A Necessary Role for PKC-2 and TPA-1 in Olfactory Memory and Synaptic AMPAR Trafficking in Caenorhabditis elegans

Protein kinase C (PKC) functions are essential for synaptic plasticity, learning, and memory. However, the roles of specific members of the PKC family in synaptic function, learning, and memory are poorly understood. Here, we investigated the role of individual PKC homologs for synaptic plasticity in Caenorhabditis elegans and found a differential role for pkc-2 and tpa-1, but not pkc-1 and pkc-3 in associative olfactory learning and memory. More specifically we show that PKC-2 is essential for associative learning and TPA-1 for short-term associative memory (STAM). Using endogenous labeling and cell-specific rescues, we show that TPA-1 and PKC-2 are required in AVA for their functions. Previous studies demonstrated that olfactory learning and memory in C. elegans are tied to proper synaptic content and trafficking of AMPA-type ionotropic glutamate receptor homolog GLR-1 in the AVA command interneurons. Therefore, we quantified synaptic content, transport, and delivery of GLR-1 in AVA and showed that loss of pkc-2 and tpa-1 leads to decreased transport and delivery but only a subtle decrease in GLR-1 levels at synapses. AVA-specific expression of both PKC-2 and TPA-1 rescued these defects. Finally, genetic epistasis showed that PKC-2 and TPA-1 likely act in the same pathway to control GLR-1 transport and delivery, while regulating different aspects of olfactory learning and STAM. Thus, our data tie together cell-specific functions of 2 PKCs to neuronal and behavioral outcomes in C. elegans, enabling comparative approaches to understand the evolutionarily conserved role of PKC in synaptic plasticity, learning, and memory.