The chemical synapse is an asymmetric structure consisting of presynaptic and postsynaptic terminals in direct apposition to each other. Synapses function to mediate the transmission of signals between neurons and their targets. The formation of synapses is a tightly regulated process requiring the interaction of many genes and molecular pathways. I am interested in identifying genes and signaling pathways that are required for proper synapse formation.
Using the GABAergic neuromuscular junctions of C. elegans as a model system, I have identified fsn-1 (F-box synaptic protein), a gene required for the control of synaptic growth. fsn-1 mutants exhibit a synaptic defect characterized by both synaptic over differentiation and under differentiation. FSN-1 is an F-box protein with a SPRY (SPla and RYanodine receptor) domain that functions cell-autonomously in neurons to regulate synaptic growth. I have shown that it functions in an E3 ubiquitin ligase-like complex with the RING-H2 finger protein RPM-1 (Regulator of presynaptic morphology), SKR-1 and Cullin. The composition of this complex is similar to SCF (Skp1, Cullin, F-box) E3 ubiquitin ligases. We hypothesize that this complex controls synapse formation by down regulating synapse promoting factors through an ubiquitin mediated process.
We have identified two receptor tyrosine kinases that genetically interact with fsn-1, the Anaplastic Lymphoma Kinase homolog SCD-2 (Suppressor of Constitutive Dauer) and the C. elegans insulin receptor DAF-2 (abnormal DAuer Formation). Loss of function mutations in scd-2 or daf-2 partially suppress the synaptic differentiation defects of fsn-1 mutants, suggesting that they participate in signaling pathways whose activities are normally inhibited by FSN-1 during synapse formation. Unlike FSN-1 that functions in GABAergic neurons, I found that SCD-2 and DAF-2 have cell non-autonomous functions at GABAergic neuromuscular junctions. SCD-2 is required in the nervous system in the RID interneuron where it could modulate synapse formation through ligands present on the motoneuron cell surface. The DAF-2/insulin pathway functions in postsynaptic muscle cells to regulate FSN-1 dependent presynaptic growth likely through a retrograde or feedback mechanism. I propose a model where FSN-1 regulates synapse formation by attenuating signals that converge upon the presynaptic terminal to stimulate or inhibit synaptic growth.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/11225 |
| Date | 31 July 2008 |
| Creators | Liao, Edward Hai Dhow |
| Contributors | Zhen, Mei |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
| Format | 8838039 bytes, application/pdf |
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