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At least 19 recordsLinked to original sources

PubMed1990

Pattern formation in imaginal discs.

Imaginal discs are sacs of folded epithelium arising during embryogenesis. They proliferate during the larval instars, and at metamorphosis secrete the adult cuticle, therefore being responsible for the characteristic surface patterning of this insect. Each disc has intrinsic growth controls and their cell lineage shows constraints known as compartments. Spatial patterns emerge through interaction between adjacent cells. Molecular genetic analysis of mutants with changed pattern has implicated transcription factors, secreted, membrane-bound and growth factor related proteins in the position-signalling mechanism. Their accessibility to contemporary cell biological techniques makes imaginal discs a model system for investigating patterning in animal tissues.

Animals↗

PubMed1990

The genetic control of cell proliferation in Drosophila imaginal discs.

The imaginal discs of Drosophila provide a favorable system for the analysis of the mechanisms controlling developmental cell proliferation, because of the separation in time between cell proliferation and differentiation, and the facility with which controlling genes can be identified and characterized. Imaginal discs are established in the embryo, and grow by cell proliferation throughout the larval period. Proliferation terminates in a regular spatial pattern during the final stages of larval development and the first day of pupal development. Cell proliferation can be locally reactivated in growth-terminated imaginal discs by removing part of the disc and culturing the remaining fragment in an adult host. The pattern of proliferation in these fragments suggests that cell proliferation in imaginal discs is controlled by direct interactions between cells and their neighbors. Proliferation appears to be stimulated by positional information differences, and these differences are reduced by the addition of new cells during tissue growth. Genes involved in cell proliferation control have been identified by collecting and analyzing recessive lethal mutations which cause overgrowth of imaginal discs. In some of these mutants (fat, lgd, c43, dco) the overgrowing tissue is hyperplastic; it retains its single-layered epithelial structure and is capable of differentiating. In two of the hyperplastic mutants (dco and c43), the imaginal discs show a failure of gap-junctional cell communication, suggesting that this form of cell communication may be involved in termination of proliferation. In other mutants the overgrowing disc tissue is neoplastic: it loses its structure and ability to differentiate, becoming a tumorous growth. The two genes that give a neoplastic phenotype (dlg and lgl) have been cloned and cDNAs of one of them (lgl) sequenced. The lgl gene encodes a cell surface molecule with significant homology to calcium-dependent cell adhesion molecules (cadherins). The expression of lgl at the time of termination of cell proliferation suggests that there are changes in the way that cells interact with one another at these times, and that these changes may be implemented by cell adhesion molecules. Direct cell contact within the epithelium, as well as signalling through gap junctions, appears to be involved in the cell interactions needed for the termination of cell proliferation. Mutations in genes encoding the Drosophila homologs of growth factors, growth factor receptors and oncogenes usually show an effect on cell-fate decisions rather than cell proliferation control, but this may be because oncogenic mutations in these genes would be dominant lethals and would therefore not be identified by conventional genetic analysis.

Aging↗

PubMed1992

Sequence and expression of IMP-L1, an ecdysone-inducible gene expressed during Drosophila imaginal disc morphogenesis.

Drosophila imaginal discs are induced by the steroid hormone 20-hydroxyecdysone to initiate morphogenesis leading to formation of the adult appendages and thoracic epidermis at the end of the third larval instar. Ecdysone-dependent transcriptional activation of a set of genes that encode imaginal disc transcripts found on membrane-bound polysomes precedes and may be responsible for some aspects of the cellular changes that mediate epithelial morphogenesis in this system. A 1.35 kb transcript from one of these genes, IMP-L1, is first observed in vivo at or just prior to pupariation, as ecdysone titers are peaking and beginning to decline. Expression is initiated in proximal areas of the antennal disc, later spreading to a more widespread but nonuniform distribution throughout other thoracic imaginal discs. IMP-L1 is not, however, expressed in other ecdysone target tissues such as salivary glands or fat body. The IMP-L1 gene encodes a novel protein product containing a signal peptide, a possible transmembrane domain, two highly charged domains and a proline rich C-terminal domain. We suggest that the delayed timing of expression of this secondary response gene is necessary for proper ordering of cellular events associated with disc morphogenesis.

Amino Acid Sequence↗

PubMed1991

Involvement of Sarcophaga lectin in the development of imaginal discs of Sarcophaga peregrina in an autocrine manner.

The imaginal discs of Sarcophaga were found not to develop normally in the presence of galactose, a hapten sugar of Sarcophaga lectin, or anti-Sarcophaga lectin antibody. Wing and leg discs cultured with these substances became morphologically abnormal and no imaginal discs reached the stage of terminal differentiation, even in the presence of 20-hydroxyecdysone. The development of the imaginal discs was shown to be autonomously regulated in an autocrine manner by Sarcophaga lectin; namely Sarcophaga lectin was secreted by the imaginal discs in the presence of 20-hydroxyecdysone, and the stimulus of self-induced Sarcophaga lectin seemed to be indispensable for further development of the imaginal discs. Sarcophaga lectin was originally found as a defense protein, but these results show that it plays independent roles in both defense and development.

Animals↗

PubMed1992

Genetic, cytogenetic and developmental analysis of the Drosophila melanogaster tumor suppressor gene lethal(2)tumorous imaginal discs (1(2)tid).

Three of the twenty recessive-lethal tumor suppressor genes of Drosophila cause imaginal disc tumors in the homozygously mutated state. One of these is the lethal(2)tumorous imaginal discs (l(2)tid) gene. Histological preparations show the tumorous imaginal disc epithelium to consist of a mosaic of cells in monolayer and cells in clumped arrangement. In contrast, the wild-type imaginal disc epithelium is comprised exclusively of cells in monolayer arrangement. Mutant imaginal disc tissue pieces implanted into ready-to-pupariate wild-type larvae fail to differentiate. Implantation of l(2)tid imaginal disc tissue pieces in vivo into wild-type adult flies revealed a lethal, tumorous growth comparable to that in situ, thus characterizing the l(2)tid imaginal discs as truly malignant. The phenotypes of double mutants between two l(2)tid alleles and tumor suppressor genes, such as lethal(2)giant larvae and lethal(2)brain tumor, and the epithelial overgrowth mutant lethal(2)fat are described and discussed. Finally, we present the genetic, cytogenetic and molecular localization of the l(2)tid gene to the giant chromosome bands 59F4-6.

Alleles↗

PubMed1977

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.

Animals↗

PubMed1992

What are and what are not imaginal discs: reevaluation of some basic concepts (Insecta, Holometabola).

Some general aspects of the concept of imaginal discs in the Holometabola are reevaluated. Their monolayer character and continuity with the surrounding epidermis are confirmed. Studies on the imaginal discs of the silkworm (Bombyx mori) and data from the literature show that the discs and their peripodial cells produce cuticle during larval life, as well as at metamorphosis. In B. mori it is demonstrated that adult and larval antennae are produced by the same cells or their progeny. The results also suggest that segments of the typically three-segmented larval antenna of Holometabola are not scape, pedicel, and one-segmented flagellum; at least segments 2 and 3 are of flagellar origin. Based on these and some additional facts it is argued that: (1) No larval organs are "replaced" at metamorphosis, but strict "sequential homology" is always maintained. (2) Imaginal discs are not undifferentiated structures destined to form the adult after larval breakdown, cannot be unambiguously defined, and do not represent qualitatively different epidermal structures. Classical imaginal discs (invaginated and present also in pre-final larval instars) arose several times independently and were not present in the larvae of ancestral Holometabola. (3) Since the disc cells are not undifferentiated and "embryonic" (if these words have a defined meaning at all), it is unreasonable to expect that the processes taking place in discs at metamorphosis would differ fundamentally from those occurring in other diploid metamorphosing epidermal cells.

Animals↗

PubMed1991

The embryonic origin of imaginal discs in Drosophila.

The thoracic imaginal discs of Drosophila melanogaster can be observed during embryogenesis as clusters of cells with particular shapes, sizes and behaviours. These structures can be detected soon after germ band shortening and their development appears to be tightly linked to that of the larval epidermis.

Animals↗

PubMed1992

A mechanistic model for morphogenesis and regeneration of limbs and imaginal discs.

When an amphibian limb, cockroach leg or Drosophila imaginal disc is subjected to a surgical operation, it is capable of regenerating or duplicating certain parts. Although the structure of the regenerated tissue varies depending on the location and mass of the amputated or transplanted part, it can be predicted from a set of formal rules, called the polar coordinate model [French et al., (1976) Science 193, 969-983; Bryant et al., (1981) Science 212, 993-1002]. In the polar coordinate model, it is assumed (and experimentally proven) that the juxtaposition of normally non-adjacent cells stimulates cell proliferation locally, which implies that the underlying mechanism which gives positional values to each cell, is also responsible for the control of cell growth. Because locally activated proliferation alters the shape and size of the developmental field, the question of how to control the cell growth is the central problem in the regeneration of the limbs and imaginal discs. In this paper, I propose a possible underlying mechanism for the 'polar coordinate rules', and show how this mechanistic model explains the experimental results using computer simulation. The proposed mechanism is an extension of Turing's model (1952). In addition to the reaction-diffusion of the molecules, cell proliferation is taken into consideration. With appropriate initial conditions, the computer simulation shows that a small mass of cells grows up to form a mature limb, and that the mature limb is able to respond to surgical operations as predicted by the polar coordinate model.

Amphibians↗

PubMed1990

The Drosophila IMP-E2 gene encodes an apically secreted protein expressed during imaginal disc morphogenesis.

During metamorphosis, the steroid hormone 20-hydroxyecdysone induces morphogenesis of imaginal discs, including the formation of appendages. IMP-E2 is an ecdysone-dependent, single-copy Drosophila gene, whose transcripts accumulate rapidly in imaginal discs in response to the hormone. The IMP-E2 product is secreted at the apical surface of the disc epithelium in association with disc morphogenesis. The product is also secreted apically by the embryonic ectoderm during mid embryogenesis. The deduced primary structure of the protein reveals the presence of 16, short 3-amino acid repeat motifs (such as EIK and EVK) toward the N-terminal end of the protein, and three long, uncharged domains, containing 43 to 78 residues each, toward the C-terminal end. The predicted structure of the protein suggests that it may participate in multimolecular aggregates. Although the temporal and spatial expression of the IMP-E2 gene are consistent with a role in disc morphogenesis, its specific functions remain to be determined.

Amino Acid Sequence↗

PubMed1990

Characterization of IMP-E3, a gene active during imaginal disc morphogenesis in Drosophila melanogaster.

The steroid hormone 20-hydroxyecdysone (20-HE) induces imaginal discs to form adult appendages in Drosophila. We have isolated a set of six ecdysone-responsive genes that apparently encode disc cell-surface or secreted proteins. Transcripts from one of these genes, IMP-E3, accumulate rapidly within 1-2 h in response to hormone. Developmentally, IMP-E3 transcripts reach maximum levels during the first stages of metamorphosis (white prepupae, WPP) and are primarily limited to imaginal tissues. Transcripts are also present during embryogenesis (0-3 h and 12-18 h). Two different-sized transcripts (1.2 and 1.4 kb) result from differential polyadenylation, with the larger transcript predominating in WPP. The conceptual IMP-E3 protein contains a signal peptide, an RGD sequence, and a potential glycosylphosphatidylinositol anchor. We speculate that the protein provides a transient cue important for imaginal disc morphogenesis.

Amino Acid Sequence↗

PubMed1979

Specific binding of 20-hydroxyecdysone to nuclei of imaginal discs of Drosophila melanogaster.

Specific binding of the insect steroid hormone 20-hydroxyecdysone to imaginal discs of Drosophila melanogaster has been investigated. Evidence is presented showing that most of the specific binding is located in the nuclear fraction at the time changes in gene function are observed. Nuclear binding is high affinity, analog specific, apparently saturable, and unaffected by inhibitors of RNA and protein synthesis. The association kinetics of nuclear binding are very similar to those of specific binding in whole cells. Specific binding to whole discs and to disc nuclei is temperature-dependent, but equal levels of nuclear binding are achieved after 1 h at 25 degrees C and 8 h at 0-4 degrees C. There is little or no lag in the nuclear location of specific binding at either temperature. The biochemical properties of the specific nuclear binding are consistent with the involvement of these sites in the hormone detection and response system mediating imaginal disc morphogenesis.

Amanitins↗

PubMed1991

Parameters of growth in primary cultures and cell lines established from Drosophila imaginal discs.

We have further characterised our tissue culture system for the growth in vitro of Drosophila imaginal disc cells, including the culture medium requirements for optimum growth and we have adjusted the protocol recommended for the initiation of cultures. Many imaginal disc fragments become organised into vesicles, and some of these secrete extracellular material into the lumen. Sensory axons differentiate in primary disc cultures, in the absence of bristle formation. The early stages of cell division to form a cell line are recorded.

Animals↗

PubMed1992

Localization of DER and the pattern of cell divisions in wild-type and Ellipse eye imaginal discs.

The compound eye of Drosophila develops from a uniform layer of epithelial cells in the eye imaginal disc. One intriguing aspect of eye development is the establishment of the correct number and spacing of the photoreceptor clusters which give rise to the mature ommatidia. Ellipse (Elp) has been implicated as playing a role in this process because the Elp dominant gain of function mutation dramatically reduces the number of photoreceptor clusters in the compound eye without affecting the morphology of individual clusters that are formed (Baker and Rubin, 1989). Since Elp represents an allele of the Drosophila EGF receptor (DER) locus, it encodes a protein which is structurally capable of mediating inductive cell-cell interactions. In an effort to better understand the role of the DER locus in ommatidial patterning, we compared the localization of DER protein in eye imaginal discs of wild-type and Elp larvae. The distribution of this receptor is consistent with the notion of its mediating interactions between cells at the initial stages of photoreceptor precluster positioning and differentiation. However, the basis of the Elp gain of function mutation is not ectopic or increased expression of the DER protein. Rather, expression of the Elp form of the EGF receptor homolog in the normal localization leads to changes in the proliferative pattern of cells dividing posterior to the morphogenetic furrow.

Animals↗

PubMed1975

Regeneration and duplication in imaginal discs.

When two complementary fragments of a Drosophila imaginal disc are cultured in adult abdomens before transfer to host larvae for metamorphosis, the usual result is that one of the two fragments regenerates the missing parts while the other fragment duplicates the anlagen already present. To account for this it is proposed that in the disc there is a gradient of developmental capacity, by which new positional information can be generated from a cut surface only in the downward direction in the gradient, irrespective of the physical direction faced by the cut surface. The same kind of behaviour is shown by other epimorphic systems, such as the regenerating appendages of amphibians and of hemmimetabolous insects, and the regenerating body segments of annelids. The regeneration-duplication rule has been shown to apply for thirteen different cuts in the wing disc, some across the proximodistal and others across the anteroposterior axis. In both axes there is a reversal in the direction of regenerative ability at the approximate centre of the disc. As an alternative to the hypothesis of orthogonal double gradients, it is proposed that the wing disc has multiple gradients of developmental capacity which radiate from the centre of the disc. The location of this centre is known, and its properties are being studied.

Animals↗

PubMed1990

Ecdysone-dependent proteolysis of an apical surface glycoprotein may play a role in imaginal disc morphogenesis in Drosophila.

An apical surface glycoprotein, designated gp125 for its apparent molecular weight of 125,000, appears in Ca2(+)-free, ionic detergent extracts of imaginal discs of Drosophila melanogaster in response to the steroid hormone, 20-hydroxyecdysone (20-HE). Gp125 is not synthesized in response to 20-HE, but results from modification of an existing macromolecule. Treatment of discs or larval epidermis with serine protease (e.g., trypsin) results in hormone-independent production of gp125. Antiserum raised to electrophoretically purified gp125 recognizes, in addition to gp125, two closely related glycoproteins with higher apparent molecular weights, gp200 and gp180. This family of glycoproteins is localized at the apical surface of imaginal disc cells and of the epidermal epithelium in embryos, larvae and prepupae. Ca2+ affects both the solubility and the proteolytic products of this family of glycoproteins. We discuss the possibility that gp125 is generated through the action of a hormonally controlled serine protease in a process that is necessary for disc morphogenesis.

Animals↗

PubMed1992

apterous, a gene required for imaginal disc development in Drosophila encodes a member of the LIM family of developmental regulatory proteins.

The apterous (ap) gene is required for the normal development of the wing and haltere imaginal discs in Drosophila melanogaster. ap encodes a new member of the LIM family of developmental regulatory genes. The deduced amino acid sequence of ap predicts a homeo domain and a cysteine/histidine-rich domain known as the LIM domain. In these domains ap is highly similar to the mec-3 and lin-11 proteins of Caenorhabditis elegans and to the vertebrate insulin enhancer-binding protein isl-1. ap is presumably required for transcriptional regulation of genes involved in wing and haltere development. The nature of the defects in homozygous null mutant flies is consistent with the pattern of ap expression in the larval imaginal discs. ap is also expressed in a complex pattern in the embryo, including portions of the peripheral nervous system (PNS) and central nervous system (CNS). A requirement for ap expression in the larval and adult CNS may be the underlying cause of the defects in hormone production and vitellogenesis described for ap mutations.

Amino Acid Sequence↗

PubMed1976

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.

Animals↗