Proteomic analysis of the wing imaginal discs of Drosophila melanogaster

We have combined high-resolution two-dimensional (2-D) gel electrophoresis and mass spectrometry with the aim of identifying proteins represented in the 2-D gel database of the wing imaginal discs of Drosophila melanogaster. First, we obtained a high-resolution 2-D gel pattern of [35S]methionine + [35S]cysteine-labeled polypeptides of Schneider cells, a permanent cell line of Drosophila embryonic origin, and compared it with the standard pattern of polypeptides of the wing imaginal disc. These studies reveal qualitative and quantitative differences between the two samples, but have more than 600 polypeptides in common. Second, we carried out preparative 2-D polyacrylamide gel electrophoresis using Schneider cells mixed with radioactively labeled wing imaginal discs in order to isolate some of the shared polypeptides and characterize them by matrix-assisted laser desorption/ionization-time of flight MALDI-TOF analysis. Using this strategy we identified 100 shared proteins represented in the database, and in each case confirmed their identity by MALDI-TOF/TOF analysis.     

Metamorphosis of imaginal discs of Drosophila melanogaster

Summary Imaginal discs ofDrosophila melanogaster larvae, 24–53 hrs after oviposition, were transplanted into mature immobile larval hosts. The transplants did not respond to the hormonal stimuli of metamorphosis, but instead completed their larval development. When reinjected into mature larval hosts, they now differentiated the full set of their presumptive imaginal structures. The process of acquiring competence for metamorphosis appears to be independent of the hormonal conditions.Supported by a credit of the Swiss National Foundation granted to Prof. Dr. E. Hadorn. I thank Dr. R. Nöthiger for his valuable criticism during this investigation.     

Absence of distal to proximal intercalary regeneration in imaginal wing discs of Drosophila melanogaster.

The fate of an imaginal disc cell of Drosophila can be affected by the associations and interactions that it has with other cells in the disc. A fragment of an imaginal disc, not regenerating under conditions allowing a complementary fragment to do so, can be stimulated to regenerate by interactions with cells of the complementary fragment [Haynie, J. L., and Bryant, P. J. (1976) Nature (London)259, 659–662]. We report here that one nonregenerating fragment of an imaginal wing disc cannot be stimulated to regenerate by interactions with cells from other parts of the disc. This fragment, containing the anlagen of the distal wing, fails to regenerate proximally when combined with a proximal fragment even though this association stimulates some proximal fragments to regenerate distally. We suggest that this may be a phenomenon similar to that observed in cockroach legs by H. Bohn (1970, Wilhelm Roux Arch. Entwicklungsmech. Organismen165, 303–341), in which proximal regeneration from grafted distal leg segments proceeds only to a limited extent. We consider the possibility that there exist reiterated sets of positional information arranged concentrically in the wing disc.     

Distribution of S-phase cells during the regeneration of Drosophila imaginal wing discs

We investigated the distribution of S-phase cells during regeneration of the imaginal wing disc of Drosophila melanogaster following excision of 30 degrees, 90 degrees, and 150 degrees sectors of tissue. The fragments were cultured in adult abdomens for 1-5 days, labeled in vitro with tritiated thymidine, serially sectioned, and subjected to autoradiography. There was negligible thymidine incorporation in unoperated controls and in the undamaged parts of the operated discs, indicating that DNA synthesis in undamaged tissue is terminated during the first day of the culture period. Almost all of the fragments from which tissue had been removed, as well as controls which were simply cut without the removal of any tissue, showed a cluster of labeled cells (blastema) even after only 1 day of culture. The blastemas in control discs were short-lived, with over 50% of these discs showing no blastema by the third day in culture. Blastemas in discs from which sectors were removed were more persistent; the time at which 50% of the fragments no longer showed a blastema was 4 days for the -30 degrees fragments, 5 days for the -90 degrees fragments, and greater than 5 days for the -150 degrees fragments. The average blastema size, measured as number of labeled cells, was directly related to the amount of tissue removed, and in most cases did not change significantly during the culture period. Both wound edges incorporated tritiated thymidine initially and the S-phase cells remained tightly clustered throughout regeneration; maximum blastema width varied from about 8 to 25 cell diameters. The results are consistent with the idea that regenerative cell proliferation is stimulated and maintained by positional information discontinuities, and terminated when these discontinuities are resolved by the addition of an appropriate number of new cells.     

Transplanted wing and leg imaginal discs in Drosophila melanogaster demonstrate interactions between epidermis and myoblasts in muscle formation

 Adult muscle development in Drosophila is intimately associated with the development of the nervous system and epidermis. During metamorphosis, myoblasts from the wing imaginal disc reach target sites on the developing pupal epidermis and begin the formation of multinucleate myofibres of the dorsal thorax. The paths taken by pupal myoblasts could be specified by the nervous system and/or the epidermis. Using genetically marked donor pupal wing and leg discs transplanted onto pupal hosts, we have generated animals that have ectopic wings or legs and have examined the formation of adult muscle types. We show that thoracic myoblasts migrate over both host and donor epidermis when the transplant site on the host is thoracic. However, when the transplant site is on the abdomen, thoracic myoblasts do not migrate over abdominal epidermis. Our results show that the epidermis plays an important role in determining the migration pattern of myoblasts. Since muscles are multinucleate cells that form by the fusion of myoblasts, one way in which their molecular characteristics could be achieved is by some myoblasts acting as ”founders”. These myoblasts could influence the pattern of gene expression of those nuclei that fuse with them. We have examined, again using disc transplant experiments, if myoblasts on discs have the capacity to express fibre-specific genes as distinct from this property being conferred by other extra-discs myoblasts. Our results demonstrate that disc-associated myoblasts can indeed fuse with each other to express fibre-specific genes. We synthesize the results presented here with those from earlier experiments to suggest a mechanism for muscle patterning in the adult thorax. Received: 8 January 1995 / Accepted in revised form: 22 January 1996     

Extracellular peptidases of imaginal discs of Drosophila melanogaster

The imaginal discs of Drosophila melanogaster give rise to the adult epidermis during metamorphosis. During this developmental period several peptidase genes are expressed in disc cells, but there is a paucity of biochemical information regarding substrate specificity. We have used peptides and peptidyl 7-amino-4-methylcoumarin (AMC) substrates to detect several peptidases either positioned on the surface of wing discs or secreted by the imaginal cells. Using [Leu(5)]enkephalin as a substrate, a captopril sensitive dipeptidyl carboxypeptidase (angiotensin I-converting enzyme) and an amastatin-sensitive aminopeptidase were detected as prominent activities associated with intact discs. The formation of [Leu(5)]enkephalin-derived Phe was attributed to the concerted action of the D. melanogaster angiotensin I-converting enzyme (Ance) and a dipeptidase. The disc Ance also showed endopeptidic activity towards locust tachykinin-1 (LomTK-I) by cleaving the Gly-Val peptide bond, but this enzyme was not the sole endopeptidase activity associated with discs. Complete inhibition of the endopeptidic hydrolysis of the LomTK-1 by a disc homogenate required a combination of captopril and the neprilysin inhibitor, phosphoramidon, providing biochemical evidence for a neprilysin-like peptidase, in addition to Ance, in imaginal discs of D. melanogaster. Peptidyl AMC substrates for furin, prohormone convertase and tryptase provided evidence for trypsin-like serine endopeptidases in addition to the metalloendopeptidases. We conclude that imaginal discs are endowed with a variety of peptidases from different families that together are capable of hydrolyzing a broad range of peptides and proteins. Some of these peptidases might be responsible for the metabolic activation/inactivation of signaling peptides, as well as being involved in the production of dipeptides and free amino acids required for protein synthesis and osmotic balance during adult morphogenesis.     

Origin and proliferation of blastema cells during regeneration of Drosophila wing imaginal discs

Following a period of neglect, there has been a resurgence of interest in Drosophila imaginal discs as a model with which to analyze the relationships between growth and pattern formation during regeneration. To broaden our understanding of this process, we used cell lineage techniques to trace the origin of blastema cells and the early and late boundaries of the blastema in regenerating 3/4 wing disc fragments, examined the distribution of S-phase, mitotic and dead cells, and undertook clonal analysis to determine the topology of cell proliferation and its relationship to pattern formation. Using lineage tagging with the JNK phosphatase puckered (puc), we demonstrate that a substantial number of blastema cells arise from cells in which JNK is activated. Furthermore, we show that DNA synthesis and mitosis are activated well before wound healing is completed, in a region where the JNK pathway is activated; later, DNA synthesis and mitosis are observed in scattered cells throughout the blastema. Finally, clonal analysis shows a close relationship between the size and shape of clones and disparities in the positional values of the apposed surfaces.     

A comparison of protein synthesis in imaginal wing discs of wild-type and vestigial of Drosophila melanogaster

In vitro incorporation of labelled amino acids into TCA insoluble protein in the imaginal wing discs of vg mutant and wild-type Drosophila melanogaster is compared and correlated with the extent of cellular degeneration during development. (1) With 96–100-hr-old larvae, wing discs isolated from vg mutant incorporate radiolabelled amino acids at a higher rate than wild-type discs, although cellular degeneration is more extensive in vg discs than wild-type discs. This may reflect the larger size of the vg discs since they have more protein than the wild-type discs. (2) The vg discs of 105–110-hr-old larvae have a lower rate of incorporation than the wild-type disc, although both types of discs have the same protein content. This may be due to the presence of more degenerating cells in the vg discs. (3) The rate of incorporation in vg discs of 115–118-hr-old larvae is lower than that of wild-type discs; the vg discs have less protein but more degenerative cells than the wild-type discs. The rates of protein degradation are similar in both discs. Electrophoretic comparison reveals a general reduction in protein synthesis in vg discs as compared with wild-type discs.     

Necrosis-induced apoptosis promotes regeneration in Drosophila wing imaginal discs

Regeneration is a complex process that requires a coordinated genetic response to tissue loss. Signals from dying cells are crucial to this process and are best understood in the context of regeneration following programmed cell death, like apoptosis. Conversely, regeneration following unregulated forms of death, such as necrosis, have yet to be fully explored. Here, we have developed a method to investigate regeneration following necrosis using the Drosophila wing imaginal disc. We show that necrosis stimulates regeneration at an equivalent level to that of apoptosis-mediated cell death and activates a similar response at the wound edge involving localized JNK signaling. Unexpectedly, however, necrosis also results in significant apoptosis far from the site of ablation, which we have termed necrosis-induced apoptosis (NiA). This apoptosis occurs independent of changes at the wound edge and importantly does not rely on JNK signaling. Furthermore, we find that blocking NiA limits proliferation and subsequently inhibits regeneration, suggesting that tissues damaged by necrosis can activate programmed cell death at a distance from the injury to promote regeneration.     

Patterns of protein synthesis in imaginal discs of Drosophila melanogaster.

Patterns of polypeptide synthesis in wing, leg and eye-antenna imaginal discs and in whole larvae of wild-type and and mutant Drosophila melanogaster have been examined using two-dimensional polyacrylamide gel electrophoresis and autoradiography. After 2 hr of labeling with 35S during the third larval instar, the synthesis of more than 318 polypeptides has been detected in imaginal discs. Of these, 268 are present in similar amounts in all three disc types. The remaining polypeptides detected in the three imaginal disc types fall into two categories: those unique to a particular disc type, and those specific for a particular pair of disc types. These results are discussed in relation to the spectrum of gene expression in imaginal discs.     

Regulation of Wingless and Vestigial expression in wing and haltere discs of Drosophila

In the third thoracic segment of Drosophila, wing development is suppressed by the homeotic selector gene Ultrabithorax (Ubx) in order to mediate haltere development. Previously, we have shown that Ubx represses dorsoventral (DV) signaling to specify haltere fate. Here we examine the mechanism of Ubx-mediated downregulation of DV signaling. We show that Wingless (Wg) and Vestigial (Vg) are differentially regulated in wing and haltere discs. In wing discs, although Vg expression in non-DV cells is dependent on DV boundary function of Wg, it maintains its expression by autoregulation. Thus, overexpression of Vg in non-DV cells can bypass the requirement for Wg signaling from the DV boundary. Ubx functions, at least, at two levels to repress Vestigial expression in non-DV cells of haltere discs. At the DV boundary, it functions downstream of Shaggy/GSK3 beta to enhance the degradation of Armadillo (Arm), which causes downregulation of Wg signaling. In non-DV cells, Ubx inhibits event(s) downstream of Arm, but upstream of Vg autoregulation. Repression of Vg at multiple levels appears to be crucial for Ubx-mediated specification of the haltere fate. Overexpression of Vg in haltere discs is enough to override Ubx function and cause haltere-to-wing homeotic transformations.     

Transdetermination of imaginal wing disc fragments of Drosophila melanogaster

Fragments of the imaginal wing disc of Drosophila melanogaster were cultured in adult hosts before transfer to larvae for metamorphosis. Transdetermination occurred only after at least 2 weeks of culture in vivo, producing structures of the leg, antenna, head, and thoracic spiracle. Details of the transdetermined structures and their locations with respect to normal wing disc structures are reported. We present evidence suggesting that regulation can occur between the wing and the second leg imaginal discs, and we propose that many transdeterminations which involve neighboring discs may result from such interdisc regulation.     

Pyridine nucleotide metabolism in imaginal discs of Drosophila melanogaster

The pyridine nucleotide metabolism of imaginal discs of Drosophila melanogaster has been studied in vitro by incubating discs with labeled nicotinic acid in the presence and absence of ecdysterone. The major labeled compounds found within the discs are NAD, NADP, and nicotinic acid. There is preferential uptake of nicotinamide over nicotinic acid, although the Priess-Handler pathway is used exclusively. The presence of ecdysterone produces a small increase in the NADP/NAD ratio, and an increase in NAD synthesis, probably to compensate for increased NAD turnover.Supported by Grant GB 43569 from the National Science Foundation.     

Ecdysone-stimulated RNA synthesis in imaginal discs of Drosophila melanogaster

Cytoplasmic RNA from imaginal discs of Drosophila melanogaster, labeled by uridine incorporation in organ culture, has been assayed by hybridization to cytological preparations of polytene chromosomes. RNA labeled during the early stages (first four hours) of ecdysone stimulation was compared to RNA labeled in the absence of the hormone. For the poly(A)-containing fraction (oligo-dT bound), several loci hybridize only RNA labeled in the presence of ecdysone; one locus hybridizes only control RNA. The majority of hybridizing loci are unaffected by the hormone. Of the loci hybridizing RNA not bound to oligo-dT, several appear specific for the ecdysone-treated sample, though most are labeled more heavily with this RNA than with the control. None of the ecdysone-sensitive loci visualized by in situ hybridization are the sites of salivary gland puffs induced by ecdysone on the same time scale.     

Modifiers of bx1 alter the distribution of Ubx proteins in haltere imaginal discs of Drosophila.

The bithorax (bx) mutations in the Ultrabithorax (Ubx) gene of Drosophila melanogaster cause homeotic transformations of anterior third thoracic structures (T3a) toward anterior second thoracic structures (T2a) in the adult fly. A corresponding loss of Ubx protein expression in T3a of bx imaginal discs has been observed (White and Wilcox, 1985). We describe two genetic loci which modify the bx-induced transformation. A locus which we map very close to the pink peach (pp) gene suppresses the bx1 phenotype. In contrast, mutations in the suppressor of sable (su(s)) gene enhance the bx1 phenotype. A correlation was observed between patterns of Ubx protein expression and the phenotypic transformations observed.     

Minute mutations of Drosophila melanogaster change aldehyde oxidase and pyridoxal oxidase distribution patterns in imaginal wing discs

Aldehyde oxidase (AO) and pyridoxal oxidase (PO) distribution patterns were determined in the imaginal wing discs for a series of strains of Drosophila melanogaster heterozygous for different Minute mutations. The mutant severity ranged from very weak to strong. The results shown an inverse response of AO and PO to the expressivity of the Minute mutation: in weaker Minutes the extent of the AO positive area increases, whereas PO activity disappears. The results are discussed with reference to an impaired protein synthesis in Minutes.     

Aldehyde oxidase distribution in haltere discs of homoeotic bithorax mutants in Drosophila melanogaster.

Summary Distribution of the enzyme aldehyde oxidase in transformed haltere discs from the homoeotic bithorax series of mutants was investigated by histochemical means. The bithorax (bx) mutant, which transforms the anterior part of the haltere into an alterior with blade, possesses in the haltere disc an aldehyde oxidase staining pattern similar to that of the anterior side of the wing disc. The postbithorax (pbx) mutant, which transforms the posterior haltere into a structure resembling the posterior wing blade, reveals an aldehyde oxidase staining pattern in the haltere disc characteristic of the posterior side of the wing disc pouch. When both (bx ³ (pbx) mutants are present the haltere develops into a metathoracic wing. It is shown here that the transformed haltere disc closely resembles the previously established pattern in the wing disc with respect to aldehyde oxidase distribution. Change in the pattern of aldehyde oxidase in bithorax mutants signals alteration in gene expression which at least for this particular enzyme correlates well with the morphological transformation from haltere to wing. A possible correlation between pattern of enzyme activity and developmental compartmentalization has been discussed.