Title:
Molecular mechanism for neuronal individuality

Takeshi Yagi
Graduate School for Frontier Biosciences, Osaka University

Abstract:
The brain contains an enormous, but finite, number of neurons. The ability of this limited number of neurons to produce nearly limitless neural information over a lifetime is typically explained by combinatorial explosion; that is, by the exponential amplification of each neuron’s contribution through its incorporation into “cell assemblies” and neural networks. In development, each neuron expresses diverse cellular recognition molecules that permit the formation of the appropriate neural cell assemblies to elicit various brain functions. The mechanism for generating neural networks must involve molecular codes that give neurons individuality and allow them to recognize one another and join appropriate networks. The extensive molecular diversity of cell-surface proteins on neurons is likely to contribute to their individual identities. The clustered protocadherin (Pcdh) is a large subfamily within the diverse cadherin superfamily. The Pcdh genes are encoded in tandem by three gene clusters, and are present in all known vertebrate genomes. The set of Pcdh genes is expressed in a stochastic and combinatorial manner in each neuron. Here I present neuronal individuality based on the stochastic and combinatorial expression ofPcdh isoforms in individual neurons. Their molecular and biological features suggest that the diverse Pcdh molecules provide the molecular code by which neuronal individuality and cell assembly permit the combinatorial explosion of networks that supports enormous processing capability and plasticity of the brain.

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