Neural development in an imaginal disc mutant of Drosophila melanogaster

The neural phenotype of an imaginal disc degenerate mutant l(1)d deg-3 was studied in histological sections. The mutant larvae showed severe abnormalities in the imaginal neural development. Gynandromorphs, which are composed of genetically mutant and nonmutant cells, were generated and analyzed as late larvae. The results of mosaic analysis were consistent with l(1)d deg-3 gene acting autonomously in the imaginal disc and imaginal neural cells. The optic lobe development patterns observed in the larval mosaics provided evidence for an eye disc-optic lobe interaction during the late third instar larval stage.     

Characterisation of a new tumorous-head mutant of Drosophila melanogaster

Summary A new homoeotic mutant, I127, showing abnormal growths in the head region including homoeotic transformation of eye to genitalia and antenna to leg, was isolated in a screen designed to find new alleles of the tumorous head (tuh-3), mutation. Similarities in the phenotype and genetics of the mutant, and complementation studies with tuh-1; tuh-3, suggest that I127 is indeed an allele of tuh-3. In combination with the first chromosome modifier tuh-1, the mutant is temperature-sensitive during the third larval instar, giving an increased penetrance of the tumorous head phenotype when reared at 25° C as opposed to 18° C. The isolation of further alleles at the tumorous-head locus are essential. The types of morphological defects which can result from mutations at this locus would enable us to establish if this is a complex locus, and if null mutations are lethal during development. The interactions of the tumorous-head gene with first chromosome modifiers and other homoeotic mutations will only be understood if we able to induce a number of mutations at this locus, and as a consequence begin to elucidate the role of the wild-type gene product in normal development.     

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.     

Transdetermination in the homeotic eye--antenna imaginal disc of Drosophila melanogaster

The effects of homeotic mutations on transdetermination in eye-antenna imaginal discs of Drosophila melanogaster were studied. After 12 days of culture in vivo, antenna discs transformed to ventral mesothorax by AntpNs or AntpZ, transdetermined to notum and wing structures four to five times more frequently than the corresponding wild-type antenna discs. Likewise, eye discs transformed to dorsal mesothorax by eyopt transdetermined to leg structures, also extremely frequently (90%). It seems that, during culture, homeotic antenna as well as homeotic eye discs tend to complete the structural inventory of the mesothoracic segment. Transdetermination in the homeotic disc parts is interpreted as a regeneration process which reestablishes an entire segment, i.e., the ventral mesothoracic portion (leg) in the antenna disc regenerates dorsal mesothoracic parts, and the dorsal mesothoracic portion in the eye disc (wing) regenerates ventral mesothoracic parts, respectively. This implies that antenna and leg discs (ventral qualities) as well as eye and wing discs (dorsal qualities) are serially homologous. The transdetermination frequency of the untransformed eye disc to notum and wing structures is enhanced by Antp to the same extent as is the transdetermination frequency of the antenna disc. The first allotypic wing disc structure formed by the eye disc is notum, followed by structures of the anterior wing compartment and finally by posterior wing structures. No evidence for such a sequence was found in the transdetermination pattern of the antenna disc.     

Analysis of the autonomy of imaginal disc defects in a small-disc mutant of Drosophila melanogaster.

Lethal mutations which cause imaginal disc abnormalities in Drosophila melanogaster identify genes whose function is necessary for normal disc development, and these mutant genes may be used as probes of the role of their wild-type alleles in normal development. It is crucial to the interpretation of the disc phenotype of such mutants to know which abnormalities are autonomous (caused by expression of the mutant gene in imaginal cells) and which are nonautonomous (indirectly caused, for example, by expression of the mutant gene in larval cells). We chose for study l(3)c21R (3-67.8), a late-larval lethal mutation with a complex phenotype, to test the adequacy of available techniques for assessing autonomy. We employed surgical and genetic techniques to determine the imaginal cell autonomy of the defects in cell viability, growth, and differentiation in c21R discs. The imaginal cell viability defect is nonautonomous. The disc growth and differentiation defects are autonomous; however, in genetic mosaics these two autonomous defects are separable. These results show that c21R belongs to the class of mutations which affect both larval and imaginal cells. In combination, the available methods were adequate to resolve the issue of autonomy in this complex case. However, in isolation several of the methods could have led to incomplete or misleading interpretations. This emphasizes that to analyze any developmental mutant it is necessary to examine the issue of autonomy from several points of view.     

The type and location of homeotic transformations in the tumorous-head mutant of Drosophila melanogaster

Summary Transformations of tumorous-head Drosophila melanogaster were examined in order to investigate whether head structures were replaced by specific abdominal structures. Heads selected for the presence of genital structures were analyzed in detail. Female abnormalities included any combination of vaginal teeth, vulvar papillae, sensilla trichodea, abdominal tergites 6 (T6), 7 (T7), 8 (T8) and anal plate. Anal plate was observed in the prefrons and rostral membrane, while all other genital structures were intimately associated with modified shingle cuticle. Male abnormalities included transformation of antennal structures to penis, clasper teeth, lateral plate, anal plate and eye to T6. The distribution of each type of homeotic structure was confined to general regions of the eye-antenna, with no precise dividing lines between them. However, the spatial sequence of homeotic structures in the eye-antenna was generally the same as the sequence of the same structures in the posterior abdomen.     

Fate map of the eye-antennal imaginal disc in the stalk-eyed fly <Emphasis Type="Italic">Cyrtodiopsis dalmanni</Emphasis>

Hypercephaly, in the form of lateral extensions of the head capsule, is observed in several families of Diptera. A particularly extreme form is found in diopsid stalk-eyed flies, in which both eyes and antennae are laterally displaced at the end of eyestalks. We have studied the developmental basis of this exaggerated morphology in Cyrtodiopsis dalmanni. Diopsid eye-antennal imaginal discs are divided into anterior and posterior portions, which are joined by a narrow "disc-stalk" of intervening tissue. We established a fate map for this disc by cutting it into fragments and culturing them in vivo by injecting them into host larvae. The adult eye and dorsal head capsule structures, including the eyestalk and the ocelli, are derived from the posterior portion of the disc, while ventral adult structures such as the antenna and the palpus are derived from the anterior portion of the disc. Thus both posterior and anterior disc portions give rise to structures that are widely separated in the adult head. Moreover, structures that are adjacent in the adult are derived from different regions of the disc. These results confirm and extend previous conclusions about regional identity in diopsid eye-antennal discs that were based on the analysis of molecular markers.     

Morphological analysis and fate map of the intersexual genital disc of the mutant doublesex-dominant in Drosophila melanogaster

The organization of the genital disc in $\text{XX;dsx}{}^{\mathrm{D}}\text{+}$ animals, which have elements of both male and female genitalia, has been analyzed. The intersexual disc contains three major regions, which were isolated by fragmentation. After metamorphosis in host larvae, these regions produced the male genitalia, the female genitalia, and the analia, respectively. Thus, in contrast to the wild-type male and female constitution, the intersexual genetic constitution of $\text{XX;dsx}{}^{\mathrm{D}}\text{+}$ animals allows both genital primordia to develop and to differentiate adult structures. A fate map of the intersexual disc is presented. Observations made on the morphology of the genital disc and its derivatives in $\text{XX;dsx}{}^{\mathrm{D}}\text{+}$ animals and other “intersexual” genetic constitutions are compared and discussed in terms of the development of the sexual dimorphism.     

Dynamics of decapentaplegic expression during regeneration of the Drosophila melanogaster wing imaginal disc

Regeneration of an imaginal disc involves highly ordered proliferation and pattern regulation of the newly formed tissue. Although the general principles of imaginal disc regeneration have been extensively studied, knowledge of the underlying molecular mechanisms is far from complete. Results from other model organisms suggest that regeneration is the result of local recapitulation of the normal patterning genes. To analyze the dynamics of one major Drosophila patterning gene, decapentaplegic (dpp), in wing imaginal disc regeneration, a vital GFP reporter together with iontophoretic cell labeling were used. Our observations reveal that the restoration of compartment-border-specific dpp expression is a common event in imaginal disc regeneration. However, we did not find evidence of an upregulation of dpp expression during the regeneration process.     

Cell proliferation and DNA replication in the imaginal wing disc of Drosophila melanogaster

Cell proliferation in the imaginal wing disc of Drosophila has been analyzed by both pulse and chronic labeling with [3H]thymidine. We find neither spatial nor temporal variation in the fraction of S phase cells during the third instar. At or near the time of white prepupae formation the fraction of S phase cells falls sharply. Our chronic labeling experiments have demonstrated that almost all (and perhaps all) of the cells in a mid third instar wing disc are cycling. By examining sectioned material from such experiments we have found that the collumnar epithelial cell and the adepithetial cell populations become labeled with similar kinetics. The peripodial membrane cell population becomes labeled more slowly. We have also obtained estimates of cell cycle parameters for the imaginal wing disc cells.     

The expression of PS integrins in Drosophila melanogaster imaginal disc cell lines

Summary Drosophila imaginal disc cell lines show a characteristic pattern of aggregation in culture, which appears to be due to cell-cell rather than cell-substrate interactions. We have examined the distribution of PS integrins in wing and leg cell lines, and find that these integrin homologues are expressed preferentially in aggregates. Cell sheets, small cell clumps and chains of cells express antigen at points of cell-cell contact only.     

Aldehyde oxidase activity in the tumorous-head strain of Drosophila melanogaster

Gross aldehyde oxidase activity from the egg-stage through 10-day-old adults and distribution of the enzyme in eye-antennal imaginal discs in third instar larvae were determined for the tumorous-head strain of Drosophila melanogaster. Aldehyde oxidase activity of several laboratory strains was measured for comparative purposes. Aldehyde oxidase activity was 100% higher during embryogenesis in tuh(ASU) eggs than in Oregon-R-C eggs. A second period of elevated aldehyde oxidase activity was observed during metamorphosis where tuh(ASU) pupae averaged 65% more enzyme activity than Oregon-R-C. Therefore, during determination and differentiation of the eye-antennal imaginal disc, the tuh(ASU) strain possesses a high aldehyde oxidase activity. Wild-type Drosophila melanogaster antennal imaginal discs are aldehyde oxidase positive, whereas attached eye imaginal discs are apparently aldehyde oxidase negative. A sample of eye-antennal imaginal discs from tuh(ASU) third instar larvae revealed that either one or both eye discs of 64% of the larvae were aldehyde oxidase positive. Aldehyde oxidase activity may be correlated with the homoeotic transformation in parts of the eye disc.     

Pattern formation in the imaginal discs of a temperature-sensitive cell-lethal mutant of Drosophila melanogaster

To explore the effects of cell death on pattern formation in the developing imaginal discs of Drosophila melanogaster, I have isolated a number of cell-autonomous temperature-sensitive lethal mutants. Sex-linked temperature-sensitive lethals were screened for cell-autonomy by scoring the survival of lethal-bearing clones in genetic mosaics. The mutant with the strongest effect on clone viability gave rise to a high frequency of structural deficiencies and duplications in the derivatives of the eye-antennal discs, when subjected to pulse-treatments at the nonpermissive temperature during the late second and third instars. The patterns produced were nonrandom, with some structures showing a tendency to become deficient, and others a tendency to duplicate. Duplicated structures were only found in heads in which other structures were missing. Genetic tests identified the lethal as a point mutation at the suppressor-of-forked locus. Recombination, and complementation tests with a small duplication of this region showed that a second mutational lesion is in all probability not involved in the generation of abnormal patterns in the imaginal discs. It is therefore proposed that the cell-lethal action of the mutant is sufficient to account for phenotypic effects described. According to this hypothesis, cell death primarily causes deficiencies, and duplications occur as a response of the discs to injury. In agreement with this, it was found that in gynandromorphs, pattern duplications can be found in wild-type tissue in the presence of lethal tissue in the same disc. Thus, a cell-autonomous lethal may affect the process of pattern formation in a nonautonomous way.