Pattern Formation in Asymmetrical and Symmetrical Imaginal Discs ofDrosophila melanogaster

Abstract

The polar coordinate model for pattern regulation in epimorphic fields (French et al., 1976) predicts that bilaterally symmetrical fields will show different kinds of regulative behavior depending on the direction of the cut. These predictions have been tested using the male genital disc of Drosophila melanogaster. First, a detailed fate map was established by examining the fate of disc fragments subjected to immediate metamorphosis in host larvae. Then the regulative abilities of various fragments were examined by culturing them for seven days in adult abdomens, before transfer to larvae for metamorphosis. When the disc was bisected by a vertical cut (parallel to the line of symmetry) then fragments smaller than half of the disc underwent duplication with some simultaneous regeneration, while fragments larger than half of the disc underwent regeneration. If the disc was bisected by a bilaterally symmetrical cut across the line of symmetry, wound healing resulted in the confrontation of cells from similar positions on the right and left sides of the fragment, and no regulation occurred. With the exception of regeneration occurring during duplication of small lateral fragments, these results are as predicted by the polar coordinate model.