Head-activator and the neuroectodermal differentiation of P19 mouse embryonal carcinoma cells.

P19 embryonal carcinoma cells differentiate into neuroectodermal derivates upon aggregation and treatment with retinoic acid (RA). Such RA-induced P19 cells, concomitant with neuronal differentiation, produce the neuropeptide head activator (HA) and release HA into the culture medium. The amount of HA produced by such differentiating P19 cells is more than 100-fold higher than that of uninduced P19 cells. RA-induced P19 cells respond to HA treatment with a two-fold increase in total number of neuronally differentiating P19 progeny. As early response to HA, an increase in intracellular calcium concentration is observed.