Sustainable Development Goals

Abstract/Objectives

KIF1A/UNC-104 is the major transporter of synaptic vesicles. Mutations in this molecular motor are linked to KIF1A-associated neurological disorders (KAND). UNC-104 binds only weakly to synaptic vesicles via its PH domain and we hypothesize that other interaction schemes exist. It is known that UNC-104 regulator SYD-2 interacts with UNC-10 and that UNC-10 itself interacts with RAB-3 bound to synaptic vesicles. RT-PCR and Western blot experiments expose genetic relationships between unc-10 and syd-2, but not between unc-10 and rab-3. Neither unc-10 nor rab-3 affects UNC-104 expression. However, co-immunoprecipitation and BiFC assays reveal functional interactions between UNC-104, SYD-2, UNC-10 and RAB-3. Though both SNB-1 and RAB-3 are actively transported by UNC-104, motility of RAB-3 is facilitated in the presence of SYD-2 and UNC-10. Deletion of UNC-104's PH domain did not affect UNC-104/RAB-3 colocalization, but significantly affected UNC-104/SNB-1 colocalization. Similarly, motility of RAB-3-labeled vesicles is only slightly altered when carrying a point mutation in the PH domain, whereas movement of SNB-1 is reduced. Western blots of purified synaptic vesicles reveal strong reduction of UNC-104 in rab-3/unc-10 double mutants. Our findings suggest that the UNC-10/SYD-2 complex acts as a novel linker to connect UNC-104 to RAB-3-containing vesicles contributing to the specificity of motor/cargo interactions.

Results/Contributions

KIF1A-associated neurological disorder (KAND) is a rare genetic condition caused by mutations in the KIF1A gene, which encodes for the major axonal transporter of synaptic vesicles. Mostly children are affected by this disorder and symptoms commonly include developmental delays, intellectual disability, hypotonia (low muscle tone) progressing to hypertonia (stiffness), spastic paraplegia, ataxia (coordination issues), and epilepsy. Severity depends on the mutation type and location, with some cases leading to life-threatening complications. There is currently no cure. Dr. Wagner’s (王歐力教授) lab believes that understanding the underlying molecular mechanisms how this transporter is regulated will lead to the development of novel drugs to delay or cure KAND disease. 

KIF1A is termed UNC-104 in C. elegans and due to the its high homology, this model organism provides an excellent platform to study KAND disease. Dr. Oliver Wagner’s lab has published a dozen papers on the regulation of UNC-104 unraveling deep insights how this synaptic vesicle transporter is controlled on the molecular level. For example, the lab found that SYD-2 (liprin-α) is an adaptor protein that controls speed regulation of UNC-104 as well as acting as a scaffold for this motor along the lengthy neurons. Another protein PTP-3 (LAR) regulates phosphorylation of SYD-2 depending on its intramolecular folding. The lab also identified a protein LIN-2 (CASK) that is responsible for UNC-104’s long-range travels. Moreover, it was found that UNC-104 transports tau protein and mutations in tau affect the motility of this motor. Neurofilaments running in parallel to microtubules seem to promote long motor runs as well. 

Critically, UNC-104 interacts with synaptic vesicles only weakly via its PH (pleckstrin homology) domain. Therefore, the lab wanted to know whether perhaps other, more specific and stronger interactions between motor and synaptic vesicle exist. Using a large set of molecular biology techniques, the lab identified that UNC-104 specifically interacts with synaptic vesicles that bind RAB-3. Here, the motor employs a novel linker composed of two proteins UNC-10 (Rims1) and SYD-2. Interestingly, this interaction seems highly specific such as the transport of SNB-1 (Synaptobrevin). 


Keywords

Liprin-α(SYD-2), RIMS1(UNC-10), RAB3A(RAB-3), VAMP2(SNB-1), KIF1A(UNC-104), kinesin-3, C. elegans, molecular motors, axonal transport, synaptic vesicles

References

1. https://www.sciencedirect.com/science/article/pii/S0969996124003681

《Neurobiology of Disease》UNC-10/SYD-2 links kinesin-3 to RAB-3-containing vesicles in the absence of the motor's PH domain.

Contact Information

王歐力教授
owagner@life.nthu.edu.tw