In the multiheaded strain (mh-1) of Hydra magnipapillata the ectodermal epithelial cells are responsible for the formation of additional heads and the endodermal epithelial cells for the reduced ability to regenerate a foot.
Hydra consist of three self-renewing cell lineages: the ectodermal epithelial, endodermal epithelial and interstitial cell lineages. The role of these cell lineages in head formation and foot regeneration in Hydra magnipapillata was studied by comparing the multiheaded strain mh-1 with the wild-type. Adult polyps of this strain show a reduced ability to regenerate a foot in the apical body half several days before additional heads are formed there. Cell lineage chimeras were produced, and it was found that in mh-1, the ectodermal epithelial cell lineage is responsible for the formation of additional heads, whereas the endodermal epithelial cell lineage and, to a lesser extent, the derivatives of the interstitial cell lineage, are responsible for the reduced ability of foot regeneration.