Mutational Dissection of Imaginal Disc Development inDrosophila melanogaster

Abstract

The imaginal discs are groups of proliferating cells that are present in larvae of Drosophila melanogaster but which are not essential for larval functions. During metamorphosis these discs evaginate and differentiate giving rise to the external adult structures. We have identified genes which are essential for normal imaginal disc development by isolating lethal mutants with imaginal disc abnormalities. These mutants have been classified according to the kinds of abnormalities which they express and whether they are expressed in all of the discs, some of the discs, or only in a single disc pair. Of 66 mutants only 5 cannot be placed in a single phenotypic class. Most of the mutants (64%) affect all of the discs. Among these are two groups (discless and small-disc) which block the proliferative phase of development that normally occurs during larval life. Complementation analysis of those two groups of mutants indicates that a large number of genes can give rise to mutations causing either of these phenotypes. Detailed analyses of five of the small-disc mutants suggest that this phenotype can result not only from changes in imaginal disc specific functions but also from changes in functions common to larval and imaginal cells and even in functions which don't occur in imaginal disc cells. At the same time in development that many genes required for all imaginal cells are functioning, some genes not required by all of the discs are also functioning. One of these has been identified by a heat-sensitive mutation which causes a wide variety of defects. Using heat pulses we have shown that each abnormality characteristic of the mutant has a discrete temperature sensitive period during the larval stage.