Spontaneous calcium transients are required for neuronal differentiation of murine neural crest

We have shown that cultured mouse neural crest (NC) cells exhibit transient increases in intracellular calcium. Up to 50% of the cultured NC-derived cells exhibited calcium transients during the period of neuronal differentiation. As neurogenic activity declined, so did the percentage of active NC-derived cells and their calcium spiking frequency. The decrease in calcium transient activity correlated with a decreased sensitivity to thimerosal, which sensitizes inositol 1,4,5-triphosphate receptors. Thimerosal increased the frequency of oscillations in active NC-derived cells and induced them in a subpopulation of quiescent cells. As neurogenesis ended, NC-derived cells became nonresponsive to thimerosal. Using the expression of time-dependent neuronal traits, we determined that neurons exhibited spontaneous calcium transients as early as a neuronal phenotype could be detected and continued through the acquisition of caffeine sensitivity, soon after which calcium transient activity stopped. A subpopulation of nonneuronal NC-derived cells exhibited calcium transient activity within the same time frame as neurogenesis in culture. Exposing NC-derived cells to 20 mM Mg2+ blocked calcium transient activity and reduced neuronal number without affecting the survival of differentiated neurons. Using lineage-tracing analysis, we found that 50% of active NC-derived cells gave rise to clones containing neurons, while inactive cells did not. We hypothesize that calcium transient activity establishes a neuronal competence for undifferentiated NC cells. (C) 1999 Academic Press.