Analysis of the autonomy of imaginal disc defects in a small-disc mutant of Drosophila melanogaster

Abstract

Lethal mutations which cause imaginal disc abnormalities in Drosophila melanogaster identify genes whose function is necessary for normal disc development, and these mutant genes may be used as probes of the role of their wild-type alleles in normal development. It is crucial to the interpretation of the disc phenotype of such mutants to know which abnormalities are autonomous (caused by expression of the mutant gene in imaginal cells) and which are nonautonomous (indirectly caused, for example, by expression of the mutant gene in larval cells). We chose for study l(3)c21R (3-67.8), a late-larval lethal mutation with a complex phenotype, to test the adequacy of available techniques for assessing autonomy. We employed surgical and genetic techniques to determine the imaginal cell autonomy of the defects in cell viability, growth, and differentiation in c21R discs. The imaginal cell viability defect is nonautonomous. The disc growth and differentiation defects are autonomous; however, in genetic mosaics these two autonomous defects are separable. These results show that c21R belongs to the class of mutations which affect both larval and imaginal cells. In combination, the available methods were adequate to resolve the issue of autonomy in this complex case. However, in isolation several of the methods could have led to incomplete or misleading interpretations. This emphasizes that to analyze any developmental mutant it is necessary to examine the issue of autonomy from several points of view.