Mutations affecting axonal growth and guidance of motor neurons and mechanosensory neurons in the nematode Caenorhabditis elegans.

In the nematode Caenorhabditis elegans, each of its 302 individual neurons is an identified neuron. We have screened more than 100 mutations affecting locomotion in C. elegans immunocytochemically, using monoclonal antibodies that recognize specific subsets of neurons. Mutations in 25 genes affect the axonal outgrowth and guidance of a set of 6 mechanosensory receptor neurons (ALML, ALMR, AVM, PVM, PLML and PLMR). Similarly, mutations in 14 genes alter the axonal growth and process placement of two classes of inhibitory motor neurons (DD and VD). Most of these genes affect both embryonic and postembryonic development of the C. elegans nervous system, and have variable expressivity. Our results suggest that different neuron types are specified by a combination of genes that are activated in different cell types. Molecular characterization of such genes could lead to the identification of molecules critical in axonal outgrowth and guidance in higher organisms.