Migrating interstitial cells differentiate into neurons in hydra.

Interstitial cell migration has been observed numerous times in grafted hydra, but the extent to which graft injuries might stimulate the migration of otherwise nonmotile cells was unknown. The present study describes the migration and differentiation of vital dye-labeled interstitial cells in intact, normal hydra. Interstitial cells, stained with a fluorescent vital dye, migrated away from a labeled patch of ectodermal cells and subsequently were found throughout the body column. Shortly thereafter, labeled neurons began to appear among the migrating cells. The number of migrating interstitial cells remained constant over 5 days, whereas the number of labeled neurons increased. Labeled interstitial cells and neurons accumulated primarily in the head and peduncle, as observed in previous studies of short-term migration patterns in grafted hydra. The present study shows that migration of interstitial cells occurs in normal nongrafted hydra and that the accumulation patterns parallel results from graft experiments. The population of migrating cells appears to be limited to neuron precursors.