The Complex Secretions of the Salivary Glands of Drosophila melanogaster, A Model System
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
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The Complex Secretions of the Salivary Glands of Drosophila melanogaster, A Model System Robert Farkaš
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.
R. Farkaš (*) Institute of Experimental Endocrinology, Slovak Academy of Sciences, Dúbravská cesta 9, 845 05, Slovakia e-mail: [email protected] © Springer International Publishing Switzerland 2016 E. Cohen, B. Moussian (eds.), Extracellular Composite Matrices in Arthropods, DOI 10.1007/978-3-319-40740-1_15
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Introduction
The larval salivary glands (SGs) of the fruit fly Drosophila are a single layer of unbranched, tubular epithelial tissue of ectodermal origin. The SG is the largest secretory organ in Drosophila, and is composed of just two principal cell types: duct cells and secretory cells. During embryogenesis, the future larval salivary glands arise from a contiguous primordia on the ventral ectodermal surface of parasegment 2 (Skaer 1993; Andrew et al. 1994; Campos-Ortega and Hartenstein 1997; Henderson and Andrew 2000; Bradley et al. 2001; Myat 2005; Vining et al. 2005; Kerman et al. 2006). Once specified, salivary gland cells do not undergo further rounds of cell division or cell death, with each lobe having approximately 130–145 large polarized epithelial cells specialized for secretion (Poulson 1937; Makino 1938; Sonnenblick 1940, 1950; Skaer 1993; Campos-Ortega and Hartenstein 1997). The abs
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