Development of oriented motion in regenerating hydra cell aggregates

Hydra can regenerate its complete adult form from aggregates of dissociated cells. Aggregates of hydra cells are made by dissociating hydra tissue int o a suspension of cells and then re-aggregating the cells by centrifugation . An aggregate formed in this way is a disorganized mass of individual cell s and does not possess any regeneration polarity. In this study, we analyze d the development of motion in cell aggregates during the regeneration stag es in which a new body axis was being established. Two perpendicular diamet ers (widths) of binalized projection images of an aggregate were continuous ly measured in order to detect changes in form, i.e., motion. Between 30-35 hr, when the aggregates still appeared spherical, slight motion along a di stinct axis was detected along with a simple expansion in the size of the m ass. After that, quick twitches along a distinct axis, also seen in intact hydra, began to develop. The axis of the motion corresponded to the future body axis of the regenerated animal, and the future head-end of the body ax is showed a larger degree motion than the foot-end. Motion in the aggregate s made of cells from hydroxyurea-treated animals in which the stem cells of nerve cells has been eliminated, suggested that the stow one-directional m otion observed was due to the epithelial cells, while the twitches were con trolled by nerve cells. These results show that the development of motion c ould provide a useful index to the recovery of organization in the cell agg regates.