Splice-activated UAS hairpin vector gives complete RNAi knockout of single or double target transcripts in Drosophila melanogaster

Drosophila Mcm10 is required for DNA replication and differentiation in the compound eye

Mini chromosome maintenance 10 (Mcm10) is an essential protein, which is conserved from S. cerevisiae to Drosophila and human, and is required for the initiation of DNA replication. Knockdown of Drosophila Mcm10 (dMcm10) by RNA interference in eye imaginal discs induces abnormal eye morphology (rough eye phenotype), and the number of ommatidia is decreased in adult eyes. We also observed a delay in the S phase and M phase in eye discs of dMcm10 knockdown fly lines. These results show important roles for dMcm10 in the progression of S and M phases. Furthermore, genome damage and apoptosis were induced by dMcm10 knockdown in eye imaginal discs. Surprisingly, when we used deadpan-lacZ and klingon-lacZ enhancer trap lines to monitor the photoreceptor cells in eye discs, knockdown of dMcm10 by the GMR-GAL4 driver reduced the signals of R7 photoreceptor cells. These data suggest an involvement of dMcm10 in R7 cell differentiation. This involvement appears to be independent of the apoptosis induced by dMcm10 knockdown. Together, these results suggest that dMcm10 knockdown has an effect on DNA replication and R7 cell differentiation.

In vivo RNAi: today and tomorrow

RNA interference (RNAi) provides a powerful reverse genetics approach to analyze gene functions both in tissue culture and in vivo. Because of its widespread applicability and effectiveness it has become an essential part of the tool box kits of model organisms such as Caenorhabditis elegans, Drosophila, and the mouse. In addition, the use of RNAi in animals in which genetic tools are either poorly developed or nonexistent enables a myriad of fundamental questions to be asked. Here, we review the methods and applications of in vivo RNAi to characterize gene functions in model organisms and discuss their impact to the study of developmental as well as evolutionary questions. Further, we discuss the applications of RNAi technologies to crop improvement, pest control and RNAi therapeutics, thus providing an appreciation of the potential for phenomenal applications of RNAi to agriculture and medicine.

Drosophila as a model for antiviral immunity

The fruit fly Drosophila melanogaster has been successfully used to study numerous biological processes including immune response. Flies are naturally infected with more than twenty RNA viruses making it a valid model organism to study host-pathogen interactions during viral infections. The Drosophila antiviral immunity includes RNA interference, activation of the JAK/STAT and other signaling cascades and other mechanisms such as autophagy and interactions with other microorganisms. Here we review Drosophila as an immunological research model as well as recent advances in the field of Drosophila antiviral immunity.

The nuclear receptor DHR3 modulates dS6 kinase-dependent growth in Drosophila

S6 kinases (S6Ks) act to integrate nutrient and insulin signaling pathways and, as such, function as positive effectors in cell growth and organismal development. However, they also have been shown to play a key role in limiting insulin signaling and in mediating the autophagic response. To identify novel regulators of S6K signaling, we have used a Drosophila-based, sensitized, gain-of-function genetic screen. Unexpectedly, one of the strongest enhancers to emerge from this screen was the nuclear receptor (NR), Drosophila hormone receptor 3 (DHR3), a critical constituent in the coordination of Drosophila metamorphosis. Here we demonstrate that DHR3, through dS6K, also acts to regulate cell-autonomous growth. Moreover, we show that the ligand-binding domain (LBD) of DHR3 is essential for mediating this response. Consistent with these findings, we have identified an endogenous DHR3 isoform that lacks the DBD. These results provide the first molecular link between the dS6K pathway, critical in controlling nutrient-dependent growth, and that of DHR3, a major mediator of ecdysone signaling, which, acting together, coordinate metamorphosis.

A Drosophila resource of transgenic RNAi lines for neurogenetics

Conditional expression of hairpin constructs in Drosophila is a powerful method to disrupt the activity of single genes with a spatial and temporal resolution that is impossible, or exceedingly difficult, using classical genetic methods. We previously described a method (Ni et al. 2008) whereby RNAi constructs are targeted into the genome by the phiC31-mediated integration approach using Vermilion-AttB-Loxp-Intron-UAS-MCS (VALIUM), a vector that contains vermilion as a selectable marker, an attB sequence to allow for phiC31-targeted integration at genomic attP landing sites, two pentamers of UAS, the hsp70 core promoter, a multiple cloning site, and two introns. As the level of gene activity knockdown associated with transgenic RNAi depends on the level of expression of the hairpin constructs, we generated a number of derivatives of our initial vector, called the "VALIUM" series, to improve the efficiency of the method. Here, we report the results from the systematic analysis of these derivatives and characterize VALIUM10 as the most optimal vector of this series. A critical feature of VALIUM10 is the presence of gypsy insulator sequences that boost dramatically the level of knockdown. We document the efficacy of VALIUM as a vector to analyze the phenotype of genes expressed in the nervous system and have generated a library of 2282 constructs targeting 2043 genes that will be particularly useful for studies of the nervous system as they target, in particular, transcription factors, ion channels, and transporters.

JNK signalling influences intracellular trafficking during Drosophila morphogenesis through regulation of the novel target gene Rab30

JNK-mediated closure of the Drosophila dorsal epidermis during embryogenesis is a well-characterised model for morphogenesis. However, little is known about how JNK signalling modifies particular cellular behaviours such as intracellular transport. Here we demonstrate that the gene encoding the small GTPase Rab30 is a new JNK transcriptional target whose function is required during embryonic and adult morphogenesis including JNK-dependent dorsal closure, embryonic head involution and thorax closure. Using immuno-fluorescence and live imaging, we show that EGFP-Rab30 localises to trans-Golgi in addition to small unidentified vesicles, and moves in a microtubule-dependent, polarised dorso-ventral manner in the leading edge during dorsal closure. We propose that JNK activity upregulates genes involved in intracellular transport in order to provide an increased level of trafficking activity in cells undergoing complex morphogenetic arrangements such as dorsal closure.

The DExD/H-box helicase Dicer-2 mediates the induction of antiviral activity in drosophila

Drosophila, like other invertebrates and plants, relies mainly on RNA interference for its defense against viruses. In flies, viral infection also triggers the expression of many genes. One of the genes induced, Vago, encodes a 18-kilodalton cysteine-rich polypeptide. Here we provide genetic evidence that the Vago gene product controlled viral load in the fat body after infection with drosophila C virus. Induction of Vago was dependent on the helicase Dicer-2. Dicer-2 belongs to the same DExD/H-box helicase family as do the RIG-I-like receptors, which sense viral infection and mediate interferon induction in mammals. We propose that this family represents an evolutionary conserved set of sensors that detect viral nucleic acids and direct antiviral responses.

Molecular dissection of Drosophila Prickle isoforms distinguishes their essential and overlapping roles in planar cell polarity

Prickle-Spiny-Legs (Pk) is an essential component of the planar cell polarity (PCP) pathway, together with Frizzled (Fz) and Dishevelled (Dsh). A role for Pk was proposed to mediate feedback amplification of asymmetric Fz/Dsh activity across cell boundaries, ensuring a single prehair initiates at each distal vertex. Here we show that apical localisation of Pk(Pk) and Pk(Sple) isoforms are mutually independent and regulated by the C-terminal domain. The N-terminus of Pk(Pk) is dispensable for PCP, whereas the unique N-terminal domain of Pk(Sple) contains an additional localisation function, which confers a qualitatively different activity. Our results suggest that endogenous Pk(Pk) and Pk(Sple) can affect each other's function via the C-terminal domain, yet may not form heteromeric complexes. Overexpressing PET domain-deleted Pk variants interferes with a branch of Fz/Dsh signalling that regulates the number of wing hairs, and blocks non-cell-autonomous repolarisation. We infer that Pk(Pk) is sufficient to mediate the intercellular feedback signalling. Significantly, Pk(Pk) but not Pk(Sple) is required for hexagonal cell packing in the pupal wing. We propose that Fz-dependent PCP readout reflects short-range, cell-contact based, interactions between hexagonal cells, rather than a direct response to an as yet unidentified diffusible ligand.

Palisade is required in the Drosophila ovary for assembly and function of the protective vitelline membrane

The innermost layer of the Drosophila eggshell, the vitelline membrane, provides structural support and positional information to the embryo. It is assembled in an incompletely understood manner from four major proteins to form a homogeneous, transparent extracellular matrix. Here we show that RNAi knockdown or genetic deletion of a minor constituent of this matrix, Palisade, results in structural disruptions during the initial synthesis of the vitelline membrane by somatic follicle cells surrounding the oocyte, including wide size variation among the precursor vitelline bodies and disorganization of follicle cell microvilli. Loss of Palisade or the microvillar protein Cad99C results in abnormal uptake into the oocyte of sV17, a major vitelline membrane protein, and defects in non-disulfide cross-linking of sV17 and sV23, while loss of Palisade has additional effects on processing and disulfide cross-linking of these proteins. Embryos surrounded by the abnormal vitelline membranes synthesized when Palisade is reduced are fertilized but undergo developmental arrest, usually during the first 13 nuclear divisions, with a nuclear phenotype of chromatin margination similar to that described for wild-type embryos subjected to anoxia. Our results demonstrate that Palisade is involved in coordinating assembly of the vitelline membrane and is required for functional properties of the eggshell.

Akirins are highly conserved nuclear proteins required for NF-kappaB-dependent gene expression in drosophila and mice

During a genome-wide RNAi screen, we isolated CG8580 as a gene involved in the innate immune response of Drosophila. CG8580, which we named Akirin, acts in parallel with the NF-κB transcription factor downstream of the Imd pathway and was required for defense against Gram-negative bacteria. Akirin is highly conserved and the human genome contains two homologues, one of which was able to rescue the loss of function phenotype in Drosophila cells. Akirins had a strict nuclear localization. Knockout of both Akirin homologues in mice revealed that one had an essential function downstream of Toll-like receptor, tumor necrosis factor and interleukin 1-β (IL-1β) signaling pathways leading to the production of IL-6. Thus, Akirin is a conserved nuclear factor required for innate immune responses.

A genome-wide transgenic RNAi library for conditional gene inactivation in Drosophila

Forward genetic screens in model organisms have provided important insights into numerous aspects of development, physiology and pathology. With the availability of complete genome sequences and the introduction of RNA-mediated gene interference (RNAi), systematic reverse genetic screens are now also possible. Until now, such genome-wide RNAi screens have mostly been restricted to cultured cells and ubiquitous gene inactivation in Caenorhabditis elegans. This powerful approach has not yet been applied in a tissue-specific manner. Here we report the generation and validation of a genome-wide library of Drosophila melanogaster RNAi transgenes, enabling the conditional inactivation of gene function in specific tissues of the intact organism. Our RNAi transgenes consist of short gene fragments cloned as inverted repeats and expressed using the binary GAL4/UAS system. We generated 22,270 transgenic lines, covering 88% of the predicted protein-coding genes in the Drosophila genome. Molecular and phenotypic assays indicate that the majority of these transgenes are functional. Our transgenic RNAi library thus opens up the prospect of systematically analysing gene functions in any tissue and at any stage of the Drosophila lifespan.

The effects of spacer sequences on silencing efficiency of plant RNAi vectors

RNA interference (RNAi) has been used to suppress gene expression in various eukaryotic organisms. In plants, RNAi can be induced by introduction of an RNAi vector that transcribes a self-complementary hairpin RNA. Most basic RNAi constructs have an inverted repeat interrupted with a spacer sequence. To test silencing capability of RNAi constructs, we developed an in vivo assay that is based on the RNAi-mediated changes of the alpha-linolenic acid content in hairy roots. A tobacco endoplasmic reticulum omega-3 fatty acid desaturase (NtFAD3) is the main enzyme for production of alpha-linolenic acid of root membrane lipids. Tobacco hairy roots transformed with the RNAi vectors against the NtFAD3 gene showed a decrease in alpha-linolenic acid content. The frequency of RNA silencing was more affected by spacer sequence than by spacer length, at least between 100 and 1800 bp. Since significant amounts of hairpin RNA against the NtFAD3 gene remained in the transgenic plants displaying a weak silencing phenotype, low degree of silencing was attributed to low efficiency of hairpin RNA processing mediated by Dicer-like proteins. Our results show the possibility of producing a broad range of the RNAi-induced silencing phenotypes by replacing the spacer sequence of RNAi construct.

Drosophila Dystrophin is required for integrity of the musculature

Duchenne muscular dystrophy is caused by mutations in the dystrophin gene and is characterized by progressive muscle wasting. The highly conserved dystrophin gene encodes a number of protein isoforms. The Dystrophin protein is part of a large protein assembly, the Dystrophin glycoprotein complex, which stabilizes the muscle membrane during contraction and acts as a scaffold for signaling molecules. How the absence of Dystrophin results in the onset of muscular dystrophy remains unclear. Here, we have used transgenic RNA interference to examine the roles of the Drosophila Dystrophin isoforms in muscle. We previously reported that one of the Drosophila Dystrophin orthologs, the DLP2 isoform, is not required to maintain muscle integrity, but plays a role in neuromuscular homeostasis by regulating neurotransmitter release. In this report, we show that reduction of all Dystrophin isoform expression levels in the musculature does not apparently affect myogenesis or muscle attachment, but results in progressive muscle degeneration in larvae and adult flies. We find that a recently identified Dystrophin isoform, Dp117, is expressed in the musculature and is required for muscle integrity. Muscle fibers with reduced levels of Dp117 display disorganized actin-myosin filaments and the cellular hallmarks of necrosis. Our results indicate the existence of at least two possibly separate roles of dystrophin in muscle, maintaining synaptic homeostasis and preserving the structural stability of the muscle.

RNAi in the Hedgehog signaling pathway: pFRiPE, a vector for temporally and spatially controlled RNAi in Drosophila

RNA interference (RNAi) has become an irreplaceable tool for reverse genetics in plants and animals. The universality and specificity of this phenomenon allows silencing of virtually any chosen gene to examine its involvement in biological processes. Many strategies exist to reduce the expression of a particular gene using RNAi. Some rely on delivering directly to cells the approximately 21-nucleotide long interfering double-stranded RNA (dsRNA) species that are central mediators of the silencing process. Others rely on the transgenic expression of longer dsRNA molecules, leaving it to the cellular machinery to process these hairpins into short active dsRNA. In this chapter, we describe a transgenic method to deplete a chosen protein from a specific Drosophila tissue following induction of long dsRNA. It was used to uncover the role of lipidic particles in Hedgehog signaling by silencing lipophorin in the fat body (1), and we routinely use it to deplete specific proteins from wing imaginal disc subdomains (2). The method, certainly not restricted to the study of Hedgehog signaling, allows fast and efficient construction of a plasmid incorporating various Drosophila genetic tools to allow heat-shock-induced expression of dsRNA at the desired time and in the desired tissue. For protocols involving injection of in vitro synthesized dsRNA in embryos to study Hedgehog signaling, see for example (3). For genomic screens to identify Hedgehog pathway components in tissue culture cells by transfection of small interfering RNAs, see refs. (4,5).

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

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

Differential display of genes expressed in the filarial nematode Litomosoides sigmodontis reveals a putative phosphate permease up-regulated after depletion of Wolbachia endobacteria

Mutualist symbiotic Wolbachia endobacteria are found in most filarial nematodes. Wolbachia are essential for embryogenesis and for larval development into adults, and thus represent a new target for anti-filarial drug development. Tetracycline antibiotics deplete Wolbachia in animal model filaria Litomosoides sigmodontis and Brugia pahangi, as well as in the human parasites Brugia malayi, Onchocerca volvulus and Wuchereria bancrofti. Very little is known about the molecular details of the symbiotic interaction between Wolbachia and filarial nematodes. Nematode genes that respond to anti-Wolbachia antibiotic treatment may play important roles in the symbiosis. Differential display PCR was used to detect several candidate genes that are up-regulated after 3, 6, 15, 30 and 36 days of tetracycline treatment. One of these genes, Ls-ppe-1, was similar to a family of phosphate permeases, and had putative orthologues in O. volvulus and B. malayi. Ls-ppe-1 steady-state mRNA levels were elevated by day 3-6 of treatment, and remained elevated through to 70 days post-treatment. In Caenorhabditis elegans, the knockdown of a homologous phosphate permease results in embryonic lethality, with the production of degenerating embryos, a phenotype also seen in filarial nematodes after depletion of Wolbachia with tetracycline. The potential role of Ls-ppe-1 in the nematode-bacterial symbiosis is discussed.

Drosophila immunity: a large-scale in vivo RNAi screen identifies five serine proteases required for Toll activation

Unlike mammalian Toll-like Receptors, the Drosophila Toll receptor does not interact directly with microbial determinants but is rather activated upon binding a cleaved form of the cytokine-like molecule Spatzle (Spz). During the immune response, Spz is thought to be processed by secreted serine proteases (SPs) present in the hemolymph that are activated by the recognition of gram-positive bacteria or fungi . In the present study, we have used an in vivo RNAi strategy to inactivate 75 distinct Drosophila SP genes. We then screened this collection for SPs regulating the activation of the Toll pathway by gram-positive bacteria. Here, we report the identification of five novel SPs that function in an extracellular pathway linking the recognition proteins GNBP1 and PGRP-SA to Spz. Interestingly, four of these genes are also required for Toll activation by fungi, while one is specifically associated with signaling in response to gram-positive bacterial infections. These results demonstrate the existence of a common cascade of SPs upstream of Spz, integrating signals sent by various secreted recognition molecules via more specialized SPs.

Dystrophin is required for appropriate retrograde control of neurotransmitter release at the Drosophila neuromuscular junction

Mutations in the human dystrophin gene cause the Duchenne and Becker muscular dystrophies. The Dystrophin protein provides a structural link between the muscle cytoskeleton and extracellular matrix to maintain muscle integrity. Recently, Dystrophin has also been found to act as a scaffold for several signaling molecules, but the roles of dystrophin-mediated signaling pathways remain unknown. To further our understanding of this aspect of the function of dystrophin, we have generated Drosophila mutants that lack the large dystrophin isoforms and analyzed their role in synapse function at the neuromuscular junction. In expression and rescue studies, we show that lack of the large dystrophin isoforms in the postsynaptic muscle cell leads to elevated evoked neurotransmitter release from the presynaptic apparatus. Overall synapse size, the size of the readily releasable vesicle pool as assessed with hypertonic shock, and the number of presynaptic neurotransmitter release sites (active zones) are not changed in the mutants. Short-term synaptic facilitation of evoked transmitter release is decreased in the mutants, suggesting that the absence of dystrophin results in increased probability of release. Absence of the large dystrophin isoforms does not lead to changes in muscle cell morphology or alterations in the postsynaptic electrical response to spontaneously released neurotransmitter. Therefore, postsynaptic glutamate receptor function does not appear to be affected. Our results indicate that the postsynaptically localized scaffolding protein Dystrophin is required for appropriate control of neuromuscular synaptic homeostasis.

A Spätzle-processing enzyme required for toll signaling activation in Drosophila innate immunity

The Toll receptor was originally identified as an indispensable molecule for Drosophila embryonic development and subsequently as an essential component of innate immunity from insects to humans. Although in Drosophila the Easter protease processes the pro-Spätzle protein to generate the Toll ligand during development, the identification of the protease responsible for pro-Spätzle processing during the immune response has remained elusive for a decade. Here, we report a protease, called Spätzle-processing enzyme (SPE), required for Toll-dependent antimicrobial response. Flies with reduced SPE expression show no noticeable pro-Spätzle processing and become highly susceptible to microbial infection. Furthermore, activated SPE can rescue ventral and lateral development in embryos lacking Easter, showing the functional homology between SPE and Easter. These results imply that a single ligand/receptor-mediated signaling event can be utilized for different biological processes, such as immunity and development, by recruiting similar ligand-processing proteases with distinct activation modes.

Rapid construction of Drosophila RNAi transgenes using pRISE, a P-element-mediated transformation vector exploiting an in vitro recombination system

RNAi is a gene-silencing phenomenon mediated by double-stranded RNA (dsRNA) and has become a powerful tool to elucidate gene function. To accomplish rapid construction of transgenes expressing dsRNA in Drosophila, we developed a novel transformation vector, pRISE, which contains an inverted repeat of the attR1-ccdB-attR2 cassette for in vitro recombination and a pentameric GAL4 binding site for conditional expression. These features enabled us to construct RNAi transgenes without a complicated cloning scheme. In cultured cells and transgenic flies, pRISE constructs carrying dsRNA transgenes induced effective RNAi against an EGFP transgene and the endogenous white gene, respectively. These results indicate that pRISE is a convenient transformation vector for studies of multiple Drosophila genes for which functional information is lacking.

A Drosophila model of Alzheimer's disease

The development of a model of Alzheimer's disease in Drosophila allows us to identify and dissect pathological pathways using the most powerful genetic tools available to biology. By reconstructing essential steps in Alzheimer's pathology, such as amyloid beta peptide and tau overexpression, we can observe clear and rapid phenotypes that are surrogate markers for human disease. The characterization of progressive phenotypes by immunohistochemistry of the brain combined with longevity, climbing, and pseudopupil assays allows the investigator to generate quantitative data. Phenotypes may be modulated by changes in gene expression as part of a genetic screen or by potential therapeutic compounds.

Drosophila U6 promoter-driven short hairpin RNAs effectively induce RNA interference in Schneider 2 cells

The effect of RNA interference (RNAi) is generally more potent in Drosophila Schneider 2 (S2) cells than in mammalian cells. In mammalian cells, PolIII promoter-based DNA vectors can be used to express small interfering RNA (siRNA) or short hairpin RNA (shRNA); however, this has not been demonstrated in cultured Drosophila cells. Here we show that shRNAs transcribed from the Drosophila U6 promoter can efficiently trigger gene silencing in S2 cells. By targeting firefly luciferase mRNA, we assessed the efficacy of the shRNAs and examined the structural requirements for highly effective shRNAs. The silencing effect was dependent on the length of the stem region and the sequence of the loop region. Furthermore, we demonstrate that the expression of the endogenous cyclin E protein can be repressed by the U6 promoter-driven shRNAs. Drosophila U6 promoter-based shRNA expression systems may permit stable gene silencing in S2 cells.

RNAi-mediated inhibition of gene function in the follicle cell layer of the Drosophila ovary

RNA-mediated interference (RNAi) has been reported to be an effective reverse genetic approach for studying gene function in various organisms. To assess RNAi as a means of examining genes expressed in ovarian follicle cells for their involvement in embryonic dorsal-ventral patterning, we tested the ability of transgenically expressed double-stranded RNA (dsRNA) directed against the dorsal group gene windbeutel to generate phenotypic effects in the progeny of expressing females. We observed that expression in follicle cells under the control of Gal4 transcribed from the strong and widely expressed alphaTub84B or Actin5C promoters led to efficient dorsalization of progeny embryos. Surprisingly, a variety of strongly expressed follicle cell-specific Gal4 enhancer trap lines failed to elicit an RNAi phenotype in combination with the windbeutel-specific dsRNA. These results stress the importance of careful choice of expression system and of conditions for use in transgenic RNAi-mediated studies of gene function.

The genetics of Drosophila transgenics

In Drosophila, the genetic approach is still the method of choice for answering fundamental questions on cell biology, signal transduction, development, physiology and behavior. In this approach, a gene's function is ascertained by altering either the amount or quality of the gene product, and then observing the consequences. The genetic approach is itself polymorphous, encompassing new and more complex techniques that typically employ the growing collections of transgenes. The keystone of these modern Drosophila transgenic techniques has been the Gal4 binary system. Recently, several new techniques have modified this binary system to offer greater control over the timing, tissue specificity and magnitude of gene expression. Additionally, the advances in post-transcriptional gene silencing, or RNAi, have greatly expanded the ability to knockdown almost any gene's function. Regardless of the growing experimental intricacy, the application of these advances to modify gene activity still obeys the fundamental principles of genetic analysis. Several of these transgenic techniques, which offer more precise control over a gene's activity, will be reviewed here with a discussion on how they may be used for determining a gene's function.

In Vivo RNA Interference Analysis Reveals an Unexpected Role for GNBP1 in the Defense against Gram-positive Bacterial Infection in Drosophila Adults

The Drosophila immune system discriminates between different classes of infectious microbes and responds with pathogen-specific defense reactions via the selective activation of the Toll and the immune deficiency (Imd) signaling pathways. The Toll pathway mediates most defenses against Gram-positive bacteria and fungi, whereas the Imd pathway is required to resist Gram-negative bacterial infection. Microbial recognition is achieved through peptidoglycan recognition proteins (PGRPs); Gram-positive bacteria activate the Toll pathway through a circulating PGRP (PGRP-SA), and Gram-negative bacteria activate the Imd pathway via PGRP-LC, a putative transmembrane receptor, and PGRP-LE. Gram-negative binding proteins (GNBPs) were originally identified in Bombyx mori for their capacity to bind various microbial compounds. Three GNBPs and two related proteins are encoded in the Drosophila genome, but their function is not known. Using inducible expression of GNBP1 double-stranded RNA, we now demonstrate that GNBP1 is required for Toll activation in response to Gram-positive bacterial infection; GNBP1 double-stranded RNA expression renders flies susceptible to Gram-positive bacterial infection and reduces the induction of the antifungal peptide encoding gene Drosomycin after infection by Gram-positive bacteria but not after fungal infection. This phenotype induced by GNBP1 inactivation is identical to a loss-of-function mutation in PGRP-SA, and our genetic studies suggest that GNBP1 acts upstream of the Toll ligand Spätzle. Altogether, our results demonstrate that the detection of Gram-positive bacteria in Drosophila requires two putative pattern recognition receptors, PGRP-SA and GNBP1.

The Drosophila immune defense against gram-negative infection requires the death protein dFADD

Drosophila responds to Gram-negative infections by mounting an immune response that depends on components of the IMD pathway. We recently showed that imd encodes a protein with a death domain with high similarity to that of mammalian RIP. Using a two-hybrid screen in yeast, we have isolated the death protein dFADD as a molecule that associates with IMD. Our data show that loss of dFADD function renders flies highly susceptible to Gram-negative infections without affecting resistance to Gram-positive bacteria. By genetic analysis we show that dFADD acts downstream of IMD in the pathway that controls inducibility of the antibacterial peptide genes.