Left-right asymmetry in the nervous system:: The Caenorhabditis elegans model

Although the overall architecture of the nervous system of most animals shows a large degree of bilateral symmetry, there are striking patterns of left-right (L-R) asymmetry in the brains of some species. Some structures show L-R-specific differences in size, whereas others show asymmetrical patterns of gene expression and have diversified at the functional level. The nematode Caenorhabditis elegans offers a unique opportunity to address how symmetrical neuronal assemblies deviate to create functional lateralizations. Here, we provide a detailed cellular and molecular perspective on L-R asymmetry in the nervous system of C. elegans. We also give an overview of symmetry and asymmetry in the nervous systems of other organisms. We will relate these observations to general concepts of the mechanistic and phylogenetic origin of laterality.