Why do pupating insects lack an activity for the repair of uracil-containing DNA? One explanation involves apoptosis

Although uracil-DNA glycosylases were at one time considered to be ubiquitous in nature, this DNA repair activity is notably absent in Drosophila melanogaster and other pupating insects. On the other hand, a nuclease has been identified in Drosophila that is specific for uracil-containing DNA, but curiously the expression of this activity is restricted to late larval stages of development. Since the nuclease activity is only detected near the time of histolysation, we began questioning the possible role uracil might play in the events associated with the eventual DNA degradation that is involved in the metamorphotic process. The results of these studies have provided us with a molecular model for pupating insects that contains all the necessary elements to program cells for their ultimate death, and in so doing, shows why uracil-DNA glycosylases would be incompatible with our proposed pathway for apoptosis.