Structure and evolution of neuronal wiring receptors and ligands.

One of the fundamental properties of a neuronal circuit is the map of its connections. The cellular and developmental processes that allow for the growth of axons and dendrites, selection of synaptic targets, and formation of functional synapses use neuronal surface receptors and their interactions with other surface receptors, secreted ligands, and matrix molecules. Spatiotemporal regulation of the expression of these receptors and cues allows for specificity in the developmental pathways that wire stereotyped circuits. The families of molecules controlling axon guidance and synapse formation are generally conserved across animals, with some important exceptions, which have consequences for neuronal connectivity. Here, we summarize the distribution of such molecules across multiple taxa, with a focus on model organisms, evolutionary processes that led to the multitude of such molecules, and functional consequences for the diversification or loss of these receptors. Key Findings: An expanding number of cell surface receptors and their ligands are known to control and regulate axon guidance, synapse targeting, synapse formation and function.The evolution and expansion of these protein families may concur with the growth of complexity of nervous systems and organisms in metazoans.Evolutionary histories of these protein families give clues to their function in neuronal connectivity.While highly diverse molecules, the rise and expansion of these protein families are closely influenced by the evolutionary events and processes that accompanied the rise of metazoans, bilaterians and vertebrates [ABSTRACT FROM AUTHOR]