Advertisement
  • Loading metrics

Drosophila as a model for homeostatic, antibacterial, and antiviral mechanisms in the gut

  • Xi Liu,

    Affiliation Cornell Institute for Host Microbe Interactions and Disease, Department of Entomology, Cornell University, Ithaca, New York, United States of America

  • Jeffrey J. Hodgson,

    Affiliations Cornell Institute for Host Microbe Interactions and Disease, Department of Entomology, Cornell University, Ithaca, New York, United States of America, Boyce Thompson Institute, Cornell University, Ithaca, New York, United States of America

  • Nicolas Buchon

    nicolas.buchon@cornell.edu

    Affiliation Cornell Institute for Host Microbe Interactions and Disease, Department of Entomology, Cornell University, Ithaca, New York, United States of America

    ORCID http://orcid.org/0000-0003-3636-8387

Drosophila as a model for homeostatic, antibacterial, and antiviral mechanisms in the gut

  • Xi Liu, 
  • Jeffrey J. Hodgson, 
  • Nicolas Buchon
PLOS
x

A conserved midgut structure from fly to human

The gastrointestinal (GI) tract serves as an active barrier and a first layer of defense against the numerous microbes that populate the gut lumen. The fly GI tract is composed of self-renewing digestive and absorptive tissues and shares several properties with the mammalian counterparts, the stomach, small intestine, and colon. The gut epithelium is physically protected by the mucus layer in mammals and by a chitinous peritrophic matrix (PM) in Drosophila [1] (Fig 1). Underneath the protective layer is an epithelial monolayer surrounded by a basal lamina and visceral muscles (Fig 1). In both Drosophila and mammals, gut tissue maintenance is extremely important to help maintain physical barrier integrity and proper immune function. The GI epithelium is continuously renewed by intestinal stem cells (ISCs). In flies, ISCs self-renew and give rise to either a transient enteroblast (EB) that terminally differentiates into an absorptive enterocyte (EC) or a pre-enteroendocrine cell that becomes a secretory enteroendocrine cell (EE) [2] (Fig 1A). Similarly, in mammals, ISCs self-renew and differentiate into intermediate cell types the transit amplifying cells, which proliferate and further differentiate into ECs or secretory cells (EEs, Goblet cells, and Tuft cells), and dedicated Paneth cell progenitors that mature into Paneth cells (Fig 1B). This striking structural similarity, the fact that several key signaling pathways involved in immunity and tissue regeneration are conserved from Drosophila to humans, and the development of cutting edge techniques, including live imaging and RNA-seq of select cell types in the midgut [3], make the Drosophila midgut an ideal model for revelatory studies of host–microbiome associations, innate immunity, tissue regeneration, and arbovirus–vector interactions.

thumbnail
Fig 1. Parallels between the Drosophila and mammalian gut epithelia.

(A) The fly midgut is composed of absorptive enterocytes (ECs) and secretory enteroendocrine cells (EEs) that arise from differentiation of the basally embedded intestinal stem cells (ISCs). Enteroblasts (EBs) are transient progenitors destined to differentiate into ECs. The epithelium is protected by the peritrophic matrix and thin mucus layer apically and is sheathed in a basal lamina and visceral muscle cells. (B) Similarly, the mammalian intestinal epithelium is composed of progenitor and Paneth cells residing at the base of crypts and absorptive cells (ECs) and secretory cells (EE and Goblet cells) that progress towards the apex of the villus. The mucus layer protects the gut epithelial cells from direct contact with commensal microbes. Hemocytes (A) or Neutrophils (B) transmit secreted signals to the gastrointestinal tract.

https://doi.org/10.1371/journal.ppat.1006277.g001

Drosophila as a model to dissect host interaction with its gut microbes

The microbial diversity in the Drosophila gut is lower compared to that of mammals. A major difference is that the Drosophila gut lumen is likely more of an aerobic environment because of its limited size, in contrast to some parts of the mammalian GI tract. Although around 30 bacterial species have been identified in the midgut of Drosophila, Acetobacter and Lactobacillus are the two genera predominantly isolated from both wild-caught and laboratory-reared flies [49]. Germ-free and derivative gnotobiotic flies (i.e., reassociated with one or more bacteria) provide a less complex approach for in-depth analyses of the impact individual microbes have on gut and/or whole fly homeostasis. For example, Acetobacter pomorum and Lactobacillus plantarum trigger the insulin and Target of Rapamycin (TOR) pathways (respectively), both of which provide growth advantages to fly larvae in limiting nutrient conditions [10,11]. Similarly, L. plantarum was found to benefit the growth of infant mice during chronic undernutrition [12]. Studies in flies have shown that the gut microbiota can also become deleterious with age. In aged flies, the load and diversity of gut microbes increase, perhaps as a consequence of immune dysregulation, and this dysbiosis impairs gut function, ultimately driving mortality [1316].

The gut microbiota has significant effects on midgut immune responses and epithelium physiology [17]. Gut microbes increase the tightly regulated basal level of NF-κB pathway-dependent immune activity, and NF-κB–induced antimicrobial peptides limit bacterial growth in a feedback loop [13,1822]. In addition, certain bacteria, including Lactobacilli, trigger production of reactive oxygen species (ROS) by the NADPH oxidases Duox and Nox [2325]. In Drosophila, ROS (1) are directly antimicrobial, (2) promote secretion of cytokines that result in para- and autocrine JAK-STAT and/or Jun N-terminal kinase (JNK) signaling [13], and (3) synergize with NF-κB–mediated responses to control microbial invaders [26]. Drosophila gut microbes also affect the cellular composition of gut epithelium [6]. Likewise, the mammalian gut microbiota has also been proposed to influence intestinal development and function [27], possibly by promoting cytokine signaling and reparative inflammation [28]. Therefore, elucidating the dialogue between Drosophila and its gut microbiota will benefit studies on gut development, homeostasis, and physiology across otherwise disparate animals.

The gut response to pathogens: From mucosal immunity to tissue repair

Bacterial pathogens are also controlled by the conjunction of physical barriers and the production of ROS and antimicrobial peptides, but the immune responses are induced to a higher level compared to that caused by the microbiota [6,29]. In mammals, intracellular intestinal pathogens such as Salmonella, Listeria, and Shigella are commonly used, while in Drosophila, most pathogens studied are extracellular gram-negative bacteria (e.g., Pectinobacteria, Pseudomonas, and Serratia). In mice, intestinal infections trigger NF-κB activation downstream of Toll-like receptors (TLRs) and Nod-like receptors (NLRs). Similarly, activation of the Immune Deficiency (Imd) pathway in Drosophila depends on both membrane-bound (PGRP-LC) and cytoplasmic (PGRP-LE) receptors [30,31]. In mice, the intestine relies on the lumenal secretion of antimicrobial peptides by Paneth cells as well as the recruitment of immune cells such as neutrophils to prevent infection [32]. Recently, a role for hemocytes, the circulating immune cells of Drosophila, has been described in controlling inflammatory signaling and intestinal regeneration in the gut [3335], suggesting that the interplay between immune cells and the gut epithelium is also conserved from flies to mammals.

Tissue repair and regeneration is integral to maintaining intestinal homeostasis in both healthy and disease states. GI recovery from microbial pathogenesis relies largely on cellular replenishment by the ISCs. As a consequence, pathogenic infection-induced ISC proliferation synergizes with oncogenic lesions to promote tumor formation [36]. Evolutionarily conserved pathways such as JAK-STAT, epidermal growth factor receptor (EGFR), Wingless (Wg)/Wnt, and Hippo maintain ISC homeostasis in both insect and mammalian models [28,29]. Unpaired 3 (Upd3), a Drosophila member of the interleukin 6 (IL-6) family of cytokines, triggers JAK-STAT in progenitor cells (ISC and EB) and visceral muscles [13,37,38]. JAK-STAT activation in progenitor cells stimulates ISC proliferation and EB differentiation (Fig 2A). In addition, JAK-STAT signaling also reprograms the stem cell niche to secrete epidermal growth factors (EGFs), thus indirectly promoting ISC proliferation [3941]. IL-6 and IL-22 have been shown to mediate inflammation regulated tissue regeneration upon GI injury in mice [42,43] (Fig 2A). Hippo signaling also regulates ISC proliferation in homeostasis and upon stress [44,45] (Fig 2A). Wg/Wnt signals in both models are essential to maintaining ISC activity for tissue homeostasis (Fig 2A). Upon damage to fly guts, Wg secreted by ISCs and EBs elicits cMyc-dependent ISC proliferation (Fig 2A) [46]. In Drosophila, diverse mitotic signals converge on regulating calcium (Ca2+) oscillations in ISCs, and high cytoplasmic Ca2+ levels ultimately trigger ISC proliferation [47]. The conservation between fly and murine signaling pathways suggests that the Drosophila midgut will be an instrumental model for defining or clarifying how regenerative pathways are activated in response to microbes. It remains uncertain whether the homeostatic responses of the GI tract to pathogenic and indigenous microbes are the same, but future studies dissecting immune and damage responses induced by different microbes will delineate this.

thumbnail
Fig 2. A conserved gene regulatory network controls tissue homeostasis in flies and mammals.

(A) In both flies and mammals, the gut epithelium produces immune effectors, including reactive oxygen species (ROS) and antimicrobial peptides (AMPs). Epithelial cells and immune cells secrete cytokines that stimulate tissue regeneration. The Hippo pathway is a conserved regulator of intestinal stem cell (ISC) activity. In Drosophila, activation of the JAK-STAT pathway by the cytokine Unpaired 3 (Upd3) triggers the release of epidermal growth factors (EGFs) by the stem cell niche, which then induces stem cell proliferation. JAK-STAT activation also directly stimulates ISC proliferation and differentiation. The Wingless (Wnt/Wg) pathway is a major regulator of ISC proliferation in mammals and also promotes tissue regeneration through cMyc in the infected Drosophila midgut. The dashed arrows indicate presumed activities but as yet are undefined. (B) Gut microbes and viruses coordinately stimulate a PDGF-VEGF Receptor and Extracellular Signal-Regulated Kinase dependent (pvf2/PVR/ERK) antiviral response through the Immune Deficiency (Imd) pathway and Cyclin-dependent-kinase 9 (Cdk9) induction, respectively, in the midgut of Drosophila. The ERK-stimulated antiviral activities/effectors have not been determined. In addition, exogenous insulin initiates ERK mediated antiviral activity.

https://doi.org/10.1371/journal.ppat.1006277.g002

The Drosophila gut as a model for arbovirus–vector interactions

The emergence of several arboviruses impacting human health (e.g., Zika, dengue, chikungunya, Rift Valley fever virus) in the past decade has instigated vast research into arbovirus–vector interactions. Mosquitoes and other biting insects are natural virus vectors, but arboviruses belonging to the Flavivirus, Alphavirus, and Bunyavirus families can infect Drosophila experimentally, thus establishing a pertinent model to study innate immune signaling and other aspects of virus vectoring capacity [48]. Systemic virus infections of Drosophila and other insects are controlled by a combination of RNA interference (RNAi), apoptosis, and immune responses downstream of key signaling pathways (e.g., Toll, NF-κB, JAK-STAT) [49]. However, little is known about the activation and function of antiviral pathways in the insect midgut.

Most insect-specific viruses are sublethal upon oral infection but often lethal when injected into the hemocoel [49]. Viruses acquired orally by Drosophila adults [50,51] and larvae [52] face antiviral processes, which limit virus ability to breach the midgut barrier and spread systemically. The Toll pathway in Drosophila has recently been shown to limit viral infection initiated in the midgut. The Spätzle (Spz)-Toll-Dorsal pathway was required and sufficient to survive oral infection with Drosophila C virus (DCV) but, consistent with another study [53], this pathway did not have a role when the virus was injected directly into the hemocoel [50]. The realization in Drosophila that the nutrient-sensitive Extracellular signal-Regulated Kinase (ERK) pathway restricts infection by diverse orally acquired viruses has demonstrated a link between the nutritional status of the host and the function of the gut as an active barrier against infection [51]. Indeed, Xu et al. showed that ingestion of human insulin by Drosophila is capable of stimulating antiviral ERK activity in the midgut (Fig 2B) [51]. This antiviral ERK activity is also conserved in mosquito (Aedes) cells, suggesting that exposure to insulin during a blood meal could reduce the ability of arboviruses to naturally infect mosquitoes [51].

In insects, endosymbionts such as Wolbachia are potent regulators of viral infection and are used to control the vector capacity of some mosquitoes [5456]. In mammals, the gut microbiota influences viral infectivity both positively and negatively, albeit via largely unknown mechanisms [57]. Recently, Sansone et al. have shown that midgut antiviral activity is primed by commensal microbes in the Drosophila midgut [58]. This study showed that the integration of two distinct microbial signals in the gut is necessary to stimulate antiviral ERK activity. First, peptidoglycan from the commensal bacterium Acetobacter pomorum activates the NF-κB cascade, leading to the transcriptional induction of the Platelet-Derived-Growth Factor/Vascular Endothelial Growth Factor (PDGF-VEGF) homologue, Pvf2 (Fig 2B). In parallel, oral exposure to several viruses (Sindbis, Vesicular Stomatitis Virus [VSV], Dengue virus [DENV-2], and Drosophila C Virus, [DCV]) triggers expression of the transcriptionally paused Cyclin-dependent-kinase 9 (Cdk9) that potentiates Pvf2 secretion (Fig 2B) and binding to the PDGF-VEGF Receptor (PVR) that in turn stimulates antiviral ERK signaling. Many other such details of insect GI antiviral mechanisms and virus–vector interactions are yet to be discovered using Drosophila in this era of (re)emerging arboviruses.

Conclusions and future directions

The gut is a major interface between a host and microbes. Whether we consider the emerging notion that the gut microbiota influences host physiology, the relation of GI inflammation to health and disease, or that the gut of insect vectors is a first point of contact with human parasites, it is increasingly important to elucidate the complexity and plethora of interactions between the GI tract and microbes. Due to the strong conservation of both structure and function of the gut epithelium, the less complex microbial community that composes the Drosophila gut microbiota, and the ease of genetically manipulating Drosophila, the fruit fly will continue to thrive as a workhorse for biological discoveries in this area.

Acknowledgments

We thank Alessandro Bonfini and Philip L. Houtz for insightful discussions.

References

  1. 1. Buchon N, Silverman N, Cherry S. Immunity in Drosophila melanogaster—from microbial recognition to whole-organism physiology. Nat Rev Immunol. 2014;14: 796–810. pmid:25421701
  2. 2. Bonfini A, Liu X, Buchon N. From pathogens to microbiota: How Drosophila intestinal stem cells react to gut microbes. Dev Comp Immunol. 2016;64: 22–38. pmid:26855015
  3. 3. Dutta D, Dobson AJ, Houtz PL, Gläßer C, Revah J, Korzelius J, et al. Regional Cell-Specific Transcriptome Mapping Reveals Regulatory Complexity in the Adult Drosophila Midgut. Cell Rep. 2015;12: 346–358. pmid:26146076
  4. 4. Cox CR, Gilmore MS. Native microbial colonization of Drosophila melanogaster and its use as a model of Enterococcus faecalis pathogenesis. Infection and Immunity. 2007;75: 1565–1576. pmid:17220307
  5. 5. Chandler J, Lang J, Bhatnagar S, Eisen J. Bacterial Communities of Diverse Drosophila Species: Ecological Context of a Host–Microbe Model System. PLoS Genet. 2011.
  6. 6. Broderick NA, Buchon N, Lemaitre B. Microbiota-induced changes in drosophila melanogaster host gene expression and gut morphology. MBio. American Society for Microbiology; 2014;5: e01117–14.
  7. 7. Wong CNA, Ng P, Douglas AE. Low-diversity bacterial community in the gut of the fruitfly Drosophila melanogaster. Environ Microbiol. Blackwell Publishing Ltd; 2011;13: 1889–1900. pmid:21631690
  8. 8. Wong AC-N, Chaston JM, Douglas AE. The inconstant gut microbiota of Drosophila species revealed by 16S rRNA gene analysis. ISME J. 2013;7: 1922–1932. pmid:23719154
  9. 9. Broderick NA, Lemaitre B. Gut-associated microbes of Drosophila melanogaster. Gut Microbes. 2012;3: 307–321. pmid:22572876
  10. 10. Shin SC, Kim S-H, You H, Kim B, Kim AC, Lee K-A, et al. Drosophila microbiome modulates host developmental and metabolic homeostasis via insulin signaling. Science. 2011;334: 670–674. pmid:22053049
  11. 11. Storelli G, Defaye A, Erkosar B, Hols P, Royet J, Leulier F. Lactobacillus plantarum promotes Drosophila systemic growth by modulating hormonal signals through TOR-dependent nutrient sensing. Cell Metab. 2011;14: 403–414. pmid:21907145
  12. 12. Schwarzer M, Makki K, Storelli G, Machuca-Gayet I, Srutkova D, Hermanova P, et al. Lactobacillus plantarum strain maintains growth of infant mice during chronic undernutrition. Science. 2016;351: 854–857. pmid:26912894
  13. 13. Buchon N, Broderick NA, Chakrabarti S, Lemaitre B. Invasive and indigenous microbiota impact intestinal stem cell activity through multiple pathways in Drosophila. Genes Dev. Cold Spring Harbor Lab; 2009;23: 2333–2344. pmid:19797770
  14. 14. Guo L, Karpac J, Tran SL, Jasper H. PGRP-SC2 Promotes Gut Immune Homeostasis to Limit Commensal Dysbiosis and Extend Lifespan. Cell. 2014;156: 109–122. pmid:24439372
  15. 15. Li H, Qi Y, Jasper H. Preventing Age-Related Decline of Gut Compartmentalization Limits Microbiota Dysbiosis and Extends Lifespan. Cell Host Microbe. 2016;19: 240–253. pmid:26867182
  16. 16. Clark RI, Salazar A, Yamada R, Fitz-Gibbon S, Morselli M, Alcaraz J, et al. Distinct Shifts in Microbiota Composition during Drosophila Aging Impair Intestinal Function and Drive Mortality.—PubMed—NCBI. Cell Rep. 2015;12: 1656–1667. pmid:26321641
  17. 17. Erkosar B, Leulier F. Transient adult microbiota, gut homeostasis and longevity: novel insights from the Drosophila model. FEBS Lett. 2014;588: 4250–4257. pmid:24983497
  18. 18. Lhocine N, Ribeiro PS, Buchon N, Wepf A, Wilson R, Tenev T, et al. PIMS modulates immune tolerance by negatively regulating Drosophila innate immune signaling. Cell Host Microbe. 2008;4: 147–158. pmid:18692774
  19. 19. Ryu J-H, Nam K-B, Oh C-T, Nam H-J, Kim S-H, Yoon J-H, et al. The homeobox gene Caudal regulates constitutive local expression of antimicrobial peptide genes in Drosophila epithelia. Mol Cell Biol. 2004;24: 172–185. pmid:14673153
  20. 20. Paredes JC, Welchman DP, Poidevin M, Lemaitre B. Negative Regulation by Amidase PGRPs Shapes the Drosophila Antibacterial Response and Protects the Fly from Innocuous Infection. Immunity. 2011;35: 770–779. pmid:22118526
  21. 21. Morris O, Liu X, Domingues C, Runchel C, Chai A, Basith S, et al. Signal Integration by the IκB Protein Pickle Shapes Drosophila Innate Host Defense. Cell Host Microbe. 2016;20: 283–295. pmid:27631699
  22. 22. Salzman NH, Hung K, Haribhai D, Chu H, Karlsson-Sjöberg J, Amir E, et al. Enteric defensins are essential regulators of intestinal microbial ecology. Nat Immunol. 2009;: 1–8.
  23. 23. Ha E-M, Lee K-A, Park SH, Kim S-H, Nam H-J, Lee H-Y, et al. Regulation of DUOX by the Galphaq-phospholipase Cbeta-Ca2+ pathway in Drosophila gut immunity. Dev Cell. 2009;16: 386–397. pmid:19289084
  24. 24. Lee K-A, Kim S-H, Kim E-K, Ha E-M, You H, Kim B, et al. Bacterial-Derived Uracil as a Modulator of Mucosal Immunity and Gut-Microbe Homeostasis in Drosophila. Cell. Elsevier; 2013;153: 797–811. pmid:23663779
  25. 25. Jones RM, Luo L, Ardita CS, Richardson AN, Kwon YM, Mercante JW, et al. Symbiotic lactobacilli stimulate gut epithelial proliferation via Nox-mediated generation of reactive oxygen species. EMBO J. 2013;32: 3017–3028. pmid:24141879
  26. 26. Ryu J-H, Ha E-M, Oh C-T, Seol J-H, Brey PT, Jin I, et al. An essential complementary role of NF-kappaB pathway to microbicidal oxidants in Drosophila gut immunity. EMBO J. 2006;25: 3693–3701. pmid:16858400
  27. 27. Sommer F, Bäckhed F. The gut microbiota—masters of host development and physiology.—PubMed—NCBI. Nature Reviews Microbiology. 2013;11: 227–238.
  28. 28. Karin M, Clevers H. Reparative inflammation takes charge of tissue regeneration. Nature. 2016;529: 307–315. pmid:26791721
  29. 29. Buchon N, Broderick NA, Lemaitre B. Gut homeostasis in a microbial world: insights from Drosophila melanogaster. Nat Rev Micro. 2013;11: 615–626.
  30. 30. Bosco-Drayon V, Poidevin M, Boneca IG, Narbonne-Reveau K, Royet J, Charroux B. Peptidoglycan Sensing by the Receptor PGRP-LE in the Drosophila Gut Induces Immune Responses to Infectious Bacteria and Tolerance to Microbiota. Cell Host Microbe. 2012;12: 153–165. pmid:22901536
  31. 31. Neyen C, Poidevin M, Roussel A, Lemaitre B. Tissue- and Ligand-Specific Sensing of Gram-Negative Infection in Drosophila by PGRP-LC Isoforms and PGRP-LE. J Immunol. 2012.
  32. 32. Fournier BM, Parkos CA. The role of neutrophils during intestinal inflammation. Mucosal immunology. 2012;5: 354–366. pmid:22491176
  33. 33. Chakrabarti S, Dudzic JP, Li X, Collas EJ, Boquete J-P, Lemaitre B. Remote Control of Intestinal Stem Cell Activity by Haemocytes in Drosophila. Banerjee U, editor. 2016;12: e1006089. pmid:27231872
  34. 34. Guillou A, Troha K, Wang H, Franc NC, Buchon N. The Drosophila CD36 Homologue croquemort Is Required to Maintain Immune and Gut Homeostasis during Development and Aging.—PubMed—NCBI. O'Riordan M, editor. PLoS Pathog. 2016;12: e1005961. pmid:27780230
  35. 35. Ayyaz A, Li H, Jasper H. Haemocytes control stem cell activity in the Drosophila intestine. Nat Cell Biol. 2015;17: 736–748. pmid:26005834
  36. 36. Apidianakis Y, Pitsouli C, Perrimon N, Rahme L. Synergy between bacterial infection and genetic predisposition in intestinal dysplasia. Proceedings of the National Academy of Sciences. 2009;106: 20883–20888.
  37. 37. Buchon N, Broderick NA, Poidevin M, Pradervand S, Lemaitre B. Drosophila intestinal response to bacterial infection: activation of host defense and stem cell proliferation. Cell Host Microbe. 2009;5: 200–211. pmid:19218090
  38. 38. Jiang H, Patel PH, Kohlmaier A, Grenley MO, Mcewen DG, Edgar BA. Cytokine/Jak/Stat signaling mediates regeneration and homeostasis in the Drosophila midgut. Cell. 2009;137: 1343–1355. pmid:19563763
  39. 39. Jiang H, Grenley MO, Bravo M-J, Blumhagen RZ, Edgar BA. EGFR/Ras/MAPK signaling mediates adult midgut epithelial homeostasis and regeneration in Drosophila. Cell Stem Cell. 2011;8: 84–95. pmid:21167805
  40. 40. Buchon N, Broderick NA, Kuraishi T, Lemaitre B. Drosophila EGFR pathway coordinates stem cell proliferation and gut remodeling following infection. BMC Biol. BioMed Central Ltd; 2010;8: 152. pmid:21176204
  41. 41. Biteau B, Jasper H. EGF signaling regulates the proliferation of intestinal stem cells in Drosophila. 2011;138: 1045–1055. pmid:21307097
  42. 42. Lindemans CA, Calafiore M, Mertelsmann AM, O’Connor MH, Dudakov JA, Jenq RR, et al. Interleukin-22 promotes intestinal-stem-cell-mediated epithelial regeneration. Nature. 2015;528: 560–564. pmid:26649819
  43. 43. Kuhn KA, Manieri NA, Liu T-C, Stappenbeck TS. IL-6 Stimulates Intestinal Epithelial Proliferation and Repair after Injury. Karhausen J, editor. 2014;9: e114195. pmid:25478789
  44. 44. Ren F, Wang B, Yue T, Yun E-Y, Ip YT, Jiang J. Hippo signaling regulates Drosophila intestine stem cell proliferation through multiple pathways. Proceedings of the National Academy of Sciences. 2010;107: 21064–21069.
  45. 45. Gregorieff A, Liu Y, Inanlou MR, Khomchuk Y, Wrana JL. Yap-dependent reprogramming of Lgr5+ stem cells drives intestinal regeneration and cancer. Nature. Nature Research; 2015;526: 715–718. pmid:26503053
  46. 46. Cordero JB, Stefanatos RK, Scopelliti A, Vidal M, Sansom OJ. Inducible progenitor-derived Wingless regulates adult midgut regeneration in Drosophila. EMBO J. 2012.
  47. 47. Deng H, Gerencser AA, Jasper H. Signal integration by Ca2+ regulates intestinal stem-cell activity. Nature. 2015;528: 212–217. pmid:26633624
  48. 48. Martins N, Imler J-L, Meignin C. Discovery of novel targets for antivirals: learning from flies. Curr Opin Virol. 2016;20: 64–70. pmid:27657660
  49. 49. Marques JT, Imler J-L. The diversity of insect antiviral immunity: insights from viruses. Current Opinion in Microbiology. 2016;32: 71–76. pmid:27232381
  50. 50. Ferreira ÁG, Naylor H, Esteves SS, Pais IS, Martins NE, Teixeira L. The Toll-dorsal pathway is required for resistance to viral oral infection in Drosophila. PLoS Pathog. 2014;10: e1004507. pmid:25473839
  51. 51. Xu J, Hopkins K, Sabin L, Yasunaga A, Subramanian H, Lamborn I, et al. ERK signaling couples nutrient status to antiviral defense in the insect gut. Proceedings of the National Academy of Sciences. 2013;110: 15025–15030.
  52. 52. Stevanovic AL, Arnold PA, Johnson KN. Wolbachia-Mediated Antiviral Protection in Drosophila Larvae and Adults following Oral Infection. Goodrich-Blai H, editor. Applied and Environmental Microbiology. 2015;81: 8215–8223. pmid:26407882
  53. 53. Lamiable O, Arnold J, de Faria IJDS, Olmo RP, Bergami F, Meignin C, et al. Analysis of the Contribution of Hemocytes and Autophagy to Drosophila Antiviral Immunity. J Virol. American Society for Microbiology; 2016;90: 5415–5426. pmid:27009948
  54. 54. Teixeira L, Ferreira A, Ashburner M. The bacterial symbiont Wolbachia induces resistance to RNA viral infections in Drosophila melanogaster. Keller L, editor. PLoS Biol. 2008;6: e2.
  55. 55. Hedges LM, Brownlie JC, O'Neill SL, Johnson KN. Wolbachia and virus protection in insects. Science. 2008;322: 702. pmid:18974344
  56. 56. Mohanty I, Rath A, Mahapatra N, Hazra RK. Wolbachia: A biological control strategy against arboviral diseases. J Vector Borne Dis. 2016;53: 199–207. pmid:27681542
  57. 57. Robinson CM, Pfeiffer JK. Viruses and the Microbiota. Annu Rev Virol. 2014;1: 55–69. pmid:25821837
  58. 58. Sansone CL, Cohen J, Yasunaga A, Xu J, Osborn G, Subramanian H, et al. Microbiota-Dependent Priming of Antiviral Intestinal Immunity in Drosophila. Cell Host Microbe. 2015;18: 571–581. pmid:26567510