Localization of domains within the Drosophila Ref(2)P protein involved in the intracellular control of sigma rhabdovirus multiplication

Intracellular Density of Wolbachia Is Mediated by Host Autophagy and the Bacterial Cytoplasmic Incompatibility Gene cifB in a Cell Type-Dependent Manner in Drosophila melanogaster

Autophagy is an intracellular degradation pathway involved in innate immunity. Pathogenic bacteria have evolved several mechanisms to escape degradation or exploit autophagy to acquire host nutrients. In the case of endosymbionts, which often have commensal or mutualistic interactions with the host, autophagy is not well characterized. We utilized tissue-specific autophagy mutants to determine if Wolbachia, a vertically transmitted obligate endosymbiont of Drosophila melanogaster, is regulated by autophagy in somatic and germ line cell types. Our analysis revealed core autophagy proteins Atg1 and Atg8 and a selective autophagy-specific protein Ref(2)p negatively regulate Wolbachia in the hub, a male gonad somatic cell type. Furthermore, we determined that the Wolbachia effector protein, CifB, modulates autophagy-Wolbachia interactions, identifying a new host-related pathway which these bacterial proteins interact with. In the female germ line, the cell type necessary for inheritance of Wolbachia through vertical transmission, we discovered that bulk autophagy mediated by Atg1 and Atg8 positively regulates Wolbachia density, whereas Ref(2)p had no effect. Global metabolomics of fly ovaries deficient in germ line autophagy revealed reduced lipid and carbon metabolism, implicating metabolites from these pathways as positive regulators of Wolbachia Our work provides further understanding of how autophagy affects bacteria in a cell type-dependent manner.IMPORTANCE Autophagy is a eukaryotic intracellular degradation pathway which can act as an innate immune response to eliminate pathogens. Conversely, pathogens can evolve proteins which modulate the autophagy pathway to subvert degradation and establish an infection. Wolbachia, a vertically transmitted obligate endosymbiont which infects up to 40% of insect species, is negatively regulated by autophagy in whole animals, but the specific molecular mechanism and tissue which govern this interaction remain unknown. Our studies use cell type-specific autophagy mutants to reveal that Wolbachia is negatively regulated by selective autophagy in the soma, while nonselective autophagy positively regulates Wolbachia in the female germ line. These data provide evidence that cell type can drive different basal autophagy programs which modulate intracellular microbes differently. Additionally, we identified that the Wolbachia effector CifB acts in the selective autophagy pathway to aid in intracellular bacterial survival, providing a new function for CifB beyond its previously identified role in reproductive manipulation.

Mutations in CHCHD2 cause α-synuclein aggregation

Mutations in CHCHD2 are linked to a familial, autosomal dominant form of Parkinson’s disease (PD). The gene product may regulate mitochondrial respiratory function. However, whether mitochondrial dysfunction induced by CHCHD2 mutations further yields α-synuclein pathology is unclear. Here, we provide compelling genetic evidence that mitochondrial dysfunction induced by PD-linked CHCHD2 T61I mutation promotes α-synuclein aggregation using brain autopsy, induced pluripotent stem cells (iPSCs) and Drosophila genetics. An autopsy of an individual with CHCHD2 T61I revealed widespread Lewy pathology with both amyloid plaques and neurofibrillary tangles that appeared in the brain stem, limbic regions and neocortex. A prominent accumulation of sarkosyl-insoluble α-synuclein aggregates, the extent of which was comparable to that of a case with α-synuclein (SNCA) duplication, was observed in CHCHD2 T61I brain tissue. The prion-like activity and morphology of α-synuclein fibrils from the CHCHD2 T61I brain tissue were similar to those of fibrils from SNCA duplication and sporadic PD brain tissues. α-Synuclein insolubilization was reproduced in dopaminergic neuron cultures from CHCHD2 T61I iPSCs and Drosophila lacking the CHCHD2 ortholog or expressing the human CHCHD2 T61I. Moreover, the combination of ectopic α-synuclein expression and CHCHD2 null or T61I enhanced the toxicity in Drosophila dopaminergic neurons, altering the proteolysis pathways. Furthermore, CHCHD2 T61I lost its mitochondrial localization by α-synuclein in Drosophila. The mislocalization of CHCHD2 T61I was also observed in the patient brain. Our study suggests that CHCHD2 is a significant mitochondrial factor that determines α-synuclein stability in the etiology of PD.

Glial Draper Rescues Aβ Toxicity in a Drosophila Model of Alzheimer's Disease

Pathological hallmarks of Alzheimer's disease (AD) include amyloid-β (Aβ) plaques, neurofibrillary tangles, and reactive gliosis. Glial cells offer protection against AD by engulfing extracellular Aβ peptides, but the repertoire of molecules required for glial recognition and destruction of Aβ are still unclear. Here, we show that the highly conserved glial engulfment receptor Draper/MEGF10 provides neuroprotection in an AD model of Drosophila (both sexes). Neuronal expression of human Aβ42^arc in adult flies results in robust Aβ accumulation, neurodegeneration, locomotor dysfunction, and reduced lifespan. Notably, all of these phenotypes are more severe in draper mutant animals, whereas enhanced expression of glial Draper reverses Aβ accumulation, as well as behavioral phenotypes. We also show that the signal transducer and activator of transcription (Stat92E), c-Jun N-terminal kinase (JNK)/AP-1 signaling, and expression of matrix metalloproteinase-1 (Mmp1) are activated downstream of Draper in glia in response to Aβ42^arc exposure. Furthermore, Aβ42-induced upregulation of the phagolysosomal markers Atg8 and p62 was notably reduced in draper mutant flies. Based on our findings, we propose that glia clear neurotoxic Aβ peptides in the AD model Drosophila brain through a Draper/STAT92E/JNK cascade that may be coupled to protein degradation pathways such as autophagy or more traditional phagolysosomal destruction methods.SIGNIFICANCE STATEMENT Alzheimer's disease (AD) and similar dementias are common incurable neurodegenerative disorders in the aging population. As the primary immune responders in the brain, glial cells are implicated as key players in the onset and progression of AD and related disorders. Here we show that the glial engulfment receptor Draper is protective in a Drosophila model of AD, reducing levels of amyloid β (Aβ) peptides, reversing locomotor defects, and extending lifespan. We further show that protein degradation pathways are induced downstream of Draper in AD model flies, supporting a model in which glia engulf and destroy Aβ peptides to reduce amyloid-associated toxicity.

An AMPK-dependent regulatory pathway in tau-mediated toxicity

Neurodegenerative tauopathies are characterised by accumulation of hyperphosphorylated tau aggregates primarily degraded by autophagy. The 5′AMP-activated protein kinase (AMPK) is expressed in most cells, including neurons. Alongside its metabolic functions, it is also known to be activated in Alzheimer's brains, phosphorylate tau, and be a critical autophagy activator. Whether it plays a neurotoxic or neuroprotective role remains unclear. In tauopathies stress conditions can result in AMPK activation, enhancing tau-mediated toxicity. Paradoxically, in these cases AMPK activation does not always lead to protective autophagic responses. Using a Drosophila in vivo quantitative approach, we have analysed the impact of AMPK and autophagy on tau-mediated toxicity, recapitulating the AMPK-mediated tauopathy condition: increased tau phosphorylation, without corresponding autophagy activation. We have demonstrated that AMPK binding to and phosphorylating tau at Ser-262, a site reported to facilitate soluble tau accumulation, affects its degradation. This phosphorylation results in exacerbation of tau toxicity and is ameliorated via rapamycin-induced autophagy stimulation. Our findings support the development of combinatorial therapies effective at reducing tau toxicity targeting tau phosphorylation and AMPK-independent autophagic induction. The proposed in vivo tool represents an ideal readout to perform preliminary screening for drugs promoting this process.

Summary: Dissection of the impact of AMPK and autophagy on tau-mediated toxicity by using an in vivo Drosophila tool as readout to perform preliminary drug screening supported by quantitative analyses.

Drosophila Vps13 Is Required for Protein Homeostasis in the Brain

Chorea-Acanthocytosis is a rare, neurodegenerative disorder characterized by progressive loss of locomotor and cognitive function. It is caused by loss of function mutations in the Vacuolar Protein Sorting 13A (VPS13A) gene, which is conserved from yeast to human. The consequences of VPS13A dysfunction in the nervous system are still largely unspecified. In order to study the consequences of VPS13A protein dysfunction in the ageing central nervous system we characterized a Drosophila melanogaster Vps13 mutant line. The Drosophila Vps13 gene encoded a protein of similar size as human VPS13A. Our data suggest that Vps13 is a peripheral membrane protein located to endosomal membranes and enriched in the fly head. Vps13 mutant flies showed a shortened life span and age associated neurodegeneration. Vps13 mutant flies were sensitive to proteotoxic stress and accumulated ubiquitylated proteins. Levels of Ref(2)P, the Drosophila orthologue of p62, were increased and protein aggregates accumulated in the central nervous system. Overexpression of the human Vps13A protein in the mutant flies partly rescued apparent phenotypes. This suggests a functional conservation of human VPS13A and Drosophila Vps13. Our results demonstrate that Vps13 is essential to maintain protein homeostasis in the larval and adult Drosophila brain. Drosophila Vps13 mutants are suitable to investigate the function of Vps13 in the brain, to identify genetic enhancers and suppressors and to screen for potential therapeutic targets for Chorea-Acanthocytosis.

The Drosophila TIPE family member Sigmar interacts with the Ste20-like kinase Misshapen and modulates JNK signaling, cytoskeletal remodeling and autophagy

TNFAIP8 and other mammalian TIPE family proteins have attracted increased interest due to their associations with disease-related processes including oncogenic transformation, metastasis, and inflammation. The molecular and cellular functions of TIPE family proteins are still not well understood. Here we report the molecular and genetic characterization of the Drosophila TNFAIP8 homolog, CG4091/sigmar. Previous gene expression studies revealed dynamic expression of sigmar in larval salivary glands prior to histolysis. Here we demonstrate that in sigmar loss-of-function mutants, the salivary glands are morphologically abnormal with defects in the tubulin network and decreased autophagic flux. Sigmar localizes subcellularly to microtubule-containing projections in Drosophila S2 cells, and co-immunoprecipitates with the Ste20-like kinase Misshapen, a regulator of the JNK pathway. Further, the Drosophila TNF ligand Eiger can induce sigmar expression, and sigmar loss-of-function leads to altered localization of pDJNK in salivary glands. Together, these findings link Sigmar to the JNK pathway, cytoskeletal remodeling and autophagy activity during salivary gland development, and provide new insights into TIPE family member function.

p62 plays a protective role in the autophagic degradation of polyglutamine protein oligomers in polyglutamine disease model flies

Oligomer formation and accumulation of pathogenic proteins are key events in the pathomechanisms of many neurodegenerative diseases, such as Alzheimer disease, ALS, and the polyglutamine (polyQ) diseases. The autophagy-lysosome degradation system may have therapeutic potential against these diseases because it can degrade even large oligomers. Although p62/sequestosome 1 plays a physiological role in selective autophagy of ubiquitinated proteins, whether p62 recognizes and degrades pathogenic proteins in neurodegenerative diseases has remained unclear. In this study, to elucidate the role of p62 in such pathogenic conditions in vivo, we used Drosophila models of neurodegenerative diseases. We found that p62 predominantly co-localizes with cytoplasmic polyQ protein aggregates in the MJDtr-Q78 polyQ disease model flies. Loss of p62 function resulted in significant exacerbation of eye degeneration in these flies. Immunohistochemical analyses revealed enhanced accumulation of cytoplasmic aggregates by p62 knockdown in the MJDtr-Q78 flies, similarly to knockdown of autophagy-related genes (Atgs). Knockdown of both p62 and Atgs did not show any additive effects in the MJDtr-Q78 flies, implying that p62 function is mediated by autophagy. Biochemical analyses showed that loss of p62 function delays the degradation of the MJDtr-Q78 protein, especially its oligomeric species. We also found that loss of p62 function exacerbates eye degeneration in another polyQ disease fly model as well as in ALS model flies. We therefore conclude that p62 plays a protective role against polyQ-induced neurodegeneration, by the autophagic degradation of polyQ protein oligomers in vivo, indicating its therapeutic potential for the polyQ diseases and possibly for other neurodegenerative diseases.

Drosophila ref(2)P is required for the parkin-mediated suppression of mitochondrial dysfunction in pink1 mutants

Autophagy is a critical regulator of organellar homeostasis, particularly of mitochondria. Upon the loss of membrane potential, dysfunctional mitochondria are selectively removed by autophagy through recruitment of the E3 ligase Parkin by the PTEN-induced kinase 1 (PINK1) and subsequent ubiquitination of mitochondrial membrane proteins. Mammalian sequestrome-1 (p62/SQSTM1) is an autophagy adaptor, which has been proposed to shuttle ubiquitinated cargo for autophagic degradation downstream of Parkin. Here, we show that loss of ref(2)P, the Drosophila orthologue of mammalian P62, results in abnormalities, including mitochondrial defects and an accumulation of mitochondrial DNA with heteroplasmic mutations, correlated with locomotor defects. Furthermore, we show that expression of Ref(2)P is able to ameliorate the defects caused by loss of Pink1 and that this depends on the presence of functional Parkin. Finally, we show that both the PB1 and UBA domains of Ref(2)P are crucial for mitochondrial clustering. We conclude that Ref(2)P is a crucial downstream effector of a pathway involving Pink1 and Parkin and is responsible for the maintenance of a viable pool of cellular mitochondria by promoting their aggregation and autophagic clearance.

The CRISPRs, they are a-changin': how prokaryotes generate adaptive immunity

All organisms need to continuously adapt to changes in their environment. Through horizontal gene transfer, bacteria and archaea can rapidly acquire new traits that may contribute to their survival. However, because new DNA may also cause damage, removal of imported DNA and protection against selfish invading DNA elements are also important. Hence, there should be a delicate balance between DNA uptake and DNA degradation. Here, we describe prokaryotic antiviral defense systems, such as receptor masking or mutagenesis, blocking of phage DNA injection, restriction/modification, and abortive infection. The main focus of this review is on CRISPR (clustered regularly interspaced short palindromic repeats)/Cas (CRISPR-associated), a prokaryotic adaptive immune system. Since its recent discovery, our biochemical understanding of this defense system has made a major leap forward. Three highly diverse CRISPR/Cas types exist that display major structural and functional differences in their mode of generating resistance against invading nucleic acids. Because several excellent recent reviews cover all CRISPR subtypes, we mainly focus on a detailed description of the type I-E CRISPR/Cas system of the model bacterium Escherichia coli K12.

The deubiquitinating enzyme USP36 controls selective autophagy activation by ubiquitinated proteins

Initially described as a nonspecific degradation process induced upon starvation, autophagy is now known also to be involved in the degradation of specific ubiquitinated substrates such as mitochondria, bacteria and aggregated proteins, ensuring crucial functions in cell physiology and immunity. We report here that the deubiquitinating enzyme USP36 controls selective autophagy activation in Drosophila and in human cells. We show that dUsp36 loss of function autonomously inhibits cell growth while activating autophagy. Despite the phenotypic similarity, dUSP36 is not part of the TOR signaling pathway. Autophagy induced by dUsp36 loss of function depends on p62/SQSTM1, an adaptor for delivering cargo marked by polyubiquitin to autophagosomes. Consistent with p62 requirement, dUsp36 mutant cells display nuclear aggregates of ubiquitinated proteins, including Histone H2B, and cytoplasmic ubiquitinated proteins; the latter are eliminated by autophagy. Importantly, USP36 function in p62-dependent selective autophagy is conserved in human cells. Our work identifies a novel, crucial role for a deubiquitinating enzyme in selective autophagy.

Drosophila Golgi membrane protein Ema promotes autophagosomal growth and function

Autophagy is a self-degradative process in which cellular material is enclosed within autophagosomes and trafficked to lysosomes for degradation. Autophagosomal biogenesis is well described; however mechanisms controlling the growth and ultimate size of autophagosomes are unclear. Here we demonstrate that the Drosophila membrane protein Ema is required for the growth of autophagosomes. In an ema mutant, autophagosomes form in response to starvation and developmental cues, and these autophagosomes can mature into autolysosomes; however the autophagosomes are very small, and autophagy is impaired. In fat body cells, Ema localizes to the Golgi complex and is recruited to the membrane of autophagosomes in response to starvation. The Drosophila Golgi protein Lva also is recruited to the periphery of autophagosomes in response to starvation, and this recruitment requires ema. Therefore, we propose that Golgi is a membrane source for autophagosomal growth and that Ema facilitates this process. Clec16A, the human ortholog of Ema, is a candidate autoimmune susceptibility locus. Expression of Clec16A can rescue the autophagosome size defect in the ema mutant, suggesting that regulation of autophagosome morphogenesis may be a fundamental function of this gene family.

Genetic analysis of mitochondrial protein misfolding in Drosophila melanogaster

Protein misfolding has a key role in several neurological disorders including Parkinson's disease. Although a clear mechanism for such proteinopathic diseases is well established when aggregated proteins accumulate in the cytosol, cell nucleus, endoplasmic reticulum and extracellular space, little is known about the role of protein aggregation in the mitochondria. Here we show that mutations in both human and fly PINK1 result in higher levels of misfolded components of respiratory complexes and increase in markers of the mitochondrial unfolded protein response. Through the development of a genetic model of mitochondrial protein misfolding employing Drosophila melanogaster, we show that the in vivo accumulation of an unfolded protein in mitochondria results in the activation of AMP-activated protein kinase-dependent autophagy and phenocopies of pink1 and parkin mutants. Parkin expression acts to clear mitochondria with enhanced levels of misfolded proteins by promoting their autophagic degradation in vivo, and refractory to Sigma P (ref(2)P), the Drosophila orthologue of mammalian p62, is a critical downstream effector of this quality control pathway. We show that in flies, a pathway involving pink1, parkin and ref(2)P has a role in the maintenance of a viable pool of cellular mitochondria by promoting organellar quality control.

Manipulation or capitulation: virus interactions with autophagy

Autophagy is a homeostatic process that functions to balance cellular metabolism and promote cell survival during stressful conditions by delivering cytoplasmic components for lysosomal degradation and subsequent recycling. During viral infection, autophagy can act as a surveillance mechanism that delivers viral antigens to the endosomal/lysosomal compartments that are enriched in immune sensors. Additionally, activated immune sensors can signal to activate autophagy. To evade this antiviral activity, many viruses elaborate functions to block the autophagy pathway at a variety of steps. Alternatively, some viruses actively subvert autophagy for their own benefit. Manipulated autophagy has been proposed to facilitate nearly every stage of the viral lifecycle in direct and indirect ways. In this review, we synthesize the extensive literature on virus–autophagy interactions, emphasizing the role of autophagy in antiviral immunity and the mechanisms by which viruses subvert autophagy for their own benefit.

The transcriptional response of Drosophila melanogaster to infection with the sigma virus (Rhabdoviridae)

Background

Bacterial and fungal infections induce a potent immune response in Drosophila melanogaster, but it is unclear whether viral infections induce an antiviral immune response. Using microarrays, we examined the changes in gene expression in Drosophila that occur in response to infection with the sigma virus, a negative-stranded RNA virus (Rhabdoviridae) that occurs in wild populations of D. melanogaster.

Principal Findings

We detected many changes in gene expression in infected flies, but found no evidence for the activation of the Toll, IMD or Jak-STAT pathways, which control immune responses against bacteria and fungi. We identified a number of functional categories of genes, including serine proteases, ribosomal proteins and chorion proteins that were overrepresented among the differentially expressed genes. We also found that the sigma virus alters the expression of many more genes in males than in females.

Conclusions

These data suggest that either Drosophila do not mount an immune response against the sigma virus, or that the immune response is not controlled by known immune pathways. If the latter is true, the genes that we identified as differentially expressed after infection are promising candidates for controlling the host's response to the sigma virus.

Ref(2)P, the Drosophila melanogaster homologue of mammalian p62, is required for the formation of protein aggregates in adult brain

p62 has been proposed to mark ubiquitinated protein bodies for autophagic degradation. We report that the Drosophila melanogaster p62 orthologue, Ref(2)P, is a regulator of protein aggregation in the adult brain. We demonstrate that Ref(2)P localizes to age-induced protein aggregates as well as to aggregates caused by reduced autophagic or proteasomal activity. A similar localization to protein aggregates is also observed in D. melanogaster models of human neurodegenerative diseases. Although atg8a autophagy mutant flies show accumulation of ubiquitin- and Ref(2)P-positive protein aggregates, this is abrogated in atg8a/ref(2)P double mutants. Both the multimerization and ubiquitin binding domains of Ref(2)P are required for aggregate formation in vivo. Our findings reveal a major role for Ref(2)P in the formation of ubiquitin-positive protein aggregates both under physiological conditions and when normal protein turnover is inhibited.

The host defense of Drosophila melanogaster

To combat infection, the fruit fly Drosophila melanogaster relies on multiple innate defense reactions, many of which are shared with higher organisms. These reactions include the use of physical barriers together with local and systemic immune responses. First, epithelia, such as those beneath the cuticle, in the alimentary tract, and in tracheae, act both as a physical barrier and local defense against pathogens by producing antimicrobial peptides and reactive oxygen species. Second, specialized hemocytes participate in phagocytosis and encapsulation of foreign intruders in the hemolymph. Finally, the fat body, a functional equivalent of the mammalian liver, produces humoral response molecules including antimicrobial peptides. Here we review our current knowledge of the molecular mechanisms underlying Drosophila defense reactions together with strategies evolved by pathogens to evade them.

Control of sigma virus multiplication by the ref(2)P gene of Drosophila melanogaster: an in vivo study of the PB1 domain of Ref(2)P

Ref(2)P has been described as one of the Drosophila proteins that interacts with the sigma virus cycle. We generated alleles to identify critical residues involved in the restrictive (inhibiting viral multiplication) or permissive (allowing viral multiplication) character of Ref(2)P. We demonstrate that permissive alleles increase the ability of the sigma virus to infect Drosophila when compared to null alleles and we confirm that restrictive alleles decrease this capacity. Moreover, we have created alleles unfunctional in viral cycling while functional for Ref(2)P fly functions. This type of allele had never been observed before and shows that fly- and virus-related activities of Ref(2)P are separable. The viral status of Ref(2)P variants is determined by the amino-terminal PB1 domain polymorphism. In addition, an isolated PB1 domain mimics virus-related functions even if it is similar to a loss of function toward fly-related activities. The evolutionary tree of the Ref(2)P PB1 domain that we could build on the basis of the natural allele sequences is in agreement with an evolution of PB1 domain due to successive transient selection waves.

Silencing of Toll pathway components by direct injection of double-stranded RNA into Drosophila adult flies

Double-stranded RNA (dsRNA) gene interference is an efficient method to silence gene expression in a sequence-specific manner. Here we show that the direct injection of dsRNA can be used in adult Drosophila flies to disrupt function of endogenous genes in vivo. As a proof of principle, we have used this method to silence components of a major signaling cascade, the Toll pathway, which controls fruit fly resistance to fungal and Gram-positive bacterial infections. We demonstrate that the knockout is efficient only if dsRNA is injected in 4- or more day-old flies and that it lasts for at least 1 week. Furthermore, we report dsRNA-based epistatic gene analysis via injection of a mixture of two dsRNAs and propose that injection of dsRNA represents a powerful method for rapid functional analysis of genes in Drosophila melanogaster adults, particularly of those whose mutations are lethal during development.

Drosophila: The Genetics of Innate Immune Recognition and Response

Because of the evolutionary conservation of innate mechanisms of host defense, Drosophila has emerged as an ideal animal in which to study the genetic control of immune recognition and responses. The discovery that the Toll pathway is required for defense against fungal infection in Drosophila was pivotal in studies of both mammalian and Drosophila immunity. Subsequent genetic screens in Drosophila to isolate additional mutants unable to induce humoral responses to infection have identified and ordered the function of components of two signaling cascades, the Toll and Imd pathways, that activate responses to infection. Drosophila blood cells also contribute to host defense through phagocytosis and signaling, and may carry out a form of self-nonself recognition that is independent of microbial pattern recognition. Recent work suggests that Drosophila will be a useful model for dissecting virulence mechanisms of several medically important pathogens.

Plant and animal rhabdovirus host range: a bug's view

Rhabdoviruses affect human health, terrestrial and aquatic livestock and crops. Most rhabdoviruses are transmitted by insects to their vertebrate or plant hosts. For insect transmission to occur, rhabdoviruses must negotiate barriers to acquisition, replication, movement, escape and inoculation. A better understanding of the molecular interactions of rhabdoviruses with insects will clarify the complexities of rhabdovirus infection processes and epidemiology. A unique opportunity for studying how insects become hosts and vectors of rhabdoviruses is provided by five maize-infecting rhabdoviruses that are differentially transmitted by one or more related species of two divergent homopteran families.

The Drosophila atypical protein kinase C-ref(2)p complex constitutes a conserved module for signaling in the toll pathway

Recent results showed the critical role of the mammalian p62-atypical protein kinase C (aPKC) complex in the activation of NF-kappaB in response to different stimuli. Here we demonstrate using the RNA interference technique on Schneider cells that the Drosophila aPKC (DaPKC) is required for the stimulation of the Toll-signaling pathway, which activates the NF-kappaB homologues Dif and Dorsal. However, DaPKC does not appear to be important for the other Drosophila NF-kappaB signaling cascade, which activates the NF-kappaB homologue Relish in response to lipopolysaccharides. Interestingly, DaPKC functions downstream of the nuclear translocation of Dorsal or Dif, controlling the transcriptional activity of the Drosomycin promoter. We also show that the Drosophila Ref(2)P protein is the homologue of mammalian p62 as it binds to DaPKC, its overexpression is sufficient to activate the Drosomycin but not the Attacin promoter, and its depletion severely impairs Toll signaling. Collectively, these results demonstrate the conservation of the p62-aPKC complex for the control of innate immunity signal transduction in Drosophila melanogaster.

Rapid decline of fitness in panmictic populations of Drosophila melanogaster maintained under relaxed natural selection

The parameters of the spontaneous deleterious mutation process remain poorly known, despite their importance. Here, we report the results of a mutation accumulation experiment performed on panmictic populations of Drosophila melanogaster without any genetic manipulations. Two experimental populations were kept for 30 generations under relaxed natural selection. Each generation, 100 pairs were formed randomly, and every fecund pair contributed a son and a daughter to the next generation. Comparison with two controls, one cryopreserved and the other kept as the experimental populations but with long generation time, showed that the number of surviving offspring per female declined by 0.2% and 2.0% per generation under benign and harsh, competitive conditions, respectively. Thus, the mutational pressure on fitness may be strong and depends critically on the conditions under which fitness is assayed.