An ultrastructural and histochemical developmental study of Drosophila auraria salivary gland cells during the third-instar period

Abstract

Early in the third-instar stage of Drosophila auraria, the salivary gland cells produce small secretory granules of low electron density which empty their flocculent contents into the lumen of the gland. At that stage, the Golgi complexes consist of vesiculated, round cisternae which, as middle third instar is approached, change to their classical appearance. Cytoplasmic protrusions, intramitochondrial granules, and close contacts of mitochondria with lipid droplets are observed during the early developmental stages. At about the middle of the third instar the glue secretory granules start being produced. These secretory granules contain a granular material (where small amounts of vicinal glycol and sulfated groups of complex carbohydrates have been detected) of medium electron density. The glue secretory granules can be classified according to their electron density into two populations. Before exocytosis large amounts of glycogen particles are observed, providing some of the energy needed during the final step of exocytosis. Two different types of ribonucleoprotein particles in puffing sites of the chromosomes are observed. Of these, the larger ones consist of a core surrounded by smaller particles; we suspect that they may be produced in the Balbiani rings observed in the polytene chromosomes of this species. Nuclear blebs and oval bodies are common, particularly during the late developmental stages. The functional significance of these findings during development is discussed.

Rearrangement of the tubulin and actin cytoskeleton during programmed cell death in Drosophila salivary glands

“…The changes included an increase in the density of the microtubular network and dissolution of the regular arrangement of actin filament structures along the basal membrane. This is consistent with the findings of earlier ultrastructural studies that in L1 the gland cells undergo major restructuring as they switch from secretion of saliva to intense production of the mucoprotein glue (Harrod andKastritsis, 1972, von Gaudecker andSchmale, 1974;Thomopoulos et al, 1989;Riparbelli et al, 1993). It has been suggested (Riparbelli et al, 1993) that the microtubular network provides mechanical support of the gland epithelium rather than being directly involved in the secretion process.…”

“…Microtubules mediate transport of membraneous compartments during secretion (Schroer and Sheetz, 1991) and abundant microtubules are present in salivary glands of Drosophila larvae (Riparbelli et al, 1993). Although various aspects of the intracellular morphology of Drosophila salivary glands during development have been extensively studied in the past (Poels et al, 1971;Harrod and Kastritsis, 1972;von Gaudecker, 1974;Thomopoulos et al, 1989Thomopoulos et al, , 1992Riparbelli et al, 1993), remarkably little is known about the mechanism of PCD of the gland cells and especially the role of cytoskeleton in this process. This paper describes changes in organization of tubulin and actin cytoskeleton during cell death.…”

Glycogen distribution in the larval salivary gland cells during the development ofDrosophila melanogasterandDrosophila auraria: an ultrastructural cytochemical study

“…This is the ®rst time OsFeCN has been used for the detection of glycogen in the salivary glands of Drosophila. Glycogen has been detected, at the electron microscopic level, in the salivary gland cells of D. auraria (Thomopoulos, Neophytou et al, 1989) using the periodic acid±thiocarbohydrazide±silver proteinate technique (Thiery, 1967), but the use of OsFeCN produces a more delicate staining of glycogen particles and enhances the membrane contrast.…”

“…Substantial amounts can also be found in other tissues, e.g. in larval salivary glands (Thomopoulos, Neophytou & Kastritsis, 1989). The extent of glycogen deposits varies between species and depends further on the developmental stage and activity level of the insect (Rockstein, 1978).…”

“…The secretion of the material contained in the secretory granules occurs via exocytosis (Harrod & Kastritsis, 1972;Thomopoulos & Kastritsis, 1979). Since large amounts of glycogen are present in the salivary glands of D. auraria during the late third instar (Thomopoulos, Neophytou et al, 1989), and secretion is a highly energy-demanding process, we studied, cytochemically, the developmental distribution of glycogen in the larval salivary glands of Drosophila. The scope of this work was to examine the distribution of glycogen during larval development of two Drosophila species, belonging in two different subgroups, in order to ®nd if glycogen (used as an energy source during Drosophila larval development) is similarly distributed in these two phylogenetically distant species.…”