsequent growth cone pathfinding. Results showed that despite abnormal decisions at the midline, subsequent pathways and synaptic targeting in all cases were the perfect mirror-images of those seen in wildtype. This suggests that a growth cones' particular molecular experience and decision at the midline does not affects its ability to respond normally to subsequently presented cues. Further examination of the aCC, RP3, and RP2 motoneurons revealed that the midline mutants commissureless, netrin, frazzled and roundabout disrupt dendritic growth cone guidance at the CNS midline. Specifically, frazzled and roundabout act cell autonomously to mediate dendritic attraction and repulsion, respectively, at the midline supported by mutant analysis, cell autonomous rescue of function and protein localization to dendritic growth cones. In addition to its expression and function at the CNS midline, commissureless is also initially expressed on all muscle surfaces and then endocytosed during the period of neuro-musclar contact. Motoneurons fail to initiated synaptogenesis in commissureless mutants and resupplying wildtype commissureless back to commissureless null muscles restores motoneuron synaptogenesis. Misexpression of a cytoplasmically truncated commissureless construct in muscles functions as a dominant negative by inhibiting internalization and synaptogenesis. My findings support a role for commissureless modifying the molecular profile of the muscle surface allowing motoneuron synaptogenesis initiation. My research demonstrates that Drosophila midline mutants function not only in axon guidance but also in dendritic growth cone guidance and synaptogenesis initiation.
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