The origin and evolution of synapses

Key Points The molecular composition of the synapse has recently been proved to be useful for studying the evolution of the brain. Synapse proteomics data sets, such as those of the postsynaptic density (PSD) and associated protein complexes when combined with comparative genomics have provided unprecedented insights into the evolution of synapses. The PSD that is found in organisms with nervous systems has evolved from an ancient protosynaptic core that exists in unicellular organisms and multicellular organisms without nervous systems. Comparisons of vertebrate PSD and synaptogenesis genes with orthologues from sponges and cnidarians open an avenue for speculating as to what may have contributed to the origin of the first synapse. Comparative proteomics has shown that vertebrate excitatory synapses have evolved to be significantly more complex than invertebrates. Tracing the phylogeny of the molecular components of synapses, Ryan and Grant speculate on the core components of the last common ancestor of all synapses and posit that the diversification of upstream signalling components contributed to increased signalling complexity later in evolution. Understanding the evolutionary origins of behaviour is a central aim in the study of biology and may lead to insights into human disorders. Synaptic transmission is observed in a wide range of invertebrate and vertebrate organisms and underlies their behaviour. Proteomic studies of the molecular components of the highly complex mammalian postsynaptic machinery point to an ancestral molecular machinery in unicellular organisms — the protosynapse — that existed before the evolution of metazoans and neurons, and hence challenges existing views on the origins of the brain. The phylogeny of the molecular components of the synapse provides a new model for studying synapse diversity and complexity, and their implications for brain evolution. See more Darwin-related content in our Nature Publishing Group collection .