A head signal influences apical migration of interstitial cells in Hydra vulgaris

Although interstitial cells of hydra can migrate either apically or basally along the body column, there is a distinct bias toward apical cell accumulation. This apical bias could be produced by a local vectorial property of the tissue or it may be controlled by a more global property, such as a signal from the apical head region. The migration behavior of BrdU-labeled interstitial cells was examined in several types of grafts to distinguish between these two general types of migration control. Grafting BrdU-labeled midgastric region tissue into a host in either the normal or the reverse orientation had no effect on the apical bias, indicating that a local vectorial cue was probably not guiding cells apically. In grafts with heads or with feet at both ends of the body column, there was no directional bias in migration if the labeled tissue was equidistant from both ends. In the two-headed grafts, if the labeled tissue was closer to one end, there was a bias in the direction of the closer head. The results suggest that a graded signal emanating from the head creates the apical bias and may attract cells via chemotaxis. The apical bias is enhanced in decapitated animals regenerating a head, indicating that the attracting signal is present and is possibly stronger in regenerating heads. The signal for cell migration may be involved in a patterning process underlying head regeneration.