Transdetermination in leg imaginal discs ofDrosophila melanogaster undDrosophila nigromelanica

Summary The transdetermination capacities of leg discs ofDrosophila melanogaster were examined by mechanically disrupting and kneading whole discs from late third instar larvae and by culturing the resulting tissue mass for 10–14 days in adult female abdomens where the cells continued to divide. The grown implants were then dissected from the abdomens and injected into third instar larvae to undergo metamorphosis.After this treatment, prothoracic leg discs ofDrosophila melanogaster transdetermined with a high frequency (59% of all implants) to wing. Mesothoracic leg discs also transdetermined to wing, but at a very low frequency (4%). Metathoracic leg discs exhibited the same low frequency of transdetermination (4%), but in this case the direction of transdetermination was to haltere (Table 1,D. melanogaster).Very similar results were obtained with leg discs ofDrosophila nigromelanica (Table 1,D. nigromelanica), showing that the peculiar behavior of the three leg discs is not unique forDrosophila melanogaster.The homeotic mutation Polycomb (Pc ³) which partially transforms meso- and metathoracic legs into prothoracic legs did not significantly increase the frequencies of transdetermination in these leg dises and had clearly no effect on the direction of transdetermination (Table 1).We dedicate this publication to the memory of our teacher and advisor, the late Professor Ernst Hadorn, whose enthusiasm and interest stimulated our work     

Growth is required for cell competition in the imaginal discs ofDrosophila melanogaster

Summary Imaginal wing discs from late third-instar larvae were gammairradiated to induce clones of rapidly growingMinute ^– cells in a background of slowly growingMinute cells and culturedin vivo for periods up to 18 days. Clones in discs cultured for 16 to 18 days did not grow significantly larger than clones in uncultured controls, indicating that competition between populations of cells having potentially different mitotic rates does not occur in imaginal discs after their growth is completed.     

Homologies of positional information in thoracic imaginal discs ofDrosophila melanogaster

Summary The regulative behavior of fragments of the imaginal discs of the wing and first leg was studied when these fragments were combined with fragments of other thoracic imaginal discs. A fragment of the wing disc which does not normally regenerate when cultured could be stimulated to regenerate by combination with certain fragments of the haltere disc. When combined with a haltere disc fragment thought to be homologous by the criteria of morphology and the pattern of homoeotic transformation, such stimulated intercalary regeneration was not observed. Combinations of first and second leg disc fragments showed that a lateral first leg fragment could be stimulated to regenerate medial structures when combined with a medial second leg disc fragment but not when combined with a lateral second leg disc fragment. Combinations of wing and second leg disc fragments showed that one fragment of the second leg disc is capable of stimulating regeneration from a wing disc fragment while another second leg disc fragment fails to stimulate such regeneration. It is suggested that absence of intercalary regeneration in combinations of fragments of different thoracic imaginal discs is a result of homology or identity of the positional information residing in the cells of the fragments. The pattern of correspondence of positional information revealed by this analysis is consistant with the pattern of homology determined by morphological observation and by analysis of the positional specificity of homoeotic transformation among serially homologous appendages. The implications of the existence of homologous positional information in wing and second leg discs which share a common cell lineage early in development are discussed.     

Pattern specification in imaginal discs ofDrosophila melanogaster

Summary l(1)su(f)^mad-ts (mad) is a new temperature-sensitive (ts) lethal mutant ofDrosophila melanogaster which produces duplicated legs after temperature pulse treatment during larval development. The ts-lethality was studied in temperature experiments and genetic mosaics. Temperature pulses given during two distinct TSPs of larval development result in two different types of leg pattern duplication. Total differ from partial duplications with respect to the affected leg compartments and the orientation of the planes of symmetry which are perpendicular to the dorso-ventral and the proximo-distal leg axes in total and partial duplications, respectively. Genetic mosaic studies indicate (i) disc autonomy of leg pattern duplication, (ii) clonal separation of the anlagen of the two pattern copies, and (iii) clonal restriction along the antero-posterior compartment border in the two pattern copies of totally duplicated legs.The results suggest thatmad leg pattern duplication is caused by a change in positional information rather than by cell death and subsequent regeneration. Our data are compatible with the assumption that during normal development the leg disc cells acquire information about their position within the disc with respect to the different leg axes independently and at different times.     

The effect of fat body on the differentiation in vitro of wing imaginal discs ofDrosophila melanogaster

Summary The effect of suboptimal levels of -ecdysone on the differentiation in vitro ofDrosophila melanogaster wing discs was enhanced by the addition of larval fat body to the cultures. However, similar experiments with -ecdysome showed no enhancement. It is suggested that a partial conversion of -ecdysone to -ecdysone by the fat body may well account for these results.     

The effects of X-rays on the proliferation dynamics of cells in the imaginal wing disc ofDrosophila melanogaster

Summary We report on the size distribution of clones marked by mitotic recombination induced by several different doses of X-rays applied to 72 h oldDrosophila larvae. The results indicate that the radiation significantly reduces the number of cells which undergo normal proliferation in the imaginal wing disc. We estimate that 1000 r reduces by 40–60% the number of cells capable of making a normal contribution to the development of the adult wing. Part of this reduction is due to severe curtailment in the proliferative ability of cells which nevertheless remain capable of adult differentiation; this effect is possibly due to radiation-induced aneuploidy. Cytological evidence suggests that immediate cell death also occurs as a result of radiation doses as low as 100 r. The surviving cells are stimulated to undergo additional proliferation in response to the X-ray damage so that the result is the differentiation of a normal wing.     

Screening of larval/pupal P-element induced lethals on the second chromosome in Drosophila melanogaster : clonal analysis and morphology of imaginal discs

We have carried out screens for lethal mutations on the second chromosome of Drosophila melanogaster that are associated with abnormal imaginal disc morphologies, particularly in the wing disc. From a collection of 164 P element-induced mutations with a late larva/pupa lethal phase we have identified 56 new loci whose gene products are required for normal wing disc development and for normal morphology of other larval organs. Genetic mosaics of these 56 mutant lines show clonal mutant phenotypes for 23 cell-viable mutations. These phenotypes result from altered cell parameters. Causal relationships between disc and clonal phenotypes are discussed. Received: 19 June 1997 / Accepted: 4 August 1997     

Differentiation capacities of the labial imaginal disc ofDrosophila melanogaster

Summary The mature labial disc, when implanted into a larva of the same age, undergoes metamorphosis along with the host and produces one lateral half of the medi- and distiproboscis. On the basis of results obtained from transplanted disc halves (including the separate peripodial membrane) a tentative fate map of the labial disc was constructed, which shows most of the presumptive mediproboscis to be located in the dorsal, and most of the presumptive distiproboscis in the ventral part of the disc. The distal protion of the peripodial membrane also contains imaginal anlagen, viz. part of the mediproboscis, prementum, and labellar cap anlagen. The involvement of this part of the peripodial membrane was checked by a careful histological analysis of labial disc development during the first ten hours after prepupation. The results were compared with the situation described forCalliphora imaginal discs.In addition, a detailed morphological analysis was made of the proboscis of the homoeotic mutantproboscipedia (pb). At 27°C,pb changes the distiproboscis into a telopodite (leg segments distal to the coxa); the (unchanged) prementum may therefore correspond to the coxa. At 15° C, the tarsus of this homoeotic telopodite is replaced to a greater or lesser extent by an arista. The present analysis thus confirms (a) the fundamental morphological correspondence of the medi- and distiproboscis with the labium of other insects, and (b) the fundamental developmental correspondence of the labial, antennal, and leg discs.K. K. was a member of the 8th International Research Group in Developmental Biology, and was the recipient of a UNESCO travel grant.)     

Integument and sensory nerve differentiation ofDrosophila leg and wing imaginal discs in vitro

Summary An ultrastructural analysis is presented of the cuticular and neural structures formed by the prothoracic leg and wing imaginal discs of maleDrosophila melanogaster larvae during culture in vitro with 0.2 g/ml of -ecdysone. A pupal cuticle, and subsequently an imaginal cuticle with a well-defined epicuticle and a laminated endocuticle is formed. The ultrastructure of the epidermis and of cuticular structures such as bristles, trichomes, apodemes, and tracheoles is very similar to that found in situ. Dendrites and nerve cell bodies are formed in vitro, and sensory axons form nerve bundles similar to those of normal appendages in situ, despite their isolation from the central nervous system. It is concluded that at the ultrastructural level, differentiation in vitro closely parallels the normal course of development.     

Enzyme distribution patterns in the imaginal wing disc ofDrosophila melanogaster and other diptera

Summary Analysis of the development of the aldehyde oxidase (AO) pattern in the wing pouch ofD. melanogaster showed that the extension of areas with AO activity occurs in steps. This indicates that the activation of this enzyme is regulated in groups of cells. It is proposed to use the term territory for such a cell group. In the wing pouches ofD. melanogaster, D. simulans andMusca, corresponding parts of the disc become AO positive at comparable developmental stages. This indicates that AO becomes active in individual territories in a specific sequence.Borderlines of the distribution pattern of different enzymes in the wing pouch ofDrosophila and other dipteran species are in agreement with those found for the development of the AO pattern or are complementary to them. This indicates the existence of a common set of territories in the wing pouches of all higher diptera. Borderlines of patterns, as caused by different genetic constitution, are also in accord with this set of territories. The borderlines of some territories coincide with the compartmental A/P or D/V boundary. The results support the idea that both the location of compartmental boundaries and that of borderlines of enzyme territories are determined by a single mechanism.The distribution and the shape of the territories in the wing pouch is best explained by the reaction-diffusion model proposed by Meinhardt (1980), which involves three different gradients.     

Correlation between adult transformation and aldehyde oxidase staining pattern in wing discs ofApterous genotypes inDrosophila melanogaster

Summary The aldehyde oxidase staining pattern in wing discs ofDrosophila melanogaster bearing the genotypesap ^blt /ap ^blt andap ^blt andap ^blt /ap ⁷³ⁿ showns changes from the wild-type pattern. Extensive areas of the presumptive dorsal posterior wing blade, which are normally unstained, have enzyme activity in these mutants. In wings of these genotypes, dorsal posterior structures are replaced by dorsal anterior wing structures. A strong correlation has been found between the frequencies of various staining patterns in the discs and the extent of transformation in the cuticular structures of the wing, which is consistent with the idea that aldehyde oxidase activity can be used as an indicator in the wing disc of this transformation. Unlike the homoeotic mutationengrailed, apterous has not been interpreted as a selector gene yet the work reported here shows thatapterous alleles can cause changes resembling those of theengrailed phenotype both in aldehyde oxidase staining behaviour and in the cuticular transformation.     

Compartments and distal outgrowth in theDrosophila imaginal wing disc

Summary Peripheral tissue of the imaginal wing disc gives rise to the proximal mesothoracic structures of the adult. Pieces of peripheral tissue, which have no regenerative capacity when cultured as intact fragments, are capable of distal outgrowth (regeneration) after dissociation and reaggregation. This ability depends on the region of the disc periphery from which the fragment is taken. Extensive distal outgrowth occurs in reaggreages of a fragment containing equal proportions of tissue from anterior and posterior developmental compartments. The extent of outgrowth decreases as the proportion of posterior tissue is reduced, so that a fragment containing only anterior tissue shows no regeneration after dissociation. Limited distal outgrowth occurs in reaggregates of a wholly posterior fragment, but the regenerative capacity is increased greatly when a small amount of anterior tissue is included. It is concluded that distal outgrowth in the wing disc requires an interaction between cells of the anterior and posterior compartments.     

Cell interactions during the fusionin vitro ofDrosophila eye-antennal imaginal discs

Summary The fusion of the eye-antennal discs during culturein vitro has been investigated, and the complex morphogenetic movements which occur during the formation of the head capsule of the insect are described. The initial contact between the eye anlagen is by means of cell processes spanning the gap between the two discs. Subsequently the two epithelia become firmly apposed, and then the integrity of the epithelium in the region of fusion breaks down, cells appearing to move to new positions in order to form an epithelium which unites the two discs. The epithelium eventually secretes a pattern of cuticular structures which is continuous between the derivatives of the two discs. Bristles on either side of the line of fusion are perfectly aligned, and structures such as the median ocellus, which are formed jointly by the cells of the two discs, differentiate normally. This is also found when left and right eye-antennal discs of different genotypes are placed side-by-side, indicating that processes of pattern regulation can occur in culture.     

Development of cuticular patterns in the legs of a cell lethal mutant ofDrosophila melanogaster

Summary The development of cuticular patterns in the legs ofDrosophila melanogaster was studied in the temperature-sensitive cell autonomous lethal mutant1 (1)ts726 by treating animals with heat pulses of two days' duration at different developmental stages, in order to find out whether or not models which account for regulation of imaginal discs in the late third instar also hold for earlier developmental periods. Eight kinds of phenotypes were found, each of which occurred only after heat pulses that started at particular time: (1) complete and incomplete mirror image duplications of mesothoracic legs: early second instar; (2) homoeotic transformation to wing hinge in mesothoracic legs: early second instar; (3) prothoracic leg fusions: early second instar; (4) hypertrophied sex combs: early third instar; (5) outgrowths: early third instar; (6) sex comb teeth on second tarsal segment: early third instar; (7) reversed bristle polarity in intersegmental membrane gaps: early third instar; (8) deleted individual bristles: middle of third instar. These phenotypes were compared with patterns predicted by two models that have been devised to account for regeneration data: the polar coordinate model, and the gradient-of-morphogenetic-potential model. Some of the data (especially the finding of circumferentially incomplete partial duplicates) are more readily predicted by the polar coordinate model, although neither model can be ruled out. Phenotypes (6) and (7) can be accounted for by postulating a tandemly repeated positional signal corresponding to tarsal segmentation. The homoeotic transformation may be due to a transdetermination event occurring in situ during regulative growth following cell death. Since deletion of individual sex comb teeth leads to altered sex comb rotation, it is suggested that adjacent sex comb tooth cells interact during rotation.Address until September 1978: Institute of Molecular Biology, Billrothstraße 11, 5020 Salzburg, Austria     

Fusion ofDrosophila eye-antennal imaginal discs during differentiation in vitro

Summary Pairs of eye-antennal discs, attached to the cephalic ganglia, were cultured in vitro with a concentration of -ecdysone optimal for imaginal differentiation. The eye-antennal discs fused to form a vesicle inside which the antennae were partially everted, and on the inner surface of which imaginal structures differentiated. The epithelium of the discs was continuous, and an integrated pattern of bristles and hairs differentiated in vitro. In particular, the median ocellus, a unified structure derived partially from each disc, differentiated normally.     

The evagination of the genital imaginal discs ofDrosophila melanogaster

Summary The morphology of the evaginating female genital disc ofDrosophila melanogaster was examined at different stages of metamorphosis. The observations show that the internal genital organs are derived from the anterior half of the disc and that their morphogenesis is mainly a protrusion of the different primordial areas of the disc epithelium. The external genital and anal derivatives originate from the posterior half of the disc, which undergoes complex rearrangements during metamorphosis. The disc opens along the posterior margin and the dorsal and ventral epithelia evert and thereby completely reverse their anteroposterior orientation. Dramatic elongation has been observed during the formation of the seminal receptacle. The cells of the repressed male genital primordium do not form any recognizable structures and are assumed to be eliminated during metamorphosis.     

Maintenance of determination by cells of imaginal discs ofDrosophila after dissociation and culture in vivo

Summary Wild type cells of imaginal wing discs or embryos were dissociated and mixed in different proportions with cells of genetically marked wing and/or leg discs. These latter were X-irradiated to such an extent that their rate of proliferation was drastically lowered. They served as a feeding layer in which the interspersed wild type cells could be cultured. The reaggregates were allowed to grow in vivo, and fragments of them were tested for recovery of imaginal structures formed by wild-type cells.The experimental conditions for maximal dilution and maximal recovery of wildtype cells were first analysed. Under these conditions the progeny of cells deriving from different fragments of mature wing discs are capable of forming large territories of cuticle. These consisted preferentially of structures located in the region from which their ancestral cells were derived. The proliferating cells remained confined to either the anterior or the posterior wing compartments, but were apparently able to transgress the dorsalventral compartment border. Cells with qualities for distinct imaginal discs and possibly regions could also be recovered from dissociated embryos of 7 h age. The efficiency with which imaginal structures could be recovered as well at the types or qualities of these structures did not depend on the histotype of the feeding layer.