Rapid Preparation of Living Drosophila Pupal Macrophages for Ex Vivo Imaging

The fruit fly Drosophila is a well-established invertebrate model that enables in vivo imaging of innate immune cell (e.g., macrophage) migration and signaling at high spatiotemporal resolution within the intact, living animal. While optimized methods already exist to enable flow cytometry-based macrophage isolation from Drosophila at various stages of development, there remains a need for more rapid and gentle methods to isolate living macrophages for downstream ex vivo applications. Here, we describe techniques for rapid and direct isolation of living macrophages from mature Drosophila pupae and their downstream ex vivo preparation for live imaging and immunostaining. This strategy enables straightforward access to physiologically relevant innate immune cells, both circulating and tissue-resident populations, for subsequent imaging of signal transduction.

High-Resolution Live Imaging of Axonal RNP Granules in Drosophila Pupal Brain Explants

Dynamic and local adjustments of the axonal proteome are observed in response to extracellular cues and achieved via translation of axonally localized mRNAs. To be localized, these mRNAs must be recognized by RNA binding proteins and packaged into higher-order ribonucleoprotein (RNP) granules transported along axonal microtubules via molecular motors. Axonal recruitment of RNP granules is not constitutive, but rather regulated by external signals such as developmental cues, through pathways yet to be identified. The Drosophila brain represents an excellent model system where to study the transport of RNP granules as it is triggered in specific populations of neurons undergoing remodeling during metamorphosis. Here, we describe a protocol enabling live imaging of axonal RNP granule transport with high spatiotemporal resolution in Drosophila maturing brains. In this protocol, pupal brains expressing endogenous or ectopic fluorescent RNP components are dissected, mounted in a customized imaging chamber, and imaged with an inverted confocal microscope equipped with sensitive detectors. Axonal RNP granules are then individually tracked for further analysis of their trajectories. This protocol is rapid (less than 1 hour to prepare brains for imaging) and is easy to handle and to implement.

Role of autophagy in midgut stem cells of silkworm Bombyx mori, during larval-pupal metamorphosis

Autophagy is a critical mechanism for the self-renewal, proliferation, and differentiation of stem cells. Bombyx mori midgut has stem cells that play a role in the regeneration of the larval epithelium in larval stages and the formation of the pupal midgut epithelium during larval-pupal metamorphosis. In this study, the role of the autophagy mechanism in midgut stem cells during the formation of the pupal midgut was investigated. For this purpose, two different doses of autophagy inhibitor chloroquine were administered to B. mori larvae on days 7 and 8 of the fifth larval stage. Morphological changes during the formation process of the pupal epithelium, expression levels of autophagy-related genes Atg8 and Atg12 in stem cells, and the amounts of lysosomal enzyme acid phosphatase were determined after the application. The obtained findings were evaluated in comparison with the control groups. Abnormalities in the formation of the pupal midgut after inhibition of autophagy showed the significance of the autophagy mechanism during this period.

Novel structure in the nuclei of honey bee brain neurons revealed by immunostaining

In the course of a screen designed to produce antibodies (ABs) with affinity to proteins in the honey bee brain we found an interesting AB that detects a highly specific epitope predominantly in the nuclei of Kenyon cells (KCs). The observed staining pattern is unique, and its unfamiliarity indicates a novel previously unseen nuclear structure that does not colocalize with the cytoskeletal protein f-actin. A single rod-like assembly, 3.7-4.1 µm long, is present in each nucleus of KCs in adult brains of worker bees and drones with the strongest immuno-labelling found in foraging bees. In brains of young queens, the labelling is more sporadic, and the rod-like structure appears to be shorter (~ 2.1 µm). No immunostaining is detectable in worker larvae. In pupal stage 5 during a peak of brain development only some occasional staining was identified. Although the cellular function of this unexpected structure has not been determined, the unusual distinctiveness of the revealed pattern suggests an unknown and potentially important protein assembly. One possibility is that this nuclear assembly is part of the KCs plasticity underlying the brain maturation in adult honey bees. Because no labelling with this AB is detectable in brains of the fly Drosophila melanogaster and the ant Camponotus floridanus, we tentatively named this antibody AmBNSab (Apis mellifera Brain Neurons Specific antibody). Here we report our results to make them accessible to a broader community and invite further research to unravel the biological role of this curious nuclear structure in the honey bee central brain.

Differential cell adhesion implemented by Drosophila Toll corrects local distortions of the anterior-posterior compartment boundary

Maintaining lineage restriction boundaries in proliferating tissues is vital to animal development. A long-standing thermodynamics theory, the differential adhesion hypothesis, attributes cell sorting phenomena to differentially expressed adhesion molecules. However, the contribution of the differential adhesion system during tissue morphogenesis has been unsubstantiated despite substantial theoretical support. Here, we report that Toll-1, a transmembrane receptor protein, acts as a differentially expressed adhesion molecule that straightens the fluctuating anteroposterior compartment boundary in the abdominal epidermal epithelium of the Drosophila pupa. Toll-1 is expressed across the entire posterior compartment under the control of the selector gene engrailed and displays a sharp expression boundary that coincides with the compartment boundary. Toll-1 corrects local distortions of the boundary in the absence of cable-like Myosin II enrichment along the boundary. The reinforced adhesion of homotypic cell contacts, together with pulsed cell contraction, achieves a biased vertex sliding action by resisting the separation of homotypic cell contacts in boundary cells. This work reveals a self-organizing system that integrates a differential adhesion system with pulsed contraction of cells to maintain lineage restriction boundaries.

Cell migration by swimming: Drosophila adipocytes as a new in vivo model of adhesion-independent motility

Several cell lineages migrate through the developing and adult tissues of our bodies utilising a variety of modes of motility to suit the different substrates and environments they encounter en route to their destinations. Here we describe a novel adhesion-independent mode of single cell locomotion utilised by Drosophila fat body cells - the equivalent of vertebrate adipocytes. Like their human counterpart, these large cells were previously presumed to be immotile. However, in the Drosophila pupa fat body cells appear to be motile and migrate in a directed way towards wounds by peristaltic swimming through the hemolymph. The propulsive force is generated from a wave of cortical actomyosin that travels rearwards along the length of the cell. We discuss how this swimming mode of motility overcomes the physical constraints of microscopic objects moving in fluids, how fat body cells switch on other "motility machinery" to plug the wound on arrival, and whether other cell lineages in Drosophila and other organisms may, under certain circumstances, also adopt swimming as an effective mode of migration.

Drosophila Myoblast Fusion: Invasion and Resistance for the Ultimate Union

Cell-cell fusion is indispensable for creating life and building syncytial tissues and organs. Ever since the discovery of cell-cell fusion, how cells join together to form zygotes and multinucleated syncytia has remained a fundamental question in cell and developmental biology. In the past two decades, Drosophila myoblast fusion has been used as a powerful genetic model to unravel mechanisms underlying cell-cell fusion in vivo. Many evolutionarily conserved fusion-promoting factors have been identified and so has a surprising and conserved cellular mechanism. In this review, we revisit key findings in Drosophila myoblast fusion and highlight the critical roles of cellular invasion and resistance in driving cell membrane fusion.

Target of rapamycin (TOR) determines appendage size during pupa formation of the red flour beetle Tribolium castaneum

The adult body size is species-specific and controlled by complex interactions between hormones and the IIS/TOR pathway. To analyze the role of target of rapamycin (TOR) in the growth and development of the insect, expression levels of TOR were silenced in the model and pest insect red flour beetle, Tribolium castaneum. Injection of dsRNA into the last larval instar decreased pupal mass and size, while the amount of food intake by the larvae was not affected. These results place TcTOR downstream of nutrition as a transducer for nutritional signals to increase larval growth. In addition, TcTOR-silencing notably decreased the size of the adult appendages. Analysis of the wings and elytra revealed a decrease in cell size and number of these appendages in the TcTOR-silenced insects. This reduction in size was correlated with a decrease of transcriptional levels of marker genes controlling the cell cycle. Altogether, these results suggest a pivotal role for TcTOR in integrating nutritional signals and regulation of body and appendages growth.

Fast determination of coarse-grained cell anisotropy and size in epithelial tissue images using Fourier transform

Mechanical strain and stress play a major role in biological processes such as wound healing or morphogenesis. To assess this role quantitatively, fixed or live images of tissues are acquired at a cellular precision in large fields of views. To exploit these data, large numbers of cells have to be analyzed to extract cell shape anisotropy and cell size. Most frequently, this is performed through detailed individual cell contour determination, using so-called segmentation computer programs, complemented if necessary by manual detection and error corrections. However, a coarse-grained and faster technique can be recommended in at least three situations: first, when detailed information on individual cell contours is not required; for instance, in studies which require only coarse-grained average information on cell anisotropy. Second, as an exploratory step to determine whether full segmentation can be potentially useful. Third, when segmentation is too difficult, for instance due to poor image quality or too large a cell number. We developed a user-friendly, Fourier-transform-based image analysis pipeline. It is fast (typically 10^{4} cells per minute with a current laptop computer) and suitable for time, space, or ensemble averages. We validate it on one set of artificial images and on two sets of fully segmented images, one from a Drosophila pupa and the other from a chicken embryo; the pipeline results are robust. Perspectives include in vitro tissues, nonbiological cellular patterns such as foams and xyz stacks.

High-resolution ultramicroscopy of the developing and adult nervous system in optically cleared Drosophila melanogaster

The fruit fly, Drosophila melanogaster, is an important experimental model to address central questions in neuroscience at an organismic level. However, imaging of neural circuits in intact fruit flies is limited due to structural properties of the cuticle. Here we present a novel approach combining tissue clearing, ultramicroscopy, and data analysis that enables the visualisation of neuronal networks with single-cell resolution from the larval stage up to the adult Drosophila. FlyClear, the signal preserving clearing technique we developed, stabilises tissue integrity and fluorescence signal intensity for over a month and efficiently removes the overall pigmentation. An aspheric ultramicroscope set-up utilising an improved light-sheet generator allows us to visualise long-range connections of peripheral sensory and central neurons in the visual and olfactory system. High-resolution 3D reconstructions with isotropic resolution from entire GFP-expressing flies are obtained by applying image fusion from orthogonal directions. This methodological integration of novel chemical, optical, and computational techniques allows a major advance in the analysis of global neural circuit organisation.

A New Species of the Simulium (Simulium) striatum Species Group (Diptera: Simuliidae) from Thailand, and Its Differentiation from Two Related Species Based on a Fast-Evolving Nuclear Gene

Simulium (Simulium) phraense sp. nov. (Diptera: Simuliidae) is described from females, males, pupae, and larvae from Thailand. This new species is placed in the Simulium striatum species group and is most similar to Simulium (Simulium) nakhonense Takaoka & Suzuki (Diptera: Simuliidae) from Thailand among species of the same species group but is barely distinguished from the latter species by lacking annular ridges on the surface of the pupal gill filaments. The fast-evolving nuclear big zinc finger (BZF) gene has successfully differentiated this new species from its allies, S. (S.) nakhonense and Simulium (Simulium) chiangmaiense Takaoka & Suzuki (Diptera: Simuliidae) of the S. striatum species group. The BZF gene sequences show that this new species is more closely related to S. (S.) nakhonense than to S. (S.) chiangmaiense, further supporting its morphological classification.

Post-embryonic development of the Malpighian tubules in Apis mellifera (Hymenoptera) workers: morphology, remodeling, apoptosis, and cell proliferation

The honeybee Apis mellifera has ecological and economic importance; however, it experiences a population decline, perhaps due to exposure to toxic compounds, which are excreted by Malpighian tubules. During metamorphosis of A. mellifera, the Malpighian tubules degenerate and are formed de novo. The objective of this work was to verify the cellular events of the Malpighian tubule renewal in the metamorphosis, which are the gradual steps of cell remodeling, determining different cell types and their roles in the excretory activity in A. mellifera. Immunofluorescence and ultrastructural analyses showed that the cells of the larval Malpighian tubules degenerate by apoptosis and autophagy, and the new Malpighian tubules are formed by cell proliferation. The ultrastructure of the cells in the Malpighian tubules suggest that cellular remodeling only occurs from dark-brown-eyed pupae, indicating the onset of excretion activity in pupal Malpighian tubules. In adult forager workers, two cell types occur in the Malpighian tubules, one with ultrastructural features (abundance of mitochondria, vacuoles, microvilli, and narrow basal labyrinth) for primary urine production and another cell type with dilated basal labyrinth, long microvilli, and absence of spherocrystals, which suggest a role in primary urine re-absorpotion. This study suggests that during the metamorphosis, Malpighian tubules are non-functional until the light-brown-eyed pupae, indicating that A. mellifera may be more vulnerable to toxic compounds at early pupal stages. In addition, cell ultrastructure suggests that the Malpighian tubules may be functional from dark-brown-eyed pupae and acquire greater complexity in the forager worker bee.

Analysis of Cell Shape and Cell Migration of Drosophila Macrophages In Vivo

The most abundant immune cells in Drosophila are macrophage-like plasmatocytes that fulfill central roles in morphogenesis, immune and tissue damage response. The various genetic tools available in Drosophila together with high-resolution and live-imaging microscopy techniques make Drosophila macrophages an excellent model system that combines many advantages of cultured cells with in vivo genetics. Here, we describe the isolation and staining of macrophages from larvae for ex vivo structured illumination microscopy (SIM), the preparation of white prepupae for in vivo 2D random cell migration analysis, and the preparation of pupae (18 h after puparium formation, APF) for in vivo 3D directed cell migration analysis upon wounding using spinning disk microscopy.

Classifying Drosophila Olfactory Projection Neuron Subtypes by Single-Cell RNA Sequencing

The definition of neuronal type and how it relates to the transcriptome are open questions. Drosophila olfactory projection neurons (PNs) are among the best-characterized neuronal types: different PN classes target dendrites to distinct olfactory glomeruli, while PNs of the same class exhibit indistinguishable anatomical and physiological properties. Using single-cell RNA sequencing, we comprehensively characterized the transcriptomes of most PN classes and unequivocally mapped transcriptomes to specific olfactory function for six classes. Transcriptomes of closely related PN classes exhibit the largest differences during circuit assembly but become indistinguishable in adults, suggesting that neuronal subtype diversity peaks during development. Transcription factors and cell-surface molecules are the most differentially expressed genes between classes and are highly informative in encoding cell identity, enabling us to identify a new lineage-specific transcription factor that instructs PN dendrite targeting. These findings establish that neuronal transcriptomic identity corresponds with anatomical and physiological identity defined by connectivity and function.

Live Cell Imaging of Butterfly Pupal and Larval Wings In Vivo

Butterfly wing color patterns are determined during the late larval and early pupal stages. Characterization of wing epithelial cells at these stages is thus critical to understand how wing structures, including color patterns, are determined. Previously, we successfully recorded real-time in vivo images of developing butterfly wings over time at the tissue level. In this study, we employed similar in vivo fluorescent imaging techniques to visualize developing wing epithelial cells in the late larval and early pupal stages 1 hour post-pupation. Both larval and pupal epithelial cells were rich in mitochondria and intracellular networks of endoplasmic reticulum, suggesting high metabolic activities, likely in preparation for cellular division, polyploidization, and differentiation. Larval epithelial cells in the wing imaginal disk were relatively large horizontally and tightly packed, whereas pupal epithelial cells were smaller and relatively loosely packed. Furthermore, larval cells were flat, whereas pupal cells were vertically elongated as deep as 130 μm. In pupal cells, many endosome-like or autophagosome-like structures were present in the cellular periphery down to approximately 10 μm in depth, and extensive epidermal feet or filopodia-like processes were observed a few micrometers deep from the cellular surface. Cells were clustered or bundled from approximately 50 μm in depth to deeper levels. From 60 μm to 80 μm in depth, horizontal connections between these clusters were observed. The prospective eyespot and marginal focus areas were resistant to fluorescent dyes, likely because of their non-flat cone-like structures with a relatively thick cuticle. These in vivo images provide important information with which to understand processes of epithelial cell differentiation and color pattern determination in butterfly wings.

Inhibition of Polo kinase by BI2536 affects centriole separation during Drosophila male meiosis

Pharmacological inhibition of Drosophila Polo kinase with BI2536 has allowed us to re-examine the requirements for Polo during Drosophila male gametogenesis. BI2536-treated spermatocytes persisted in a pro-metaphase state without dividing and had condensed chromosomes that did not separate. Centrosomes failed to recruit γ-tubulin and centrosomin (Cnn) and were not associated with microtubule arrays that were abnormal and did not form proper bipolar spindles. Centrioles, which usually separate during the anaphase of the first meiosis, remained held together in a V-shaped configuration suggesting that Polo kinase regulates the proteolysis that breaks centriole linkage to ensure their disengagement. Despite these defects spermatid differentiation proceeds, leading to axoneme formation.

Flybow to dissect circuit assembly in the Drosophila brain

Visualization of single neurons within their complex environment is a pivotal step towards uncovering the mechanisms that control neural circuit development and function. This chapter provides detailed technical information on how to use Drosophila variants of the mouse Brainbow-2 system, called Flybow, for stochastic labeling of cells with different fluorescent proteins in one sample. We first describe the genetic strategies and the heat shock regime required for induction of recombination events. This is followed by a detailed protocol as to how to prepare samples for imaging. Finally, we provide specifications to facilitate multichannel image acquisition using confocal microscopy.

Histochemistry and ultrastructure of urocytes in the pupae of the stingless bee Melipona quadrifasciata (Hymenoptera: Meliponini)

The main cell types of the adult bee fat body are trophocytes and oenocytes; however, in pupae of some newly emerged bees, trophocytes are modified into cells called urocytes, which possibly function as a substitute for Malpighian tubules during metamorphosis when larval tubules are not functional and/or storage of urate salts is required. This study evaluated the morphology of urocytes in the stingless bee Melipona quadrifasciata and the possibility of maintaining these cells in primary culture. The urocytes M. quadrifasciata are white spherical cells with an irregular surface as observed by stereomicroscopy. They may be found individually or in groups associated with tracheae. Urocytes have a single, small, and spherical nucleus and cytoplasm rich in neutral polysaccharides, lipid droplets, protein, and granules containing calcium and urate salts. Our findings suggest that urocytes play a role in storage of neutral polysaccharides and calcium in M. quadrifasciata pupae and that these cells can be cultured for 72 h.

Drosophila Dyrk2 plays a role in the development of the visual system

The DYRKs (dual-specificity tyrosine phosphorylation-regulated kinases) are a conserved family of protein kinases that are associated with a number of neurological disorders, but whose biological targets are poorly understood. Drosophila encodes three Dyrks: minibrain/Dyrk1A, DmDyrk2, and DmDyrk3. Here we describe the creation and characterization of a DmDyrk2 null allele, DmDyrk2^1w17. We provide evidence that the smell impaired allele smi35A¹, is likely to encode DmDyrk2. We also demonstrate that DmDyrk2 is expressed late in the developing third antennal segment, an anatomical structure associated with smell. In addition, we find that DmDyrk2 is expressed in the morphogenetic furrow of the developing eye, that loss of DmDyrk2 in the eye produced a subtle but measurable defect, and that ectopic DmDyrk2 expression in the eye produced a strong rough eye phenotype characterized by increased secondary, tertiary and bristle interommatidial cells. This phenotype was dependent on DmDyrk2 kinase activity and was only manifest when expressed in post-mitotic non-neuronal progenitors. Together, these data indicate that DmDyrk2 is expressed in developing sensory systems, that it is required for the development of the visual system, and that the eye is a good model to identify DmDyrk2 targets.

Phenoloxidase activity among developmental stages and pupal cell types of the ground beetle Carabus (Chaetocarabus) lefebvrei (Coleoptera, Carabidae)

In ecological immunology is of great importance the study of the immune defense plasticity as response to a variable environment. In holometabolous insects the fitness of each developmental stage depends on the capacity to mount a response (i.e. physiological, behavioral) under environmental pressure. The immune response is a highly dynamic trait closely related to the ecology of organism and the variation in the expression of an immune system component may affect another fitness relevant trait of organism (i.e. growth, reproduction). The present research quantified immune function (total and differential number of hemocytes, phagocytosis in vivo and activity of phenoloxidase) in the pupal stage of Carabus (Chaetocarabus) lefebvrei. Moreover, the cellular and humoral immune function was compared across the larval, pupal and adult stages to evaluate the changes in immunocompetence across the developmental stages. Four types of circulating hemocytes were characterized via transmission electron microscopy in the pupal stage: prohemocytes, plasmatocytes, granulocytes and oenocytoids. The artificial non-self-challenge treatments performed in vivo have shown that plasmatocytes and granulocytes are responsible for phagocytosis. The level of active phenoloxidase increases with the degree of pigmentation of the cuticle in each stage. In C. lefebvrei, there are different strategies in term of immune response to enhance the fitness of each life stage. The results have shown that the variation in speed and specificity of immune function across the developmental stages is correlated with differences in infection risk, life expectancy and biological function of the life cycle.

Genetic and cytogenetic characterization of genetic sexing strains of Bactrocera dorsalis and Bactrocera cucurbitae (Diptera: Tephritidae)

In the current study, we performed genetic and cytogenetic analyses of two genetic sexing strains (GSSs), one for Bactrocera dorsalis s.s. and one for melon fly, Bactrocera cucurbitae Coquillett, the first such strains ever constructed in these species. In both strains, the genetic sexing mechanism is based on a pupal color dimorphism (white or brown) and is the result of a reciprocal translocation between the Y chromosome and the autosome bearing the white pupae (wp) locus. Based on genetic analysis and cytological data on mitotic metaphases and larval salivary gland polytene chromosomes, we succeeded in mapping the autosome breakpoints in the two Y-autosome translocations even though the Y chromosome is not visible in polytene nuclei. We show that polytene chromosomes can be used in cytogenetic analyses toward the development of genetic control methods in these pest species. The results of the genetic analysis are in full agreement with the cytological description of the strains.

Neuroblast lineage-specific origin of the neurons of the Drosophila larval olfactory system

The complete neuronal repertoire of the central brain of Drosophila originates from only approximately 100 pairs of neural stem cells, or neuroblasts. Each neuroblast produces a highly stereotyped lineage of neurons which innervate specific compartments of the brain. Neuroblasts undergo two rounds of mitotic activity: embryonic divisions produce lineages of primary neurons that build the larval nervous system; after a brief quiescence, the neuroblasts go through a second round of divisions in larval stage to produce secondary neurons which are integrated into the adult nervous system. Here we investigate the lineages that are associated with the larval antennal lobe, one of the most widely studied neuronal systems in fly. We find that the same five neuroblasts responsible for the adult antennal lobe also produce the antennal lobe of the larval brain. However, there are notable differences in the composition of larval (primary) lineages and their adult (secondary) counterparts. Significantly, in the adult, two lineages (lNB/BAlc and adNB/BAmv3) produce uniglomerular projection neurons connecting the antennal lobe with the mushroom body and lateral horn; another lineage, vNB/BAla1, generates multiglomerular neurons reaching the lateral horn directly. lNB/BAlc, as well as a fourth lineage, vlNB/BAla2, generate a diversity of local interneurons. We describe a fifth, previously unknown lineage, BAlp4, which connects the posterior part of the antennal lobe and the neighboring tritocerebrum (gustatory center) with a higher brain center located adjacent to the mushroom body. In the larva, only one of these lineages, adNB/BAmv3, generates all uniglomerular projection neurons. Also as in the adult, lNB/BAlc and vlNB/BAla2 produce local interneurons which, in terms of diversity in architecture and transmitter expression, resemble their adult counterparts. In addition, lineages lNB/BAlc and vNB/BAla1, as well as the newly described BAlp4, form numerous types of projection neurons which along the same major axon pathways (antennal tracts) used by the antennal projection neurons, but which form connections that include regions outside the "classical" olfactory circuit triad antennal lobe-mushroom body-lateral horn. Our work will benefit functional studies of the larval olfactory circuit, and shed light on the relationship between larval and adult neurons.

Development of polyploidy of scale-building cells in the wings of Manduca sexta

The developing wings of butterflies and moths are composed of two epithelial monolayers. Each epithelial sheet is made up of two kinds of cells, diploid cells that make up the epidermal surface and body of the wing, and large polyploid cells that become the scale-building cells whose cytoplasmic projections develop into the scales that will cover the adult wing and bear the pigment pattern. We studied the development of polyploidization of the scale-building cells during the pupal stage of the tobacco hornworm moth, Manduca sexta. The endomitotic divisions of the presumptive scale-building cells and the mitotic divisions of the diploid epithelial cells begin on day 3 of the pupal stage and continue until day 7. We show that scales of different colors and positions on the wing differ in size, and that the size of the scale is proportional to the ploidy of the scale-building cell. Scale-building cells are arranged in irregular rows and within each row there is an alternation of ploidy levels, with the lower ploidy cells giving rise to the underscales and the higher ploidy cells giving rise to the cover scales that carry the color pattern. Along the wing there is a proximo-distal decreasing gradient of average ploidy and scale size. Scale-building cells of high ploidy are surrounded by fewer epidermal cells than those of low ploidy. This inverse relationship is known as Henke's compensation principle, which posits that the number of endomitoses of a pre-polyploid cell and the number of mitotic divisions of its diploid daughter cell add up to a constant. We show that the inverse relationship fits the predictions of the compensation principle and does not fit constraints imposed by packing density, and we discuss mechanisms that could give rise to the inverse relationship.

NR5A nuclear receptor Hr39 controls three-cell secretory unit formation in Drosophila female reproductive glands

BACKGROUND

Secretions within the adult female reproductive tract mediate sperm survival, storage, activation, and selection. Drosophila female reproductive gland secretory cells reside within the adult spermathecae and parovaria, but their development remains poorly characterized.

RESULTS

With cell-lineage tracing, we found that precursor cells downregulate lozenge and divide stereotypically to generate three-cell secretory units during pupal development. The NR5A-class nuclear hormone receptor Hr39 is essential for precursor cell division and secretory unit formation. Moreover, ectopic Hr39 in multiple tissues generates reproductive gland-like primordia. Rarely, in male genital discs these primordia can develop into sperm-filled testicular spermathecae.

CONCLUSION

Drosophila spermathecae provide a powerful model for studying gland development. Hr39 functions as a master regulator of a program that may have been conserved throughout animal evolution for the production of female reproductive glands and other secretory tissues.

Drosophila nociceptors mediate larval aversion to dry surface environments utilizing both the painless TRP channel and the DEG/ENaC subunit, PPK1

A subset of sensory neurons embedded within the Drosophila larval body wall have been characterized as high-threshold polymodal nociceptors capable of responding to noxious heat and noxious mechanical stimulation. They are also sensitized by UV-induced tissue damage leading to both thermal hyperalgesia and allodynia very similar to that observed in vertebrate nociceptors. We show that the class IV multiple-dendritic(mdIV) nociceptors are also required for a normal larval aversion to locomotion on to a dry surface environment. Drosophila melanogaster larvae are acutely susceptible to desiccation displaying a strong aversion to locomotion on dry surfaces severely limiting the distance of movement away from a moist food source. Transgenic inactivation of mdIV nociceptor neurons resulted in larvae moving inappropriately into regions of low humidity at the top of the vial reflected as an increased overall pupation height and larval desiccation. This larval lethal desiccation phenotype was not observed in wild-type controls and was completely suppressed by growth in conditions of high humidity. Transgenic hyperactivation of mdIV nociceptors caused a reciprocal hypersensitivity to dry surfaces resulting in drastically decreased pupation height but did not induce the writhing nocifensive response previously associated with mdIV nociceptor activation by noxious heat or harsh mechanical stimuli. Larvae carrying mutations in either the Drosophila TRP channel, Painless, or the degenerin/epithelial sodium channel subunit Pickpocket1(PPK1), both expressed in mdIV nociceptors, showed the same inappropriate increased pupation height and lethal desiccation observed with mdIV nociceptor inactivation. Larval aversion to dry surfaces appears to utilize the same or overlapping sensory transduction pathways activated by noxious heat and harsh mechanical stimulation but with strikingly different sensitivities and disparate physiological responses.

Real-time analysis of Drosophila post-embryonic haemocyte behaviour

BACKGROUND

The larval stage of the model organism Drosophila is frequently used to study host-pathogen interactions. During embryogenesis the cellular arm of the immune response, consisting of macrophage-like cells known as plasmatocytes, is extremely motile and functions to phagocytise pathogens and apoptotic bodies, as well as produce extracellular matrix. The cellular branch of the larval (post-embryonic) innate immune system consists of three cell types--plasmatocytes, crystal cells and lamellocytes--which are involved in the phagocytosis, encapsulation and melanisation of invading pathogens. Post-embryonic haemocyte motility is poorly understood thus further characterisation is required, for the purpose of standardisation.

METHODOLOGY

In order to examine post-embryonic haemocyte cytoskeletal dynamics or migration, the most commonly used system is in vitro cell lines. The current study employs an ex vivo system (an adaptation of in vitro cell incubation using primary cells), in which primary larval or pre-pupal haemocytes are isolated for short term analysis, in order to discover various aspects of their behaviour during events requiring cytoskeleton dynamics.

SIGNIFICANCE

The ex vivo method allows for real-time analysis and manipulation of primary post-embryonic haemocytes. This technique was used to characterise, and potentially standardised, larval and pre-pupal haemocyte cytoskeleton dynamics, assayed on different extracellular matrices. Using this method it was determined that, while larval haemocytes are unable to migrate, haemocytes recovered from pre-pupae are capable of migration.

Role of spectraplakin in Drosophila photoreceptor morphogenesis

Background

Crumbs (Crb), a cell polarity gene, has been shown to provide a positional cue for the apical membrane domain and adherens junction during Drosophila photoreceptor morphogenesis. It has recently been found that stable microtubules in developing Drosophila photoreceptors were linked to Crb localization. Coordinated interactions between microtubule and actin cytoskeletons are involved in many polarized cellular processes. Since Spectraplakin is able to bind both microtubule and actin cytoskeletons, the role of Spectraplakin was analyzed in the regulations of apical Crb domain in developing Drosophila photoreceptors.

Methodology/Principal Findings

The localization pattern of Spectraplakin in developing pupal photoreceptors showed a unique intracellular distribution. Spectraplakin localized at rhabdomere terminal web which is at the basal side of the apical Crb or rhabdomere, and in between the adherens junctions. The spectraplakin mutant photoreceptors showed dramatic mislocalizations of Crb, adherens junctions, and the stable microtubules. This role of Spectraplakin in Crb and adherens junction regulation was further supported by spectraplakin's gain-of-function phenotype. Spectraplakin overexpression in photoreceptors caused a cell polarity defect including dramatic mislocalization of Crb, adherens junctions and the stable microtubules in the developing photoreceptors. Furthermore, a strong genetic interaction between spectraplakin and crb was found using a genetic modifier test.

Conclusions/Significance

In summary, we found a unique localization of Spectraplakin in photoreceptors, and identified the role of spectraplakin in the regulation of the apical Crb domain and adherens junctions through genetic mutational analysis. Our data suggest that Spectraplakin, an actin-microtubule cross-linker, is essential in the apical and adherens junction controls during the photoreceptors morphogenesis.

Role of kinesin heavy chain in Crumbs localization along the rhabdomere elongation in Drosophila photoreceptor

Background

Crumbs (Crb), a cell polarity gene, has been shown to provide a positional cue for the extension of the apical membrane domain, adherens junction (AJ), and rhabdomere along the growing proximal-distal axis during Drosophila photoreceptor morphogenesis. In developing Drosophila photoreceptors, a stabilized microtubule structure was discovered and its presence was linked to polarity protein localization. It was therefore hypothesized that the microtubules may provide trafficking routes for the polarity proteins during photoreceptor morphogenesis. This study has examined whether Kinesin heavy chain (Khc), a subunit of the microtubule-based motor Kinesin-1, is essential in polarity protein localization in developing photoreceptors.

Methodology/Principal Findings

Because a genetic interaction was found between crb and khc, Crb localization was examined in the developing photoreceptors of khc mutants. khc was dispensable during early eye differentiation and development. However, khc mutant photoreceptors showed a range of abnormalities in the apical membrane domain depending on the position along the proximal-distal axis in pupal photoreceptors. The khc mutant showed a progressive mislocalization in the apical domain along the distal-proximal axis during rhabdomere elongation. The khc mutation also led to a similar progressive defect in the stabilized microtubule structures, strongly suggesting that Khc is essential for microtubule structure and Crb localization during distal to proximal rhabdomere elongation in pupal morphogenesis. This role of Khc in apical domain control was further supported by khc's gain-of-function phenotype. Khc overexpression in photoreceptors caused disruption of the apical membrane domain and the stabilized microtubules in the developing photoreceptors.

Conclusions/Significance

In summary, we examined the role of khc in the regulation of the apical Crb domain in developing photoreceptors. Since the rhabdomeres in developing pupal eyes grow along the distal-proximal axis, these phenotypes suggest that Khc is essential for the microtubule structures and apical membrane domains during the distal-proximal elongation of photoreceptors, but is dispensable for early eye development.

Identification of the starting point for spermatogenesis resumption in the post-diapause development of the sweet potato hornworm, Agrius convolvuli L

The resumption of spermatogenesis in post-diapause development was examined in the sweet potato hornworm (Agrius convolvuli) with in vivo bromodeoxyuridine (BrdU) incorporation experiments used to determine the starting point. Diapausing pupae were "overwintered" by chilling at 10 °C for over 4 months, after which they initiated post-diapause development by transferring the pupae to 25 °C with a 12-h light/12-h dark photoperiod. The testes of living, post-diapause pupae were injected with BrdU, which is incorporated into newly synthesized DNA strands. During the first 2 days after diapause termination, the nuclei of spermatogonia and spermatocytes failed to label with BrdU. However, on day 3 of post-diapause pupae (PDP3), labeling studies showed that cell proliferation was initiated by spermatogonia, but not by spermatocytes. In both hemolymph and testes, ecdysteroid concentrations rose gradually, reaching 0.3 μg/ml hemolymph at PDP3. These results led to the following three conclusions. The spermatogonial cell division is highly suppressed during diapause. After a long-term diapause, spermatogenesis resumes in the spermatogonia but not in the spermatocytes of diapause-terminated pupae. Cell division begins in advance of peak ecdysteroid concentrations. The latter result indicates that in post-diapause development, high concentrations of the hormone are not required to initiate spermatogonial proliferation.

Comparative genomic analysis of chitinase and chitinase-like genes in the African malaria mosquito (Anopheles gambiae)

Chitinase is an important enzyme responsible for chitin metabolism in a wide range of organisms including bacteria, yeasts and other fungi, nematodes and arthropods. However, current knowledge on chitinolytic enzymes, especially their structures, functions and regulation is very limited. In this study we have identified 20 chitinase and chitinase-like genes in the African malaria mosquito, Anopheles gambiae, through genome-wide searching and transcript profiling. We assigned these genes into eight different chitinase groupings (groups I–VIII). Domain analysis of their predicted proteins showed that all contained at least one catalytic domain. However, only seven (AgCht4, AgCht5-1, AgCht6, AgCht7, AgCht8, AgCht10 and AgCht23) displayed one or more chitin-binding domains. Analyses of stage- and tissue-specific gene expression revealed that most of these genes were expressed in larval stages. However, AgCht8 was mainly expressed in the pupal and adult stages. AgCht2 and AgCht12 were specifically expressed in the foregut, whereas AgCht13 was only expressed in the midgut. The high diversity and complexity of An. gambiae chitinase and chitinase-like genes suggest their diverse functions during different developmental stages and in different tissues of the insect. A comparative genomic analysis of these genes along with those present in Drosophila melanogaster, Tribolium castaneum and several other insect species led to a uniform classification and nomenclature of these genes. Our investigation also provided important information for conducting future studies on the functions of chitinase and chitinase-like genes in this important malaria vector and other species of arthropods.

Cell flow reorients the axis of planar polarity in the wing epithelium of Drosophila

Planar cell polarity (PCP) proteins form polarized cortical domains that govern polarity of external structures such as hairs and cilia in both vertebrate and invertebrate epithelia. The mechanisms that globally orient planar polarity are not understood, and are investigated here in the Drosophila wing using a combination of experiment and theory. Planar polarity arises during growth and PCP domains are initially oriented toward the well-characterized organizer regions that control growth and patterning. At pupal stages, the wing hinge contracts, subjecting wing-blade epithelial cells to anisotropic tension in the proximal-distal axis. This results in precise patterns of oriented cell elongation, cell rearrangement and cell division that elongate the blade proximo-distally and realign planar polarity with the proximal-distal axis. Mutation of the atypical Cadherin Dachsous perturbs the global polarity pattern by altering epithelial dynamics. This mechanism utilizes the cellular movements that sculpt tissues to align planar polarity with tissue shape.

Live imaging of Drosophila imaginal disc development

Live imaging has revolutionized the analysis of developmental biology over the last few years. The ability to track in real time the dynamic processes that occur at tissue and cellular levels gives a much clearer view of development, and allows greater temporal resolution, than is possible with fixed tissue. Drosophila imaginal discs are a particularly important model of many aspects of development, but their small size and location inside the larva and pupa has prevented live imaging techniques from extensively being used in their study. Here, we introduce the use of viscous culture medium to enable high resolution imaging of imaginal disc development. As a proof of principle, we have analyzed the transformation that occurs during metamorphosis of the wing imaginal disc into the mature wing and report several previously unobserved stages of this model of organogenesis. These imaging methods are especially useful to study the complex and dynamic changes that occur during morphogenesis, but we show that they can also be used to analyze other developmental and cellular events. Moreover, our viscous medium creates a platform for future adaptation of other tissue culture conditions to allow imaging of a wide range of developmental events and systems.

Protocerebral Mediodorsal A2′ Neurosecretory Neurons in Late Pupae of Yellow Mealworm (Tenebrio molitor) after Exposure to a Static Magnetic Field

The activity of large dorsomedial protocerebral A2' neurosecretory neurons were investigated in late pupae of Tenebrio molitor L, which were exposed to a static magnetic field of 320 mT. Experimental groups were C: the control group which was kept at 5 meters from the magnet; CMF: pupae which were reared in control conditions and sacrificed on the eighth day of pupal stage (parents were kept in a magnetic field); and MF: pupae kept in a permanent magnetic field for eight days. Our results indicate the effects of a static magnetic field on the cytological characteristics and activity of large A2' neurosecretory neurons of Tenebrio molitor pupae.

Hormonal and nutritional regulation of insect fat body development and function

The insect fat body is an organ analogue to vertebrate adipose tissue and liver and functions as a major organ for nutrient storage and energy metabolism. Similar to other larval organs, fat body undergoes a developmental "remodeling" process during the period of insect metamorphosis, with the massive destruction of obsolete larval tissues by programmed cell death and the simultaneous growth and differentiation of adult tissues from small clusters of progenitor cells. Genetic ablation of Drosophila fat body cells during larval-pupal transition results in lethality at the late pupal stage and changes sizes of other larval organs indicating that fat body is the center for pupal development and adult formation. Fat body development and function are largely regulated by several hormonal (i.e. insulin and ecdysteroids) and nutritional signals, including oncogenes and tumor suppressors in these pathways. Combining silkworm physiology with fruitfly genetics might provide a valuable system to understand the mystery of hormonal regulation of insect fat body development and function.

S-phase favours notch cell responsiveness in the Drosophila bristle lineage

We have studied cell sensitivity to Notch pathway signalling throughout the cell cycle. As model system, we used the Drosophila bristle lineage where at each division N plays a crucial role in fate determination. Using in vivo imaging, we followed this lineage and activated the N-pathway at different moments of the secondary precursor cell cycle. We show that cells are more susceptible to respond to N-signalling during the S-phase. Thus, the period of heightened sensitivity coincided with the period of the S-phase. More importantly, modifications of S-phase temporality induced corresponding changes in the period of the cell's reactivity to N-activation. Moreover, S-phase abolition was correlated with a decrease in the expression of tramtrack, a downstream N-target gene. Finally, N cell responsiveness was modified after changes in chromatin packaging. We suggest that high-order chromatin structures associated with the S-phase create favourable conditions that increase the efficiency of the transcriptional machinery with respect to N-target genes.

MsSOCS expression indicates a potential role for JAK/STAT signalling in the early stages of Manduca sexta spermatogenesis

Our understanding of the Drosophila melanogaster testis stem cell niche has identified the signalling pathways required to maintain stem cells and promote self-renewal. Here we present the first detailed examination of the testes stem cell niche in the lepidopteran Manduca sexta . We show that larval testes contain hub-like structures surrounded by mitotically active cells likely to represent a self-renewing stem cell population. In addition, we have cloned DNA fragments encoding parts of M. sexta Signal Transducer and Activators of Transcription (STAT) and Suppressor of Cytokine Signalling (SOCS) homologues and show that expression of MsSOCS is upregulated in hub-adjacent cells. Given the conservation of socs-like genes and their regulation as Janus Kinases/Signal Transducer and Activators Transcription (JAK/STAT) pathway targets, we suggest that increased expression within the testis stem cells indicates increased levels of JAK/STAT signalling and a conserved role for pathway signalling in testis stem cell maintenance.

Prostaglandins A1 and E1 influence gene expression in an established insect cell line (BCIRL-HzAM1 cells)

Prostaglandins (PGs) and other eicosanoids exert important physiological actions in insects and other invertebrates, including influencing ion transport and mediating cellular immune defense functions. Although these actions are very well documented, we have no information on the mechanisms of PGs actions in insect cells. Here we report on the outcomes of experiments designed to test our hypothesis that PGs modulate gene expression in an insect cell line established from pupal ovarian tissue of the moth Helicoverpa zea (BCIRL-HzAM1 cells). We treated cells with either PGA(1) or PGE(1) for 12 or 24h then analyzed cell lysates by 2-D electrophoresis. Analysis of the gels by densitometry revealed substantial changes in protein expression in some of the protein spots we analyzed. These spots were processed for mass spectrometric analysis by MALDI TOF/TOF, which yielded in silico protein identities for all 34 spots. The apparent changes in three of the proteins were confirmed by semi-quantative PCR, showing that the changes in mRNA expression were reflected in changes in protein expression. The 34 proteins were sorted into six categories, protein actions, lipid metabolism, signal transduction, protection, cell functions and metabolism. The findings support the hypothesis that one mechanism of PG action in insect cells is the modulation of gene expression.

Immunofluorescent staining and imaging of the pupal and adult Drosophila visual system

This immunofluorescence protocol can be used to assay cell morphology, cell positioning and subcellular localization of proteins in the fly eye at stages of development from early pupation to adult. The protocol includes the following procedures: collecting and developmentally staging Drosophila pupae, dissecting fly eyes at defined stages of development, immunostaining of retina and preparing visual system samples (i.e., retina and optic lobe) for confocal microscopy. It is supplemented with images of key dissection steps, guidelines for troubleshooting and examples of data obtained using these methods. Overall, this protocol takes up to 9 d to complete. The amount of hands-on time required on each day varies, ranging from 30 min to several hours depending on the number of stages and/or genotypes one wishes to study.

A cell line (NTU-MV) established from Maruca vitrata (Lepidoptera: Pyralidae): Characterization, viral susceptibility, and polyhedra production

Here we describe the establishment of a new cell line, NTU-MV, derived from pupal tissues of an economically important pest, the legume pod borer Maruca vitrata. This cell line contained four major cell types: polymorphic cells, round cells, spindle-shaped cells, and comma cells. The doubling time of MV cells in TNM-FH medium supplemented with 8% FBS at 28 degrees C was 27h. The chromosome numbers of MV cells varied widely from 16 to 268. Compared to other insect cell lines, the MV cell line produced distinct isozyme patterns with esterase, malate dehydrogenase (MDH), and lactate dehydrogenase (LDH). Confirmation that NTU-MV was derived from M. vitrata was demonstrated by showing that the sequence of the internal transcribed spacer regions (ITS) of the MV cells was 98% identical to that of M. vitrata larvae. Two NTU-MV cell strains, NTU-MV1 and NTU-MV56, were selected based on susceptibility to MaviMNPV (M. vitrata multiple nucleopolyhedrovirus). NTU-MV, MV1, and MV56 cells showed a high susceptibility to MaviMNPV and produced high yields of polyhedra (47-50OBs/cell, 4x10(7)-5.96x10(7)OBs/ml) after 2 weeks of MaviMNPV infection. We conclude that the NTU-MV cell line will be a useful tool for studying MaviMNPV as well as for the mass production of MaviMNPV polyhedra for the biocontrol of M. vitrata.

Modulation of the ecdysteroid-induced cell death by juvenile hormone during pupal wing development of Lepidoptera

Females of the tussock moth Orgyia recens have only vestigial wings, whereas the males have normal wings. We previously found that ecdysteroid induces both apoptotic events and phagocytotic activation in sex-specific and region-specific manners. To investigate whether different responses to ecdysteroid are controlled at the receptor level, we cloned ecdysteroid receptor isoforms, EcR-A and EcR-B1, in O. recens. In both male and female wings, EcR-A signal was detected in the distal region of the bordering lacuna (BL), whereas EcR-B1 signal was detected in the proximal region of the BL. The similar expression patterns of both EcR isoforms suggested that molecules other than EcR should be involved in different ecdysteroid responses between male and female of O. recens. We next tested juvenile hormone (JH) effects on pupal wing morphogenesis in O. recens. Interestingly, both JH and 20E addition induced wing degeneration not only in females but also in males. In addition, higher concentration of JH pre-treatment of the pupal wings of the silkworm, Bombyx mori, also caused wing degeneration under ecdysteroid treatment. These results indicate that JH modulates the ecdysteroid action to induce the cell death on pupal wings, generally in Lepidoptera.

The flare gene, which encodes the AIP1 protein of Drosophila, functions to regulate F-actin disassembly in pupal epidermal cells

Adult Drosophila are decorated with several types of polarized cuticular structures, such as hairs and bristles. The morphogenesis of these takes place in pupal cells and is mediated by the actin and microtubule cytoskeletons. Mutations in flare (flr) result in grossly abnormal epidermal hairs. We report here that flr encodes the Drosophila actin interacting protein 1 (AIP1). In other systems this protein has been found to promote cofilin-mediated F-actin disassembly. In Drosophila cofilin is encoded by twinstar (tsr). We show that flr mutations result in increased levels of F-actin accumulation and increased F-actin stability in vivo. Further, flr is essential for cell proliferation and viability and for the function of the frizzled planar cell polarity system. All of these phenotypes are similar to those seen for tsr mutations. This differs from the situation in yeast where cofilin is essential while aip1 mutations result in only subtle defects in the actin cytoskeleton. Surprisingly, we found that mutations in flr and tsr also result in greatly increased tubulin staining, suggesting a tight linkage between the actin and microtubule cytoskeleton in these cells.

Eph receptor and ephrin signaling in developing and adult brain of the honeybee (Apis mellifera)

Roles for Eph receptor tyrosine kinase and ephrin signaling in vertebrate brain development are well established. Their involvement in the modulation of mammalian synaptic structure and physiology is also emerging. However, less is known of their effects on brain development and their function in adult invertebrate nervous systems. Here, we report on the characterization of Eph receptor and ephrin orthologs in the honeybee, Apis mellifera (Am), and their role in learning and memory. In situ hybridization for mRNA expression showed a uniform distribution of expression of both genes across the developing pupal and adult brain. However, in situ labeling with Fc fusion proteins indicated that the AmEphR and Amephrin proteins were differentially localized to cell body regions in the mushroom bodies and the developing neuropiles of the antennal and optic lobes. In adults, AmEphR protein was localized to regions of synaptic contacts in optic lobes, in the glomeruli of antennal lobes, and in the medial lobe of the mushroom body. The latter two regions are involved in olfactory learning and memory in the honeybee. Injections of EphR-Fc and ephrin-Fc proteins into the brains of adult bees, 1 h before olfactory conditioning of the proboscis extension reflex, significantly reduced memory 24 h later. Experimental amnesia in the group injected with ephrin-Fc was apparent 1 h post-training. Experimental amnesia was also induced by post-training injections with ephrin-Fc suggesting a role in recall. This is the first demonstration that Eph molecules function to regulate the formation of memory in insects.

Basement membrane remodeling is essential for Drosophila disc eversion and tumor invasion

Organ and tissue integrity is often maintained in animals by a specialized extracellular matrix structure called the basement membrane (BM). Accumulated evidence indicates that BM remodeling occurs during development and tumor invasion. Although the BM organizes and functions at the organ level, most past studies have explored its biochemical and in vitro properties. In this study, we monitor the BM in vivo during developmental tissue invasion for disc eversion and tumor invasion in Drosophila and modulate BM integrity with genetic alterations affecting either the whole organism or the targeted discs or tumors. We observe that the degradation of BM by the discs or the tumors is an early event during invasion processes and that preventing BM degradation completely blocks both tissue and tumor invasion, indicating that modulation of BM is essential for developmental and tumor invasion. Furthermore, elements of the invasion machinery, including JNK-induced matrix metalloproteinase (MMP) expression, are shared by both disc eversion and tumor invasion processes. Moreover, we show that although expression of MMP inhibitor, TIMP, is sufficient to halt developmental invasion, inhibition of proteases by both TIMP and RECK are required to block tumor invasion. These data suggest that tumor cells have a more robust invasion mechanism and could acquire metastatic behavior by co-opting developmental invasion programs. This type of co-option may be a general feature contributing to the progression of tumors. Finally, although past efforts using MMP inhibitors have not yielded much success, our results strongly argue that BM modulation could be a critical target for cancer therapy.

Developmental and hormonal regulation of midgut remodeling in a lepidopteran insect, Heliothis virescens

Midgut tissue undergoes remodeling during metamorphosis in insects belonging to orders Lepidoptera and Diptera. We investigated the developmental and hormonal regulation of these remodeling events in lepidopteran insect, Heliothis virescens. In H. virescens, programmed cell death (PCD) of larval midgut cells as well as proliferation and differentiation of imaginal cells began at 108 h after ecdysis to the final larval instar (AEFL) and proceeded through the pupal stages. Expression patterns of pro- cell death factors (caspase-1 and ICE) and anti-cell death factor, Inhibitor of Apoptosis (IAP) were studied in midguts during last larval and pupal stages. IAP, Caspase-1 and ICE mRNAs showed peaks at 48 h AEFL, 96 h AEFL and in newly formed pupae, respectively. Immunohistochemical analysis substantiated high caspase-3 activity in midgut at 108 h AEFL. Application of methoprene, a juvenile hormone analog (JHA) blocked PCD by maintaining high levels of IAP, downregulating the expression of caspase-1, ICE and inhibiting an increase in caspase-3 protein levels in midgut tissue. Also, the differentiation of imaginal cells was impaired by methoprene treatment. These studies demonstrate that presence of JHA during final instar larvae affects both midgut remodeling and larval-pupal metamorphosis leading to larval/pupal deformities in lepidopteran insects, a mechanism that is different from that in mosquito, Ae. aegypti where JHA uncouples midgut remodeling from metamorphosis.

New cell lines from Lymantria xylina (Lepidoptera: Lymantriidae): Characterization and susceptibility to baculoviruses

Four new cell lines, designated as NTU-LY-1 to -4, respectively, were established from the pupal tissues of Lymantria xylina Swinhoe (Lepidoptera: Lymantriidae). These cell lines have been cultured approximately 80 passages during 2 years in TNM-FH medium supplemented with 8% fetal bovine serum, at a constant temperature of 28 degrees C. Each line consists of three major morphological types: round cells, spindle-shaped cells, and giant cells. The characterization of these cell lines showed that they are different from previously established lines derived from related Lepidopteran species. All new lines were susceptible to the L. xylina multiple nucleopolyhedrovirus (LyxyMNPV) and appeared to have a good potential for studying this virus.

Functional analysis of genes differentially expressed in the Drosophila wing disc: role of transcripts enriched in the wing region

Differential gene expression is the major mechanism underlying the development of specific body regions. Here we assessed the role of genes differentially expressed in the Drosophila wing imaginal disc, which gives rise to two distinct adult structures: the body wall and the wing. Reverse genetics was used to test the function of uncharacterized genes first identified in a microarray screen as having high levels of expression in the presumptive wing. Such genes could participate in elaborating the specific morphological characteristics of the wing. The activity of the genes was modulated using misexpression and RNAi-mediated silencing. Misexpression of eight of nine genes tested caused phenotypes. Of 12 genes tested, 10 showed effective silencing with RNAi transgenes, but only 3 of these had resulting phenotypes. The wing phenotypes resulting from RNAi suggest that CG8780 is involved in patterning the veins in the proximal region of the wing blade and that CG17278 and CG30069 are required for adhesion of wing surfaces. Venation and apposition of the wing surfaces are processes specific to wing development providing a correlation between the expression and function of these genes. The results show that a combination of expression profiling and tissue-specific gene silencing has the potential to identify new genes involved in wing development and hence to contribute to our understanding of this process. However, there are both technical and biological limitations to this approach, including the efficacy of RNAi and the role that gene redundancy may play in masking phenotypes.

Identification of the death zone: a spatially restricted region for programmed cell death that sculpts the fly eye

Programmed cell death (PCD) sculpts many developing tissues. The final patterning step of the Drosophila retina is the elimination, through PCD, of a subset of interommatidial lattice cells during pupation. It is not understood how this process is spatially regulated to ensure that cells die in the proper positions. To address this, we observed PCD of lattice cells in the pupal retina in real time. This live-visualization method demonstrates that lattice cell apoptosis is a highly specific process. In all, 85% of lattice cells die in exclusive 'death zone' positions between adjacent ommatidia. In contrast, cells that make specific contacts with primary pigment cells are protected from death. Two signaling pathways, Drosophila epidermal growth factor receptor (dEgfr) and Notch, that are thought to be central to the regulation of lattice cell survival and death, are not sufficient to establish the death zone. Thus, application of live visualization to the fly eye gives new insight into a dynamic developmental process.

Primary Culture of Gustatory Receptor Neurons from the Blowfly, Phormia regina

Flies provide a powerful model system for exploring signaling systems in gustatory receptor neurons (GRNs). To elucidate the cellular and molecular bases of these signaling systems, we sought to develop techniques to dissociate GRNs. We developed a primary culture of GRNs isolated from the labella of the blowfly, Phormia regina, 4-5 days after pupation. Dissected labella were treated with papain in a low Ca2+ saline solution and shaken in Leibovitz's L-15 medium supplemented with 20-hydroxyecdysone, L-ascorbic acid, and trehalose with a test tube mixer. Released cells were plated and kept at 29 degrees C in a medium containing fetal bovine serum. After a minimum of 2 days in culture, we observed survival or growth of bipolar cells with the characteristic morphology of GRNs. We also examined taste responsiveness by monitoring intracellular Ca2+ with a Ca2+-sensitive fluorescent dye, fluo-3. For some bipolar cells, application of sucrose, NaCl, or LiCl for 5-20 s transiently increased the intracellular Ca2+ levels in cell bodies for 20-30 s. The primary cell culture described here is useful for functional analysis of GRNs.

Exposure to low-dose X-rays promotes peculiar autophagic cell death in Drosophila melanogaster, an effect that can be regulated by the inducible expression of Hml dsRNA

We previously reported that to induce an early emergence effect with low-dose X-irradiation in Drosophila, exposure during the prepupae stage is necessary. The present study examined the mechanism by which low-dose radiation rapidly eliminates larval cells and activates the formation of the imaginal discs during metamorphosis. Upon exposure to 0.5 Gy X-rays at 2 h after puparium formation (APF), the larval salivary glands swelled and were surrounded by remarkably thick structures containing an acid phosphatase (Acph) enzyme, implicating a peculiar autophagic cell death. TUNEL staining revealed the presence of DNA fragmentations compared with cells from sham controls which remained unchanged until 12 h APF. Additionally, the salivary glands of exposed flies were completely destroyed by 10 h APF. Furthermore, exposure to 0.5 Gy X-rays also facilitated the activity of the engulfment function of dendritic cells (DCs); they were generated in the larval salivary glands, engulfed the cell corpses and finally moved to the fat body. Data from an experiment demonstrating the inducible expression of Hml double-stranded RNA (dsRNA) indicate that a slow rate of engulfment of larval cells results in a longer time to emergence. Thus, the animals subjected to low-dose X-rays activated autophagic processes, resulting in significantly faster adult eclosion.

The myb-related gene stonewall induces both hyperplasia and cell death in Drosophila: rescue of fly lethality by coexpression of apoptosis inducers

We carried out gain-of-function mutagenesis screening and identified a mutant in which GAL4 induction led to both hyperplasia and apoptosis. The gene involved was identified as stonewall (stwl), a myb-related gene involved in germ cell proliferation and differentiation during oogenesis. As observed with dmyb, the ectopic expression of stwl(UY823) inhibited endoreplication in salivary glands. We also found that stwl(UY823) overexpression, like overexpression of the wild-type gene, activated G1/S transition and apoptosis. The apoptosis triggered by stwl(UY823) expression is correlated to induction of the proapoptotic gene reaper. Finally, the death of flies induced by ectopic stwl(UY823) expression is efficiently prevented in vivo by triggering cell death in stwl(UY823)-expressing cells. Our results suggest that stwl(UY823) kills flies by causing inappropriate cell cycle entry, and that triggering the death of these overproliferating cells or slowing their proliferation restores viability.