Maintenance of Boundaries between Developing Organs in Insects

Abstract

CLONAL analysis of developing insect embryos has shown that the origin of an organ (such as the leg imaginai disk of Drosophila¹) can be traced to a small group of primordial cells. This subset of cells, which is not a clone, becomes partitioned from the cells around it. Subsequently, cells within it divide and generate a coherent body of leg cells to which the surrounding cells probably never contribute. Although clonal analysis cannot reveal whether the cells are individually determined as leg cells (such a conclusion conventionally depending on transplantation experiments) it is clear that an early expression of the “legness” of the group is the formation of a permanent growth boundary between it and its neighbours.