Synthesis and secretion of mucoprotein glue in the salivary gland ofDrosophila melanogaster

Abstract

The processes of involved in the accumulation and secretion of adhesive mucoprotein ("glue") in third instar larvae ofD. melanogaster are described. The RNA templates for glue protein seem to be synthesized within 72-85 hours after oviposition, because treatment of larvae at this age with actinomycin D inhibits the accumulation of the secretion. The secretory granules appear in the salivary gland cells of 90 hour larvae and are discharged into the gland lumen of 118 hour larvae.Secretion of mucoprotein material by salivary gland cells into the gland lumen depends on high ecdysone concentration. Mucoproteins are synthesized, but not discharged, by these cells in ecdysone-deficient homozygousl ₍₂₎ gl larvae as well as in normal larvae isolated from ecdysone by ligatures or transplantation of the salivary glands into adult abdomens. Ecdysterone injection into normal 100 hour larvae, 7 dayl ₍₂₎ gl larvae or into adult imaginal abdomens into which salivary glands have previously been stimulates mucoprotein secretion into the gland lumen.Determination of total protein content in the salivary gland by Lowry's method has shown that "glue" proteins make up 21-32% of the total protein content in the gland.The glands of thel ₍₃₎ tl mutant do not give a PAS-positive reaction, nor are the granules of the secretion observed under the phase contrast microscope.