Positional information around the segments of the cockroach leg

Abstract

Epidermal cells from different circumferential positions around the femur of Blabera craniifer can interact to form an intercalary regenerate consisting of that section of the circumference normally separating graft and host positions, by the shorter route. This results is extended to other leg segments; the tibia and coxa (TT and CC Grafts). Grafting strips of integument from the tibia (TF Grafts) or the coxa (CF Grafts) to a corresponding position on the host femur results in simple healing. Grafting to a non-corresponding position leads to intercalation of the shorter intermediate arc of circumference, composed partly of graft-segment and partly of host-segment structures. These results show that that same continuous sequence of positional values is distributed around the circumferences of the coxa, femur and tibia. Cellular interactions along the edges of strip-grafts obey the Shortest Intercalation Rule. At the ends of strip-grafts intercalation usually restores continuity of positional values where possible but, when a complete circumference is generated, a supernumerary distal regenerate is usually formed. This is in general agreement with the Complete Circle Rule and the exceptions are discussed. In intercalary regeneration following the intersegmental strip-grafts, the host femur cells seem unable to intercalate beyond two positions (posterior/internal and posterior/external). These lineage restrictions operating during regeneration indicate that the cockroach leg, like the Drosophila leg disc, may consist of an anterior and a (smaller) posterior 'compartment'.