The hormonal control of salivary gland secretion in Drosophila melanogaster: Studies in vitro

The larval salivary gland of Drosophila melanogaster synthesises a complex secretion, known as ‘glue’. which is secreted at puparium formation and then cements the puparium to its substrate. This secretion is made during the third larval instar and is stored in the gland cells as large granules. A few hours before puparium formation it is secreted into the gland's lumen by exocytosis. This process is induced by ecdysone and can be studied in vitro. Secretion is initiated about 3.5 hr after exposure of glands to ecdysone and is complete by 8 hr. The effects of varying the ecdysone concentration, of inhibitors of RNA or protein synthesis, and of withdrawing the hormone at various times after initial exposure on the process of secretion have been studied. We conclude that some event(s) occurring during the first 3 hr exposure to ecdysone is necessary to initiate secretion of the glue into the gland lumen. The possible relationship between this event(s) and the ecdysone induced changes in gene activity (puffs) which occur in the salivary glands at the same time is discussed.