The Complex Secretions of the Salivary Glands of Drosophila melanogaster, A Model System

Abstract

The Drosophila salivary glands (SGs) are historically well known for their polytene chromosomes and became a tissue of choice to study sequential gene activation by the steroid hormone ecdysone. The widely accepted and most well documented function of the Drosophila salivary gland is the production of a secretory glue released during pupariation to fix the freshly formed puparia to a substrate. Besides fulfilling this function, which is tightly associated with the enormous production and exocytosis of a small group of secretory glycoproteins (Sgs proteins), the same SGs display also massive apocrine secretion 8–10 h after puparium formation (APF). A detailed analysis of the apocrine activity provided compelling evidence that this is non-vesicular transport and secretory mechanism which substantially differs from canonical exocytosis taking place 14–16 h prior to apocrine release. From the point of view of Drosophila fast development, this is significant time gap between two different cellular activities. This system offers a unique opportunity to dissect the molecular mechanistic aspects of the apocrine transport and secretory machinery using specific genetic tools available in the fruitfly. Although these obviously different cellular activities serve two very different purposes, in both cases the SG behaves as a distinct and also typical exocrine organ capable of two independent and separated functions, one in the late larva, the second in the late prepupa. A comparison of the secretory material and its properties from the exocytotic Sgs proteins and the apocrine secretion reveals the unexpected capabilities of this organ in reprogramming its function for two deeply different roles.