Netrins are a small family of secreted proteins that function as chemotropic cues directing cell and axon migration during neural development. They are bifunctional molecules attracting and repelling different classes of axons. DCC (deleted in colorectal cancer) is a transmembrane receptor for netrin-1 implicated in mediating both responses. The intracellular mechanisms mediating the response of an axon to netrin-1 are currently unclear. Previous studies indicated that extracellular guidance cues induce the neuronal growth cone to advance, retract, or turn by regulating the actin cytoskeleton within the growth cone. The Rho family GTPases, in particular, RhoA, Rac1 and Cdc42, are well-described regulators of actin reorganization in non-neuronal cells, and there is now compelling evidence implicating a role for them as signaling components within the neuronal growth cone. / In the first part of this thesis, we have demonstrated that the Rho GTPases are required for embryonic spinal commissural axon outgrowth induced by netrin-1. Using NIE-115 neuroblastoma cells we found that both Rac1 and Cdc42 activities are required for DCC-induced neurite outgrowth. In Swiss 3T3 fibroblasts, DCC was found to trigger actin reorganization through activation of Rac1. These results implicate the small GTPases as important signaling components in the molecular mechanisms underlying DCC. / In the second part, we found that DCC interacts constitutively with the adaptor protein Nck in commissural neurons. Moreover, dominant negative Nck-1 inhibits the ability of DCC to induce neurite outgrowth in NIE-115 cells and to activate Rac1 in fibroblasts in response to netrin-1. These studies provide evidence for an important role of Nck-1 in a novel signaling pathway from an extracellular guidance cue to changes in the actin-based cytoskeleton responsible for axonal guidance. / In the last part, we found that disruption of each of the PxxP motifs in the cytoplasmic domain of DCC is not able to block the interaction of DCC with Nck-1, suggesting that more than one PxxP motifs or non-PxxP sequences may mediate the interaction of DCC with Nck-1. / Taken together, the data in this thesis contribute to our understanding of the intracellular mechanisms mediating the response of an axon to netrin-1 during neural development.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.84281 |
| Date | January 2003 |
| Creators | Li, Xiaodong, 1966- |
| Contributors | Lamarche-Vane, Nathalie (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Anatomy and Cell Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002030990, proquestno: AAINQ98304, Theses scanned by UMI/ProQuest. |
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