Compartmental restrictions and blastema formation during pattern regulation in Drosophila imaginal leg discs

Clonal analysis was used to study the regulative behavior of cells in Drosophila imaginal leg discs. Such studies performed during normal development of the leg have revealed a clonal restriction known as the anterior-posterior compartment boundary (E. Steiner, 1976, Wilhelm Roux Arch. Entwicklungsmech. Organismen180, 9–30). When we tested a regulating fragment that contained cells from both anterior and posterior compartments this clonal restriction was maintained in the original fragment. However, in material produced by regulation, clones of cells induced at the time of fragmentation differentiated anterior and posterior structures. Clonal restriction was observed in the regulated material when clones were induced during in vivo culture. We deduced the position of the dividing cells that contributed to regulative growth from the positions of the clones within the differentiated disc tissue. We observed that initially the majority of dividing cells originated from and were localized to an area close to a region of the wound, resembling a blastema. As regulation proceeded, a localization of dividing cells was maintained. However, the blastema changed its position from the original material into the regulated part.