Biology subjects

Hanson, M. A.

Publications and source records attributed to Hanson, M. A..

At least 19 recordsLinked to original sources

bioRxiv2026

Horizontal transfer of an antimicrobial peptide across insects

Antimicrobial peptides (AMPs) are key defence molecules of the innate immune system of plants and animals. Understanding the evolutionary origins of AMPs can help to explain how immune systems acquire novelty and vary in their defensive capabilities. However, AMPs evolve rapidly, and so the origins of similar AMPs across organisms is often unclear. Furthermore, false negatives due to low search sensitivity are common and can hinder confident annotations about true absences. Due to these difficulties, understanding whether similar AMP genes found in diverse organisms represent ancestral molecules or evolutionary novelties has been challenging. In this report, we present evidence of horizontal gene transfer (HGT) of the antifungal peptide gene Drosomycin across insects. We show that in Diptera, the presence of Drosomycin is restricted to the Melanogaster group and additionally the distant relative Drosophila busckii. We go on to recover Drosomycin genes in cockroaches (Blattodea), mantises (Mantodea), one katydid (Orthoptera), various beetles (Coleoptera), and a recently acquired pseudogenized Drosomycin locus in Liposcelis booklice (Psocodea), but no other insects. Explaining this diversity through shared ancestry requires at least 50 independent loss events, or just seven HGT events. Previous studies have suggested that similar AMPs found across divergent species reflect conservation from a common ancestor, or due to their small size, that they arose via convergent evolution resulting from pathogen-imposed selection. Our findings suggest horizontal gene transfer can be responsible for the presence of some AMP genes found scattered across the tree of life. By presenting a mechanism through which immune systems can acquire novelty, our study also suggests a possible explanation for certain lineage-specific competencies for defence against infectious disease. While loss of AMP genes is common in certain lineages, here we suggest gain of AMPs can occur just as suddenly.

evolutionary biology↗

bioRxiv2025

Life history and infection susceptibility parameters of Drosophila species reared on a common diet

The fruit fly Drosophila is a powerful model organism for many biological questions. While Drosophila melanogaster has been the most widely used species owing to its versatile genetic tools, comparative studies also take advantage of the rich evolutionary, ecological, and behavioural diversity of Drosophilidae. This model system has only benefitted from the sequencing of hundreds of genomes assembled to chromosome level, and rich array of publicly-available datasets. However, labs that typically use just D. melanogaster can have difficulties adopting other species into their experiments due to unique dietary needs and care regimens. While dedicated research groups can rear dozens of fly species, this often requires preparing a variety of food media, which can be logistically taxing. In this study, we report an agar food recipe that we have used to rear >70 species of Drosophilidae (Prop recipe). This list includes ecological specialists such as D. sechellia, major pest species including D. suzukii, cactophiles, slime flux feeders, detritivores, and even mushroom-feeding species of the Quinaria and Testacea groups. This food recipe uses only standard powdered ingredients and molasses, and is already in use by one commercial transgenic injection provider. We provide life history parameters for dozens of species reared on this recipe, including comparisons in a subset of species across a variety of diets, finding fly fitness to be comparable or better on the Prop recipe among tested species. We further provide comparative data for 42 species after systemic infection by Acetobacter bacteria. However, unexpectedly, we found a striking interaction of diet and the microbiota that impacts susceptibility to infection in species-specific fashion. Our results suggest certain experiment types may be impacted by diet due to the microbiome that the diet itself supports. By providing rearing advice, life history parameters, and this infection dataset and experience, we hope to enable researchers to take advantage of the diversity of Drosophila as a model system for evolutionary research.

evolutionary biology↗

bioRxiv2025

Plant coumarins enhance viral pathogenicity by miRNA-mediated apoptosis in insect herbivores

Plant secondary metabolites (PSM) influence the susceptibility of insect herbivores to entomoviruses, but the apoptosis mechanism is not clear. Among plant hosts screened, the level of coumarin is correlated with NPV-mediated mortality, with high coumarin levels associated with high mortality and low coumarin levels with low mortality. Flow cytometry and morphological experiments showed that coumarins increased the apoptosis rate in NPV-infected larvae. miRNA transcriptomic analysis of coumarin-exposed larvae identified downregulation of miR-8 and miR-6497-3p, which negatively correlate with expression of pro-apoptotic kinases MAPK and ASK1. In addition, miR-9c-5p is upregulated, suppressing the apoptosis inhibitor 14-3-3 protein zeta. Our study suggests plant coumarins increase the susceptibility of larvae to NPV through miRNA-mediated regulation of apoptotic pathways. These findings suggest viral biocontrol efforts may be more successful on certain host plants, and provide molecular insight into how plant defense chemicals synergize with entomoviruses to control agricultural pests.

ecology↗

bioRxiv2025

Drosophila host defense mechanisms against filamentous fungal pathogens with diverse lifestyles

Entomopathogenic fungi serve as powerful regulators of insect populations in nature. However, how immune effectors combat fungal pathogens remains incompletely understood. We employ Drosophila melanogaster as a genetically tractable model to dissect immune defense mechanisms against diverse fungal pathogens. We show that the Toll pathway is the key determinant of immunity against all species tested regardless of their ecological strategy, primarily through resistance mechanisms that limit fungal proliferation. In addition, melanization, but not phagocytosis or the Imd pathway, also has a role in limiting fungal entry and proliferation. Additionally, we show that fungal protease detection by Persephone has a quantitatively more critical role than the glucan sensor GNBP3 in the activation of the Toll pathway upon fungal infection. Our study also reveals that the fly-obligate fungus Entomophthora muscae employs a vegetative development strategy to hide from the host immune response. These findings reveal that Drosophila immune mechanisms effectively defend against a broad range of fungal pathogens, while highlighting striking adaptations to overcome these defenses in highly specialized fungal pathogens such as E. muscae.

immunology↗

bioRxiv2025

Reproducibility of Scientific Claims in Drosophila Immunity: A Retrospective Analysis of 400 Publications

Drosophila immunity has been the focus of intense study and has impacted other research fields including innate immunity and agriculturally or epidemiologically relevant investigations of insect pests and vectors. Unsurprisingly for such a large body of work, some published results were later found to be irreplicable. Although some results have been contradicted in the literature, many have no published follow-up, either due to a lack of research or low motivation to publish negative or contradictory results. We have addressed this by performing a reproducibility project that analyses the conceptual replicability of claims from articles published on Drosophila immunity before 2011. To assess replicability, we extracted claims from 400 articles on the Drosophila immune response to bacteria and fungi and performed preliminary verification by comparing these claims to other published literature in the field. Using alternative approaches, we also experimentally tested some unchallenged claims, with no published follow-up. The intent of this analysis was to centralize evidence on insights and findings to improve clarity for scientists that may base research programs on these data. Although the aim of the ReproSci project is to assess the replicability of claims made in articles published in the field of Drosophila immunity, it is in no way an assessment of the scientific value of the research. All our data are published on a publicly available website associated with this article (https://ReproSci.epfl.ch/) that encourages community participation. This article provides a short summary of claims that were found to have contradictory evidence, which may help the community to assess past findings on Drosophila immunity and improve clarity going forward. Statistical analysis of this reproducibility study and metascience insights obtained from this approach are discussed in a companion article.

genetics↗

bioRxiv2025

A retrospective analysis of 400 publications reveals patterns of irreproducibility across an entire life sciences research field

The ReproSci project retrospectively analyzed the conceptual replicability of 1006 claims from 400 papers published between 1959 and 2011 in the field of Drosophila immunity. This project attempts to provide a comprehensive assessment, 14 years later, of the replicability of nearly all publications across an entire scientific community in experimental life sciences. We found that 61% of claims were verified, while only 7% were directly challenged (not replicable), a replicability rate higher than previous assessments. Notably, 24% of claims had never been independently tested and remain unchallenged. We performed experimental validations of a selection of 45 unchallenged claim, that revealed that a significant fraction (38/45) of them is in fact non-replicable. We also found that high-impact journals and top-ranked institutions are more likely to publish challenged claims. In line with the reproducibility crisis narrative, the rates of both challenged and unchallenged claims increased over time, especially as the field gained popularity. We characterized the uneven distribution of irreplicability among first and last authors. Surprisingly, irreplicability rates were similar between PhD students and postdocs, and did not decrease with experience or publication count. However, group leaders, who had prior experience as first authors in another Drosophila immunity team, had lower irreplicability rates, underscoring the importance of early-career training. Finally, authors with a more exploratory, short-term engagement with the field exhibited slightly higher rates of challenged claims and a markedly higher proportion of unchallenged ones. While limited by its reliance on published literature, this systematic, field-wide retrospective study offers meaningful perspective into the ongoing discussion on reproducibility in experimental life sciences.

scientific communication and education↗

bioRxiv2025

Dendrite-targeting inhibitory interneurons form biased circuits with deep and superficial pyramidal cells in hippocampal CA1

In CA1 hippocampus, pyramidal cells (PCs) can be classified as deep or superficial based on their radial position within the stratum pyramidale. Deep and superficial PCs form biased circuits with perisomatic-targeting PV+ basket cells, but it is unknown if such cell-type-specific circuit motifs extend to dendrite-targeting interneurons. Using male and female mice, we investigated synaptic connectivity and physiology in brain slices from four transgenic lines thought to capture distinct subsets of interneurons: SST-IRES-Cre, Nkx2.1-Cre, Chrna2-Cre, and Htr3a-GFP. First, we found that oriens-lacunosum moleculare (OLM) cells captured by the Chrna2-Cre line are a subset of Htr3a-GFP+ cells in the hippocampus. This novel finding is consistent with previous work showing Nkx2.1-Cre OLM cells are distinct from both Chrna2-Cre and Htr3a-GFP+ cells. Indeed, in paired whole-cell recordings, Nkx2.1-Cre+ interneurons in the stratum oriens, but not Chrna2-Cre+ or Htr3a-GFP+ cells, received more excitatory synaptic connections from superficial PCs relative to deep PCs. Next, we used optogenetic-assisted circuit mapping to investigate inhibition along the proximal and distal dendrites of PCs. We found that superficial PCs received stronger inhibition along their proximal dendrites than deep PCs from SST+ interneurons. Furthermore, this circuit motif was dependent on layer but not PC projection class. Finally, Chrna2-Cre OLM cells provided stronger inhibition to the distal dendrites of deep PCs relative to superficial PCs. Our data reveal that superficial and deep PCs engage in cell-type-specific circuits with dendrite-targeting interneurons. Furthermore, they support that Nkx2.1-Cre OLM cells and Chrna2-Cre/Htr3a-GFP OLM cells are distinct subtypes that form unique circuits in CA1.

neuroscience↗

bioRxiv2025

Functional Characterization of Paillotin: An Immune Peptide Regulated by the Imd Pathway with Pathogen-Specific Roles in Drosophila Immunity

Insects, such as Drosophila melanogaster, rely on innate immune defenses to combat microbial threats. Antimicrobial peptides (AMPs) play an important role in limiting pathogen entry and colonization. Despite intensive research into the regulation and biochemical properties of AMPs, their exact significance in vivo has remained uncertain due to the challenges of mutating small genes. Fortunately, recent technologies have enabled the mutation of individual AMP genes, overcome previous obstacles, and opened new avenues for research. In this study, we characterized one novel host-defense peptide, Paillotin (IM18, CG33706), using loss-of-function mutants. Paillotin is an ancient host defense peptide of Diptera, regulated by the Imd pathway. Loss of Paillotin does not impact the activity of either the Imd or Toll pathways. Importantly, we found that Paillotin mutants are viable but exhibit increased susceptibility to specific infections, particularly Providencia burhodogranariea. Paillotin was further found to contribute synergistically to defense against P. burhodogranariea when combined with other AMPs. However, we did not detect direct microbicidal activity of Paillotin in vitro in our hands. Taken together, our findings identify Paillotin as a novel host defense peptide acting downstream of Imd signaling, advancing our understanding of the Drosophila antimicrobial response.

immunology↗

bioRxiv2025

Layers of immunity: Deconstructing the Drosophila effector response

The host innate immune response relies on the cooperation of multiple defence modules. In insects and other arthropods, which have only innate immune mechanisms, four main immune-specific modules have been described in the defence against microbial invaders: the Toll pathway, the Imd pathway, the melanization response, and phagocytosis by plasmatocytes. Our present understanding of their relative importance remains fragmented as their contribution to host defence has never been simultaneously assessed across a large panel of pathogens. Here, we have taken advantage of newly-described immune mutants in a controlled genetic background to systematically delete these four immune modules individually, in pairs, or even all four simultaneously. Surprisingly, immune deficient flies simultaneously deficient in all four immune modules are viable, homozygous fertile, and display no overt morphological defects, suggesting these immune mechanisms are not strictly required for organismal development. With this new set of lines, we assessed the contribution of each module individually and collectively to host defense against five viruses, three fungi, eight Gram-positive bacteria, and eight Gram-negative bacteria. Our findings show that these four modules largely function independently and additively in host defense, although synergistic effects can occur for select pairs of modules. Our study confirmed the importance of the Imd pathway against Gram-negative bacteria and the Toll pathway against Gram-positive bacteria and fungi, largely via the induction of effectors such as antimicrobial peptides (AMPs) and Bomanins (Bom), but also reveals the important role of melanization against viruses, and the contribution of phagocytosis against various germs. Additionally, by examining microbial load kinetics in different mutants, we provide insight into how these modules contribute to tolerance or resistance against specific microbes. Our study provides insights into the architecture of the Drosophila immune system, revealing differential requirements of immune modules according to each pathogen. The set of immune deficient lines provided here offer tools to better assess the role of these immune modules in host defense.

immunology↗

bioRxiv2024

Arid1b haploinsufficiency in cortical inhibitory interneurons causes cell-type-dependent changes in cellular and synaptic development

Autism spectrum disorder (ASD) presents with diverse cognitive and behavioral abnormalities beginning during early development. Although the neural circuit mechanisms remain unclear, recent work suggests pathology in cortical inhibitory interneurons (INs) plays a crucial role. However, we lack fundamental information regarding changes in the physiology of synapses to and from INs in ASD. Here, we used transgenic mice to conditionally knockout one copy of the high confidence ASD risk gene Arid1b from the progenitors of parvalbumin-expressing fast-spiking (PV-FS) INs and somatostatin-expressing non-fast-spiking (SST-NFS) INs. In brain slices, we performed paired whole-cell recordings between INs and excitatory projection neurons (PNs) to investigate changes in synaptic physiology. In neonates, we found reduced synaptic input to INs but not PNs, with a concomitant reduction in the frequency of spontaneous network events, which are driven by INs in immature circuits. In mature mice, we found a reduction in the number of PV-FS INs in cortical layers 2/3 and 5. However, changes in PV-FS IN synaptic physiology were cortical layer and PN cell-type dependent. In layer 5, synapses from PV-FS INs to subcortical-projecting PNs were weakened. In contrast, in layer 2/3, synapses to and from PV-FS INs and corticocortical-projecting PNs were strengthened, leading to enhanced feedforward inhibition of input from layer 4. Finally, we found a novel synaptic deficit among SST-NFS INs, in which excitatory synapses from layer 2/3 PNs failed to facilitate. Our data highlight that changes in unitary synaptic dynamics among INs in ASD depend on neuronal cell-type.

neuroscience↗

bioRxiv2024

Arid1b haploinsufficiency in pyramidal neurons causes cellular and circuit changes in neocortex but is not sufficient to produce behavioral or seizure phenotypes

Arid1b is a high confidence risk gene for autism spectrum disorder that encodes a subunit of a chromatin remodeling complex expressed in neuronal progenitors. Haploinsufficiency causes a broad range of social, behavioral, and intellectual disability phenotypes, including Coffin-Siris syndrome. Recent work using transgenic mouse models suggests pathology is due to deficits in proliferation, survival, and synaptic development of cortical neurons. However, there is conflicting evidence regarding the relative roles of excitatory projection neurons and inhibitory interneurons in generating abnormal cognitive and behavioral phenotypes. Here, we conditionally knocked out either one or both copies of Arid1b from excitatory projection neuron progenitors and systematically investigated the effects on intrinsic membrane properties, synaptic physiology, social behavior, and seizure susceptibility. We found that disrupting Arid1b expression in excitatory neurons alters their membrane properties, including hyperpolarizing action potential threshold; however, these changes depend on neuronal subtype. Using paired whole-cell recordings, we found increased synaptic connectivity rate between projection neurons. Furthermore, we found reduced strength of excitatory synapses to parvalbumin (PV)-expression inhibitory interneurons. These data suggest an increase in the ratio of excitation to inhibition. However, the strength of inhibitory synapses from PV interneurons to excitatory neurons was enhanced, which may rebalance this ratio. Indeed, Arid1b haploinsufficiency in projection neurons was insufficient to cause social deficits and seizure phenotypes observed in a preclinical germline haploinsufficient mouse model. Our data suggest that while excitatory projection neurons likely contribute to autistic phenotypes, pathology in these cells is not the primary cause.

neuroscience↗

bioRxiv2024

Varying phylogenetic signal to four bacterial pathogens across species of Drosophilidae

Bacterial infections are one of the major sources threatening public health. Pathogen host shifts - where a pathogen jumps from one host species to another - are important sources of emerging infectious diseases. However, compared to viruses, we know relatively little about the factors that determine whether a bacteria can infect a novel host, such as how host phylogenetics constrains variation in pathogen-host range and the link between host phylogeny and the infectivity and virulence of a pathogen. Here, we experimentally examined susceptibility to bacterial infections using a panel of 36 Drosophilidae species and four pathogens (Providencia rettgeri, Pseudomonas entomophila, Enterococcus faecalis, Staphylococcus aureus). The outcomes of infection differed greatly among pathogens and across host species. The host phylogeny explains a considerable amount of variation in susceptibility, with the greatest phylogenetic signal for P. rettgeri infection, explaining 94% of the variation in mortality. Positive correlations were observed between mortality and bacterial load for three out of the four pathogens. Correlations in susceptibility between the four pathogens were positive but largely non-significant, suggesting susceptibility is mostly pathogen-specific. These results suggest that susceptibility to bacterial pathogens may be predicted by the host phylogeny, but the effect may vary in magnitude between different bacteria.

evolutionary biology↗

bioRxiv2024

Satb2 regulates pyramidal cell differentiation and the development of feedforward inhibitory circuits in CA1 hippocampus

Pyramidal cells (PCs) in CA1 hippocampus can be classified by their radial position as deep or superficial and organize into subtype-specific circuits necessary for differential information processing. Specifically, superficial PCs receive fewer inhibitory synapses from parvalbumin (PV)-expressing interneurons than deep PCs, resulting in weaker feedforward inhibition of input from CA3 Schaffer collaterals. Using mice, we investigated mechanisms underlying PC differentiation and the development of this inhibitory circuit motif. We found that expression of the transcriptional regulator SATB2 is biased towards superficial PCs during early postnatal development and necessary to suppress PV+ interneuron synapse formation. In the absence of SATB2, the number of PV+ interneuron synaptic puncta surrounding superficial PCs increases during development to match deep PCs. This results in equivalent inhibitory current strength observed in paired whole-cell recordings, and equivalent feedforward inhibition of Schaffer collateral input. Thus, SATB2 is necessary for superficial PC differentiation and biased feedforward inhibition in CA1.

neuroscience↗

bioRxiv2022

Single innate immune effectors control ecological microbiome bacteria across evolutionary timescales

Antimicrobial peptides are host-encoded immune effectors that combat pathogens and shape the microbiome in plants and animals. However, little is known about how the host antimicrobial peptide repertoire is adapted to its microbiome. Here we characterize the function and evolution of the Diptericin antimicrobial peptide family of Diptera. Using mutations affecting the two Diptericins (Dpt) of Drosophila melanogaster, we reveal the specific role of DptA for the pathogen Providencia rettgeri and DptB for the gut mutualist Acetobacter. Strikingly, presence of DptA- or DptB-like genes across Diptera correlates with the presence of Providencia and Acetobacter in their environment. Moreover, DptA- and DptB-like sequence predicts host resistance against infection by these bacteria across the genus Drosophila. Our study explains the evolutionary logic behind the bursts of rapid evolution of an antimicrobial peptide family, and reveals how the host immune repertoire adapts to changing microbial environments.

immunology↗

bioRxiv2022

Antimicrobial peptides do not directly contribute to aging in Drosophila, but improve lifespan by preventing dysbiosis

Antimicrobial peptides (AMPs) are innate immune effectors first studied for their role in host defense against bacterial and fungal infections. Recent studies have implicated these peptides in the clearance of aberrant cells and various neurological processes including neurodegenerative syndromes. In Drosophila, an array of AMPs are produced downstream of the Toll and Imd NF-{kappa}B pathways in response to infection. Many studies have suggested a role for the Imd pathway and AMPs in aging in this insect, supported by the upregulation of AMPs with aging (so-called "inflammaging"). However, functional studies using RNAi or over-expression have been inconclusive on whether and how these immune effectors impact aging. Leveraging a new set of single and compound AMP gene deletions in a controlled genetic background, we have investigated how AMPs contribute to aging. Overall, we found no major effect of individual AMPs on lifespan, with a possible exception of Defensin. However,{Delta} AMP14 flies lacking 14 AMP genes from seven families display a reduced lifespan. Interestingly, we found an increased bacterial load in the food medium of aged{Delta} AMP14 flies, suggesting that the lifespan reduction of these flies was due to a failure in controlling the microbiome. Consistent with this idea, use of germ-free conditions extends the lifespan of{Delta} AMP14 flies. Overall, our results do not point to an overt role of individual AMPs in lifespan. Instead, we find that AMPs collectively impact lifespan by preventing dysbiosis over aging. This is consistent with our previous study showing that AMPs control the gut microbiome, and many works showing that dysbiosis is detrimental upon aging. In the course of our experiments, we also uncovered a strong impact of a Drosophila nora virus infection on lifespan, and share our experience in reconciling our data given this confounding cryptic factor.

immunology↗

bioRxiv2022

Drosophila immunity: The Drosocin gene encodes two host defence peptides with pathogen-specific roles

1.1Antimicrobial peptides (AMPs) are key players in innate defence against infection in plants and animals. In Drosophila, many host defence peptides are produced downstream of the Toll and Imd NF-{kappa}B pathways. Use of single and compound AMP mutations in Drosophila has revealed that AMPs can additively or synergistically contribute to combat pathogens in vivo. However, these studies also revealed a high degree of specificity, wherein just one AMP can play a major role in combatting a specific pathogen. We recently uncovered a specific importance of the antibacterial peptide Drosocin for defence against Enterobacter cloacae. Here, we show that the Drosocin locus (CG10816) is more complex than previously described. In addition to its namesake peptide "Drosocin", it encodes a second peptide generated from a precursor via furin cleavage. We name this peptide "Buletin", and show that it corresponds to the uncharacterized "Immune-induced Molecule 7" previously identified by MALDI-TOF. The existence of a naturally occurring polymorphism (Thr52Ala) in the CG10816 precursor protein masked the identification of this peptide previously. Using mutations differently affecting the production of these two CG10816 gene products, we show that Drosocin, but not Buletin, contributes to the CG10816-mediated defence against E. cloacae. Strikingly, we observed that Buletin, but not Drosocin, contributes to the CG10816-mediated defence against Providencia burhodogranariea. Moreover, the Thr52Ala polymorphism in Buletin affects survival to P. burhodogranariea, wherein the Alanine allele confers better defence than the Threonine allele. However, we found no activity of Buletin against either P. burhodogranariea or E. coli in vitro. Collectively, our study reveals that CG10816 encodes not one but two prominent host defence peptides with different specificity against different pathogens. This finding emphasizes the complexity of the Drosophila humoral response consisting of multiple host defence peptides with specific activities, and demonstrates how natural polymorphisms found in Drosophila populations can affect host susceptibility.

immunology↗

bioRxiv2021

Cecropins contribute to Drosophila host defense against fungal and Gram-negative bacterial infection

Cecropins are small helical secreted peptides with antimicrobial activity that are widely distributed among insects. Genes encoding Cecropins are strongly induced upon infection, pointing to their role in host-defence. In Drosophila, four Cecropin genes clustered in the genome (CecA1, CecA2, CecB and CecC) are expressed upon infection downstream of the Toll and Imd pathways. In this study, we generated a short deletion{Delta} CecA-C removing the whole Cecropin locus. Using the{Delta} CecA-C deficiency alone or in combination with other antimicrobial peptide (AMP) mutations, we addressed the function of Cecropins in the systemic immune response.{Delta} CecA-C flies were viable and resisted challenge with various microbes as wild-type. However, removing{Delta} CecA-C in flies already lacking ten other AMP genes revealed a role for Cecropins in defence against Gram-negative bacteria and fungi. Measurements of pathogen loads confirm that Cecropins contribute to the control of certain Gram-negative bacteria, notably Enterobacter cloacae and Providencia heimbachae. Collectively, our work provides the first genetic demonstration of a role for Cecropins in insect host defence, and confirms their in vivo activity primarily against Gram-negative bacteria and fungi. Generation of a fly line ({Delta}AMP14) that lacks fourteen immune inducible AMPs provides a powerful tool to address the function of these immune effectors in host-pathogen interactions and beyond.

immunology↗

bioRxiv2021

Drosophila antimicrobial peptides and lysozymes regulate gut microbiota composition and abundance

The gut microbiota affects the physiology and metabolism of animals and its alteration can lead to diseases such as gut dysplasia or metabolic disorders. Several reports have shown that the immune system plays an important role in shaping both bacterial community composition and abundance in Drosophila, and that immune deficit, especially during aging, negatively affects microbiota richness and diversity. However, there has been little study at the effector level to demonstrate how immune pathways regulate the microbiota. A key set of Drosophila immune effectors are the antimicrobial peptides (AMPs), which confer defense upon systemic infection. AMPs and lysozymes, a group of digestive enzymes with antimicrobial properties, are expressed in the gut and are good candidates for microbiota regulation. Here, we take advantage of the model organism Drosophila melanogaster to investigate the role of AMPs and lysozymes in regulation of gut microbiota structure and diversity. Using flies lacking AMPs and newly generated lysozyme mutants, we colonized gnotobiotic flies with a defined set of commensal bacteria and analyzed changes in microbiota composition and abundance in vertical transmission and aging contexts through 16S rRNA gene amplicon sequencing. Our study shows that AMPs and, to a lesser extent, lysozymes are necessary to regulate the total and relative abundance of bacteria in the gut microbiota. We also decouple the direct function of AMPs from the IMD signaling pathway that regulates AMPs but also many other processes, more narrowly defining the role of these effectors in the microbial dysbiosis observed in IMD-deficient flies upon aging. ImportanceThis study advances current knowledge in the field of host-microbe interactions by demonstrating that the two families of immune effectors, antimicrobial peptides and lysozymes, actively regulate the gut microbiota composition and abundance. Consequences of the loss of these antimicrobial peptides and lysozymes are exacerbated during aging, and their loss contributes to increased microbiota abundance and shifted composition in old flies. This work shows that immune effectors, typically associated with resistance to pathogenic infections, also help shape the beneficial gut community, consistent with the idea that host-symbiont interactions use the same language typically associated with pathogenesis.

microbiology↗