Meeting Abstract
Hypotheses of origins and evolution of neurons and synapses are controversial, mostly due to the lack of comparative data. Here using advanced sequencing technologies and an unbiased approach we investigated the distribution of canonical ‘synaptic and neuronal machinery’ among basal metazoans and lophotrochozoans. Results of this analysis lead us to propose an alternative hypothesis that not only have neurons evolved in parallel, but also synapses. Novel techniques combining quantitative immunoblotting and mass spectrometry, electron microscopy and super-resolution fluorescence microscopy, recently employed to identify proteins and generate a 3D space of an average synapse, were used as a starting point in our comparative analysis. The presence and distribution of over 200 presumed presynaptic and postsynaptic proteins were characterized across phyla. Interestingly, Trichoplax, an organism with no neurons had more orthologs of bilaterian synapse/neuron related genes than ctenophores (e.g. Pleurobrachia) with well-defined neuronal and synaptic organization. Surprisingly, we found that most of these ‘synaptic’ genes are being expressed before neurons ever appear in development suggesting that this secretory machinery is commonly recruited for a diversity of non-neuronal functions and cannot be used as neuronal markers per se. We further expanded our list to include all known components controlling excitability and reception. As a result, we developed a model to reconstruct parallel evolution of synapses in distinct cellular lineages.
