Positional information and pattern formation in Hydra. Dynamics of regions away from the boundary

The dynamics of regions away from the head-end boundary have been investigated by a variety of assays, and the changes appear to be slow. If, for example, a head end is grafted onto a peduncle to give H/56F, region 5 does not become a region 1 with 72 h. Such results support a gradient type model, and exclude a head end inducing a region 1 in the tissue adjacent to it. The changes can be interpreted if the positional value were effectively slowly diffusible: about 10 times more slowly than the positional signal. The results also have implications for studies on polarity reversal.