The Cellular Innate Immune Response of the Invasive Pest Insect Drosophila suzukii against Pseudomonas entomophila Involves the Release of Extracellular Traps

Drosophila suzukii is a neobiotic invasive pest that causes extensive damage to fruit crops worldwide. The biological control of this species has been unsuccessful thus far, in part because of its robust cellular innate immune system, including the activity of professional phagocytes known as hemocytes and plasmatocytes. The in vitro cultivation of primary hemocytes isolated from D. suzukii third-instar larvae is a valuable tool for the investigation of hemocyte-derived effector mechanisms against pathogens such as wasp parasitoid larvae, bacteria, fungi and viruses. Here, we describe the morphological characteristics of D. suzukii hemocytes and evaluate early innate immune responses, including extracellular traps released against the entomopathogen Pseudomonas entomophila and lipopolysaccharides. We show for the first time that D. suzukii plasmatocytes cast extracellular traps to combat P. entomophila, along with other cell-mediated reactions, such as phagocytosis and the formation of filopodia.

Pilot RNAi Screen in Drosophila Neural Stem Cell Lineages to Identify Novel Tumor Suppressor Genes Involved in Asymmetric Cell Division

A connection between compromised asymmetric cell division (ACD) and tumorigenesis was proven some years ago using Drosophila larval brain neural stem cells, called neuroblasts (NBs), as a model system. Since then, we have learned that compromised ACD does not always promote tumorigenesis, as ACD is an extremely well-regulated process in which redundancy substantially overcomes potential ACD failures. Considering this, we have performed a pilot RNAi screen in Drosophila larval brain NB lineages using RasV12 scribble (scrib) mutant clones as a sensitized genetic background, in which ACD is affected but does not cause tumoral growth. First, as a proof of concept, we have tested known ACD regulators in this sensitized background, such as lethal (2) giant larvae and warts. Although the downregulation of these ACD modulators in NB clones does not induce tumorigenesis, their downregulation along with RasV12 scrib does cause tumor-like overgrowth. Based on these results, we have randomly screened 79 RNAi lines detecting 15 potential novel ACD regulators/tumor suppressor genes. We conclude that RasV12 scrib is a good sensitized genetic background in which to identify tumor suppressor genes involved in NB ACD, whose function could otherwise be masked by the high redundancy of the ACD process.

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.

FDA-Approved Drug Screening for Compounds That Facilitate Hematopoietic Stem and Progenitor Cells (HSPCs) Expansion in Zebrafish

Hematopoietic stem cells (HSCs) are a specialized subset of cells with self-renewal and multilineage differentiation potency, which are essential for their function in bone marrow or umbilical cord blood transplantation to treat blood disorders. Expanding the hematopoietic stem and progenitor cells (HSPCs) ex vivo is essential to understand the HSPCs-based therapies potency. Here, we established a screening system in zebrafish by adopting an FDA-approved drug library to identify candidates that could facilitate HSPC expansion. To date, we have screened 171 drugs of 7 categories, including antibacterial, antineoplastic, glucocorticoid, NSAIDS, vitamins, antidepressant, and antipsychotic drugs. We found 21 drugs that contributed to HSPCs expansion, 32 drugs’ administration caused HSPCs diminishment and 118 drugs’ treatment elicited no effect on HSPCs amplification. Among these drugs, we further investigated the vitamin drugs ergocalciferol and panthenol, taking advantage of their acceptability, limited side-effects, and easy delivery. These two drugs, in particular, efficiently expanded the HSPCs pool in a dose-dependent manner. Their application even mitigated the compromised hematopoiesis in an ikzf1^−/− mutant. Taken together, our study implied that the larval zebrafish is a suitable model for drug repurposing of effective molecules (especially those already approved for clinical use) that can facilitate HSPCs expansion.

Thyroid hormone deficiency during zebrafish development impairs central nervous system myelination

Thyroid hormones are messengers that bind to specific nuclear receptors and regulate a wide range of physiological processes in the early stages of vertebrate embryonic development, including neurodevelopment and myelogenesis. We here tested the effects of reduced T3 availability upon the myelination process by treating zebrafish embryos with low concentrations of iopanoic acid (IOP) to block T4 to T3 conversion. Black Gold II staining showed that T3 deficiency reduced the myelin density in the forebrain, midbrain, hindbrain and the spinal cord at 3 and 7 dpf. These observations were confirmed in 3 dpf mbp:egfp transgenic zebrafish, showing that the administration of IOP reduced the fluorescent signal in the brain. T3 rescue treatment restored brain myelination and reversed the changes in myelin-related gene expression induced by IOP exposure. NG2 immunostaining revealed that T3 deficiency reduced the amount of oligodendrocyte precursor cells in 3 dpf IOP-treated larvae. Altogether, the present results show that inhibition of T4 to T3 conversion results in hypomyelination, suggesting that THs are part of the key signaling molecules that control the timing of oligodendrocyte differentiation and myelin synthesis from very early stages of brain development.

Xenopus chip for single-egg trapping, in vitro fertilization, development, and tadpole escape

Xenopus laevis is highly suitable as a toxicology animal model owing to its advantages in embryogenesis research. For toxicological studies, a large number of embryos must be handled simultaneously because they very rapidly develop into the target stages within a short period of time. To efficiently handle the embryos, a convenient embryo housing device is essential for fast and reliable assessment and statistical evaluation of malformation caused by toxicants. Here, we suggest 3D fabrication of single-egg trapping devices in which Xenopus eggs are fertilized in vitro, and the embryos are cultured. We used manual pipetting to insert the Xenopus eggs inside the trapping sites of the chip. By introducing a liquid circulating system, we connected a sperm-mixed solution with the chip to induce in vitro fertilization of the eggs. After the eggs were fertilized, we observed embryo development involving the formation of egg cleavage, blastula, gastrula, and tadpole. After the tadpoles grew inside the chip, we saved their lives by enabling their escape from the chip through reverse flow of the culture medium. The Xenopus chip can serve as an incubator to induce fertilization and monitor normal and abnormal development of the Xenopus from egg to tadpole.

Protocol for quantitative analysis of pulsatile contractions and cell extrusion in epithelial tissues of larval zebrafish

Cell elimination by extrusion is important for epithelial homeostasis, but knowing when and where cells will extrude has made in vivo studies difficult. Here, we describe a step-by-step protocol for inducing cell extrusion from the larval zebrafish epidermis. We detail how to capture the dynamics of extrusion via time-lapse imaging and describe how existing protocols can be implemented for the analysis of cell shape changes preceding extrusion events and derivation of mechanical measurements associated with these shape changes.

For complete details on the use and execution of this protocol, please refer to Atieh et al. (2021).

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Inducible cell extrusion in the epidermis of larval zebrafish

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Use of time-lapse confocal imaging to capture the dynamics of cell extrusion

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Description for analysis of cell shape changes preceding extrusion events

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Steps for measurements of deformation associated with the cell shape changes

Establishing Sustainable Cell Lines of a Coral, Acropora tenuis

Planula larvae of the scleractinian coral, Acropora tenuis, consist of elongated ectodermal cells and developing inner endodermal cells. To establish in vitro cell lines for future studies of cellular and developmental potential of coral cells, larvae were successfully dissociated into single cells by treating them with a tissue dissociation solution consisting of trypsin, EDTA, and collagenase. Brown-colored cells, translucent cells, and pale blue cells were the major components of dissociated larvae. Brown-colored cells began to proliferate transiently in the culture medium that was devised for the coral, while translucent cells and pale blue cells decreased in number about 1 week after cell dissociation. In addition, when a modular protease, plasmin, was added to the cell culture medium, brown-colored cells extended pseudopodia and assumed amorphous shapes. They then continued to proliferate in clumps for more than 6 months with a doubling time of approximately 4-5 days. From 3 weeks of cell culture onward, brown-colored cells often aggregated and exhibited morphogenesis-like behavior to form flat sheets, and blastula-like clusters or gastrula-like spheres. Single cells or cell-clusters of the cell lines were analyzed by RNA-seq. This analysis showed that genes expressed in these cells in vitro were A. tenuis genes. Furthermore, each cell line expressed a specific set of genes, suggesting that their properties include gastroderm, secretory cells, undifferentiated cells, neuronal cells, and epidermis. All cell properties were maintained stably throughout successive cell cultures. These results confirm the successful establishment of a coral in vitro cell line.

Photoacoustic-fluorescence microendoscopy in vivo

A miniature endoscope capable of imaging multiple tissue contrasts in high resolution is highly attractive, because it can provide complementary and detailed tissue information of internal organs. Here we present a photoacoustic (PA)-fluorescence (FL) endoscope for optical-resolution PA microscopy (PAM) and FL microscopy (FLM). The endoscope with a diameter of 2.8 mm achieves high lateral resolutions of 5.5 and 6.3 µm for PAM and FLM modes, respectively. In vivo imaging of zebrafish larvae and a mouse ear is conducted, and high-quality images are obtained. Additionally, in vivo endoscopic imaging of a rat rectum is demonstrated, showing the endoscopic imaging capability of our endoscope. By providing dual contrasts with high resolution, the endoscope may open up new opportunities for clinical endoscopic imaging applications.

Optimal combination of anti-inflammatory components from Chinese medicinal formula Liang-Ge-San

ETHNOPHARMACOLOGICAL RELEVANCE

Liang-Ge-San (LGS), a traditional Chinese medicine (TCM) formula, is usually used in acute inflammatory diseases in China.

AIM OF THE STUDY

This study aims to detect the optimal combination of anti-inflammatory components from LGS.

MATERIALS AND METHODS

Four mainly representative components (phillyrin, emodin, baicalin, and liquiritin) from LGS were chosen. The optimal combination was investigated by orthogonal design study. Zebrafish inflammation model was established by lipopolysaccharide (LPS)-yolk microinjection, and then the anti-inflammatory activities of different combinations were determined by survival analysis, changes on inflammatory cells infiltration, the MyD88/NF-κB and MAPK pathways and inflammatory cytokines production.

RESULTS

The different combinations of bioactive ingredients from LGS significantly protected zebrafish from LPS-induced inflammation, as evidenced by decreased recruitment of macrophages and neutrophils, inhibition of the MyD88/NF-κB and MAPK pathways and down-regulation of TNF-α and IL-6. Among them, the combination group 8 most significantly protected against LPS. The combination of group 8 is: 0.1 μM of emodin, 2 μM of baicalin, 20 μM of phillyrin and 12.5 μM of liquiritin.

CONCLUSION

The optimized combination group 8 exerts the most significant anti-inflammatory activity by inhibiting the recruitment of inflammatory cells, activation of the MyD88/NF-κB and MAPK pathways and the secretion of pro-inflammatory cytokines. This present study provides pharmacological evidences for the further development of new modern Chinese drug from LGS to treat acute inflammatory diseases, but indicated the use of zebrafish in the screening of components from formulas.

Diverse cellular morphologies during lumen maturation in Anopheles gambiae larval salivary glands

Mosquitoes are the greatest animal threat to human health, causing hundreds of millions of infections and around 1 million deaths each year. All mosquito-borne pathogens must traverse the salivary glands (SGs) to be transmitted to the next host, making this organ an ideal target for interventions. The adult SG develops from precursor cells located in the larval SG duct bud. Characterization of the larval SG has been limited. We sought to better understand larval SG architecture, secretion and gene expression. We developed an optimized method for larval SG staining and surveyed hundreds of larval stage 4 (L4) SGs using fluorescence confocal microscopy. Remarkable variation in SG cell and chromatin organization differed among individuals and across the L4 stage. Lumen formation occurred during L4 stage through secretion likely involving a coincident cellular apical lipid enrichment and extracellular vesicle-like structures. Meta-analysis of microarray data showed that larval SG gene expression is divergent from adult SGs, more similar to larval gastric cecae, but different from other larval gut compartments. This work highlights the variable cell architecture of larval Anopheles gambiae SGs and provides candidate targets for genetic strategies aiming to disrupt SGs and transmission of mosquito-borne pathogens.

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.

Thyroid Hormone Receptor Is Essential for Larval Epithelial Apoptosis and Adult Epithelial Stem Cell Development but Not Adult Intestinal Morphogenesis during Xenopus tropicalis Metamorphosis

Vertebrate postembryonic development is regulated by thyroid hormone (T3). Of particular interest is anuran metamorphosis, which offers several unique advantages for studying the role of T3 and its two nuclear receptor genes, TRα and TRβ, during postembryonic development. We have recently generated TR double knockout (TRDKO) Xenopus tropicalis animals and reported that TR is essential for the completion of metamorphosis. Furthermore, TRDKO tadpoles are stalled at the climax of metamorphosis before eventual death. Here we show that TRDKO intestine lacked larval epithelial cell death and adult stem cell formation/proliferation during natural metamorphosis. Interestingly, TRDKO tadpole intestine had premature formation of adult-like epithelial folds and muscle development. In addition, T3 treatment of premetamorphic TRDKO tadpoles failed to induce any metamorphic changes in the intestine. Furthermore, RNA-seq analysis revealed that TRDKO altered the expression of many genes in biological pathways such as Wnt signaling and the cell cycle that likely underlay the inhibition of larval epithelial cell death and adult stem cell development caused by removing both TR genes. Our data suggest that liganded TR is required for larval epithelial cell degeneration and adult stem cell formation, whereas unliganded TR prevents precocious adult tissue morphogenesis such as smooth-muscle development and epithelial folding.

Systemic and local effect of the Drosophila headcase gene and its role in stress protection of Adult Progenitor Cells

During the development of a holometabolous insect such as Drosophila, specific group of cells in the larva survive during metamorphosis, unlike the other larval cells, and finally give rise to the differentiated adult structures. These cells, also known as Adult Progenitor Cells (APCs), maintain their multipotent capacity, differentially respond to hormonal and nutritional signals, survive the intrinsic and environmental stress and respond to the final differentiation cues. However, not much is known about the specific molecular mechanisms that account for their unique characteristics. Here we show that a specific Drosophila APC gene, headcase (hdc), has a dual role in the normal development of these cells. It acts at a systemic level by controlling the hormone ecdysone in the prothoracic gland and at the same time it acts locally as a tissue growth suppressor in the APC clusters, where it modulates the activity of the TOR pathway and promotes their survival by contributing in the regulation of the Unfolded Protein Response. We also show that hdc provides protection against stress in the APCs and that its ectopic expression in cells that do not usually express hdc can confer these cells with an additional stress protection. Hdc is the founding member of a group of homolog proteins identified from C. elegans to humans, where has been found associated with cancer progression. The finding that the Drosophila hdc is specifically expressed in progenitor cells and that it provides protection against stress opens up a new hypothesis to be explored regarding the role of the human Heca and its contribution to carcinogenesis.

First description of the immature stages of Fannia sabroskyi Seago, 1954 (Insecta, Diptera, Fanniidae)

Egg, larvae and the puparium of Fannia sabroskyi Seago, 1954 (Diptera, Fanniidae) are described and illustrated for the first time. The following structures have been documented: pseudocephalon, antennal complex, maxillary palpus, facial mask, anterior spiracle, cephaloskeleton structures, thoracic and abdominal processes, anal division, and posterior spiracle. Due to its necrophagous habit, this species may be of potential forensic importance for estimating the postmortem interval in criminal investigations. The information presented herein may be useful to distinguish the immature forms of Fannia species and to supplement the database for identification of Neotropical species of Fanniidae. In addition, it is also important for evolutionary and phylogenetic studies.

Novel approach to enhance sensitivity while retaining morphology in fragile tissue sections for mass spectrometry imaging

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging is an effective tool for investigating the distribution of molecules. However, cryosections are made from non-fixed tissues, causing difficulties in preparing sections from fragile, high-water content tissues such as those from tadpoles. Here, we introduce a new method for preparing cryosections using an adhesive tape followed by transfer onto glass slides for MALDI-MS imaging. Signals obtained from the transferred sections were higher than those from other sections, and the transferred sections had high optical quality. This novel approach could be an effective tool for MALDI-MS imaging of aquatic animals.

The ontology of the anatomy and development of the solitary ascidian Ciona: the swimming larva and its metamorphosis

Ciona robusta (Ciona intestinalis type A), a model organism for biological studies, belongs to ascidians, the main class of tunicates, which are the closest relatives of vertebrates. In Ciona, a project on the ontology of both development and anatomy is ongoing for several years. Its goal is to standardize a resource relating each anatomical structure to developmental stages. Today, the ontology is codified until the hatching larva stage. Here, we present its extension throughout the swimming larva stages, the metamorphosis, until the juvenile stages. For standardizing the developmental ontology, we acquired different time-lapse movies, confocal microscope images and histological serial section images for each developmental event from the hatching larva stage (17.5 h post fertilization) to the juvenile stage (7 days post fertilization). Combining these data, we defined 12 new distinct developmental stages (from Stage 26 to Stage 37), in addition to the previously defined 26 stages, referred to embryonic development. The new stages were grouped into four Periods named: Adhesion, Tail Absorption, Body Axis Rotation, and Juvenile. To build the anatomical ontology, 203 anatomical entities were identified, defined according to the literature, and annotated, taking advantage from the high resolution and the complementary information obtained from confocal microscopy and histology. The ontology describes the anatomical entities in hierarchical levels, from the cell level (cell lineage) to the tissue/organ level. Comparing the number of entities during development, we found two rounds on entity increase: in addition to the one occurring after fertilization, there is a second one during the Body Axis Rotation Period, when juvenile structures appear. Vice versa, one-third of anatomical entities associated with the embryo/larval life were significantly reduced at the beginning of metamorphosis. Data was finally integrated within the web-based resource "TunicAnatO", which includes a number of anatomical images and a dictionary with synonyms. This ontology will allow the standardization of data underpinning an accurate annotation of gene expression and the comprehension of mechanisms of differentiation. It will help in understanding the emergence of elaborated structures during both embryogenesis and metamorphosis, shedding light on tissue degeneration and differentiation occurring at metamorphosis.

Rabphilin involvement in filtration and molecular uptake in Drosophila nephrocytes suggests a similar role in human podocytes

Drosophila nephrocytes share functional, structural and molecular similarities with human podocytes. It is known that podocytes express the rabphilin 3A (RPH3A)-RAB3A complex, and its expression is altered in mouse and human proteinuric disease. Furthermore, we previously identified a polymorphism that suggested a role for RPH3A protein in the development of urinary albumin excretion. As endocytosis and vesicle trafficking are fundamental pathways for nephrocytes, the objective of this study was to assess the role of the RPH3A orthologue in Drosophila, Rabphilin (Rph), in the structure and function of nephrocytes. We confirmed that Rph is required for the correct function of the endocytic pathway in pericardial Drosophila nephrocytes. Knockdown of Rph reduced the expression of the cubilin and stick and stones genes, which encode proteins that are involved in protein uptake and filtration. We also found that reduced Rph expression resulted in a disappearance of the labyrinthine channel structure and a reduction in the number of endosomes, which ultimately leads to changes in the number and volume of nephrocytes. Finally, we demonstrated that the administration of retinoic acid to IR-Rph nephrocytes rescued some altered aspects, such as filtration and molecular uptake, as well as the maintenance of cell fate. According to our data, Rph is crucial for nephrocyte filtration and reabsorption, and it is required for the maintenance of the ultrastructure, integrity and differentiation of the nephrocyte.

Diet choice: The two-factor host acceptance system of silkworm larvae

Many herbivorous insects are mono- or oligophagous, having evolved to select a limited range of host plants. They specifically identify host-plant leaves using their keen sense of taste. Plant secondary metabolites and sugars are thought to be key chemical cues that enable insects to identify host plants and evaluate their quality as food. However, the neuronal and behavioral mechanisms of host-plant recognition are poorly understood. Here, we report a two-factor host acceptance system in larvae of the silkworm Bombyx mori, a specialist on several mulberry species. The first step is controlled by a chemosensory organ, the maxillary palp (MP). During palpation at the leaf edge, the MP detects trace amounts of leaf-surface compounds, which enables host-plant recognition without biting. Chemosensory neurons in the MP are tuned with ultrahigh sensitivity (thresholds of attomolar to femtomolar) to chlorogenic acid (CGA), quercetin glycosides, and β-sitosterol (βsito). Only if these 3 compounds are detected does the larva make a test bite, which is evaluated in the second step. Low-sensitivity neurons in another chemosensory organ, the maxillary galea (MG), mainly detect sucrose in the leaf sap exuded by test biting, allowing larvae to accept the leaf and proceed to persistent biting (feeding). The two-factor host acceptance system reported here may commonly underlie stereotyped feeding behavior in many phytophagous insects and determine their feeding habits.

Mutually exclusive dendritic arbors in C. elegans neurons share a common architecture and convergent molecular cues

Stress-induced changes to the dendritic architecture of neurons have been demonstrated in numerous mammalian and invertebrate systems. Remodeling of dendrites varies tremendously among neuron types. During the stress-induced dauer stage of Caenorhabditis elegans, the IL2 neurons arborize to cover the anterior body wall. In contrast, the FLP neurons arborize to cover an identical receptive field during reproductive development. Using time-course imaging, we show that branching between these two neuron types is highly coordinated. Furthermore, we find that the IL2 and FLP arbors have a similar dendritic architecture and use an identical downstream effector complex to control branching; however, regulation of this complex differs between stress-induced IL2 branching and FLP branching during reproductive development. We demonstrate that the unfolded protein response (UPR) sensor IRE-1, required for localization of the complex in FLP branching, is dispensable for IL2 branching at standard cultivation temperatures. Exposure of ire-1 mutants to elevated temperatures results in defective IL2 branching, thereby demonstrating a previously unknown genotype by environment interaction within the UPR. We find that the FOXO homolog, DAF-16, is required cell-autonomously to control arborization during stress-induced arborization. Likewise, several aspects of the dauer formation pathway are necessary for the neuron to remodel, including the phosphatase PTEN/DAF-18 and Cytochrome P450/DAF-9. Finally, we find that the TOR associated protein, RAPTOR/DAF-15 regulates mutually exclusive branching of the IL2 and FLP dendrites. DAF-15 promotes IL2 branching during dauer and inhibits precocious FLP growth. Together, our results shed light on molecular processes that regulate stress-mediated remodeling of dendrites across neuron classes.

Flexible neural connectivity under constraints on total connection strength

Neural computation is determined by neurons’ dynamics and circuit connectivity. Uncertain and dynamic environments may require neural hardware to adapt to different computational tasks, each requiring different connectivity configurations. At the same time, connectivity is subject to a variety of constraints, placing limits on the possible computations a given neural circuit can perform. Here we examine the hypothesis that the organization of neural circuitry favors computational flexibility: that it makes many computational solutions available, given physiological constraints. From this hypothesis, we develop models of connectivity degree distributions based on constraints on a neuron’s total synaptic weight. To test these models, we examine reconstructions of the mushroom bodies from the first instar larva and adult Drosophila melanogaster. We perform a Bayesian model comparison for two constraint models and a random wiring null model. Overall, we find that flexibility under a homeostatically fixed total synaptic weight describes Kenyon cell connectivity better than other models, suggesting a principle shaping the apparently random structure of Kenyon cell wiring. Furthermore, we find evidence that larval Kenyon cells are more flexible earlier in development, suggesting a mechanism whereby neural circuits begin as flexible systems that develop into specialized computational circuits.

High-throughput electron microscopic anatomical experiments have begun to yield detailed maps of neural circuit connectivity. Uncovering the principles that govern these circuit structures is a major challenge for systems neuroscience. Healthy neural circuits must be able to perform computational tasks while satisfying physiological constraints. Those constraints can restrict a neuron’s possible connectivity, and thus potentially restrict its computation. Here we examine simple models of constraints on total synaptic weights, and calculate the number of circuit configurations they allow: a simple measure of their computational flexibility. We propose probabilistic models of connectivity that weight the number of synaptic partners according to computational flexibility under a constraint and test them using recent wiring diagrams from a learning center, the mushroom body, in the fly brain. We compare constraints that fix or bound a neuron’s total connection strength to a simple random wiring null model. Of these models, the fixed total connection strength matched the overall connectivity best in mushroom bodies from both larval and adult flies. We also provide evidence suggesting that neural circuits are more flexible in early stages of development and lose this flexibility as they grow towards specialized function.

Identification of reference markers for characterizing honey bee (Apis mellifera) hemocyte classes

Cell mediated immunity of the honey bee (Apis mellifera) involves the activity of several hemocyte populations, currently defined by morphological features and lectin binding characteristics. The objective of the present study was to identify molecular markers capable of characterizing subsets of honey bee hemocytes. We developed and employed monoclonal antibodies with restricted reactions to functionally distinct hemocyte subpopulations. Melanizing cells, known as oenocytoids, were defined by an antibody to prophenoloxidase, aggregating cells were identified by the expression of Hemolectin, and phagocytic cells were identified by a marker expressed on granulocytes. We anticipate that this combination of antibodies not only allows for the detection of functionally distinct hemocyte subtypes, but will help to further the exploration of hematopoietic compartments, as well as reveal details of the honey bee cellular immune defense against parasites and microbes.

Microtubules originate asymmetrically at the somatic golgi and are guided via Kinesin2 to maintain polarity within neurons

Neurons contain polarised microtubule arrays essential for neuronal function. How microtubule nucleation and polarity are regulated within neurons remains unclear. We show that γ-tubulin localises asymmetrically to the somatic Golgi within Drosophila neurons. Microtubules originate from the Golgi with an initial growth preference towards the axon. Their growing plus ends also turn towards and into the axon, adding to the plus-end-out microtubule pool. Any plus ends that reach a dendrite, however, do not readily enter, maintaining minus-end-out polarity. Both turning towards the axon and exclusion from dendrites depend on Kinesin-2, a plus-end-associated motor that guides growing plus ends along adjacent microtubules. We propose that Kinesin-2 engages with a polarised microtubule network within the soma to guide growing microtubules towards the axon; while at dendrite entry sites engagement with microtubules of opposite polarity generates a backward stalling force that prevents entry into dendrites and thus maintains minus-end-out polarity within proximal dendrites.

CytoCensus, mapping cell identity and division in tissues and organs using machine learning

A major challenge in cell and developmental biology is the automated identification and quantitation of cells in complex multilayered tissues. We developed CytoCensus: an easily deployed implementation of supervised machine learning that extends convenient 2D 'point-and-click' user training to 3D detection of cells in challenging datasets with ill-defined cell boundaries. In tests on such datasets, CytoCensus outperforms other freely available image analysis software in accuracy and speed of cell detection. We used CytoCensus to count stem cells and their progeny, and to quantify individual cell divisions from time-lapse movies of explanted Drosophila larval brains, comparing wild-type and mutant phenotypes. We further illustrate the general utility and future potential of CytoCensus by analysing the 3D organisation of multiple cell classes in Zebrafish retinal organoids and cell distributions in mouse embryos. CytoCensus opens the possibility of straightforward and robust automated analysis of developmental phenotypes in complex tissues.

Evidence of virus-responsive pathways in response to poly I: C challenge in a muscle cell line derived from large yellow croaker Larimichthys crocea

In this study, a new continuous muscle cell line, LYCMS (large yellow croaker muscle cell line), derived from the muscle tissue of larva of large yellow croaker (Larimichthys crocea) was developed with modified DMEM/F12 medium at 27 °C. The muscle cell line could be passaged at different ratios for different growth rates. Karyotype analysis showed that a large proportion of LYCMS cells had 48 chromosomes. The proliferation of LYCMS cell line could be affected by mammalian growth factors such as human basic fibroblast growth factor (b-FGF), epidermal growth factor (EGF), and hepatocyte growth factor (HGF). GFP expression experiments indicated that the LYCMS cell line could be used for exogenous genes' expression. Different virus response-related genes tested in this study showed diverse change types in expression before and after (0-24 h) polycytidylic acid (poly I: C) challenge of LYCMS cells. This is the first study of virus response signaling pathways of large yellow croaker based on the muscle cell line. The results showed that compared with the in vivo experiments, the use of the LYCMS cell line for immune research is more convenient, efficient, and rapid. By using this model, we demonstrated that MDA5-IPS1-TRAF6-NFκB-cytokines, MDA5-IPS1-TRAF3-IRF3-interferon or TLR22-TRIF-IRF3-interferon, TLR8-MyD88-NFκB-cytokines, and TLR3-TRIF-IRF3-interferon pathways were able to response to poly I: C challenge in the muscle cell line of large yellow croaker.

Confocal Microscopy: Principles and Modern Practices

In light microscopy, illuminating light is passed through the sample as uniformly as possible over the field of view. For thicker samples, where the objective lens does not have sufficient depth of focus, light from sample planes above and below the focal plane will also be detected. The out-of-focus light will add blur to the image, reducing the resolution. In fluorescence microscopy, any dye molecules in the field of view will be stimulated, including those in out-of-focus planes. Confocal microscopy provides a means of rejecting the out-of-focus light from the detector such that it does not contribute blur to the images being collected. This technique allows for high-resolution imaging in thick tissues. In a confocal microscope, the illumination and detection optics are focused on the same diffraction-limited spot in the sample, which is the only spot imaged by the detector during a confocal scan. To generate a complete image, the spot must be moved over the sample and data collected point by point. A significant advantage of the confocal microscope is the optical sectioning provided, which allows for 3D reconstruction of a sample from high-resolution stacks of images. Several types of confocal microscopes have been developed for this purpose, and each has different advantages and disadvantages. This article provides a concise introduction to confocal microscopy. © 2019 by John Wiley & Sons, Inc.

Embryonic development and secondary axis induction in the Brazilian white knee tarantula Acanthoscurria geniculata, C. L. Koch, 1841 (Araneae; Mygalomorphae; Theraphosidae)

Tarantulas represent some of the heaviest and most famous spiders. However, there is little information about the embryonic development of these spiders or their relatives (infraorder Mygalomorphae) and time-lapse recording of the embryonic development is entirely missing. I here describe the complete development of the Brazilian white knee tarantula, Acanthoscurria geniculata, in fixed and live embryos. The establishment of the blastoderm, the formation, migration and signalling of the cumulus and the shape changes that occur in the segment addition zone are analysed in detail. In addition, I show that there might be differences in the contraction process of early embryos of different theraphosid spider species. A new embryonic reference transcriptome was generated for this study and was used to clone and analyse the expression of several important developmental genes. Finally, I show that embryos of A. geniculata are amenable to tissue transplantation and bead insertion experiments. Using these functional approaches, I induced axis duplication in embryos via cumulus transplantation and ectopic activation of BMP signalling. Overall, the mygalomorph spider A. geniculata is a useful laboratory system to analyse evolutionary developmental questions, and the availability of such a system will help understanding conserved and divergent aspects of spider/chelicerate development.

Expression Analysis of Cnidarian-Specific Neuropeptides in a Sea Anemone Unveils an Apical-Organ-Associated Nerve Net That Disintegrates at Metamorphosis

Neuropeptides are ancient neuronal signaling molecules that have diversified across Cnidaria (e.g., jellyfish, corals, and sea anemones) and its sister group Bilateria (e.g., vertebrates, insects, and worms). Over the course of neuropeptide evolution emerged lineage-specific neuropeptides, but their roles in the evolution and diversification of nervous system function remain enigmatic. As a step toward filling in this knowledge gap, we investigated the expression pattern of a cnidarian-specific neuropeptide-RPamide-during the development of the starlet sea anemone Nematostella vectensis, using in situ hybridization and immunohistochemistry. We show that RPamide precursor transcripts first occur during gastrulation in scattered epithelial cells of the aboral ectoderm. These RPamide-positive epithelial cells exhibit a spindle-shaped, sensory-cell-like morphology, and extend basal neuronal processes that form a nerve net in the aboral ectoderm of the free-swimming planula larva. At the aboral end, RPamide-positive sensory cells become integrated into the developing apical organ that forms a bundle of long cilia referred to as the apical tuft. Later during planula development, RPamide expression becomes evident in sensory cells in the oral ectoderm of the body column and pharynx, and in the developing endodermal nervous system. At metamorphosis into a polyp, the RPamide-positive sensory nerve net in the aboral ectoderm degenerates by apoptosis, and RPamide expression begins in ectodermal sensory cells of growing oral tentacles. In addition, we find that the expression pattern of RPamide in planulae differs from that of conserved neuropeptides that are shared across Cnidaria and Bilateria, indicative of distinct functions. Our results not only provide the anatomical framework necessary to analyze the function of the cnidarian-specific neuropeptides in future studies, but also reveal previously unrecognized features of the sea anemone nervous system-the apical organ neurons of the planula larva, and metamorphosis-associated reorganization of the ectodermal nervous system.

Mitochondrial fission regulates germ cell differentiation by suppressing ROS-mediated activation of Epidermal Growth Factor Signaling in the Drosophila larval testis

Mitochondria are essential organelles that have recently emerged as hubs for several metabolic and signaling pathways in the cell. Mitochondrial morphology is regulated by constant fusion and fission events to maintain a functional mitochondrial network and to remodel the mitochondrial network in response to external stimuli. Although the role of mitochondria in later stages of spermatogenesis has been investigated in depth, the role of mitochondrial dynamics in regulating early germ cell behavior is relatively less-well understood. We previously demonstrated that mitochondrial fusion is required for germline stem cell (GSC) maintenance in the Drosophila testis. Here, we show that mitochondrial fission is also important for regulating the maintenance of early germ cells in larval testes. Inhibition of Drp1 in early germ cells resulted in the loss of GSCs and spermatogonia due to the accumulation of reactive oxygen species (ROS) and activation of the EGFR pathway in adjacent somatic cyst cells. EGFR activation contributed to premature germ cell differentiation. Our data provide insights into how mitochondrial dynamics can impact germ cell maintenance and differentiation via distinct mechanisms throughout development.

Plk1/Polo Phosphorylates Sas-4 at the Onset of Mitosis for an Efficient Recruitment of Pericentriolar Material to Centrosomes

Centrosomes are the major microtubule-organizing centers, consisting of centrioles surrounded by a pericentriolar material (PCM). Centrosomal PCM is spatiotemporally regulated to be minimal during interphase and expands as cells enter mitosis. It is unclear how PCM expansion is initiated at the onset of mitosis. Here, we identify that, in Drosophila, Plk1/Polo kinase phosphorylates the conserved centrosomal protein Sas-4 in vitro. This phosphorylation appears to occur at the onset of mitosis, enabling Sas-4's localization to expand outward from meiotic and mitotic centrosomes. The Plk1/Polo kinase site of Sas-4 is then required for an efficient recruitment of Cnn and γ-tubulin, bona fide PCM proteins that are essential for PCM expansion and centrosome maturation. Point mutations at Plk1/Polo sites of Sas-4 affect neither centrosome structure nor centriole duplication but specifically reduce the affinity to bind Cnn and γ-tubulin. These observations identify Plk1/Polo kinase regulation of Sas-4 as essential for efficient PCM expansion.

Crumbs organizes the transport machinery by regulating apical levels of PI(4,5)P2 in Drosophila

An efficient vectorial intracellular transport machinery depends on a well-established apico-basal polarity and is a prerequisite for the function of secretory epithelia. Despite extensive knowledge on individual trafficking pathways, little is known about the mechanisms coordinating their temporal and spatial regulation. Here, we report that the polarity protein Crumbs is essential for apical plasma membrane phospholipid-homeostasis and efficient apical secretion. Through recruiting βHeavy-Spectrin and MyosinV to the apical membrane, Crumbs maintains the Rab6-, Rab11- and Rab30-dependent trafficking and regulates the lipid phosphatases Pten and Ocrl. Crumbs knock-down results in increased apical levels of PI(4,5)P2 and formation of a novel, Moesin- and PI(4,5)P2-enriched apical membrane sac containing microvilli-like structures. Our results identify Crumbs as an essential hub required to maintain the organization of the apical membrane and the physiological activity of the larval salivary gland.

The Hippo pathway integrates PI3K-Akt signals with mechanical and polarity cues to control tissue growth

The Hippo signalling pathway restricts cell proliferation in animal tissues by inhibiting Yes-associated protein (YAP or YAP1) and Transcriptional Activator with a PDZ domain (TAZ or WW-domain-containing transcriptional activator [WWTR1]), coactivators of the Scalloped (Sd or TEAD) DNA-binding transcription factor. Drosophila has a single YAP/TAZ homolog named Yorkie (Yki) that is regulated by Hippo pathway signalling in response to epithelial polarity and tissue mechanics during development. Here, we show that Yki translocates to the nucleus to drive Sd-mediated cell proliferation in the ovarian follicle cell epithelium in response to mechanical stretching caused by the growth of the germline. Importantly, mechanically induced Yki nuclear localisation also requires nutritionally induced insulin/insulin-like growth factor 1 (IGF-1) signalling (IIS) via phosphatidyl inositol-3-kinase (PI3K), phosphoinositide-dependent kinase 1 (PDK1 or PDPK1), and protein kinase B (Akt or PKB) in the follicular epithelium. We find similar results in the developing Drosophila wing, where Yki becomes nuclear in the mechanically stretched cells of the wing pouch during larval feeding, which induces IIS, but translocates to the cytoplasm upon cessation of feeding in the third instar stage. Inactivating Akt prevents nuclear Yki localisation in the wing disc, while ectopic activation of the insulin receptor, PI3K, or Akt/PKB is sufficient to maintain nuclear Yki in mechanically stimulated cells of the wing pouch even after feeding ceases. Finally, IIS also promotes YAP nuclear localisation in response to mechanical cues in mammalian skin epithelia. Thus, the Hippo pathway has a physiological function as an integrator of epithelial cell polarity, tissue mechanics, and nutritional cues to control cell proliferation and tissue growth in both Drosophila and mammals.

Flumequine-Mediated Upregulation of p38 MAPK and JNK Results in Melanogenesis in B16F10 Cells and Zebrafish Larvae

Flumequine is a well-known second generation quinolone antibiotic that induces phototoxicity. However, the effect of flumequine on skin melanogenesis is unclear. Therefore, we, for the first time, investigated whether flumequine regulates melanogenesis. The present study showed that flumequine slightly inhibited in vitro mushroom tyrosinase activity but significantly increased extracellular and intracellular melanin content in B16F10 cells and promoted the expression of microphthalmia-associated transcription factor (MITF) and tyrosinase. Additionally, flumequine remarkably increased melanin pigmentation in zebrafish larvae without any toxicity. We also found that flumequine stimulated p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK) phosphorylation; inhibition of p38 MAPK and JNK resulted in significant downregulation of extracellular and intracellular melanin content in B16F10 cells and pigmentation of zebrafish larvae accompanied with suppression of MITF and tyrosinase expression, indicating that flumequine-mediated p38 and JNK promote melanogenesis in vitro and in vivo. According to the molecular docking prediction, flumequine targeted dual-specificity MAPK phosphatase 16 (DUSP16), which is a major negative regulator of p38 MAPK and JNK. Our findings demonstrate that flumequine induces an increase in melanin content in B16F10 cells and zebrafish larvae by activating p38 MAPK and JNK. These data show the potential of flumequine for use as an anti-vitiligo agent.

Dual-beam confocal light-sheet microscopy via flexible acousto-optic deflector

Confocal detection in digital scanned laser light-sheet fluorescence microscopy (DSLM) has been established as a gold standard method to improve image quality. The selective line detection of a complementary metal–oxide–semiconductor camera (CMOS) working in rolling shutter mode allows the rejection of out-of-focus and scattered light, thus reducing background signal during image formation. Most modern CMOS have two rolling shutters, but usually only a single illuminating beam is used, halving the maximum obtainable frame rate. We report on the capability to recover the full image acquisition rate via dual confocal DSLM by using an acousto-optic deflector. Such a simple solution enables us to independently generate, control and synchronize two beams with the two rolling slits on the camera. We show that the doubling of the imaging speed does not affect the confocal detection high contrast.

Ontogenetic expression of thyroid hormone signaling genes: An in vitro and in vivo species comparison

Thyroid hormone (TH) is essential for brain development. While disruption of TH signaling by environmental chemicals has been discussed as a mechanism of developmental neurotoxicity (DNT) for more than a decade, there remains a paucity of information linking specific TH disrupting chemicals to adverse neurodevelopmental outcomes. This data gap reflects, in part, the fact that the molecular machinery of TH signaling is complex and varies according to cell type and developmental time. Thus, establishing a baseline of the ontogenetic profile of expression of TH signaling molecules in relevant cell types is critical for developing in vitro and alternative systems-based models for screening TH disrupting chemicals for DNT. Here, we characterize the transcriptomic profile of molecules critical to TH signaling across three species-human, rat, and zebrafish-in vitro and in vivo across different stages of neurodevelopment. Our data indicate that while cultured human and rat neural progenitor cells, primary cultures of rat cortical cells, and larval zebrafish all express a fairly comprehensive transcriptome of TH signaling molecules, the spatiotemporal expression profiles as well as the responses to TH vary across species and developmental stages. The data presented here provides a roadmap for identifying appropriate in vitro and in simpler systems-based models for mechanistic studies and screening of chemicals that alter neurodevelopment via interference with TH action.

Developmental and transcriptomic features characterize defects of silk gland growth and silk production in silkworm naked pupa mutant

The silkworm Bombyx mori is a well-characterized model organism for studying the silk gland development and silk production process. Using positional cloning and gene sequencing, we have previously reported that a truncated fibroin heavy chain was responsible for silkworm naked pupa (Nd) mutant. However, the mechanisms by which the mutant FibH causes developmental defects and secretion-deficiency of the silk gland remain to be fully elucidated. Here, silk gland's developmental features, histomorphology, and transcriptome analyses were used to characterize changes in its structure and gene expression patterns between Nd mutant and WT/Dazao. Whole larval stage investigation showed that Nd-PSG undergoes an arrested/delayed development, which eventually resulted in a gland degeneration. By using section staining and transmission electron microscope, a blockade in intracellular vesicle transport from endoplasmic reticulum to Golgi apparatus (secretion-deficiency) and an increased number of autophagosomes and lysosomes were found in Nd-PSG's cytoplasm. Next, by using RNA sequencing and comparative transcriptomic analysis, 2178 differentially expressed genes were identified between Nd-PSG and WT-PSG, among which most of the DEGs associated with cellular stress responses (autophagy, ubiquitin-proteasome system, and heat shock response) were significantly up-regulated in Nd-PSG, suggesting that mutant FibH perturbed cellular homeostasis and resulted in an activation of adaptive responses in PSG cells. These findings reveal the molecular mechanism of the Naked pupa (Nd) mutation and provide insights into silk gland development as well as silk protein production in silkworm Bombyx mori.

Functional characterization of short-type peptidoglycan recognition proteins (PGRPs) from silkworm Bombyx mori in innate immunity

Peptidoglycan recognition proteins (PGRPs) are members of an important class of pattern recognition receptors in insects that can specifically recognize peptidoglycan (PGN) in bacterial cell walls and participate in immune regulation and bacterial clearance. Although the role of PGRPs in regulating the innate immune response in Drosophila melanogaster has been studied, little is known regarding PGRPs in Lepidoptera species. In this study, five short (S)-type Bombyx mori PGRPs (BmPGRPs) were cloned, expressed, and evaluated for their function in innate immunity. B. mori larvae that were injected with the gram-positive bacterium Bacillus megaterium or the gram-negative bacterium Escherichia coli exhibited a rapid and significant upregulation in S-type BmPGRP expression. The results showed that the five evaluated BmPGRPs have significant agglutination activity toward E. coli and B. megaterium and more notable amidase activity toward meso-diaminopimelic acid peptidoglycan (DAP-PGN). Furthermore, only in the presence of BmPGRP-S5 did B. mori larval hemocytes exhibit significant phagocytosis against E. coli and B. megaterium.

Cell type phylogenetics informs the evolutionary origin of echinoderm larval skeletogenic cell identity

The multiplicity of cell types comprising multicellular organisms begs the question as to how cell type identities evolve over time. Cell type phylogenetics informs this question by comparing gene expression of homologous cell types in distantly related taxa. We employ this approach to inform the identity of larval skeletogenic cells of echinoderms, a clade for which there are phylogenetically diverse datasets of spatial gene expression patterns. We determined ancestral spatial expression patterns of alx1, ets1, tbr, erg, and vegfr, key components of the skeletogenic gene regulatory network driving identity of the larval skeletogenic cell. Here we show ancestral state reconstructions of spatial gene expression of extant eleutherozoan echinoderms support homology and common ancestry of echinoderm larval skeletogenic cells. We propose larval skeletogenic cells arose in the stem lineage of eleutherozoans during a cell type duplication event that heterochronically activated adult skeletogenic cells in a topographically distinct tissue in early development.

Characterization of fat body cells at different developmental stages of Culex pipiens

The fat body, originates from mesoderm, has many metabolic functions which changes as the embryonic development of the insect progresses. It plays an important role in the intermediate metabolism and in the metabolism of proteins, lipids and carbohydrates. It has roles in synthesis, absorption and storage of nutrients from hemolymph. It is also responsible for the production of immunological system components, antibacterial compounds and blood clotting proteins. The most common type of fat body cells are trophocytes (the basic cells of the fat body) and oenocytes are found associated with the fat body. In this study, it is aimed at determining the cell types contained in the fat body of Culex pipiens at different developmental stages as well as identifying the molecules such as carbohydrate, protein and lipid contained in each of these cells. Knowing the regional distribution of the fat body cells and the concentration of its content at each developmental stage is important in understanding the process related to its physiology and it may help in fighting against the pest C. pipiens, which is a vector species for many contagious diseases observed in humans and other species. To achieve our goal, we have employed different histochemical techniques (fixatives and staining methods) for staining C. pipiens preparates of different developmental stages and analyzed the structure of the fat body, its distribution, its cell types and the macromolecular contents of the cells. We only observed trophocytes and oenocytes as fat body components in C. pipiens. The trophocytes had all the three macromolecules (lipids, proteins, carbohydrates) in the cytoplasm varying in concentration between the different regions and different stages. The oenocytes were observed below the integument as well as between the muscles in the larvae of Culex pipiens. They were present either as single cells or in clusters and also varied in size. Their cytoplasm was stained strongly for proteins when bromophenol blue staining was applied, but it was rather heterogeneous due to the lipid inclusions. On the contrary, oenocytes were not observed among the adult C. pipiens preparations.

Drosophila melanogaster and its nephrocytes: A versatile model for glomerular research

Glomerular disorders are a predominant cause of chronic kidney diseases and end-stage renal failure. Especially podocytes, epithelial cells which represent the outermost part of the filtration barrier, are affected by disease and experience a gradual loss of function. Despite recent advances in identifying potential pathways underlying podocyte injury, treatment remains challenging. It is therefore desirable to employ suitable model organisms in order to study glomerular disease and elucidate affected pathways. Due to its diverse ways of genetic manipulation and high genomic conservation, Drosophila melanogaster is a powerful model organism for biomedical research. The fly was recently used to assess podocytopathies by exploiting the nephrocyte system. Nephrocytes are spherical cells within the body cavity of the fly responsible for detoxification and clearance of unwanted substances. More importantly, they share many characteristics with mammalian podocytes. Here, we summarize how to use Drosophila as a model organism for podocyte research. We discuss examples of techniques that can be used to genetically manipulate nephrocytes and provide protocols for nephrocyte isolation and for morphological as well as functional analysis.

Developmental regulation of regenerative potential in Drosophila by ecdysone through a bistable loop of ZBTB transcription factors

In many organisms, the regenerative capacity of tissues progressively decreases as development progresses. However, the developmental mechanisms that restrict regenerative potential remain unclear. In Drosophila, wing imaginal discs become unable to regenerate upon damage during the third larval stage (L3). Here, we show that production of ecdysone after larvae reach their critical weight (CW) terminates the window of regenerative potential by acting on a bistable loop composed of two antagonistic Broad-complex/Tramtrack/Bric-à-brac Zinc-finger (ZBTB) genes: chinmo and broad (br). Around mid L3, ecdysone signaling silences chinmo and activates br to switch wing epithelial progenitors from a default self-renewing to a differentiation-prone state. Before mid L3, Chinmo promotes a strong regenerative response upon tissue damage. After mid L3, Br installs a nonpermissive state that represses regeneration. Transient down-regulation of ecdysone signaling or Br in late L3 larvae enhances chinmo expression in damaged cells that regain the capacity to regenerate. This work unveils a mechanism that ties the self-renewing and regenerative potential of epithelial progenitors to developmental progression.

This study finds that the loss of regeneration potential in Drosophila wing imaginal discs is induced by the production of the steroid hormone ecdysone after the larva reaches its critical weight. Manipulating ecdysone signaling or the downstream transcription factors can uncouple regenerative properties from developmental progression.

While some organisms exhibit remarkable regenerative abilities throughout their life, many animals, including mammals, present limited regenerative potential that progressively decreases during development. Understanding the mechanisms underlying this progressive loss is important to devise therapeutic approaches aiming at facilitating the regeneration of a damaged tissue throughout life. The fruitfly Drosophila is a powerful model organism to address such questions. Indeed, while tissues, such as imaginal discs, can fully regenerate if damaged during early development, they fail to do so upon damages during late development. We show here that restriction of regenerative potential occurring during midlarval stages is due to the production of a steroid hormone, named ecdysone. By genetically manipulating ecdysone signaling, we can uncouple regenerative abilities from developmental progression. In particular, we show that ecdysone signaling triggers a switch in the sequential expression of two transcription factors, Chinmo and Broad, that positively and negatively regulate the competence for imaginal disc regeneration, respectively. Our work therefore identifies a key developmental signal that restricts regenerative potential in insects and opens new perspectives on elucidating how regeneration-permissive transcriptional programs are locked as development progresses.

A chemical-genetics approach to study the role of atypical Protein Kinase C in Drosophila

Studying the function of proteins using genetics in cycling cells is complicated by the fact that there is often a delay between gene inactivation and the time point of phenotypic analysis. This is particularly true when studying kinases that have pleiotropic functions and multiple substrates. Drosophila neuroblasts (NBs) are rapidly dividing stem cells and an important model system for the study of cell polarity. Mutations in multiple kinases cause NB polarity defects, but their precise functions at particular time points in the cell cycle are unknown. Here, we use chemical genetics and report the generation of an analogue-sensitive allele of Drosophila atypical Protein Kinase C (aPKC). We demonstrate that the resulting mutant aPKC kinase can be specifically inhibited in vitro and in vivo Acute inhibition of aPKC during NB polarity establishment abolishes asymmetric localization of Miranda, whereas its inhibition during NB polarity maintenance does not in the time frame of normal mitosis. However, aPKC helps to sharpen the pattern of Miranda, by keeping it off the apical and lateral cortex after nuclear envelope breakdown.

Methods to label, isolate, and image sea urchin small micromeres, the primordial germ cells (PGCs)

Small micromeres of the sea urchin are believed to be primordial germ cells (PGCs), fated to give rise to sperm or eggs in the adult. Sea urchin PGCs are formed at the fifth cleavage, undergo one additional division during blastulation, and migrate to the coelomic pouches of the pluteus larva. The goal of this chapter is to detail classical and modern techniques used to analyze primordial germ cell specification, gene expression programs, and cell behaviors in fixed and live embryos. The transparency of the sea urchin embryo enables both live imaging techniques and in situ RNA hybridization and immunolabeling for a detailed molecular characterization of these cells. Four approaches are presented to highlight small micromeres with fluorescent molecules for analysis by live and fixed cell microscopy: (1) small molecule dye accumulation during cleavage and blastula stages, (2) primordial germ cell targeted RNA expression using the Nanos untranslated regions, (3) fusing genes of interest with a Nanos2 targeting peptide, and (4) EdU and BrdU labeling. Applications of the live labeling techniques are discussed, including sorting by fluorescence-activated cell sorting for transcriptomic analysis, and, methods to image small micromere behavior in whole and dissociated embryos by live confocal microscopy. Finally, summary table of antibody and RNA probes as well as small molecule dyes to label small micromeres at a variety of developmental stages is provided.

UBIAD1 suppresses the proliferation of bladder carcinoma cells by regulating H-Ras intracellular trafficking via interaction with the C-terminal domain of H-Ras

UbiA prenyltransferase domain-containing protein 1 (UBIAD1) plays a key role in biosynthesis of vitamin K2 and coenzyme Q10 using geranylgeranyl diphosphate (GGPP). However, the mechanism by which UBIAD1 participates in tumorigenesis remains unknown. This study show that UBIAD1 interacts with H-Ras, retains H-Ras in the Golgi apparatus, prevents H-Ras trafficking from the Golgi apparatus to the plasma membrane, blocks the aberrant activation of Ras/MAPK signaling, and inhibits the proliferation of bladder cancer cells. In addition, GGPP was required to maintain the function of UBIAD1 in regulating the Ras/ERK signaling pathway. A Drosophila model was employed to confirm the function of UBIAD1/HEIX in vivo. The activation of Ras/ERK signaling at the plasma membrane induced melanotic masses in Drosophila larvae. Our study suggests that UBIAD1 serves as a tumor suppressor in cancer and tentatively reveals the underlying mechanism of melanotic mass formation in Drosophila.

Diffuse light-sheet microscopy for stripe-free calcium imaging of neural populations

Light-sheet microscopy is used extensively in developmental biology and neuroscience. One limitation of this approach is that absorption and scattering produces shadows in the illuminating light sheet, resulting in stripe artifacts. Here, we introduce diffuse light-sheet microscopes that use a line diffuser to randomize the light propagation within the image plane, allowing the light sheets to reform after obstacles. We incorporate diffuse light sheets in two existing configurations: selective plane illumination microscopy in which the sample is illuminated with a static sheet of light, and digitally scanned light sheet (DSLS) in which a thin Gaussian beam is scanned across the image plane during each acquisition. We compare diffuse light-sheet microscopes to their conventional counterparts for calcium imaging of neural activity in larval zebrafish. We show that stripe artifacts can cast deep shadows that conceal some neurons, and that the stripes can flicker, producing spurious signals that could be interpreted as biological activity. Diffuse light-sheets mitigate these problems, illuminating the blind spots produced by stripes and removing artifacts produced by the stripes' movements. The upgrade to diffuse light sheets is simple and inexpensive, especially in the case of DSLS, where it requires the addition of one optical element.

Diffuse light-sheet microscopy for stripe-free calcium imaging of neural populations

Light-sheet microscopy is used extensively in developmental biology and neuroscience. One limitation of this approach is that absorption and scattering produces shadows in the illuminating light sheet, resulting in stripe artifacts. Here, we introduce diffuse light-sheet microscopes that use a line diffuser to randomize the light propagation within the image plane, allowing the light sheets to reform after obstacles. We incorporate diffuse light sheets in two existing configurations: selective plane illumination microscopy in which the sample is illuminated with a static sheet of light, and digitally scanned light sheet (DSLS) in which a thin Gaussian beam is scanned across the image plane during each acquisition. We compare diffuse light-sheet microscopes to their conventional counterparts for calcium imaging of neural activity in larval zebrafish. We show that stripe artifacts can cast deep shadows that conceal some neurons, and that the stripes can flicker, producing spurious signals that could be interpreted as biological activity. Diffuse light-sheets mitigate these problems, illuminating the blind spots produced by stripes and removing artifacts produced by the stripes' movements. The upgrade to diffuse light sheets is simple and inexpensive, especially in the case of DSLS, where it requires the addition of one optical element.

Ophthalmomyiasis externa due to sheep nasal botfly in rural Jamaica

We present the case of a young male patient who presented with pain, redness and foreign body sensation in his left eye. There was no associated decrease in vision. Three live larvae were removed from his left conjunctival sac and sent to the laboratory for identification. The patient was treated symptomatically and his symptoms were mostly resolved by the following day. The larvae were later identified as the first instar of the sheep nasal botfly. Poor sanitation and exposure to livestock were among the identified risk factors in this case. Physicians must have this as a differential diagnosis for conjunctivitis in patients with risk factors. This is the first reported case of ophthalmomyiasis from Jamaica.

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.

Generation of mouse-zebrafish hematopoietic tissue chimeric embryos for hematopoiesis and host-pathogen interaction studies

Xenografts of the hematopoietic system are extremely useful as disease models and for translational research. Zebrafish xenografts have been widely used to monitor blood cancer cell dissemination and homing due to the optical clarity of embryos and larvae, which allow unrestricted in vivo visualization of migratory events. Here, we have developed a xenotransplantation technique that transiently generates hundreds of hematopoietic tissue chimeric embryos by transplanting murine bone marrow cells into zebrafish blastulae. In contrast to previous methods, this procedure allows mammalian cell integration into the fish developmental hematopoietic program, which results in chimeric animals containing distinct phenotypes of murine blood cells in both circulation and the hematopoietic niche. Murine cells in chimeric animals express antigens related to (i) hematopoietic stem and progenitor cells, (ii) active cell proliferation and (iii) myeloid cell lineages. We verified the utility of this method by monitoring zebrafish chimeras during development using in vivo non-invasive imaging to show novel murine cell behaviors, such as homing to primitive and definitive hematopoietic tissues, dynamic hematopoietic cell and hematopoietic niche interactions, and response to bacterial infection. Overall, transplantation into the zebrafish blastula provides a useful method that simplifies the generation of numerous chimeric animals and expands the range of murine cell behaviors that can be studied in zebrafish chimeras. In addition, integration of murine cells into the host hematopoietic system during development suggests highly conserved molecular mechanisms of hematopoiesis between zebrafish and mammals.This article has an associated First Person interview with the first author of the paper.

Differential lateral and basal tension drive folding of Drosophila wing discs through two distinct mechanisms

Epithelial folding transforms simple sheets of cells into complex three-dimensional tissues and organs during animal development. Epithelial folding has mainly been attributed to mechanical forces generated by an apically localized actomyosin network, however, contributions of forces generated at basal and lateral cell surfaces remain largely unknown. Here we show that a local decrease of basal tension and an increased lateral tension, but not apical constriction, drive the formation of two neighboring folds in developing Drosophila wing imaginal discs. Spatially defined reduction of extracellular matrix density results in local decrease of basal tension in the first fold; fluctuations in F-actin lead to increased lateral tension in the second fold. Simulations using a 3D vertex model show that the two distinct mechanisms can drive epithelial folding. Our combination of lateral and basal tension measurements with a mechanical tissue model reveals how simple modulations of surface and edge tension drive complex three-dimensional morphological changes.