The timing of drosophila salivary gland apoptosis displays an l(2)gl-dose response

During Drosophila metamorphosis, larval tissues, such as the salivary glands, are histolysed whereas imaginal tissues differentiate into adult structures forming at eclosion a fly-shaped adult. Inactivation of the lethal(2)giant larvae (l(2)gl) gene encoding the cytoskeletal associated p127 protein, causes malignant transformation of brain neuroblasts and imaginal disc cells with developmental arrest at the larval-pupal transition phase. At this stage, p127 is expressed in wild-type salivary glands which become fully histolysed 12 - 13 h after pupariation. By contrast to wild-type, administration of 20-hydroxyecdsone to l(2)gl-deficient salivary glands is unable to induce histolysis, although it releases stored glue granules and gives rise to a nearly normal pupariation chromosome puffing, indicating that p127 is required for salivary gland apoptosis. To unravel the l(2)gl function in this tissue we used transgenic lines expressing reduced ( approximately 0.1) or increased levels of p127 (3.0). Here we show that the timing of salivary gland histolysis displays an l(2)gl-dose response. Reduced p127 expression delays histolysis whereas overexpression accelerates this process without affecting the duration of third larval instar, prepupal and pupal development. Similar l(2)gl-dependence is noticed in the timing of expression of the cell death genes reaper, head involution defective and grim, supporting the idea that p127 plays a critical role in the implementation of ecdysone-triggered apoptosis. These experiments show also that the timing of salivary gland apoptosis can be manipulated without affecting normal development and provide ways to investigate the nature of the components specifically involved in the apoptotic pathway of the salivary glands.     

Acetylcholine-induced responses in the salivary gland cells ofHelisoma trivolvis

This study describes the actions of acetylcholine (ACh) on the salivary gland cells of Helisoma. Perfusion of the salivary gland cells with ACh produces a long-lasting depolarization accompanied by an increase in the input conductance of the gland cells. The depolarization is often followed by a long-lasting hyperpolarization. Carbamylcholine, tetramethylammonium, and choline also produce depolarizing responses. Nicotine and pilocarpine produce only a small depolarization in the gland cells. The following cholinergic antagonists are effective in blocking the gland-cell response to ACh: tetraethylammonium, atropine, hexamethonium, d-tubocurarine, and strychnine. A new preparation, the "isolated acinus," was utilized to obtain the reversal potential of the ACh response. The mean reversal potential in 10 preparations was -7 +/- 8 mV. The depolarizing phase of the response is dependent on the presence of both external calcium and external sodium ions. The long-lasting hyperpolarization is produced by the activity of an electrogenic sodium-potassium pump. The properties of the acetylcholine receptors on the salivary gland cells of Helisoma are compared with those described in other gastropod preparations.     

Electron microscope studies on salivary gland cells

Summary A study of the ultrastructure of the nuclear envelope of the salivary glands cells in the sciarid Bradysia suggests that it probably consists of four membranes, instead of two as found in most cells. The fine structure associated with the pores closely resembles that described in amphibian oocytes by Wischnitzer 1958.British Empire Cancer Campaign.     

ATP-induced calcium signalling in acinar cells of the submandibular salivary gland

To study changes in the cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) and the total amount of calcium in cells, we used, respectively, the fluorescent dye fura 2/AM and the metallochrome dye arsenazo III. The total amount of calcium in acinar cells after their incubation in calcium-free ATP-containing extracellular solution decreased. The action of ATP induced a dose-dependent increase in the [Ca²⁺]_i; the EC₅₀ was, on average, 130 ± ± 36 μM. Calcium transients induced by ATP demonstrated no desensitization. Against the background of a blocker of ionotropic P2X receptors, pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid, we observed a decrease in the ATP-induced calcium transients by 72%. In addition, these transients were reduced by 65% in the calcium-free milieu, while after thapsigargin-induced exhaustion of the endoplasmic reticulum store they disappeared. This is indicative of the involvement of metabotropic P2Y receptors in the formation of the above calcium transients. Therefore, P2X and P2Y receptors participate in ATP-induced calcium signalling in acinar cells of the submandibular salivary gland; activation of these channels results in a rise in the [Ca²⁺]_i. The P2X receptors to a higher extent contribute to the formation of calcium signals; the P2Y-determined increase in the [Ca²⁺]_i is smaller (equal to about 35%). Therefore, the functionally active ligand-operated ionotropic P2Y receptors and metabotropic G protein-related P2Y receptors do exist in acinar cells of the submandibular salivary gland and play an important role in the control of functioning of this gland. Neirofiziologiya/Neurophysiology, Vol. 37, Nos. 5/6, pp. 395–402, September–December, 2005.     

Rickettsiae-like structures in the larval salivary gland cells of Drosophila auraria

Rickettsiae-like structures were found in the salivary gland cells of Drosophila auraria during different larval and prepupal developmental stages, from the early 3rd instar up to 14 hr after spiracle inversion. These microorganisms are surrounded by a membrane, are constantly intracellular, and occur singly or in groups. Their widespread occurrence in various tissues of other Drosophila species indicates that they can be considered as symbionts, but their actual functional significance (if any) is unknown.     

Early membrane injury in lethally irradiated salivary gland cells

The early manifestations of radiation injury in salivary glands were investigated in the rat. The animals received a single X-ray dose in the range of 200-2000 rad to their neck area. Glandular changes during the first 24 hours were studied by light and electron microscopy and by measuring serum amylase activity. The amount of cell necrosis was quantitated and expressed as necrosis index (NI), Parotid NI and serum amylase activity 24 hours following irradiation were directly proportional to the X-ray dose. The submandibular gland cells were radioresistant and so were the mucous cells of the sublingual gland. The major increase in parotid acinar cell necrosis occurred between 12 and 24 hours after irradiation. However, more than 100 per cent increase in serum amylase level was detected prior to the onset of any significant cell necrosis. As early as two hours following irradiation signs of cell membrane injury were demonstrable in the parotid by electron microscopy and consisted of intracellular oedema, sequestered degenerative cell membranes, and an accumulation of intramitochondrial particles. None of these changes was detectable in the submandibular gland. The implication of membrane injury in the lethal effects of radiation on parotid cells is discussed.     

Membrane junctions between salivary gland cells ofChironomus thummi

Summary Cells ofChironomus salivary glands communicate through intercellular connections of high permeability. Electron micrographs of salivary glands show two kinds of junctions between the membranes of adjacent cells, which may be responsible for cell coupling: septate junctions and close membrane junctions.A large fraction of lateral cell surfaces is occupied by septate junctions, while the area of close membrane junctions appears to be very small. Consequently septate junctions have been considered as likely sites for intercellular coupling. There are however some indications that intercellular communication is provided by structures which seem to be unstable. As osmotic effects are among the factors which can disrupt cellular communications, we have tried to eliminate possible effects of the fixing solutions on the ultrastructure of intercellular connections by using isoosmotic fixatives. Under these conditions large regions of close membrane junctions of the nexus kind have been observed to occur between gland cells. They are of similar size as septate junctions. It seems to be possible that as in other communicating cell systems nexus could be the sites for intercellular coupling of salivary gland cells.The authors would like to thank Prof. Dr. H. Leonhardt, Institut für Anatomie I, Homburg, for the use of his electron microscope (Zeiss EM 9-DFG grant LE 69–8) during part of this work and Prof. Dr. H. Kroeger, Institut für Genetik, Saarbrücken for the supply withChironomus larvae.     

Balbiani ring RNA in the cytoplasm of Chironomus thummi salivary gland cells

In this paper experimental results on the size, transport and stability of cytoplasmic Balbiani ring RNA and on its appearance in polysomes are presented. Cytoplasmic RNA of salivary gland cells from Chironomus thummi contains two large RNA fractions of about 20×10⁶ dalton and 10×10⁶ dalton in size. These RNA fractions correspond both to Balbiani ring BR 1 RNA and BR 2 RNA and are apparently transported from nucleus into cytoplasm without a significant size reduction. Chase experiments illustrate a great stability of giant cytoplasmic Balbiani ring RNA molecules and exclude the possibility of a precursor-product relationship between these and smaller BR RNA molecules also found in cytoplasm. A part of giant cytoplasmic Balbiani ring RNA molecules is bound to poly(U)-sepharose columns and should, therefore, contain poly(A)-sequences. — Polysomes of salivary gland cells extracted by a gentle lysis procedure and centrifuged through sucrose gradients are characterized by a rather broad sedimentation profile. Polysome sizes up to about 800 S have been detected, but in no case a distinct polysome fraction corresponding in size to Balbiani ring RNA has been observed. Hybridization of polysomal RNA with salivary gland chromosomes in situ resulted in labelling of both Balbiani rings BR 1 and BR 2.