Study of a kinesin adaptor in axonal transport and synapse formation

Study of a kinesin adaptor in axonal transport and synapse formation

Tahere Kalantary Dehaghi

Doctoral thesis

Date of Examination: 2018-06-27

Date of issue: 2019-02-25

Advisor: Chua, John Dr.

Referee: Chua, John Dr.

Referee: Klopfenstein, Dieter Dr.

Referee: Jakobs, Stefan Prof. Dr.

Persistent Address: http://hdl.handle.net/11858/00-1735-0000-002E-E5AB-C

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Abstract

English

To form a synaptic terminal, various components have to be targeted to specific sites in the axon. Presynaptic proteins are synthesized in the cell soma, packaged in vesicular cargos and transported by the motor complexes traveling along microtubules. During synapse development and maturation, the intracellular transport of proteins is highly regulated by mechanisms governing the interactions and movement of motor proteins. Additional specificity and regulation is provided by interaction of motor proteins with their cargos through adaptor and scaffolding proteins. Previous studies have shown that FEZ1 acts as an adaptor for kinesin-1 and its binding to the motor is regulated by serine-58 phosphorylation. FEZ1/kinesin-1 complex partakes in presynapse formation by transporting syntaxin and Munc18 in the axon. Identification of numerous synaptic vesicle and active zone proteins in the FEZ1/kinesin-1 immunoisolated vesicles suggested the association and transport of these components with this complex. Although functional studies in Caenorhabditis elegans showed synaptic disorganization, the relevance of mammalian FEZ1 in neurons have not yet been investigated. In this study, the mobility of FEZ1 and its phosphomutants were characterized in mammalian neurons. Furthermore, the role of FEZ1-mediated transport in formation of presynaptic and postsynaptic specializations was investigated by ablating the expression of FEZ1 using CRISPR/cas9 knockdown system. The data in this study show that mobility of neuronal FEZ1 is a result of precise modulation of its binding to kinesin-1 by serine-58 phosphorylation. This study also provides evidence for FEZ1 role in transport of active zone components and synaptic vesicle precursors, albeit in distinct mechanisms. Additionally, FEZ1 impacts neuronal development by regulating dendritic branching in young neurons, and dendritic spine formation during later stages.

Keywords: Axonal transport; FEZ1; kinesin; motor protein; synaptogenesis