The human nervous system consists of thousands of cell types with distinct patterns of gene expression and functions. One general way to diversify neuronal subtypes is to specify different identities and functions of individual cell types through stochastic neuronal fate choices. However, the mechanisms that generate stochastic cellular diversity in the nervous system are only partly understood. The C. elegans left and right AWC olfactory neurons specify asymmetric subtypes through a stochastic, coordinated cell signaling event, which allows the animal to discriminate between different odors. We have identified that this stochastic cell fate choice is regulated through a transient, embryonic NSY-5/innexin gap junction neural network that antagonizes a downstream Ca2+-regulated pathway to establish long-lasting asymmetric AWC identities. The overall goal of this proposal is to use this system as a model to identify the molecular mechanisms by which gap junction-mediated transient signaling events coordinate long- term stochastic neuronal fate choice. In this grant proposal, we will test the hypothesis that intercellular Ca2+ signaling mediates communication between AWCs and non-AWCs in the nsy-5 neural network to coordinate stochastic AWC subtype choice (Aim 1), investigate the role of Ca2+-activated SLO K+ channels and newly identified MOK (modifier of K+ channel) molecules in AWC subtype choice (Aim 2), and identify the mechanisms that regulate the synaptic localization of the TIR-1/Sarm1 Ca2+ signaling scaffold protein for AWC subtype choice (Aim 3). The establishment of long-lasting neuronal subtypes by a transient gap junction-dependent cell network provides an innovative, robust, and simple system to elucidate the molecular mechanisms underlying the biological function of gap junction-mediated intercellular signaling in development in vivo, which is not readily feasible in vertebrates. As mutations in the human homologs of the genes we study are associated with a variety of developmental disorders, understanding normal functions of these genes in mechanistic detail will inform novel therapeutic strategies.