Engrailed gene expression in Drosophila imaginal discs.

Genetic and molecular analyses indicate that the Drosophila engrailed gene is required to distinguish posterior from anterior compartments in each segment of the developing animal. Here, the patterns of engrailed expression in the imaginal discs and ventral ganglion of Drosophila larvae are examined, using an antiserum against the engrailed protein and a novel image processing method to reduce non-specific background. As expected, engrailed expression generally is restricted to cells in the posterior compartment of the discs, and the patterns of expression allow refinements in the fate maps of the discs to be made. More significant is the finding that expression of the gene is highly variable in different regions of posterior compartments, suggesting that engrailed may do more than simply specify 'posteriorness'. In the ventral ganglion engrailed appears to be expressed by a subset of cells, primarily in the posterior regions of each segment. In wing discs from animals that are homozygous for the en1 mutation, the pattern of expression of the gene is altered, as opposed to being simply reduced uniformly in the posterior cells.     

Segmental differences in the protein content of Drosophila imaginal discs

The protein content of various Drosophila imaginal discs was analysed by two-dimensional electrophoresis followed by silver-staining. Three proteins, identified as tropomyosins α and β and actin I, are more abundant in the metathoracic discs (haltere and third leg) than in the mesothoracic discs (wing and second leg). In the case of the wing disc, these proteins are probably contributed by the adepithelial (muscle precursor) cells, as indicated by their non-uniform localisation within the disc. Mutations in the bithorax complex have no effect on the difference between second and third leg discs. We conclude that there is a segmental difference in the protein content of homologous discs, that this difference is probably localized in the adepithelial cells, and that it is not under the direct control of known alleles of the bithorax complex.     

Regenerative interactions between Drosophila imaginal discs of different types.

We have tested the ability of fragments of one type of imaginal disc to stimulate regeneration of another type. It has been shown by others that, when extreme proximal and distal fragments of the wing disc are combined, intercalary regeneration of the missing tissue ensues. Each fragment, if cultured alone, will merely duplicate its structures. We now find that distal fragments of other thoracic discs, haltere and leg, while retaining their autonomy for differentiation, also interact with proximal wing tissue to promote regeneration of more distal wing structures. The proximal wing tissue used in these experiments was the wingless abnormal wing disc which, in the absence of interaction, yields only proximal wing structures. These results suggest that spatial organization is controlled by similar systems in the various thoracic discs. In contrast, head and genital disc material provided no regenerative stimulus to the mutant wing disc tissue.     

Localization of the Antennapedia protein in Drosophila embryos and imaginal discs

[This corrects the article on p. 3327 in vol. 5.].     

Localization of the Antennapedia protein in Drosophila embryos and imaginal discs

Antibodies have been raised against a fusion protein containing the 3' region of the coding sequence of the Antennapedia (Antp) gene fused to β-galactosidase. The distribution of the protein on whole mount embryos and imaginal discs of third instar larvae was examined by immunofluorescence. In young embryos, expression of the Antp protein was limited to the thoracic segments in the epidermis, whereas it was found in all neuromeres of head, thorax and abdomen. At the end of embryogenesis, the Antp protein mainly accumulated in the ventral nervous system in certain parts of the thoracic neuromeres, from posterior T1 to anterior T3, with a gap in posterior T2. Comparison of Antp protein distribution in nervous systems from wild-type and Df P9 embryos, lacking the genes of the Bithorax-complex (BX-C), revealed a pattern of expression which indicated that the BX-C represses Antp in the posterior segments with the exception of the last abdominal neuromeres (A8-9) which are regulated independently. The protein pattern in nervous systems from Sex combs reduced(Scr^xF9) mutant embryos was indistinguishable from that found in wild-type embryos; thus, neurogenic expression of Antp in T1 and the more anterior segments does not appear to be under the control of Scr⁺. All imaginal discs derived from the three thoracic segments express Antp protein. The distribution was distinct in each disc; strongest expression was observed in the proximal parts of the discs. In the leg discs the protein distribution seemed to be compartmentally restricted, whereas in the wing disc this was not the case. Antp protein was not detected in the eye-antennal disc. In embryos, as well as in imaginal discs, the protein is localized in the nucleus.     

Allelic variation at the frizzled locus of Drosophila

The epidermis of Drosophila has a tissue polarity that is manifested by a parallel array of polarized structures (primarily hairs and bristles). The production of normal tissue polarity requires the function of the frizzled (fz) locus. We have isolated a large number of alleles at this locus and have phenotypically characterized more than 25 of them. We have found extensive allelic variation that a previous study failed to detect. Most of the alleles fall into a hypomorphic to amorphic series. Two alleles, however, have unusual properties. These alleles, which in general are moderately strong alleles, fail to produce a rough eye phenotype that is characteristic of all the other moderate or strong fz alleles. Thus, these two alleles are tissue specific in effect. Furthermore, these two alleles also have a neomorphic or antimorphic effect on hair polarity in one region of the wing.     

Expression profiling of Drosophila imaginal discs

Background  

In the Drosophila larva, imaginal discs are programmed to produce adult structures at metamorphosis. Although their fate is precisely determined, these organs remain largely undifferentiated in the larva. To identify genes that establish and express the different states of determination in discs and larval tissues, we used DNA microarrays to analyze mRNAs isolated from single imaginal discs.     

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.     

Ultrabithorax gene expression in Drosophila imaginal discs and larval nervous system

Using a monoclonal antibody and image-processing procedures, the patterns of expression of the Ultrabithorax (Ubx) gene product have been characterized in Drosophila larvae. As reported previously, the metathoracic imaginal discs stain most intensely with anti-Ubx, with some mesothoracic and no prothoracic expression detectable. In the metathoracic discs, the greatest modulation in anti-Ubx staining is along the proximodistal axis. Ubx is generally expressed at higher levels in the posterior regions of metathoracic discs, although relatively high anterior expression is found in some areas. Expression in the mature wing disc is confined to the squamous peripodial membrane cells; in younger wings, Ubx expression fills the posterior half of the peripodial side of the disc. The mesothoracic leg stains with a pattern that is qualitatively similar (but not identical) to that of the metathoracic leg; Ubx is expressed in some anterior regions of the mesothoracic leg, in parasegment 4. Double staining with anti-Ubx and anti-engrailed reveals that discontinuities in Ubx expression that have been suggested to correspond to compartment borders do not coincide with the compartment boundaries in some cases. In the larval ventral ganglion, Ubx expression is greatest in parasegments 5 and 6, as in the embryonic nervous system.     

Muscle connections between imaginal discs in Drosophila

A comparison of the protein content of different imaginal discs of Drosophila revealed that among more than 600 protein species that can be detected, only three show differences in concentration among different types of discs. Two of them form a doublet that can be resolved only by using extended electrophoresis conditions. This doublet was also reported to have a nonhomogeneous distribution within some discs. Here we show that these two proteins are tropomyosin components, and that they are associated not with the discs themselves but with a new type of muscle that connects some of the discs together.     

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.     

Patterns of protein synthesis in the imaginal discs of Drosophila melanogaster: a comparison between different discs and stages

High-resolution two dimensional gel electrophoresis has been used to study the patterns of protein synthesis in imaginal discs of Drosophila melanogaster. In this paper we first compare the patterns of protein synthesis in wing, haltere, leg 1, leg 2, leg 3 and eye antenna imaginal discs of late third instar larvae. We have detected only quantitative changes: differences in 17 proteins among the different imaginal discs. In addition, we have analysed the variations in pattern of proteins in the wing disc of the last larval stage and early pupae as well as in wing discs cultured in vivo for 6 days. Variations in these patterns affect more than 20% of the proteins and involve both qualitative and quantitative changes. Some of the changes may correspond to protein phosphorylation. Correlations of these changes between discs and through development are also discussed. Correspondence to: F. Santaren