Effect of C-type lectin 16 on dengue virus infection in Aedes aegypti salivary glands.

C-type lectins (CTLs) are a family of carbohydrate-binding proteins and an important component of mosquito saliva. Although CTLs play key roles in immune activation and viral pathogenesis, little is known about their role in regulating dengue virus (DENV) infection and transmission. In this study, we established a homozygous CTL16 knockout Aedes aegypti mutant line using CRISPR/Cas9 to study the interaction between CTL16 and viruses in mosquito vectors. Furthermore, mouse experiments were conducted to confirm the transmission of DENV by CTL16-/- A. aegypti mutants. We found that CTL16 was mainly expressed in the medial lobe of the salivary glands (SGs) in female A. aegypti. CTL16 knockout increased DENV replication and accumulation in the SGs of female A. aegypti, suggesting that CTL16 plays an important role in DENV transmission. We also found a reduced expression of immunodeficiency and Janus kinase/signal transducer and activator of transcription pathway components correlated with increased DENV viral titer, infection rate, and transmission efficiency in the CTL16 mutant strain. The findings of this study provide insights not only for guiding future investigations on the influence of CTLs on immune responses in mosquitoes but also for developing novel mutants that can be used as vector control tools.

miR-277 targets the proapoptotic gene-hid to ameliorate Aß42-mediated neurodegeneration in Alzheimer's model.

Alzheimer's disease (AD), an age-related progressive neurodegenerative disorder, exhibits reduced cognitive function with no cure to date. One of the reasons for AD is the accumulation of Amyloid-beta 42 (Aß42) plaque(s) that trigger aberrant gene expression and signaling, which results in neuronal cell death by an unknown mechanism(s). Misexpression of human Aß42 in the developing retina of Drosophila exhibits AD-like neuropathology. Small non-coding RNAs, microRNAs (miRNAs), post-transcriptionally regulate the expression of their target genes and thereby regulate different signaling pathways. In a forward genetic screen, we identified miR-277 (human ortholog is hsa-miR-3660) as a genetic modifier of Aß42-mediated neurodegeneration. Loss-of-function of miR-277 enhances the Aß42-mediated neurodegeneration. Whereas gain-of-function of miR-277 in the GMR > Aß42 background downregulates cell death to maintain the number of neurons and thereby restores the retinal axonal targeting defects indicating the functional rescue. In addition, gain-of-function of miR-277 rescues the eclosion- and climbing assays defects observed in GMR > Aß42 background. Thus, gain-of-function of miR-277 rescues both structurally as well as functionally the Aß42-mediated neurodegeneration. Furthermore, we identified head involution defective (hid), an evolutionarily conserved proapoptotic gene, as one of the targets of miR-277 and validated these results using luciferase- and qPCR -assays. In the GMR > Aß42 background, the gain-of-function of miR-277 results in the reduction of hid transcript levels to one-third of its levels as compared to GMR > Aß42 background alone. Here, we provide a novel molecular mechanism where miR-277 targets and downregulates proapoptotic gene, hid, transcript levels to rescue Aß42-mediated neurodegeneration by blocking cell death. These studies shed light on molecular mechanism(s) that mediate cell death response following Aß42 accumulation seen in neurodegenerative disorders in humans and provide new therapeutic targets for neurodegeneration.

Transgenic refractory Aedes aegypti lines are resistant to multiple serotypes of dengue virus.

The areas where dengue virus (DENV) is endemic have expanded rapidly, driven in part by the global spread of Aedes species, which act as disease vectors. DENV replicates in the mosquito midgut and is disseminated to the mosquito's salivary glands for amplification. Thus, blocking virus infection or replication in the tissues of the mosquito may be a viable strategy for reducing the incidence of DENV transmission to humans. Here we used the mariner Mos1 transposase to create an Aedes aegypti line that expresses virus-specific miRNA hairpins capable of blocking DENV replication. These microRNA are driven by the blood-meal-inducible carboxypeptidase A promoter or by the polyubiquitin promoter. The transgenic mosquitoes exhibited significantly lower infection rates and viral titers for most DENV serotypes 7 days after receiving an infectious blood meal. The treatment was also effective at day 14 post infection after a second blood meal had been administered. In viral transmission assay, we found there was significantly reduced transmission in these lines. These transgenic mosquitoes were effective in silencing most of the DENV genome; such an approach may be employed to control a dengue fever epidemic.

Assessing the cognitive status of Drosophila by the value-based feeding decision.

Decision-making is considered an important aspect of cognitive function. Impaired decision-making is a consequence of cognitive decline caused by various physiological conditions, such as aging and neurodegenerative diseases. Here we exploited the value-based feeding decision (VBFD) assay, which is a simple sensory-motor task, to determine the cognitive status of Drosophila. Our results indicated the deterioration of VBFD is notably correlated with aging and neurodegenerative disorders. Restriction of the mushroom body (MB) neuronal activity partly blunted the proper VBFD. Furthermore, using the Drosophila polyQ disease model, we demonstrated the impaired VBFD is ameliorated by the dinitrosyl iron complex (DNIC-1), a novel and steady nitric oxide (NO)-releasing compound. Therefore we propose that the VBFD assay provides a robust assessment of Drosophila cognition and can be used to characterize additional neuroprotective interventions.

Loss of Fis1 impairs proteostasis during skeletal muscle aging in Drosophila.

Increased levels of dysfunctional mitochondria within skeletal muscle are correlated with numerous age-related physiopathological conditions. Improving our understanding of the links between mitochondrial function and muscle proteostasis, and the role played by individual genes and regulatory networks, is essential to develop treatments for these conditions. One potential player is the mitochondrial outer membrane protein Fis1, a crucial fission factor heavily involved in mitochondrial dynamics in yeast but with an unknown role in higher-order organisms. By using Drosophila melanogaster as a model, we explored the effect of Fis1 mutations generated by transposon Minos-mediated integration. Mutants exhibited a higher ratio of damaged mitochondria with age as well as elevated reactive oxygen species levels compared with controls. This caused an increase in oxidative stress, resulting in large accumulations of ubiquitinated proteins, accelerated muscle function decline, and mitochondrial myopathies in young mutant flies. Ectopic expression of Fis1 isoforms was sufficient to suppress this phenotype. Loss of Fis1 led to unbalanced mitochondrial proteostasis within fly muscle, decreasing both flight capabilities and lifespan. Fis1 thus clearly plays a role in fly mitochondrial dynamics. Further investigations into the detailed function of Fis1 are necessary for exploring how mitochondrial function correlates with muscle health during aging.

A Thioester-Containing Protein Controls Dengue Virus Infection in Aedes aegypti Through Modulating Immune Response.

Complement-like proteins in arthropods defend against invading pathogens in the early phases of infection. Thioester-containing proteins (TEPs), which exhibit high similarity to mammalian complement C3, are thought to play a key role in the innate immunity of arthropods. We identified and characterized anti-dengue virus (DENV) host factors, in particular complement-like proteins, in the mosquito Aedes aegypti. Our results indicate that TEP1 limits DENV infection in Ae. aegypti. We showed that TEP1 transcription is highly induced in mosquitoes following DENV infection. Silencing TEP1 resulted in the up-regulation of viral RNA and proteins. In addition, the production of infectious virus particles increased in the absence of TEP1. We generated a transgenic mosquito line with a TEP1 loss-of-function phenotype under a blood meal-inducible promoter. We showed that viral protein and titers increased in transgenic mosquitoes after an infectious blood meal. Interestingly, expression of transcription factor Rel2 and certain anti-microbial peptides (AMPs) were inhibited in transgenic mosquitoes. Overall, our results suggest that TEP1 regulates the immune response and consequently controls the replication of dengue virus in mosquitoes. This finding provides new insight into the molecular mechanisms of mosquito host factors in the regulation of DENV replication.

Generating mutant Aedes aegypti mosquitoes using the CRISPR/Cas9 system.

Implementation of CRISPR/Cas9 methodologies for mosquito gene editing has not yet become widespread. This protocol details the procedure for Aedes aegypti mosquito gene editing using homology-directed repair and fluorescent marker insertion, which facilitates the generation and screening of mutant mosquito lines for gene function testing. We describe optimized methods for single guide RNA plasmid preparation, homologous recombination donor plasmid construction, embryo microinjection, and precise gene knock-in confirmation. We also provide general guidance for establishing mutant mosquito lines. For details on the practical use and execution of this protocol, please refer to Li et al. (2020).

Transgenic Expression of Human C-Type Lectin Protein CLEC18A Reduces Dengue Virus Type 2 Infectivity in Aedes aegypti.

The C-type lectins, one family of lectins featuring carbohydrate binding domains which participate in a variety of bioprocesses in both humans and mosquitoes, including immune response, are known to target DENV. A human C-type lectin protein CLEC18A in particular shows extensive glycan binding abilities and correlates with type-I interferon expression, making CLEC18A a potential player in innate immune responses to DENV infection; this potential may provide additional regulatory point in improving mosquito immunity. Here, we established for the first time a transgenic Aedes aegypti line that expresses human CLEC18A. This expression enhanced the Toll immune pathway responses to DENV infection. Furthermore, viral genome and virus titers were reduced by 70% in the midgut of transgenic mosquitoes. We found significant changes in the composition of the midgut microbiome in CLEC18A expressing mosquitoes, which may result from the Toll pathway enhancement and contribute to DENV inhibition. Transgenic mosquito lines offer a compelling option for studying DENV pathogenesis, and our analyses indicate that modifying the mosquito immune system via expression of a human immune gene can significantly reduce DENV infection.

femaleless Controls Sex Determination and Dosage Compensation Pathways in Females of Anopheles Mosquitoes.

The insect sex determination and the intimately linked dosage compensation pathways represent a challenging evolutionary puzzle that has been solved only in Drosophila melanogaster. Analyses of orthologs of the Drosophila genes identified in non-drosophilid taxa1,2 revealed that evolution of sex determination pathways is consistent with a bottom-up mode,3 where only the terminal genes within the pathway are well conserved. doublesex (dsx), occupying a bottom-most position and encoding sex-specific proteins orchestrating downstream sexual differentiation processes, is an ancient sex-determining gene present in all studied species.2,4,5 With the exception of lepidopterans, its female-specific splicing is known to be regulated by transformer (tra) and its co-factor transformer-2 (tra2).6-20 Here we show that in the African malaria mosquito Anopheles gambiae, a gene, which likely arose in the Anopheles lineage and which we call femaleless (fle), controls sex determination in females by regulating splicing of dsx and fruitless (fru; another terminal gene within a branch of the sex determination pathway). Moreover, fle represents a novel molecular link between the sex determination and dosage compensation pathways. It is necessary to suppress activation of dosage compensation in females, as demonstrated by the significant upregulation of the female X chromosome genes and a correlated female-specific lethality, but no negative effect on males, in response to fle knockdown. This unexpected property, combined with a high level of conservation in sequence and function in anopheline mosquitoes, makes fle an excellent target for genetic control of all major vectors of human malaria.

C-Type Lectins Link Immunological and Reproductive Processes in Aedes aegypti.

Physiological trade-offs between mosquito immune response and reproductive capability can arise due to insufficient resource availability. C-type lectin family members may be involved in these processes. We established a GCTL-3-/- mutant Aedes aegypti using CRISPR/Cas9 to investigate the role of GCTL-3 in balancing the costs associated with immune responses to arboviral infection and reproduction. GCTL-3-/- mutants showed significantly reduced DENV-2 infection rate and gut commensal microbiota populations, as well as upregulated JAK/STAT, IMD, Toll, and AMPs immunological pathways. Mutants also had significantly shorter lifespans than controls and laid fewer eggs due to defective germ line development. dsRNA knock-down of Attacin and Gambicin, two targets of the AMPs pathway, partially rescued this reduction in reproductive capabilities. Upregulation of immune response following GCTL-3 knock-out therefore comes at a cost to reproductive fitness. Knock-out of other lectins may further improve our knowledge of the molecular and genetic mechanisms underlying reproduction-immunity trade-offs in mosquitoes.

Loss of the Drosophila branched-chain α-ketoacid dehydrogenase complex results in neuronal dysfunction.

Maple syrup urine disease (MSUD) is an inherited error in the metabolism of branched-chain amino acids (BCAAs) caused by a severe deficiency of the branched-chain α-ketoacid dehydrogenase (BCKDH) complex, which ultimately leads to neurological disorders. The limited therapies, including protein-restricted diets and liver transplants, are not as effective as they could be for the treatment of MSUD due to the current lack of molecular insights into the disease pathogenesis. To address this issue, we developed a Drosophila model of MSUD by knocking out the dDBT gene, an ortholog of the human gene encoding the dihydrolipoamide branched chain transacylase (DBT) subunit of BCKDH. The homozygous dDBT mutant larvae recapitulate an array of MSUD phenotypes, including aberrant BCAA accumulation, developmental defects, poor mobile behavior and disrupted L-glutamate homeostasis. Moreover, the dDBT mutation causes neuronal apoptosis during the developmental progression of larval brains. The genetic and functional evidence generated by in vivo depletion of dDBT expression in the eye indicates severe impairment of retinal rhabdomeres. Further, the dDBT mutant shows elevated oxidative stress and higher lipid peroxidation accumulation in the larval brain. Therefore, we conclude from in vivo evidence that the loss of dDBT results in oxidative brain damage that may lead to neuronal cell death and contribute to aspects of MSUD pathology. Importantly, when the dDBT mutants were administrated with Metformin, the aberrances in BCAA levels and motor behavior were ameliorated. This intriguing outcome strongly merits the use of the dDBT mutant as a platform for developing MSUD therapies.This article has an associated First Person interview with the joint first authors of the paper.

Vesicular transport mediates the uptake of cytoplasmic proteins into mitochondria in Drosophila melanogaster.

Mitochondrial aging, which results in mitochondrial dysfunction, is strongly linked to many age-related diseases. Aging is associated with mitochondrial enlargement and transport of cytosolic proteins into mitochondria. The underlying homeostatic mechanisms that regulate mitochondrial morphology and function, and their breakdown during aging, remain unclear. Here, we identify a mitochondrial protein trafficking pathway in Drosophila melanogaster involving the mitochondria-associated protein Dosmit. Dosmit induces mitochondrial enlargement and the formation of double-membraned vesicles containing cytosolic protein within mitochondria. The rate of vesicle formation increases with age. Vesicles originate from the outer mitochondrial membrane as observed by tracking Tom20 localization, and the process is mediated by the mitochondria-associated Rab32 protein. Dosmit expression level is closely linked to the rate of ubiquitinated protein aggregation, which are themselves associated with age-related diseases. The mitochondrial protein trafficking route mediated by Dosmit offers a promising target for future age-related mitochondrial disease therapies.

Visualization of Endogenous Type I TGF-ß Receptor Baboon in the Drosophila Brain.

The transforming growth factor ß (TGF-ß) signaling pathway is evolutionarily conserved and widely used in the animal kingdom to regulate diverse developmental processes. Prior studies have shown that Baboon (Babo), a Drosophila type I TGF-ß receptor, plays essential roles in brain development and neural circuit formation. However, the expression pattern for Babo in the developing brain has not been previously reported. We generated a knock-in fly with a human influenza hemagglutinin (HA) tag at the C-terminus of Babo and assessed its localization. Babo::HA was primarily expressed in brain structures enriched with neurites, including the mushroom body lobe and neuropils of the optic lobe, where Babo has been shown to instruct neuronal morphogenesis. Since the babo 3' untranslated region contains a predicted microRNA-34 (miR-34) target sequence, we further tested whether Babo::HA expression was affected by modulating the level of miR-34. We found that Babo was upregulated by mir-34 deletion and downregulated by miR-34 overexpression, confirming that it is indeed a miR-34 target gene. Taken together, our results demonstrate that the baboHA fly permits accurate visualization of endogenous Babo expression during brain development and the construction of functional neural circuits.

Chchd2 regulates mitochondrial morphology by modulating the levels of Opa1.

The mitochondrion is a highly dynamic organelle that is critical for energy production and numerous metabolic processes. Drosophila Chchd2, a homolog of the human disease-related genes CHCHD2 and CHCHD10, encodes a mitochondrial protein. In this study, we found that loss of Chchd2 in flies resulted in progressive degeneration of photoreceptor cells and reduced muscle integrity. In the flight muscles of adult Chchd2 mutants, some mitochondria exhibited curling cristae and a reduced number of cristae compared to those of controls. Overexpression of Chchd2 carrying human disease-related point mutations failed to fully rescue the mitochondrial defects in Chchd2 mutants. In fat body cells, loss of Chchd2 resulted in fragmented mitochondria that could be partially rescued by Marf overexpression and enhanced by Opa1 RNAi. The expression level of Opa1 was reduced in Chchd2 mutants and increased when Chchd2 was overexpressed. The chaperone-like protein P32 co-immunoprecipitated with Chchd2 and YME1L, a protease known to processes human OPA1. Moreover, the interaction between P32 and YME1L enhanced YME1L activity and promoted Opa1 degradation. Finally, Chchd2 stabilized Opa1 by competing with P32 for YME1L binding. We propose a model whereby Chchd2 regulates mitochondrial morphology and tissue homeostasis by fine-tuning the levels of OPA1.

Glia-derived exosomal miR-274 targets Sprouty in trachea and synaptic boutons to modulate growth and responses to hypoxia.

Secreted exosomal microRNAs (miRNAs) mediate interorgan/tissue communications by modulating target gene expression, thereby regulating developmental and physiological functions. However, the source, route, and function in target cells have not been formally established for specific miRNAs. Here, we show that glial miR-274 non-cell-autonomously modulates the growth of synaptic boutons and tracheal branches. Whereas the precursor form of miR-274 is expressed in glia, the mature form of miR-274 distributes broadly, including in synaptic boutons, muscle cells, and tracheal cells. Mature miR-274 is secreted from glia to the circulating hemolymph as an exosomal cargo, a process requiring ESCRT components in exosome biogenesis and Rab11 and Syx1A in exosome release. We further show that miR-274 can function in the neurons or tracheal cells to modulate the growth of synaptic boutons and tracheal branches, respectively. Also, miR-274 uptake into the target cells by AP-2-dependent mechanisms modulates target cell growth. In the target cells, miR-274 down-regulates Sprouty (Sty) through a targeting sequence at the sty 3' untranslated region, thereby enhancing MAPK signaling and promoting cell growth. miR-274 expressed in glia of an mir-274 null mutant is released as an exosomal cargo in the circulating hemolymph, and such glial-specific expression resets normal levels of Sty and MAPK signaling and modulates target cell growth. mir-274 mutant larvae are hypersensitive to hypoxia, which is suppressed by miR-274 expression in glia or by increasing tracheal branches. Thus, glia-derived miR-274 coordinates growth of synaptic boutons and tracheal branches to modulate larval hypoxia responses.

Synthetic miRNAs induce dual arboviral-resistance phenotypes in the vector mosquito Aedes aegypti.

Mosquito-borne arboviruses are responsible for recent dengue, chikungunya, and Zika pandemics. The yellow-fever mosquito, Aedes aegypti, plays an important role in the transmission of all three viruses. We developed a miRNA-based approach that results in a dual resistance phenotype in mosquitoes to dengue serotype 3 (DENV-3) and chikungunya (CHIKV) viruses. The target viruses are from two distinct arboviral families and the antiviral mechanism is designed to function through the endogenous miRNA pathway in infected mosquitoes. Challenge experiments showed reductions in viral transmission efficiency of transgenic mosquitoes. Several components of mosquito fitness were examined, and transgenic mosquitoes with the PUb promoter showed minor fitness costs at all developing stages. Further development of these strains with gene editing tools could make them candidates for releases in population replacement strategies for sustainable control of multiple arbovirus diseases.

Distinct multilevel misregulations of Parkin and PINK1 revealed in cell and animal models of TDP-43 proteinopathy.

Parkin and PINK1 play an important role in mitochondrial quality control, whose malfunction may also be involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). Excessive TDP-43 accumulation is a pathological hallmark of ALS and is associated with Parkin protein reduction in spinal cord neurons from sporadic ALS patients. In this study, we reveal that Parkin and PINK1 are differentially misregulated in TDP-43 proteinopathy at RNA and protein levels. Using knock-in flies, mouse primary neurons, and TDP-43Q331K transgenic mice, we further unveil that TDP-43 downregulates Parkin mRNA, which involves an unidentified, intron-independent mechanism and requires the RNA-binding and the protein-protein interaction functions of TDP-43. Unlike Parkin, TDP-43 does not regulate PINK1 at an RNA level. Instead, excess of TDP-43 causes cytosolic accumulation of cleaved PINK1 due to impaired proteasomal activity, leading to compromised mitochondrial functions. Consistent with the alterations at the molecular and cellular levels, we show that transgenic upregulation of Parkin but downregulation of PINK1 suppresses TDP-43-induced degenerative phenotypes in a Drosophila model of ALS. Together, these findings highlight the challenge associated with the heterogeneity and complexity of ALS pathogenesis, while pointing to Parkin-PINK1 as a common pathway that may be differentially misregulated in TDP-43 proteinopathy.

Drosophila microRNA-34 Impairs Axon Pruning of Mushroom Body γ Neurons by Downregulating the Expression of Ecdysone Receptor.

MicroRNA-34 (miR-34) is crucial for preventing chronic large-scale neurite degeneration in the aged brain of Drosophila melanogaster. Here we investigated the role of miR-34 in two other types of large-scale axon degeneration in Drosophila: axotomy-induced axon degeneration in olfactory sensory neurons (OSNs) and developmentally related axon pruning in mushroom body (MB) neurons. Ectopically overexpressed miR-34 did not inhibit axon degeneration in OSNs following axotomy, whereas ectopically overexpressed miR-34 in differentiated MB neurons impaired γ axon pruning. Intriguingly, the miR-34-induced γ axon pruning defect resulted from downregulating the expression of ecdysone receptor B1 (EcR-B1) in differentiated MB γ neurons. Notably, the separate overexpression of EcR-B1 or a transforming growth factor- ß receptor Baboon, whose activation can upregulate the EcR-B1 expression, in MB neurons rescued the miR-34-induced γ axon pruning phenotype. Future investigations of miR-34 targets that regulate the expression of EcR-B1 in MB γ neurons are warranted to elucidate pathways that regulate axon pruning, and to provide insight into mechanisms that control large-scale axon degeneration in the nervous system.

Selective Retention of an Inactive Allele of the DKK2 Tumor Suppressor Gene in Hepatocellular Carcinoma.

In an effort to identify the functional alleles associated with hepatocellular carcinoma (HCC), we investigated 152 genes found in the 4q21-25 region that exhibited loss of heterozygosity (LOH). A total of 2,293 pairs of primers were designed for 1,449 exonic and upstream promoter regions to amplify and sequence 76.8-114 Mb on human chromosome 4. Based on the results from analyzing 12 HCC patients and 12 healthy human controls, we discovered 1,574 sequence variations. Among the 99 variants associated with HCC (p < 0.05), four are from the Dickkopf 2 (DKK2) gene: three in the promoter region (g.-967A>T, g.-923C>A, and g.-441T>G) and one in the 5'UTR (c.550T>C). To verify the results, we expanded the subject cohort to 47 HCC cases and 88 healthy controls for conducting haplotype analysis. Eight haplotypes were detected in the non-tumor liver tissue samples, but one major haplotype (TAGC) was found in the tumor tissue samples. Using a reporter assay, this HCC-associated allele registered the lowest level of promoter activity among all the tested haplotype sequences. Retention of this allele in LOH was associated with reduced DKK2 transcription in the HCC tumor tissues. In HuH-7 cells, DKK2 functioned in the Wnt/ß-catenin signaling pathway, as an antagonist of Wnt3a, in a dose-dependent manner that inhibited Wnt3a-induced cell proliferation. Taken together, the genotyping and functional findings are consistent with the hypothesis that DKK2 is a tumor suppressor; by selectively retaining a transcriptionally inactive DKK2 allele, the reduction of DKK2 function results in unchecked Wnt/ß-catenin signaling, contributing to HCC oncogenesis. Thus our study reveals a new mechanism through which a tumor suppressor gene in a LOH region loses its function by allelic selection.