Developmental Interactions in the Dipteran Salivary Gland

The dipteran salivary gland is considered from several pointsof view. Its development in relation to chromosomal puffingsuggests that this tissue, perhaps more than any other, representsmajor evidence for differential activation and inactivationof genes during development. From studies of this tissue wehave gained further insight into concepts of tissue and stagespecificity. Factors regulating puffing during development includethe natural hormone, ecdysone, as well as a host of other substancesand environmental factors which affect cellular metabolism. Breakdown of the salivary gland seems ultimately to be controlledby chromsomal puffing. In this case one of the first detectablebiochemical alterations in the gland is the accumulation ofthe enzyme DNase. This enzyme may play a role in digesting thechromosomes themselves, thus accomplishing regulated self-destructionof the cell's synthetic machinery.