Evolution and diversity of synaptic transmission: Roles for voltage-gated calcium channels and PDZ-domain mediated scaffolding

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Synaptic transmission lies at the very core of nervous system function. In my research, I seek to understand how synaptic structure and function differs between distantly-related animals, and how the synapse evolved. Indeed, gaining a deep, phylogenetic understanding of the synapse and its evolution will help broaden our understanding of this complex and dynamic cell-cell signaling apparatus, basic science that can help guide future efforts to treat diseases of the nervous system involving deficiencies in synaptic transmission. Interestingly, recent genome sequencing studies have revealed that early-diverging “primitive” animals that lack nervous systems, such as the small marine invertebrate Trichoplax adhaerens, harbour a majority of genes required for synaptic transmission. Also interesting is that the most early-diverging animals known, ctenophores such as Mnemiopsis leidyi, bear nervous systems and synaptic transmission that appears to have evolved independently. My broad background in molecular biology, electrophysiology and genomics/transcriptomics uniquely positions me and my personnel to exploit these animals for gaining insights into synaptic diversity and evolution. Over this 5 year NSERC grant, my team and I will explore these subjects by completing the following objectives: 1) Objective 1: Comparative structure-function and physiology studies of voltage-gated calcium (Cav) channels, which play crucial roles in synaptic transmission and are implicated in numerous human diseases. We will compare human and other invertebrate Cav channels with highly divergent orthologues/homologues from Trichoplax and Mnemiopsis, to gain general insights into conserved and defining biophysical features of each Cav channel type, and to determine whether the roles that Cav channels play in Trichoplax and Mnemiopsis resemble known synaptic functions of Cav channels in other well-studied organisms. 2) Objective 2: High-throughput proteomics to evaluate if key protein-protein interactions that underlie synaptic scaffolding, including the association of Cav channels with pre-synaptic neurotransmitter secretion, are absent in Trichoplax, in accordance with its lack of synapses, and to define the molecular architecture of the independently evolved and poorly understood synapses of Mnemiopsis. 3) Objective 3: The absence of synapses in Trichoplax, and the independently evolved ones of Mnemiopsis, should be reflected by absences/differences in key synaptic protein-protein interactions. We will use information gathered from objectives 1 and 2 to inform in vivo rescue experiments in the fruit fly Drosophila, using wildtype vs. “in vitro evolved” synaptic genes from Trichoplax and Mnemiopsis with introduced protein interaction domains, to test hypotheses about key molecular innovations that might have facilitated synapse evolution.