Using mutants, knockdowns, and transgenesis to investigate gene function in Drosophila

SLMO transfers phosphatidylserine between the outer and inner mitochondrial membrane in Drosophila

Phospholipids are critical building blocks of mitochondria, and proper mitochondrial function and architecture rely on phospholipids that are primarily transported from the endoplasmic reticulum (ER). Here, we show that mitochondrial form and function rely on synthesis of phosphatidylserine (PS) in the ER through phosphatidylserine synthase (PSS), trafficking of PS from ER to mitochondria (and within mitochondria), and the conversion of PS to phosphatidylethanolamine (PE) by phosphatidylserine decarboxylase (PISD) in the inner mitochondrial membrane (IMM). Using a forward genetic screen in Drosophila, we found that Slowmo (SLMO) specifically transfers PS from the outer mitochondrial membrane (OMM) to the IMM within the inner boundary membrane (IBM) domain. Thus, SLMO is required for shaping mitochondrial morphology, but its putative conserved binding partner, dTRIAP, is not. Importantly, SLMO's role in maintaining mitochondrial morphology is conserved in humans via the SLMO2 protein and is independent of mitochondrial dynamics. Our results highlight the importance of a conserved PSS-SLMO-PISD pathway in maintaining the structure and function of mitochondria.

Electrostatic plasma membrane targeting contributes to Dlg function in cell polarity and tumorigenesis

Discs large (Dlg) is an essential polarity protein and a tumor suppressor originally characterized in Drosophila but also well conserved in vertebrates. Like the majority of polarity proteins, plasma membrane (PM)/cortical localization of Dlg is required for its function in polarity and tumorigenesis, but the exact mechanisms targeting Dlg to the PM remain to be fully elucidated. Here, we show that, similar to recently discovered polybasic polarity proteins such as Lgl and aPKC, Dlg also contains a positively charged polybasic domain that electrostatically binds the PM phosphoinositides PI4P and PI(4,5)P2 Electrostatic targeting by the polybasic domain contributes significantly to the PM localization of Dlg in follicular and early embryonic epithelial cells, and is crucial for Dlg to regulate both polarity and tumorigenesis. The electrostatic PM targeting of Dlg is controlled by a potential phosphorylation-dependent allosteric regulation of its polybasic domain, and is specifically enhanced by the interactions between Dlg and another basolateral polarity protein and tumor suppressor, Scrib. Our studies highlight an increasingly significant role of electrostatic PM targeting of polarity proteins in regulating cell polarity.

Genotype to Phenotype: CRISPR Gene Editing Reveals Genetic Compensation as a Mechanism for Phenotypic Disjunction of Morphants and Mutants

Forward genetic screens have shown the consequences of deleterious mutations; however, they are best suited for model organisms with fast reproductive rates and large broods. Furthermore, investigators must faithfully identify changes in phenotype, even if subtle, to realize the full benefit of the screen. Reverse genetic approaches also probe genotype to phenotype relationships, except that the genetic targets are predefined. Until recently, reverse genetic approaches relied on non-genomic gene silencing or the relatively inefficient, homology-dependent gene targeting for loss-of-function generation. Fortunately, the flexibility and simplicity of the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas system has revolutionized reverse genetics, allowing for the precise mutagenesis of virtually any gene in any organism at will. The successful integration of insertions/deletions (INDELs) and nonsense mutations that would, at face value, produce the expected loss-of-function phenotype, have been shown to have little to no effect, even if other methods of gene silencing demonstrate robust loss-of-function consequences. The disjunction between outcomes has raised important questions about our understanding of genotype to phenotype and highlights the capacity for compensation in the central dogma. This review describes recent studies in which genomic compensation appears to be at play, discusses the possible compensation mechanisms, and considers elements important for robust gene loss-of-function studies.

Animal models of pain: Diversity and benefits

Chronic pain is a maladaptive neurological disease that remains a major health problem. A deepening of our knowledge on mechanisms that cause pain is a prerequisite to developing novel treatments. A large variety of animal models of pain has been developed that recapitulate the diverse symptoms of different pain pathologies. These models reproduce different pain phenotypes and remain necessary to examine the multidimensional aspects of pain and understand the cellular and molecular basis underlying pain conditions. In this review, we propose an overview of animal models, from simple organisms to rodents and non-human primates and the specific traits of pain pathologies they model. We present the main behavioral tests for assessing pain and investing the underpinning mechanisms of chronic pathological pain. The validity of animal models is analysed based on their ability to mimic human clinical diseases and to predict treatment outcomes. Refine characterization of pathological phenotypes also requires to consider pain globally using specific procedures dedicated to study emotional comorbidities of pain. We discuss the limitations of pain models when research findings fail to be translated from animal models to human clinics. But we also point to some recent successes in analgesic drug development that highlight strategies for improving the predictive validity of animal models of pain. Finally, we emphasize the importance of using assortments of preclinical pain models to identify pain subtype mechanisms, and to foster the development of better analgesics.

Using Drosophila melanogaster To Discover Human Disease Genes: An Educational Primer for Use with "Amyotrophic Lateral Sclerosis Modifiers in Drosophila Reveal the Phospholipase D Pathway as a Potential Therapeutic Target"

Since the dawn of the 20th century, the fruit fly Drosophila melanogaster has been used as a model organism to understand the nature of genes and how they control development, behavior, and physiology. One of the most powerful experimental approaches employed in Drosophila is the forward genetic screen. In the 21st century, genome-wide screens have become popular tools for identifying evolutionarily conserved genes involved in complex human diseases. In the accompanying article "Amyotrophic Lateral Sclerosis Modifiers in Drosophila Reveal thePhospholipase DPathway as a Potential Therapeutic Target," Kankel and colleagues describe a forward genetic modifier screen to discover factors that contribute to the severe neurodegenerative disease amyotrophic lateral sclerosis (ALS). This primer briefly traces the history of genetic screens in Drosophila and introduces students to ALS. We then provide a set of guided reading questions to help students work through the data presented in the research article. Finally, several ideas for literature-based research projects are offered as opportunities for students to expand their appreciation of the potential scope of genetic screens. The primer is intended to help students and instructors thoroughly examine a current study that uses forward genetics in Drosophila to identify human disease genes.

A single-cell atlas of adult Drosophila ovary identifies transcriptional programs and somatic cell lineage regulating oogenesis

Oogenesis is a complex developmental process that involves spatiotemporally regulated coordination between the germline and supporting, somatic cell populations. This process has been modeled extensively using the Drosophila ovary. Although different ovarian cell types have been identified through traditional means, the large-scale expression profiles underlying each cell type remain unknown. Using single-cell RNA sequencing technology, we have built a transcriptomic data set for the adult Drosophila ovary and connected tissues. Using this data set, we identified the transcriptional trajectory of the entire follicle-cell population over the course of their development from stem cells to the oogenesis-to-ovulation transition. We further identify expression patterns during essential developmental events that take place in somatic and germline cell types such as differentiation, cell-cycle switching, migration, symmetry breaking, nurse-cell engulfment, egg-shell formation, and corpus luteum signaling. Extensive experimental validation of unique expression patterns in both ovarian and nearby, nonovarian cells also led to the identification of many new cell type-and stage-specific markers. The inclusion of several nearby tissue types in this data set also led to our identification of functional convergence in expression between distantly related cell types such as the immune-related genes that were similarly expressed in immune cells (hemocytes) and ovarian somatic cells (stretched cells) during their brief phagocytic role in nurse-cell engulfment. Taken together, these findings provide new insight into the temporal regulation of genes in a cell-type specific manner during oogenesis and begin to reveal the relatedness in expression between cell and tissues types.

Drosophila as a model to understand autophagy deregulation in human disorders

Autophagy has important functions in normal physiology to maintain homeostasis and protect against cellular stresses by the removal of harmful cargos such as dysfunctional organelles, protein aggregates and invading pathogens. The deregulation of autophagy is a hallmark of many diseases and therapeutic targeting of autophagy is highly topical. With the complex role of autophagy in disease it is essential to understand the genetic and molecular basis of the contribution of autophagy to pathogenesis. The model organism, Drosophila, provides a genetically amenable system to dissect out the contribution of autophagy to human disease models. Here we review the roles of autophagy in human disease and how autophagy studies in Drosophila have contributed to the understanding of pathophysiology.

Using Mouse and Drosophila Models to Investigate the Mechanistic Links between Diet, Obesity, Type II Diabetes, and Cancer

Many of the links between diet and cancer are controversial and over simplified. To date, human epidemiological studies consistently reveal that patients who suffer diet-related obesity and/or type II diabetes have an increased risk of cancer, suffer more aggressive cancers, and respond poorly to current therapies. However, the underlying molecular mechanisms that increase cancer risk and decrease the response to cancer therapies in these patients remain largely unknown. Here, we review studies in mouse cancer models in which either dietary or genetic manipulation has been used to model obesity and/or type II diabetes. These studies demonstrate an emerging role for the conserved insulin and insulin-like growth factor signaling pathways as links between diet and cancer progression. However, these models are time consuming to develop and expensive to maintain. As the world faces an epidemic of obesity and type II diabetes we argue that the development of novel animal models is urgently required. We make the case for Drosophila as providing an unparalleled opportunity to combine dietary manipulation with models of human metabolic disease and cancer. Thus, combining diet and cancer models in Drosophila can rapidly and significantly advance our understanding of the conserved molecular mechanisms that link diet and diet-related metabolic disorders to poor cancer patient prognosis.

An efficient and multiple target transgenic RNAi technique with low toxicity in Drosophila

Being relatively simple and practical, Drosophila transgenic RNAi is the technique of top priority choice to quickly study genes with pleiotropic functions. However, drawbacks have emerged over time, such as high level of false positive and negative results. To overcome these shortcomings and increase efficiency, specificity and versatility, we develop a next generation transgenic RNAi system. With this system, the leaky expression of the basal promoter is significantly reduced, as well as the heterozygous ratio of transgenic RNAi flies. In addition, it has been first achieved to precisely and efficiently modulate highly expressed genes. Furthermore, we increase versatility which can simultaneously knock down multiple genes in one step. A case illustration is provided of how this system can be used to study the synthetic developmental effect of histone acetyltransferases. Finally, we have generated a collection of transgenic RNAi lines for those genes that are highly homologous to human disease genes.

Occluding junctions as novel regulators of tissue mechanics during wound repair

Simple epithelial repair is mediated by the contraction of an actomyosin cable and cellular rearrangements at the wound edge. Carvalho et al. show that occluding junctions are required for epithelial repair by regulating these cellular rearrangements and tissue mechanical properties.

In epithelial tissues, cells tightly connect to each other through cell–cell junctions, but they also present the remarkable capacity of reorganizing themselves without compromising tissue integrity. Upon injury, simple epithelia efficiently resolve small lesions through the action of actin cytoskeleton contractile structures at the wound edge and cellular rearrangements. However, the underlying mechanisms and how they cooperate are still poorly understood. In this study, we combine live imaging and theoretical modeling to reveal a novel and indispensable role for occluding junctions (OJs) in this process. We demonstrate that OJ loss of function leads to defects in wound-closure dynamics: instead of contracting, wounds dramatically increase their area. OJ mutants exhibit phenotypes in cell shape, cellular rearrangements, and mechanical properties as well as in actin cytoskeleton dynamics at the wound edge. We propose that OJs are essential for wound closure by impacting on epithelial mechanics at the tissue level, which in turn is crucial for correct regulation of the cellular events occurring at the wound edge.

Iron Sulfur and Molybdenum Cofactor Enzymes Regulate the Drosophila Life Cycle by Controlling Cell Metabolism

Iron sulfur (Fe-S) clusters and the molybdenum cofactor (Moco) are present at enzyme sites, where the active metal facilitates electron transfer. Such enzyme systems are soluble in the mitochondrial matrix, cytosol and nucleus, or embedded in the inner mitochondrial membrane, but virtually absent from the cell secretory pathway. They are of ancient evolutionary origin supporting respiration, DNA replication, transcription, translation, the biosynthesis of steroids, heme, catabolism of purines, hydroxylation of xenobiotics, and cellular sulfur metabolism. Here, Fe-S cluster and Moco biosynthesis in Drosophila melanogaster is reviewed and the multiple biochemical and physiological functions of known Fe-S and Moco enzymes are described. We show that RNA interference of Mocs3 disrupts Moco biosynthesis and the circadian clock. Fe-S-dependent mitochondrial respiration is discussed in the context of germ line and somatic development, stem cell differentiation and aging. The subcellular compartmentalization of the Fe-S and Moco assembly machinery components and their connections to iron sensing mechanisms and intermediary metabolism are emphasized. A biochemically active Fe-S core complex of heterologously expressed fly Nfs1, Isd11, IscU, and human frataxin is presented. Based on the recent demonstration that copper displaces the Fe-S cluster of yeast and human ferredoxin, an explanation for why high dietary copper leads to cytoplasmic iron deficiency in flies is proposed. Another proposal that exosomes contribute to the transport of xanthine dehydrogenase from peripheral tissues to the eye pigment cells is put forward, where the Vps16a subunit of the HOPS complex may have a specialized role in concentrating this enzyme within pigment granules. Finally, we formulate a hypothesis that (i) mitochondrial superoxide mobilizes iron from the Fe-S clusters in aconitase and succinate dehydrogenase; (ii) increased iron transiently displaces manganese on superoxide dismutase, which may function as a mitochondrial iron sensor since it is inactivated by iron; (iii) with the Krebs cycle thus disrupted, citrate is exported to the cytosol for fatty acid synthesis, while succinyl-CoA and the iron are used for heme biosynthesis; (iv) as iron is used for heme biosynthesis its concentration in the matrix drops allowing for manganese to reactivate superoxide dismutase and Fe-S cluster biosynthesis to reestablish the Krebs cycle.

Drosophila melanogaster White Mutant w1118 Undergo Retinal Degeneration

Key scientific discoveries have resulted from genetic studies of Drosophila melanogaster, using a multitude of transgenic fly strains, the majority of which are constructed in a genetic background containing mutations in the white gene. Here we report that white mutant flies from w1118 strain undergo retinal degeneration. We observed also that w1118 mutants have progressive loss of climbing ability, shortened life span, as well as impaired resistance to various forms of stress. Retinal degeneration was abolished by transgenic expression of mini-white+ in the white null background w1118 . We conclude that beyond the classical eye-color phenotype, mutations in Drosophila white gene could impair several biological functions affecting parameters like mobility, life span and stress tolerance. Consequently, we suggest caution and attentiveness during the interpretation of old experiments employing white mutant flies and when planning new ones, especially within the research field of neurodegeneration and neuroprotection. We also encourage that the use of w1118 strain as a wild-type control should be avoided.

Neuroligins Nlg2 and Nlg4 Affect Social Behavior in Drosophila melanogaster

The genome of Drosophila melanogaster includes homologs to approximately one-third of the currently known human disease genes. Flies and humans share many biological processes, including the principles of information processing by excitable neurons, synaptic transmission, and the chemical signals involved in intercellular communication. Studies on the molecular and behavioral impact of genetic risk factors of human neuro-developmental disorders [autism spectrum disorders (ASDs), schizophrenia, attention deficit hyperactivity disorders, and Tourette syndrome] increasingly use the well-studied social behavior of D. melanogaster, an organism that is amenable to a large variety of genetic manipulations. Neuroligins (Nlgs) are a family of phylogenetically conserved postsynaptic adhesion molecules present (among others) in nematodes, insects, and mammals. Impaired function of Nlgs (particularly of Nlg 3 and 4) has been associated with ASDs in humans and impaired social and communication behavior in mice. Making use of a set of behavioral and social assays, we, here, analyzed the impact of two Drosophila Nlgs, Dnlg2 and Dnlg4, which are differentially expressed at excitatory and inhibitory central nervous synapses, respectively. Both Nlgs seem to be associated with diurnal activity and social behavior. Even though deficiencies in Dnlg2 and Dnlg4 appeared to have no effects on sensory or motor systems, they differentially impacted on social interactions, suggesting that social behavior is distinctly regulated by these Nlgs.

The in vivo genetic toolkit for studying expression and functions of Drosophila melanogaster microRNAs

Since the initial reports that a group of small RNAs, now known as microRNAs (miRNAs), regulates gene expression without being translated into proteins, there has been an explosion of studies on these important expression modulators. Drosophila melanogaster has proven to be one of the most amenable animal models for investigations of miRNA biogenesis and gene regulatory activities. Here, we highlight the publicly available genetic tools and strategies for in vivo functional studies of miRNA activity in D. melanogaster. By coupling genetic approaches using available strain libraries with technologies for miRNA expression analysis and target and pathway prediction, researchers' ability to test functional activities of miRNAs in vivo is now greatly enhanced. We also comment on the tools that need to be developed to aid in comprehensive evaluation of Drosophila miRNA activities that impact traits of interest.

A fly's eye view of zinc homeostasis: Novel insights into the genetic control of zinc metabolism from Drosophila

The core zinc transport machinery is well conserved between invertebrates and mammals, with the vinegar fly Drosophila melanogaster having clear homologues of all major groups of mammalian ZIP and ZNT transport genes. Functional characterization of several of the fly genes has revealed functional conservation between related fly and mammalian zinc transporters in some but not all cases, indicating that Drosophila is a useful model for examining mammalian zinc metabolism. Furthermore, Drosophila research, sometimes quite serendipitously, has provided novel insights into the function of zinc transporters and into zinc-related pathologies, which are highlighted here. Finally, the future research potential of the fly in nutrient metabolism is explored, with reference to emerging experimental technologies.

A genome-wide resource for the analysis of protein localisation in Drosophila

The Drosophila genome contains >13000 protein-coding genes, the majority of which remain poorly investigated. Important reasons include the lack of antibodies or reporter constructs to visualise these proteins. Here, we present a genome-wide fosmid library of 10000 GFP-tagged clones, comprising tagged genes and most of their regulatory information. For 880 tagged proteins, we created transgenic lines, and for a total of 207 lines, we assessed protein expression and localisation in ovaries, embryos, pupae or adults by stainings and live imaging approaches. Importantly, we visualised many proteins at endogenous expression levels and found a large fraction of them localising to subcellular compartments. By applying genetic complementation tests, we estimate that about two-thirds of the tagged proteins are functional. Moreover, these tagged proteins enable interaction proteomics from developing pupae and adult flies. Taken together, this resource will boost systematic analysis of protein expression and localisation in various cellular and developmental contexts.

DOI:http://dx.doi.org/10.7554/eLife.12068.001

The fruit fly Drosophila melanogaster is a popular model organism in biological research. Studies using Drosophila have led to important insights into human biology, because related proteins often fulfil similar roles in flies and humans. Thus, studying the role of a protein in Drosophila can teach us about what it might do in a human.

To fulfil their biological roles, proteins often occupy particular locations inside cells, such as the cell’s nucleus or surface membrane. Many proteins are also only found in specific types of cell, such as neurons or muscle cells. A protein’s location thus provides clues about what it does, however cells contain many thousands of proteins and identifying the location of each one is a herculean task.

Sarov et al. took on this challenge and developed a new resource to study the localisation of all Drosophila proteins during this animal’s development. First, genetic engineering was used to tag thousands of Drosophila proteins with a green fluorescent protein, so that they could be tracked under a microscope.

Sarov et al. tagged about 10000 Drosophila proteins in bacteria, and then introduced almost 900 of them into flies to create genetically modified flies. Each fly line contains an extra copy of the tagged gene that codes for one tagged protein. About two-thirds of these tagged proteins appeared to work normally after they were introduced into flies. Sarov et al. then looked at over 200 of these fly lines in more detail and observed that many of the proteins were found in particular cell types and localized to specific parts of the cells. Video imaging of the tagged proteins in living fruit fly embryos and pupae revealed the proteins’ movements, while other techniques showed which proteins bind to the tagged proteins, and may therefore work together in protein complexes.

This resource is openly available to the community, and so researchers can use it to study their favourite protein and gain new insights into how proteins work and are regulated during Drosophila development. Following on from this work, the next challenge will be to create more flies carrying tagged proteins, and to swap the green fluorescent tag with other experimentally useful tags.

DOI:http://dx.doi.org/10.7554/eLife.12068.002

Genome engineering: Drosophila melanogaster and beyond

A central challenge in investigating biological phenomena is the development of techniques to modify genomic DNA with nucleotide precision that can be transmitted through the germ line. Recent years have brought a boon in these technologies, now collectively known as genome engineering. Defined genomic manipulations at the nucleotide level enable a variety of reverse engineering paradigms, providing new opportunities to interrogate diverse biological functions. These genetic modifications include controlled removal, insertion, and substitution of genetic fragments, both small and large. Small fragments up to a few kilobases (e.g., single nucleotide mutations, small deletions, or gene tagging at single or multiple gene loci) to large fragments up to megabase resolution can be manipulated at single loci to create deletions, duplications, inversions, or translocations of substantial sections of whole chromosome arms. A specialized substitution of chromosomal portions that presumably are functionally orthologous between different organisms through syntenic replacement, can provide proof of evolutionary conservation between regulatory sequences. Large transgenes containing endogenous or synthetic DNA can be integrated at defined genomic locations, permitting an alternative proof of evolutionary conservation, and sophisticated transgenes can be used to interrogate biological phenomena. Precision engineering can additionally be used to manipulate the genomes of organelles (e.g., mitochondria). Novel genome engineering paradigms are often accelerated in existing, easily genetically tractable model organisms, primarily because these paradigms can be integrated in a rigorous, existing technology foundation. The Drosophila melanogaster fly model is ideal for these types of studies. Due to its small genome size, having just four chromosomes, the vast amount of cutting-edge genetic technologies, and its short life-cycle and inexpensive maintenance requirements, the fly is exceptionally amenable to complex genetic analysis using advanced genome engineering. Thus, highly sophisticated methods developed in the fly model can be used in nearly any sequenced organism. Here, we summarize different ways to perform precise inheritable genome engineering using integrases, recombinases, and DNA nucleases in the D. melanogaster. For further resources related to this article, please visit the WIREs website.

Drosophila oocytes as a model for understanding meiosis: an educational primer to accompany "corolla is a novel protein that contributes to the architecture of the synaptonemal complex of Drosophila"

SUMMARY Achieving a thorough understanding of the events and ramifications of meiosis is a common learning objective for undergraduate introductory biology, genetics, and cell biology courses. Meiosis is also one of the most challenging cellular processes for students to conceptualize. Connecting textbook descriptions of meiosis to current research in the field of genetics in a problem-based learning format may aid students’ understanding of this important biological concept. This primer seeks to assist students and instructors by providing an introductory framework upon which to integrate discussions of current meiosis research into traditional genetics or cell biology curriculum.

Related article in GENETICS: Collins, K. et al., 2014 Corolla Is a Novel Protein That Contributes to the Architecture of the Synaptonemal Complex of Drosophila. Genetics 198:219–228.

Alternative NF-κB Isoforms in the Drosophila Neuromuscular Junction and Brain

The Drosophila NF-κB protein Dorsal is expressed at the larval neuromuscular junction, where its expression appears unrelated to known Dorsal functions in embryonic patterning and innate immunity. Using confocal microscopy with domain-specific antisera, we demonstrate that larval muscle expresses only the B isoform of Dorsal, which arises by intron retention. We find that Dorsal B interacts with and stabilizes Cactus at the neuromuscular junction, but exhibits Cactus independent localization and an absence of detectable nuclear translocation. We further find that the Dorsal-related immune factor Dif encodes a B isoform, reflecting a conservation of B domains across a range of insect NF-κB proteins. Carrying out mutagenesis of the Dif locus via a site-specific recombineering approach, we demonstrate that Dif B is the major, if not sole, Dif isoform in the mushroom bodies of the larval brain. The Dorsal and Dif B isoforms thus share a specific association with nervous system tissues as well as an alternative protein structure.

A transgenic resource for conditional competitive inhibition of conserved Drosophila microRNAs

Although the impact of microRNAs (miRNAs) in development and disease is well established, understanding the function of individual miRNAs remains challenging. Development of competitive inhibitor molecules such as miRNA sponges has allowed the community to address individual miRNA function in vivo. However, the application of these loss-of-function strategies has been limited. Here we offer a comprehensive library of 141 conditional miRNA sponges targeting well-conserved miRNAs in Drosophila. Ubiquitous miRNA sponge delivery and consequent systemic miRNA inhibition uncovers a relatively small number of miRNA families underlying viability and gross morphogenesis, with false discovery rates in the 4-8% range. In contrast, tissue-specific silencing of muscle-enriched miRNAs reveals a surprisingly large number of novel miRNA contributions to the maintenance of adult indirect flight muscle structure and function. A strong correlation between miRNA abundance and physiological relevance is not observed, underscoring the importance of unbiased screens when assessing the contributions of miRNAs to complex biological processes.

Germ line transformation and in vivo labeling of nuclei in Diptera: report on Megaselia abdita (Phoridae) and Chironomus riparius (Chironomidae)

To understand how and when developmental traits of the fruit fly Drosophila melanogaster originated during the course of insect evolution, similar traits are functionally studied in variably related satellite species. The experimental toolkit available for relevant fly models typically comprises gene expression and loss as well as gain-of-function analyses. Here, we extend the set of available molecular tools to piggyBac-based germ line transformation in two satellite fly models, Megaselia abdita and Chironomus riparius. As proof-of-concept application, we used a Gateway variant of the piggyBac transposon vector pBac{3xP3-eGFPafm} to generate a transgenic line that expresses His2Av-mCherry as fluorescent nuclear reporter ubiquitously in the gastrulating embryo of M. abdita. Our results open two phylogenetically important nodes of the insect order Diptera for advanced developmental evolutionary genetics.

Tools for Anopheles gambiae Transgenesis

Transgenesis is an essential tool to investigate gene function and to introduce desired characters in laboratory organisms. Setting-up transgenesis in non-model organisms is challenging due to the diversity of biological life traits and due to knowledge gaps in genomic information. Some procedures will be broadly applicable to many organisms, and others have to be specifically developed for the target species. Transgenesis in disease vector mosquitoes has existed since the 2000s but has remained limited by the delicate biology of these insects. Here, we report a compilation of the transgenesis tools that we have designed for the malaria vector Anopheles gambiae, including new docking strains, convenient transgenesis plasmids, a puromycin resistance selection marker, mosquitoes expressing cre recombinase, and various reporter lines defining the activity of cloned promoters. This toolbox contributed to rendering transgenesis routine in this species and is now enabling the development of increasingly refined genetic manipulations such as targeted mutagenesis. Some of the reagents and procedures reported here are easily transferable to other nonmodel species, including other disease vector or agricultural pest insects.

Versatile genetic paintbrushes: Brainbow technologies

Advances in labeling technologies are instrumental to study the developmental mechanisms that control organ formation and function at the cellular level. Until recently, genetic tools relied on the expression of single markers to visualize individual cells or lineages in developing and adult animals. Exploiting the expanding color palette of fluorescent proteins and the power of site-specific recombinases in rearranging DNA fragments, the development of Brainbow strategies in mice made it possible to stochastically label many cells in different colors within the same sample. Over the past years, these pioneering approaches have been adapted for other experimental model organisms, including Drosophila melanogaster, zebrafish, and chicken. Balancing the distinct requirements of single cell and clonal analyses, adjustments were made that both enhance and expand the functionality of these tools. Multicolor cell labeling techniques have been successfully applied in studies analyzing the cellular components of neural circuits and other tissues, and the compositions and interactions of lineages. While being continuously refined, Brainbow technologies have thus found a firm place in the genetic toolboxes of developmental and neurobiologists. For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

A CRISPR view of development

The CRISPR (clustered regularly interspaced short palindromic repeat)-Cas9 (CRISPR-associated nuclease 9) system is poised to transform developmental biology by providing a simple, efficient method to precisely manipulate the genome of virtually any developing organism. This RNA-guided nuclease (RGN)-based approach already has been effectively used to induce targeted mutations in multiple genes simultaneously, create conditional alleles, and generate endogenously tagged proteins. Illustrating the adaptability of RGNs, the genomes of >20 different plant and animal species as well as multiple cell lines and primary cells have been successfully modified. Here we review the current and potential uses of RGNs to investigate genome function during development.

The redistribution of Drosophila vesicular monoamine transporter mutants from synaptic vesicles to large dense-core vesicles impairs amine-dependent behaviors

Monoamine neurotransmitters are stored in both synaptic vesicles (SVs), which are required for release at the synapse, and large dense-core vesicles (LDCVs), which mediate extrasynaptic release. The contributions of each type of vesicular release to specific behaviors are not known. To address this issue, we generated mutations in the C-terminal trafficking domain of the Drosophila vesicular monoamine transporter (DVMAT), which is required for the vesicular storage of monoamines in both SVs and LDCVs. Deletion of the terminal 23 aa (DVMAT-Δ3) reduced the rate of endocytosis and localization of DVMAT to SVs, but supported localization to LDCVs. An alanine substitution mutation in a tyrosine-based motif (DVMAT-Y600A) also reduced sorting to SVs and showed an endocytic deficit specific to aminergic nerve terminals. Redistribution of DVMAT-Y600A from SV to LDCV fractions was also enhanced in aminergic neurons. To determine how these changes might affect behavior, we expressed DVMAT-Δ3 and DVMAT-Y600A in a dVMAT null genetic background that lacks endogenous dVMAT activity. When expressed ubiquitously, DVMAT-Δ3 showed a specific deficit in female fertility, whereas DVMAT-Y600A rescued behavior similarly to DVMAT-wt. In contrast, when expressed more specifically in octopaminergic neurons, both DVMAT-Δ3 and DVMAT-Y600A failed to rescue female fertility, and DVMAT-Y600A showed deficits in larval locomotion. DVMAT-Y600A also showed more severe dominant effects than either DVMAT-wt or DVMAT-Δ3. We propose that these behavioral deficits result from the redistribution of DVMAT from SVs to LDCVs. By extension, our data suggest that the balance of amine release from SVs versus that from LDCVs is critical for the function of some aminergic circuits.

Chemical mutagens, transposons, and transgenes to interrogate gene function in Drosophila melanogaster

The study of genetics, genes, and chromosomal inheritance was initiated by Thomas Morgan in 1910, when the first visible mutations were identified in fruit flies. The field expanded upon the work initiated by Herman Muller in 1926 when he used X-rays to develop the first balancer chromosomes. Today, balancers are still invaluable to maintain mutations and transgenes but the arsenal of tools has expanded vastly and numerous new methods have been developed, many relying on the availability of the genome sequence and transposable elements. Forward genetic screens based on chemical mutagenesis or transposable elements have resulted in the unbiased identification of many novel players involved in processes probed by specific phenotypic assays. Reverse genetic approaches have relied on the availability of a carefully selected set of transposon insertions spread throughout the genome to allow the manipulation of the region in the vicinity of each insertion. Lastly, the ability to transform Drosophila with single copy transgenes using transposons or site-specific integration using the ΦC31 integrase has allowed numerous manipulations, including the ability to create and integrate genomic rescue constructs, generate duplications, RNAi knock-out technology, binary expression systems like the GAL4/UAS system as well as other methods. Here, we will discuss the most useful methodologies to interrogate the fruit fly genome in vivo focusing on chemical mutagenesis, transposons and transgenes. Genome engineering approaches based on nucleases and RNAi technology are discussed in following chapters.

IV. Tools and methods for studying cell migration and cell rearrangement in tissue and organ development

A vast diversity of biological systems, ranging from prokaryotes to multicellular organisms, show cell migration behavior. Many of the basic cellular and molecular concepts in cell migration apply to diverse model organisms. Drosophila, with its vast repertoire of tools for imaging and for manipulation, is one of the favorite organisms to study cell migration. Moreover, distinct Drosophila tissues and organs offer diverse cell migration models that are amenable to live imaging and genetic manipulations. In this review, we will provide an overview of the fruit fly toolbox that is of particular interest for the analysis of cell migration. We provide examples to highlight how those tools were used in diverse migration systems, with an emphasis on tracheal morphogenesis, a process that combines morphogenesis with cell migration.

Drosophila melanogaster as a genetic model system to study neurotransmitter transporters

The model genetic organism Drosophila melanogaster, commonly known as the fruit fly, uses many of the same neurotransmitters as mammals and very similar mechanisms of neurotransmitter storage, release and recycling. This system offers a variety of powerful molecular-genetic methods for the study of transporters, many of which would be difficult in mammalian models. We review here progress made using Drosophila to understand the function and regulation of neurotransmitter transporters and discuss future directions for its use.