G protein-mediated inhibition of neuronal migration requires calcium influx

Neuronal migration is an essential feature of the developing nervous system, but the intracellular signaling mechanisms that regulate this process are poorly understood. During the formation of the enteric nervous system (ENS) in the moth Manduca sexta, the migration of an identified set of neurons (the EP cells) is regulated in part by the heterotrimeric guanyl- nucleotide binding protein (G protein) G(oα). Using an in vivo culture preparation for developing embryos that allows direct access to the ENS, we have shown that EP cell migration is similarly regulated by intracellular Ca²⁺; treatments that increased intracellular Ca²⁺ inhibited the migratory process, whereas buffering intracellular Ca²⁺ induced aberrant migration onto inappropriate pathways. Imaging the spontaneous changes in intracellular Ca²⁺ within individual EP cells showed that actively migrating neurons exhibited only small fluctuations in intracellular Ca²⁺. In contrast, neurons that had reached the end of migration displayed large, transient Ca²⁺ spikes. Similar Ca²⁺ spikes were induced in the EP cells by G protein stimulation, an effect that was reversed by removal of external Ca²⁺. Stimulation of G(o) in individual EP cells (by injection of either activated G(oα) subunits or mastoparan) also inhibited migration in a Ca²⁺-dependent manner. These results suggest that the regulation of neuronal migration by G proteins involves a Ca²⁺-dependent process requiring Ca²⁺ influx.