UC San Diego

This dissertation explores the roles of endoplasmic reticulum (ER) – plasma membrane (PM) contact site proteins in Caenorhabditis elegans physiology. I first investigated the roles of ER-PM contact site proteins in axon regeneration after injury by examining mutants affecting conserved ER-PM contact site components. While most ER-PM components are individually dispensable, the sole C. elegans junctophilin jph-1 is required for axon regeneration. Additionally, the partial deletion allele jph-1(ok2823) enhances regenerative axon fusion. I further studied junctophilin using jph-1(0) null alleles generated by CRISPR-Cas9. By in vivo confocal imaging of tagged proteins, I found that junctophilin is expressed in muscles and neurons. In muscles, JPH-1 co-localizes with calcium channels EGL-19 and UNC-68 at ER-PM contact sites. I used tissue-specific rescue constructs to demonstrate that junctophilin is required in the pharyngeal and body wall muscles for feeding and locomotion, respectively. In neurons, JPH-1 co-localizes with the neuronal ER-PM contact site protein ESYT-2. Using pharmacological assays, I showed that both jph-1 and esyt-2 modulate neurotransmission at the neuromuscular junction. Interestingly, jph-1 and esyt-2 mutants displayed mutual suppression in their responses to the drug aldicarb, suggesting that they have antagonistic roles in neuromuscular synaptic transmission. Lastly, I investigated the interactions between jph-1 and calcium channels by generating double mutants, which revealed that junctophilin functions in overlapping pathways with ER- and PM-localized calcium channels for animal health and development. My data demonstrates that ER-PM contact site proteins play critical roles in diverse tissue types and support tissue-specific functions.