Drosophila salivary gland proteins and pupation

Pulse-labeling experiments of salivary glands from the prepupal stages of development showed selectively high rates of synthesis of a set of low molecular weight proteins (6K–12K). These proteins are stably maintained in the salivary glands during prepupal development and are subsequently transported to the pupation fluid (found between the pupal case and the prepupal cuticle) when pupation occurs. These small polypeptides are very basic with the major components having isoelectric points of 8.6–8.7 and the minor components having isoelectric points of 9.1–9.5. This study shows the continuing function of the salivary glands—specifically, the synthesis and secretion of a set of proteins with a putative role in pupation.     

Ecdysone receptor isoform specific regulation of secretory granule acidification in the larval Drosophila salivary gland

Bulk production and release of glue containing secretory granules takes place in the larval salivary gland during Drosophila development in order to attach the metamorphosing animal to a dry surface. These granules undergo a maturation process to prepare glue for exocytosis, which includes homotypic fusions to increase the size of granules, vesicle acidification and ion uptake. The steroid hormone 20-hydroxyecdysone is known to be required for the first and last steps of this process: glue synthesis and secretion, respectively. Here we show that the B1 isoform of Ecdysone receptor (EcR), together with its binding partner Ultraspiracle, are also necessary for the maturation of glue granules by promoting their acidification via regulation of Vha55 expression, which encodes an essential subunit of the V-ATPase proton pump. This is antagonized by the EcR-A isoform, overexpression of which decreases EcR-B1 and Vha55 expression and glue granule acidification. Our data shed light on a previously unknown, ecdysone receptor isoform-specific regulation of glue granule maturation.     

Precise temporal regulation of roughest is required for correct salivary gland autophagic cell death in Drosophila

The Drosophila roughest (rst) locus encodes an immunoglobulin superfamily transmembrane glycoprotein implicated in a variety of embryonic and postembryonic developmental processes. Here we demonstrate a previously unnoticed role for this gene in the autophagic elimination of larval salivary glands during early pupal stages by showing that overexpression of the Rst protein ectodomain in early pupa leads to persistence of salivary glands up to at least 12 hours after head eversion, although with variable penetrance. The same phenotype is observed in individuals carrying the dominant regulatory allele rst^D, but not in loss of function alleles. Analysis of persistent glands at the ultrastructural level showed that programmed cell death starts at the right time but is arrested at an early stage of the process. Finally we describe the expression pattern and intracellular distribution of Rst in wild type and rst^D mutants, showing that its downregulation in salivary glands at the beginning of pupal stage is an important factor in the correct implementation of the autophagic program of this tissue in space and time. genesis 47:492–504, 2009. © 2009 Wiley‐Liss, Inc.     

Identification of factors that function in Drosophila salivary gland cell death during development using proteomics

Proteasome inhibitors induce cell death and are used in cancer therapy, but little is known about the relationship between proteasome impairment and cell death under normal physiological conditions. Here, we investigate the relationship between proteasome function and larval salivary gland cell death during development in Drosophila. Drosophila larval salivary gland cells undergo synchronized programmed cell death requiring both caspases and autophagy (Atg) genes during development. Here, we show that ubiquitin proteasome system (UPS) function is reduced during normal salivary gland cell death, and that ectopic proteasome impairment in salivary gland cells leads to early DNA fragmentation and salivary gland condensation in vivo. Shotgun proteomic analyses of purified dying salivary glands identified the UPS as the top category of proteins enriched, suggesting a possible compensatory induction of these factors to maintain proteolysis during cell death. We compared the proteome following ectopic proteasome impairment to the proteome during developmental cell death in salivary gland cells. Proteins that were enriched in both populations of cells were screened for their function in salivary gland degradation using RNAi knockdown. We identified several factors, including trol, a novel gene CG11880, and the cop9 signalsome component cop9 signalsome 6, as required for Drosophila larval salivary gland degradation.     

Puffing in salivary gland chromosomes of picture-winged Hawaiian Drosophila

A portion of the X chromosome was examined for puffing activity shortly before puparium formation in several species of Hawaiian Drosophila. A large puff was induced by incubating excised salivary glands with ecdysone. In two of the seven species studied, the region in question has been moved by inversion to a new position relative to the banding sequence in the other species, but the reaction to ecdysone remained unchanged. Another puff, not affected by short term incubations with ecdysone, displayed different degrees of activity in some homosequential species, affording a cytological means for distinguishing these species.     

Experimental puffs in salivary gland chromosomes of Drosophila hydei

Summary In Drosophila hydei abnormal puffing activities could be induced by temperature shocks and treatments with 1.2% and 1.4% KCl solutions. After temperature shocks in vivo and in vitro, a number of puffs showed a similar change in activity.Other puffs were found to show a change in activity only after a distinct treatment.Some of the puffs, specific for temperature shocks, showed a change in activity only at a distinct stage of development.In discussing the results, particular attention is paid to puffs observed in common after all treatments.Dedicated to Prof. H. Bauer on the occasion of his sixtieth birthday.     

Nucleolus-organizing regions in salivary gland chromosomes of Drosophila melanogaster

Summary The nucleolus of the salivary gland nucleus of Drosophila melanogaster is formed by nucleolus-organizing regions which exist in the heterochromatin of the sex chromosomes. This interpretation is supported by the discovery of a series of induced chromosomal alterations involving transfer of nucleolus-forming regions to euchromatic sections of the chromosomes.     

The banding pattern of the salivary gland chromosomes of Drosophila hydei

The banding pattern of the salivary gland chromosomes of D. hydei was investigated in the electron microscope. We compared the banding pattern of squashed chromosomes with non-squashed preparations and observed that the fixation and squash procedure we used does not introduce artificial changes in the banding pattern of the chromosome. An electron microscopic map was made of the banding pattern of the distal half of the second salivary gland chromosome. On the basis of the number of bands in this part of the second chromosome we calculated a total of about 3700 bands for the whole set of polytene chromosomes of D. hydei. Our data indicate a similar number of bands in the salivary gland chromosomes of evolutionary remote Drosophila species like D. hydei and D. melanogaster.