Formation of New Organizing Regions by Cooperation of hedgehog, wingless, and dpp in Regeneration of the Insect Leg; a Verification of the Boundary Model

Summary Meinhardt [15] proposed the boundary model (BM) to explain pattern formation in developmental subfields. One of applications of his model was to explain formation of supernumerary legs after amputating a leg and reimplanting it onto a contralateral stump. The boundary model was cemented by Campbell and Tomlinson [6]. Their model (CTBM) postulates that key genes during leg development such as hedgehog (hh),wingless (wg), and decapentaplegic (dpp) are also involved in leg regeneration and that the formation of the proximodistal axis of a regenerating leg is triggered at a site where ventral wg-expressing cells abut dorsal dpp-expressing cells in the anteroposterior (AP) boundary. To verify this model, we experimentally examined whether the model would fit our results obtained during the leg regen-eration of a cricket Gryllus bimaculatus. Since the expression patterns of the three genes can be predicted in a regenerating leg by the model, we observed corresponding expression patterns in supernumerary legs formed when the distal part of an amputated leg was grafted onto the contralateral leg stump so as to reverse the AP polarity. Since our observations were essentially consistent with the C’l’BM. we concluded that we were able to verify the BM by our regeneration experiments.