THE ROLE OF SHN-1 IN AXON TERMINATION

Abstract

Previous studies have identified many genes associated with autism spectrum disorder (ASD), but the molecular mechanisms associated with these genes remain poorly understood. Our research focuses on shn-1, an ortholog of the ASD-associated gene SHANK3, and how it interacts with other ASD-associated genes to regulate PLM axon termination in C. elegans. In chapter two, we show that while shn-1 loss-of-function does not lead to PLM axon termination defects on its own, the shn-1 mutation interacts with a variety of mutations in other genes to disrupt PLM axon termination. We first demonstrate that loss of shn-1 enhances the axon termination defects caused by the egl-19 gain-of-function mutation. We then provide evidence that shn-1 interacts with components of the RPM-1 pathway, one of the main pathways responsible for axon termination and synaptogenesis in the mechanosensory neurons of C. elegans. We show that shn-1 functions in parallel to glo-4 and glo-1, but not fsn-1, to promote PLM axon termination. Furthermore, we find that shn-1 interacts with slo-1, the C. elegans ortholog of human KCNMA1, and slo-2, the C. elegans ortholog of human KCNT1 and KCNT2, to promote PLM axon termination. Our results also suggest that slo-1 promotes axon termination by limiting voltage-gated calcium channel function. Through colocalization experiments, we provide evidence that GLO-1 localizes to late endosomes throughout the PLM axon and SHN-1 localizes to late endosomes only in the proximal PLM axon. Lastly, we demonstrate that the egl-19 gain-of-function mutation decreases the number of late endosomes in the proximal PLM axon.