The ultrastructure of imaginal disc cells in primary cultures and during cell aggregation in continuous cell lines

Polarized sorting of Patched enables cytoneme-mediated Hedgehog reception in the Drosophila wing disc

Hedgehog (Hh) signal molecules play a fundamental role in development, adult stem cell maintenance and cancer. Hh can signal at a distance, and we have proposed that its graded distribution across Drosophila epithelia is mediated by filopodia-like structures called cytonemes. Hh reception by Patched (Ptc) happens at discrete sites along presenting and receiving cytonemes, reminiscent of synaptic processes. Here, we show that a vesicle fusion mechanism mediated by SNARE proteins is required for Ptc placement at contact sites. Transport of Ptc to these sites requires multivesicular bodies (MVBs) formation via ESCRT machinery, in a manner different to that regulating Ptc/Hh lysosomal degradation after reception. These MVBs include extracellular vesicle (EV) markers and, accordingly, Ptc is detected in the purified exosomal fraction from cultured cells. Blockage of Ptc trafficking and fusion to basolateral membranes result in low levels of Ptc presentation for reception, causing an extended and flattened Hh gradient.

Drosophila imaginal disc growth factor 2 is a trophic factor involved in energy balance, detoxification, and innate immunity

Drosophila imaginal disc growth factor 2 (IDGF2) is a member of chitinase-like protein family (CLPs) able to induce the proliferation of imaginal disc cells in vitro. In this study we characterized physiological concentrations and expression of IDGF2 in vivo as well as its impact on the viability and transcriptional profile of Drosophila cells in vitro. We show that IDGF2 is independent of insulin and protects cells from death caused by serum deprivation, toxicity of xenobiotics or high concentrations of extracellular adenosine (Ado) and deoxyadenosine (dAdo). Transcriptional profiling suggested that such cytoprotection is connected with the induction of genes involved in energy metabolism, detoxification and innate immunity. We also show that IDGF2 is an abundant haemolymph component, which is further induced by injury in larval stages. The highest IDGF2 accumulation was found at garland and pericardial nephrocytes supporting its role in organismal defence and detoxification. Our findings provide evidence that IDGF2 is an important trophic factor promoting cellular and organismal survival.

Cancer Drug Development Using Drosophila as an in vivo Tool: From Bedside to Bench and Back

The fruit fly Drosophila melanogaster has been used for modeling cancer and as an in vivo tool for the validation and/or development of cancer therapeutics. The impetus for the use of Drosophila in cancer research stems from the high conservation of its signaling pathways, lower genetic redundancy, short life cycle, genetic amenability, and ease of maintenance. Several cell signaling pathways in Drosophila have been used for cancer drug development. The efficacy of combination therapy and uptake/bioavailability of drugs have also been studied. Drosophila has been validated using several FDA-approved drugs, suggesting a potential application of this model in drug repurposing. The model is emerging as a powerful tool for high-throughput screening and should significantly reduce the cost and time associated with drug development. In this review we discuss the applications of Drosophila in cancer drug development. The advantages and limitations of the model are discussed.

Identification of common and cell type specific LXXLL motif EcR cofactors using a bioinformatics refined candidate RNAi screen in Drosophila melanogaster cell lines

Background

During Drosophila development, titers of the steroid ecdysone trigger and maintain temporal and tissue specific biological transitions. Decades of evidence reveal that the ecdysone response is both unique to specific tissues and distinct among developmental timepoints. To achieve this diversity in response, the several isoforms of the Ecdysone Receptor, which transduce the hormone signal to the genome level, are believed to interact with tissue specific cofactors. To date, little is known about the identity of these cofactor interactions; therefore, we conducted a bioinformatics informed, RNAi luciferase reporter screen against a subset of putative candidate cofactors identified through an in silico proteome screen. Candidates were chosen based on criteria obtained from bioinformatic consensus of known nuclear receptor cofactors and homologs, including amino acid sequence motif content and context.

Results

The bioinformatics pre-screen of the Drosophila melanogaster proteome was successful in identifying an enriched putative candidate gene cohort. Over 80% of the genes tested yielded a positive hit in our reporter screen. We have identified both cell type specific and common cofactors which appear to be necessary for proper ecdysone induced gene regulation. We have determined that certain cofactors act as co-repressors to reduce target gene expression, while others act as co-activators to increase target gene expression. Interestingly, we find that a few of the cofactors shared among cell types have a reversible roles to function as co-repressors in certain cell types while in other cell types they serve as co-activators. Lastly, these proteins are highly conserved, with higher order organism homologs also harboring the LXXLL steroid receptor interaction domains, suggesting a highly conserved mode of steroid cell target specificity.

Conclusions

In conclusion, we submit these cofactors as novel components of the ecdysone signaling pathway in order to further elucidate the dynamics of steroid specificity.

Chemical genetics and drug screening in Drosophila cancer models

Drug candidates often fail in preclinical and clinical testing because of reasons of efficacy and/or safety. It would be time- and cost-efficient to have screening models that reduce the rate of such false positive candidates that appear promising at first but fail later. In this regard, it would be particularly useful to have a rapid and inexpensive whole animal model that can pre-select hits from high-throughput screens but before testing in costly rodent assays. Drosophila melanogaster has emerged as a potential whole animal model for drug screening. Of particular interest have been drugs that must act in the context of multi-cellularity such as those for neurological disorders and cancer. A recent review provides a comprehensive summary of drug screening in Drosophila, but with an emphasis on neurodegenerative disorders. Here, we review Drosophila screens in the literature aimed at cancer therapeutics.

Chromatin state marks cell-type- and gender-specific replication of the Drosophila genome

Duplication of eukaryotic genomes during S phase is coordinated in space and time. In order to identify zones of initiation and cell-type- as well as gender-specific plasticity of DNA replication, we profiled replication timing, histone acetylation, and transcription throughout the Drosophila genome. We observed two waves of replication initiation with many distinct zones firing in early-S phase and multiple, less defined peaks at the end of S phase, suggesting that initiation becomes more promiscuous in late-S phase. A comparison of different cell types revealed widespread plasticity of replication timing on autosomes. Most occur in large regions, but only half coincide with local differences in transcription. In contrast to confined autosomal differences, a global shift in replication timing occurs throughout the single male X chromosome. Unlike in females, the dosage-compensated X chromosome replicates almost exclusively early. This difference occurs at sites that are not transcriptionally hyperactivated, but show increased acetylation of Lys 16 of histone H4 (H4K16ac). This suggests a transcription-independent, yet chromosome-wide process related to chromatin. Importantly, H4K16ac is also enriched at initiation zones as well as early replicating regions on autosomes during S phase. Together, our study reveals novel organizational principles of DNA replication of the Drosophila genome and suggests that H4K16ac is more closely correlated with replication timing than is transcription.

Parallel RNAi screens across different cell lines identify generic and cell type-specific regulators of actin organization and cell morphology

Parallel RNA interference screens and gene expression arrays in six Drosophila cell lines identified regulators of cell morphology, including a neuronal function for the kinase minibrain/DYRK1A in the regulation of protrusion morphology.

Background

In recent years RNAi screening has proven a powerful tool for dissecting gene functions in animal cells in culture. However, to date, most RNAi screens have been performed in a single cell line, and results then extrapolated across cell types and systems.

Results

Here, to dissect generic and cell type-specific mechanisms underlying cell morphology, we have performed identical kinome RNAi screens in six different Drosophila cell lines, derived from two distinct tissues of origin. This analysis identified a core set of kinases required for normal cell morphology in all lines tested, together with a number of kinases with cell type-specific functions. Most significantly, the screen identified a role for minibrain (mnb/DYRK1A), a kinase associated with Down's syndrome, in the regulation of actin-based protrusions in CNS-derived cell lines. This cell type-specific requirement was not due to the peculiarities in the morphology of CNS-derived cells and could not be attributed to differences in mnb expression. Instead, it likely reflects differences in gene expression that constitute the cell type-specific functional context in which mnb/DYRK1A acts.

Conclusions

Using parallel RNAi screens and gene expression analyses across cell types we have identified generic and cell type-specific regulators of cell morphology, which include mnb/DYRK1A in the regulation of protrusion morphology in CNS-derived cell lines. This analysis reveals the importance of using different cell types to gain a thorough understanding of gene function across the genome and, in the case of kinases, the difficulties of using the differential gene expression to predict function.

RNAi in Drosophila S2 cells as a tool for studying cell cycle progression

Genetic studies on model organisms, particularly yeasts and Drosophila melanogaster, have proven powerful in identifying the cell cycle machinery and its regulatory mechanisms. In more recent years RNAi has been used in a variety of genome-wide screens and single molecule studies to elucidate the mechanisms of cell cycle progression. In Drosophila cultured cells, RNAi is extremely simple, and a strong effect can be observed by adding the dsRNA to the cultured cells, with few complications of off-target effects. Functions in cell cycle progression can be followed by a variety of assays. One of the advantages of these cells is that they allow high-resolution spatiotemporal observations to be made by microscopy, with no particular complexity in terms of media and temperature. Here we discuss protocols for RNAi in Drosophila S2 culture cells, followed by the study of mitotic progression, through immunocytochemistry, live imaging, and flow cytometry analysis.

Regulation of the feedback antagonist naked cuticle by Wingless signaling

Signaling pathways usually activate transcriptional targets in a cell type-specific manner. Notable exceptions are pathway-specific feedback antagonists, which serve to restrict the range or duration of the signal. These factors are often activated by their respective pathways in a broad array of cell types. For example, the Wnt ligand Wingless (Wg) activates the naked cuticle (nkd) gene in all tissues examined throughout Drosophila development. How does the nkd gene respond in such an unrestricted manner to Wg signaling? Analysis in cell culture revealed regions of the nkd locus that contain Wg response elements (WREs) that are directly activated by the pathway via the transcription factor TCF. In flies, Wg signaling activates these WREs in multiple tissues, in distinct but overlapping patterns. These WREs are necessary and largely sufficient for nkd expression in late stage larval tissues, but only contribute to part of the embryonic expression pattern of nkd. These results demonstrate that nkd responsiveness to Wg signaling is achieved by several WREs which are broadly (but not universally) activated by the pathway. The existence of several WREs in the nkd locus may have been necessary to allow the Wg signaling-Nkd feedback circuit to remain intact as Wg expression diversified during animal evolution.

RNA interference in cultured Drosophila cells

RNA interference (RNAi) can be used to silence genes in a number of species, including plants, nematodes, protozoans, Drosophila melanogaster, mouse embryos, and mammalian and Drosophila cell cultures. Drosophila cell culture provides the opportunity to study signal transduction pathways and protein function in a simple, well defined cell culture paradigm. Furthermore, because Drosophila are RNAi responsive, the results obtained from experiments performed on cultured cells can be confirmed in the whole organism. RNAi takes advantage of the unique ability of double-stranded RNA (dsRNA) molecules to induce gene silencing in a highly specific manner. This phenomenon is efficacious and long lived, being passed to subsequent generations in Drosophila cell culture. To date, many Drosophila cell lines tested respond to dsRNAs by ablating expression of the target protein. Furthermore, all dsRNAs tested have been efficacious at silencing the target gene. Drosophila cell cultures are simple, easily manipulated model systems that will facilitate loss of function studies applicable to a wide variety of questions.

Drosophila cell lines as model systems and as an experimental tool

Given the power of Drosophila genetics, it may seem surprising to discover that many fly researchers are turning to Drosophila cell culture as an experimental system. However, as we will show in this chapter, there are many benefits to be gained by using cell lines as a complement to studies in a tissue and developmental context in the fly. Moreover, one can argue that Drosophila cell culture, in itself, provides an excellent model system for the study of many fundamental questions in molecular and cellular biology. In this review, we offer a summary of techniques that should be useful to researchers in the Drosophila community working with fly cell lines. These include techniques for growing and maintaining cell lines, transient and stable transfection, RNA interference, imaging, immunostaining, fluorescence-activated cell sorting, and for the isolation of RNA and protein from fly cells.

Disruption of topoisomerase II perturbs pairing in drosophila cell culture

Homolog pairing refers to the alignment and physical apposition of homologous chromosomal segments. Although commonly observed during meiosis, homolog pairing also occurs in nonmeiotic cells of several organisms, including humans and Drosophila. The mechanism underlying nonmeiotic pairing, however, remains largely unknown. Here, we explore the use of established Drosophila cell lines for the analysis of pairing in somatic cells. Using fluorescent in situ hybridization (FISH), we assayed pairing at nine regions scattered throughout the genome of Kc167 cells, observing high levels of homolog pairing at all six euchromatic regions assayed and variably lower levels in regions in or near centromeric heterochromatin. We have also observed extensive pairing in six additional cell lines representing different tissues of origin, different ploidies, and two different species, demonstrating homolog pairing in cell culture to be impervious to cell type or culture history. Furthermore, by sorting Kc167 cells into G1, S, and G2 subpopulations, we show that even progression through these stages of the cell cycle does not significantly change pairing levels. Finally, our data indicate that disrupting Drosophila topoisomerase II (Top2) gene function with RNAi and chemical inhibitors perturbs homolog pairing, suggesting Top2 to be a gene important for pairing.

Notch synergizes with axin to regulate the activity of armadillo in Drosophila

Cell fate decisions require the integration of various signalling inputs at the level of transcription and signal transduction. Wnt and Notch signalling are two important signalling systems that operate in concert in a variety of systems in vertebrates and invertebrates. There is evidence that the Notch receptor can modulate Wnt signalling and that its target is the activity and levels of Armadillo/beta-catenin. Here, we characterize this function of Notch in relation to Axin, a key element in the regulation of Wnt signalling that acts as a scaffold for the Shaggy/GSK3beta-dependent phosphorylation of Armadillo/beta-catenin. While Notch can regulate ectopic Wingless signalling caused by loss of function of Shaggy, it can only partially regulate the ectopic Wnt signalling induced by the loss of Axin function. The same interactions are observed in tissue culture cells where we observe a synergy in between Axin and Notch in the regulation of Armadillo/beta-catenin. Our results provide evidence for a function of Axin in the regulation of Armadillo that is different from its role as a scaffold for GSK3beta.

Drosophila ribosomal proteins are associated with linker histone H1 and suppress gene transcription

The dynamics and function of ribosomal proteins in the cell nucleus remain enigmatic. Here we provide evidence that specific components of Drosophila melanogaster ribosomes copurify with linker histone H1. Using various experimental approaches, we demonstrate that this association of nuclear ribosomal proteins with histone H1 is specific, and that colocalization occurs on condensed chromatin in vivo. Chromatin immunoprecipitation analysis confirmed that specific ribosomal proteins are associated with chromatin in a histone H1-dependent manner. Overexpression of either histone H1 or ribosomal protein L22 in Drosophila cells resulted in global suppression of the same set of genes, while depletion of H1 and L22 caused up-regulation of tested genes, suggesting that H1 and ribosomal proteins are essential for transcriptional gene repression. Overall, this study provides evidence for a previously undefined link between ribosomal proteins and chromatin, and suggests a role for this association in transcriptional regulation in higher eukaryotes.

High-throughput RNAi screening in cultured cells: a user's guide

RNA interference has re-energized the field of functional genomics by enabling genome-scale loss-of-function screens in cultured cells. Looking back on the lessons that have been learned from the first wave of technology developments and applications in this exciting field, we provide both a user's guide for newcomers to the field and a detailed examination of some more complex issues, particularly concerning optimization and quality control, for more advanced users. From a discussion of cell lines, screening paradigms, reagent types and read-out methodologies, we explore in particular the complexities of designing optimal controls and normalization strategies for these challenging but extremely powerful studies.

Wingless signaling modulates cadherin-mediated cell adhesion in Drosophila imaginal disc cells

Armadillo, the Drosophila homolog of beta-catenin, plays a crucial role in both the Wingless signal transduction pathway and cadherin-mediated cell-cell adhesion, raising the possibility that Wg signaling affects cell adhesion. Here, we use a tissue culture system that allows conditional activation of the Wingless signaling pathway and modulation of E-cadherin expression levels. We show that activation of the Wingless signaling pathway leads to the accumulation of hypophosphorylated Armadillo in the cytoplasm and in cellular processes, and to a concomitant reduction of membrane-associated Armadillo. Activation of the Wingless pathway causes a loss of E-cadherin from the cell surface, reduced cell adhesion and increased spreading of the cells on the substratum. After the initial loss of E-cadherin from the cell surface, E-cadherin gene expression is increased by Wingless. We suggest that Wingless signaling causes changes in Armadillo levels and subcellular localization that result in a transient reduction of cadherin-mediated cell adhesion, thus facilitating cell shape changes, division and movement of cells in epithelial tissues.

High-throughput RNA interference screens in Drosophila tissue culture cells

This chapter describes the method used to conduct high-throughput screening (HTs) by RNA interference in Drosophila tissue culture cells. It covers four main topics: (1) a brief description of the existing platforms to conduct RNAi-screens in cell-based assays; (2) a table of the Drosophila cell lines available for these screens and a brief mention of the need to establish other cell lines as well as cultures of primary cells; (3) a discussion of the considerations and protocols involved in establishing assays suitable for HTS in a 384-well format; and (A) a summary of the various ways of handling raw data from an ongoing screen, with special emphasis on how to apply normalization for experimental variation and statistical filters to sort out noise from signals.

Functional genomic analysis of the Wnt-wingless signaling pathway

The Wnt-Wingless (Wg) pathway is one of a core set of evolutionarily conserved signaling pathways that regulates many aspects of metazoan development. Aberrant Wnt signaling has been linked to human disease. In the present study, we used a genomewide RNA interference (RNAi) screen in Drosophila cells to screen for regulators of the Wnt pathway. We identified 238 potential regulators, which include known pathway components, genes with functions not previously linked to this pathway, and genes with no previously assigned functions. Reciprocal-Best-Blast analyses reveal that 50% of the genes identified in the screen have human orthologs, of which approximately 18% are associated with human disease. Functional assays of selected genes from the cell-based screen in Drosophila, mammalian cells, and zebrafish embryos demonstrated that these genes have evolutionarily conserved functions in Wnt signaling. High-throughput RNAi screens in cultured cells, followed by functional analyses in model organisms, prove to be a rapid means of identifying regulators of signaling pathways implicated in development and disease.

Notch modulates Wnt signalling by associating with Armadillo/beta-catenin and regulating its transcriptional activity

The establishment and stability of cell fates during development depend on the integration of multiple signals, which ultimately modulate specific patterns of gene expression. While there is ample evidence for this integration at the level of gene regulatory sequences, little is known about its operation at other levels of cellular activity. Wnt and Notch signalling are important elements of the circuitry that regulates gene expression in development and disease. Genetic analysis has suggested that in addition to convergence on the transcription of specific genes, there are modulatory cross-regulatory interactions between these signalling pathways. We report that the nodal point of these interactions is an activity of Notch that regulates the activity and the amount of the active/oncogenic form of Armadillo/beta-catenin. This activity of Notch is independent of that induced upon cleavage of its intracellular domain and which mediates transcription through Su(H)/CBF1. The modulatory function of Notch described here, contributes to the establishment of a robust threshold for Wnt signalling which is likely to play important roles in both normal and pathological situations.

Cell-cell and cell-substrate adhesion in cultured Drosophila imaginal disc cells

Drosophila imaginal disc cell lines were used to investigate various aspects of cellular adhesion in vitro. The distribution of PS integrins and their involvement in cell-cell and cell-substrate adhesion were assessed with the monoclonal antibody aBG-1 against the betaPS subunit, and both forms of adhesion were found to be impeded by the presence of the antibody. Adhesion to a number of extracellular matrix components was investigated, and the cells were found to adhere to human fibronectin. This adhesion was inhibited by aBG-1. The adhesion molecule fasciclin III was also found in these cells. Given that the cells are competent to perform cell-cell and cell-substrate adhesion, it was thought that apical basal polarity might be restored when other suitable conditions were provided, i.e., an artificial basement layer with feeder cells to provide nutrients basally to the cells, and some features of apical-basal morphology were seen in cells cultured under these conditions.

Adhesion of Drosophila imaginal disc cells in vitro

We have used our imaginal disc cell lines to carry out in vitro studies on the cell-cell and cell-substrate adhesion of Drosophila leg and wing disc cells. Single cells were allowed to reaggregate in roller culture, and this process was found to be partially dependent on the presence of magnesium and calcium ions in the suspension medium. Varying rates of reaggregation were observed in cells from different stages of a passage, correlating with the pattern of morphogenesis which occurs during the passage. We have demonstrated that cloned cell lines can be produced showing certain selected characteristics, such as reduced cell adhesiveness.

Filopodia: fickle fingers of cell fate?

Epithelial cells often produce extensions, known variously as filopodia, cell feet or cytonemes, which can extend across many cell diameters to directly contact non-adjacent cells. Do they function in morphogenesis, cell-cell signaling or both?.

A new family of growth factors produced by the fat body and active on Drosophila imaginal disc cells

By fractionating conditioned medium (CM) from Drosophila imaginal disc cell cultures, we have identified a family of Imaginal Disc Growth Factors (IDGFs), which are the first polypeptide growth factors to be reported from invertebrates. The active fraction from CM, as well as recombinant IDGFs, cooperate with insulin to stimulate the proliferation, polarization and motility of imaginal disc cells. The IDGF family in Drosophila includes at least five members, three of which are encoded by three genes in a tight cluster. The proteins are structurally related to chitinases, but they show an amino acid substitution that is known to abrogate catalytic activity. It therefore seems likely that they have evolved from chitinases but acquired a new growth-promoting function. The IDGF genes are expressed most strongly in the embryonic yolk cells and in the fat body of the embryo and larva. The predicted molecular structure, expression patterns, and mitogenic activity of these proteins suggest that they are secreted and transported to target tissues via the hemolymph. However, the genes are also expressed in embryonic epithelia in association with invagination movements, so the proteins may have local as well as systemic functions. Similar proteins are found in mammals and may constitute a novel class of growth factors.

Polyglutamine-expanded human huntingtin transgenes induce degeneration of Drosophila photoreceptor neurons

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder. Disease alleles contain a trinucleotide repeat expansion of variable length, which encodes polyglutamine tracts near the amino terminus of the HD protein, huntingtin. Polyglutamine-expanded huntingtin, but not normal huntingtin, forms nuclear inclusions. We describe a Drosophila model for HD. Amino-terminal fragments of human huntingtin containing tracts of 2, 75, and 120 glutamine residues were expressed in photoreceptor neurons in the compound eye. As in human neurons, polyglutamine-expanded huntingtin induced neuronal degeneration. The age of onset and severity of neuronal degeneration correlated with repeat length, and nuclear localization of huntingtin presaged neuronal degeneration. In contrast to other cell death paradigms in Drosophila, coexpression of the viral antiapoptotic protein, P35, did not rescue the cell death phenotype induced by polyglutamine-expanded huntingtin.

Effect of age on the growth and response of a Drosophila cell line to moulting hormone

Insect cell lines in culture are used for a variety of studies. In this laboratory imaginal disc cell lines have been established from primary cultures from third instar larvae, and used for a number of experiments. The effect of ageing on the morphology and physiology of Drosophila cell lines has received very little attention, although problems of genotypic or phenotypic changes in cell lines with age are recognized in other areas of animal cell culture. We tested our cell line Cl8+ for any difference in growth, morphology and response to 20-hydroxyecdysone (20HE) at different ages (passage numbers). The cells were found to multiply faster, adhere less firmly to the substrate and to lose the tendency to aggregate at higher passages. The response to 20HE in terms of cell numbers and induction of beta-galactosidase was similar at all passage numbers but morphological changes in hormone-treated cells were less obvious in the higher passages. Cell lines are likely to vary in the extent of ageing effects but workers are advised to be aware of the possibilities. We suggest the effects of age on cell lines should be established, and passage numbers noted in experimental reports.

The response of Drosophila imaginal disc cell lines to ecdysteroids

We have investigated the action of the moulting hormone 20-hydroxy ecdysone (20-HOE) on our leg and wing imaginal disc cell lines. At the morphological level, cells stop dividing and there is some cell death. The remaining cells elongate and aggregate, often producing long processes which form connections between different aggregates. 20-HOE acts within the first one or two days of a passage, at an optimum concentration of 10 ng/ml, this being about 1/100 of the optimum for ecdysone. One cloned wing cell line, C9, has been found to be relatively insensitive to the action of 20-HOE. We have been able to select for resistance to 20-HOE by growing cells in gradually increasing concentrations of hormone followed by passages in hormone-free medium. This has enabled us to isolate a wing cell line C1.8R from its parent cloned line C1.8+. This shows no response to 20-HOE, and cell growth continues even at hormone concentrations as high as 150 ng/ml. We have measured chitin synthesis by the incorporation of radioactive glucosamine into a cell fraction resistant to extensive alkali hydrolysis. The residue was incubated with chitinase, which resulted in a 50% reduction in labelled product. Treatment with 10 ng/ml of 20-HOE dramatically increased chitin synthesis in line C1.8+, but had no effect in the line C1.8R, selected for resistance to hormone.