Author response: The DBL-1/TGF-β signaling pathway tailors behavioral and molecular host responses to a variety of bacteria in Caenorhabditis elegans
Year: 2022
Type: peer-review
Abstract: Full text Figures and data Side by side Abstract Editor's evaluation Introduction Results Discussion Materials and methods Data availability References Decision letter Author response Article and author information Metrics Abstract Generating specific, robust protective responses to different bacteria is vital for animal survival. Here, we address the role of transforming growth factor β (TGF-β) member DBL-1 in regulating signature host defense responses in Caenorhabditis elegans to human opportunistic Gram-negative and Gram-positive pathogens. Canonical DBL-1 signaling is required to suppress avoidance behavior in response to Gram-negative, but not Gram-positive bacteria. We propose that in the absence of DBL-1, animals perceive some bacteria as more harmful. Animals activate DBL-1 pathway activity in response to Gram-negative bacteria and strongly repress it in response to select Gram-positive bacteria, demonstrating bacteria-responsive regulation of DBL-1 signaling. DBL-1 signaling differentially regulates expression of target innate immunity genes depending on the bacterial exposure. These findings highlight a central role for TGF-β in tailoring a suite of bacteria-specific host defenses. Editor's evaluation This study provides valuable insight into the role of the TGF-β signaling pathway in the immune response of C. elegans. The authors report a convincing analysis of molecular and behavioral responses to a broad panel of bacteria, dissecting the contribution of the TGF-β pathway to these responses. https://doi.org/10.7554/eLife.75831.sa0 Decision letter eLife's review process Introduction Organisms recognize and respond to potential environmental insults by coordinating protective defenses (Medzhitov and Janeway, 1998). Invertebrates and vertebrates both employ conserved innate immune responses as immediate front-line protection from challenges including harmful bacteria (Medzhitov and Janeway, 1998; MacGillivray and Kollmann, 2014; Cheesman et al., 2016; Pukkila-Worley, 2016; Sellegounder et al., 2018). These responses are tailored to the bacterial challenge. However, how these responses are specified and what the responses are to different bacteria remains a challenge (Akira et al., 2006). The roundworm Caenorhabditis elegans is an established model system to study the regulation of immune responses in vivo (Engelmann and Pujol, 2010). C. elegans naturally thrives in a soil environment where it feeds on bacteria and is in constant association with a diverse range of microbes that are both food and threat (Engelmann and Pujol, 2010; Cheesman et al., 2016). A limited number of microorganisms are known to infect C. elegans, including fungi, Gram-negative bacteria, and Gram-positive bacteria (Couillault and Ewbank, 2002; Gravato-Nobre et al., 2005; Begun et al., 2007; Wong et al., 2007; Singh and Aballay, 2009; Zugasti and Ewbank, 2009; Pukkila-Worley et al., 2012; Ahamefule et al., 2020). C. elegans has an innate immune system that confers protection through behavioral, physical, and molecular mechanisms (Engelmann and Pujol, 2010). C. elegans molecular responses are tailored to the pathogen, creating 'antimicrobial fingerprints' specific to the challenge (Alper et al., 2007). The molecular immune defenses in C. elegans induced by infection are coordinated by functionally conserved cell–cell signaling pathways including mitogen-activated protein kinase (MAPK), insulin-like, and DBL-1/TGF-β (transforming growth factor β) signaling pathways (Gravato-Nobre et al., 2005; Begun et al., 2007; Wong et al., 2007; Singh and Aballay, 2009; Alper et al., 2007; Zugasti and Ewbank, 2009; Berg et al., 2019). These pathways regulate an overlapping set of target defense genes, indicative of coordinated crosstalk between these signaling pathways. The roles of MAPK and insulin-like signaling pathways in immune responses to a wide variety of bacteria are well characterized. While the role of DBL-1 in defending nematodes from a few strongly pathogenic Gram-negative bacteria is reported, its role in protection against Gram-positive bacteria has not been well characterized (Tan et al., 1999; Mallo et al., 2002; Zhang and Zhang, 2012). Previous reports indicate that the DBL-1 pathway affects expression of many immune response-associated genes including lectins, saposin-like proteins, and lysozymes (Mochii et al., 1999; Wong et al., 2007; Liang et al., 2007; Roberts et al., 2010). However, a role for DBL-1/TGF-β signaling in eliciting robust targeted immune responses to different bacterial challenges is not well defined in C. elegans or other organisms (Kim et al., 2002; Mallo et al., 2002; Murphy et al., 2003; Garsin et al., 2003; Alper et al., 2007). In this work, we dissected the roles of DBL-1/TGF-β signaling in regulating a broad array of microbe-specific defense responses in C. elegans. Using behavioral and molecular approaches, we identified DBL-1-dependent and -independent defense responses that are tailored to the specific bacterial exposure. In addition, we showed that DBL-1 signaling is induced in response to Gram-negative bacteria but is repressed in response to Gram-positive bacteria. We propose that animals lacking DBL-1 signaling respond with heightened avoidance behaviors and reduced feeding to selected bacterial environments because they perceive the environment as more hostile. Collectively, our findings highlight a central role for DBL-1 in regulating a suite of bacteria-specific host defenses and also demonstrate bacteria-responsive regulation of DBL-1 signaling. Results Loss of DBL-1 reduces lifespan of animals fed on specific bacteria To study the role of DBL-1 in specific host responses to bacteria at behavioral, molecular, and physiological levels, we first established a panel of bacteria that would facilitate genetic and molecular studies over time: previous studies have been limited in range of challenge and used pathogens that killed animals in hours or a few days. The control bacteria chosen was Gram-negative Escherichia coli OP50, a commonly used strain for laboratory culture of C. elegans. The panel of test bacteria comprised Gram-negative and Gram-positive bacteria that are opportunistic pathogens in humans and are found in the natural habitat of C. elegans (Samuel et al., 2016). We selected three Gram-negative test strains, Serratia marcescens (D1), Enterobacter cloacae (ATCC 49141), and Klebsiella oxytoca (ATCC 49131), and three Gram-positive test strains, Bacillus megaterium (ATCC 14581), Enterococcus faecalis (ATCC 51299), and Staphylococcus epidermidis (ATCC 49134). We first asked if these bacteria alter lifespan of wild-type C. elegans. While pathogenic bacteria can reduce C. elegans lifespan, other microbial diets can extend lifespan of C. elegans populations (Stuhr and Curran, 2020). We noted an extended lifespan of wild-type animals on two Gram-negative bacteria (E. cloacae and K. oxytoca, by 4 d and 2 d, respectively). However, we found that wild-type animals on Gram-negative S. marcescens have lifespans comparable to E. coli-fed animals. Interestingly, we observed an extended lifespan of wild-type animals on all three Gram-positive bacteria (B. megaterium, E. faecalis, and S. epidermidis) (Supplementary file 1). Loss of DBL-1 has previously been shown to reduce lifespan of animals exposed to fungus Drechmeria coniospora, Gram-negative strains E. coli and S. marcescens Db11, and Gram-positive E. faecalis (Mallo et al., 2002; Zugasti and Ewbank, 2009; Tenor and Aballay, 2008). The reduced lifespan of animals lacking DBL-1 on E. coli OP50 was not observed when animals were grown on 5-fluorodeoxyuridine (FUdR), which blocks DNA synthesis of both bacteria and the nematodes (Mallo et al., 2002). It has also been shown that DBL-1 is required for the probiotic Lactobacillus spp. Lb21-mediated lifespan extension of C. elegans subjected to pathogenic methicillin-resistant Staphylococcus aureus (MRSA) (Mørch et al., 2021). To determine if DBL-1 is required in maintaining lifespan of animals subjected to our bacterial panel, we compared lifespans of dbl-1(-) and wild-type animals exposed to the control or test bacteria on plates containing FUdR. Loss of DBL-1 did not alter lifespan of animals fed on plates containing E. coli OP50 and FUdR (Figure 1A), consistent with previous work (Mallo et al., 2002). dbl-1 mutant animals did not have the lifespan extension seen in wild-type populations on E. cloacae or K. oxytoca: lifespans of dbl-1 mutant populations were the same on these two Gram-negative bacteria as on E. coli (Figure 1B and C, Supplementary file 1). However, loss of DBL-1 resulted in a significantly shortened lifespan on S. marcescens compared to E. coli control bacteria, unlike the wild-type (by 6 d, Supplementary file 1). This reduced lifespan of dbl-1(-) animals was significantly lower than that of wild-type animals fed on S. marcescens, which is consistent with a previous report that used the more virulent S. marcescens strain Db11 (Figure 1D; Mallo et al., 2002). The lifespan of dbl-1(-) animals was modestly extended upon exposure to Gram-positive B. megaterium and E. faecalis compared to the E. coli-fed population's lifespan, but was significantly less extended than the wild-type lifespan (by about a day, Figure 1E and F, Supplementary file 1). Lastly, dbl-1 mutant animals displayed a significantly decreased lifespan on S. epidermidis compared to E. coli-fed populations' lifespan (by almost 2 d), which was not observed in wild-type animals fed on S. epidermidis (Figure 1G, Supplementary file 1). Figure 1 with 2 supplements see all Download asset Open asset Loss of DBL-1 decreases lifespan of animals exposed to test Gram-negative and Gram-positive bacteria. Wild-type and dbl-1(-) animals were scored for survival over time from the L4 stage (t = 0 hr) on the following bacteria: (A) E. coli OP50 (control), (B) E. cloacae, (C) K. oxytoca, (D) S. marcescens, (E) B. megaterium, (F) E. faecalis, and (G) S. epidermidis. Survival fraction was calculated by the Kaplan–Meier method. p-Values were calculated using log-rank test and p<0.01 compared to wild-type animals exposed to the same bacteria was considered significant. One representative trial is presented. Figure 1—source data 1 Related to Figure 1. https://cdn.elifesciences.org/articles/75831/elife-75831-fig1-data1-v2.xlsx Download elife-75831-fig1-data1-v2.xlsx In summary, we showed that exposure to all bacteria in the test panel except S. marcescens resulted in lifespan extension of wild-type animals. Loss of DBL-1 reduced lifespan in all test bacteria in this panel to varying degrees. dbl-1(-) mutant animals have the lowest average lifespan on S. marcescens, significantly lower than the same strain on control E. coli OP50. In contrast to the wild type, dbl-1(-) animals fed S. epidermidis have reduced lifespans compared to the same strain on control E. coli OP50. Wild-type lifespan extension is lost in dbl-1(-) mutant animals fed E. cloacae and K. oxytoca, but their average lifespan is comparable to the same strain grown on E. coli OP50. On B. megaterium and E. faecalis, the lifespan of dbl-1(-) mutants was extended but to a lesser extent than the wild type (Figure 1B–G). Together, these results provide evidence that DBL-1 signaling confers protection against some bacteria and contributes to the lifespan extension observed in response to most bacteria in our panel. DBL-1 does not alter intestinal integrity of animals upon exposure to specific bacteria One cause of reduced survival upon exposure to pathogenic bacteria is disruption of intestinal integrity (Sim and Hibberd, 2016). To examine if this is the underlying reason for DBL-1-dependent differences in animal survival in response to various bacteria, we investigated the integrity of the intestinal barrier of animals fed on different bacteria over time. We compared the intestinal barrier function of wild-type and dbl-1(-) animals exposed to control and test bacteria when 50% of the population on the test bacteria was still alive using a cell-impermeable blue dye that remains in the intestinal lumen in healthy animals (Gelino et al., 2016). Animals with intact intestinal barrier function will contain dye only within the intestinal lumen, but animals with intestinal barrier dysfunction will have leakage of the dye from the intestine into the body cavity. Consistent with previous reports, wild-type populations on E. coli exhibited an increased percentage of animals with dye outside the intestine over time, indicating an age-dependent reduction of intestinal integrity (Gelino et al., 2016). dbl-1-mutant populations grown on E. coli also displayed a decline in intestinal integrity that was not significantly different from the decline observed in the wild-type populations at the tested time points (Figure 1—figure supplement 1A). Exposure of wild-type animals to any of the test bacteria in the panel did not further decrease intestinal integrity compared to E. coli (Figure 1—figure supplement 1). Similar to wild-type animals, exposure of dbl-1(-) mutants to the test bacteria did not further significantly decrease their intestinal integrity. Therefore, DBL-1 is not required for intestinal integrity or its age-related decline. Furthermore, this result suggests the lifespan changes observed in dbl-1 mutant populations are not caused by loss of intestinal integrity. Lifespan can also be reduced by increased bacterial colonization in the C. elegans gut (Portal-Celhay et al., 2012). To determine if the decrease in lifespan of dbl-1(-) animals is correlated with an increase in gut colonization, we quantified bacterial load in the intestine of wild-type and dbl-1(-) animals fed S. marcescens, the bacterial strain in the selected panel that had the most deleterious lifespan effect on dbl-1(-) populations. No significant differences in bacterial load were observed between wild-type and dbl-1(-) animals that were exposed to S. marcescens (Figure 1—figure supplement 2). This suggests that bacterial colonization is not the underlying cause for reduction in dbl-1(-) populations' survival upon exposure to S. marcescens. Loss of DBL-1 and exposure to specific bacteria reduce feeding We next asked if our panel of bacteria affect feeding behavior in C. elegans. C. elegans reduce their food intake in response to bacteria they perceive as harmful (O'Quinn et al., 2001). To determine if loss of DBL-1 alters animals' perception of test bacteria as potential threat, we assessed pharyngeal pumping of wild-type and dbl-1(-) populations fed on control and test bacteria. Loss of DBL-1 does not alter the pharyngeal pumping rate of animals fed on the control E. coli OP50 bacteria (Figure 2A and B). Overall, animals fed the Gram-negative bacteria did not have major changes in pharyngeal pumping rates (Figure 2A). Wild-type animals fed on E. cloacae exhibited a small but significant decrease in pharyngeal pumping that was not further decreased in dbl-1(-) animals. Pharyngeal pumping of wild-type animals was not significantly reduced after exposure to K. oxytoca, but animals lacking DBL-1 had a mild but significant decrease in pumping rate. Wild-type and dbl-1(-) animals fed on S. marcescens had a similar pumping rate as on the control bacteria (Figure 2A). There is no clear correlation between lifespan phenotypes and feeding rate for populations fed on the Gram-negative bacteria. For wild-type animals fed on the three Gram-positive bacteria, though, the pharyngeal pumping rate was dramatically decreased, consistent with the lifespan extension these strains conferred to wild-type C. elegans (Figure 2B, Supplementary file 1). Interestingly, the feeding rate of dbl-1(-) animals is further reduced from the wild-type rate on E. faecalis and S. epidermidis. However, there is no reproducibly significant decrease in the pharyngeal pumping rate of dbl-1(-) animals fed on B. megaterium in comparison to that of the wild type (Figure 2B). These results indicate that while the feeding reduction caused by exposure to the Gram-positive bacteria is partially independent of DBL-1, a stronger pharyngeal pumping reduction in dbl-1(-) populations occurs in response to some bacteria, providing support to the idea that loss of DBL-1 sensitizes animals to certain bacterial stressors. Figure 2 Download asset Open asset Loss of DBL-1 and exposure to specific bacteria results in decreased pharyngeal pumping. Wild-type and dbl-1(-) animals at the L4 stage were exposed to the following bacteria: (A, B) E. coli OP50 (control); (A) E. cloacae, K. oxytoca, S. marcescens; (B) B. megaterium, E. faecalis, or S. epidermidis. After 48 hr of exposure, the number of pharyngeal pumps was counted twice per 20 s. The pharyngeal pumps were averaged for each animal. One representative trial is presented. Error bars represent standard deviation. n = 8–12 per condition. *p<0.01, ns, not significant, compared to wild-type animals exposed to the same bacteria, and #p<0.01, respective genotype exposed to test bacteria in comparison to control bacteria by two-way ANOVA using Tukey's post hoc test. Figure 2—source data 1 Related to Figure 2. https://cdn.elifesciences.org/articles/75831/elife-75831-fig2-data1-v2.xlsx Download elife-75831-fig2-data1-v2.xlsx DBL-1 signaling is required to suppress avoidance of specific Gram-negative but not Gram-positive bacteria C. elegans can also respond to potentially pathogenic bacteria or harmful environments by avoiding such challenges (Pradel et al., 2007; Beale et al., 2006; Anderson and McMullan, 2018). To further investigate the role of DBL-1 in perceiving harmful environments, we performed an avoidance assay. First, we measured the avoidance response of wild-type animals fed on the test bacteria over the first 2 d of adulthood and compared it with the avoidance response on the control bacteria. Wild-type animals do not avoid E. coli (Figure 3A). We found that wild-type animals do not avoid E. cloacae but do avoid Gram-negative K. oxytoca and S. marcescens (Figure 3B–D). While wild-type animals displayed a moderate to strong response to Gram-positive B. megaterium, they exhibited mild or no avoidance of E. faecalis and S. epidermidis (Figure 3E–G). This indicates that wild-type animals perceive K. oxytoca, S. marcescens, and B. megaterium as harmful. Figure 3 Download asset Open asset Avoidance to Gram-negative bacteria increases upon loss of canonical DBL-1 signaling over time while avoidance to specific Gram-positive is independent of DBL-1 signaling. Wild-type, dbl-1(-), sma-2(-), sma-3(-), and two sma-4(-) strains at the L4 stage (t = 0 hr) were exposed to the following bacteria: (A) E. coli OP50 (control), (B) E. cloacae, (C) K. oxytoca, (D) S. marcescens, (E) B. megaterium, (F) E. faecalis, or (G) S. epidermidis. The avoidance ratio was calculated and compared to the wild-type control animals. Each trial used three plates of 30 animals each per condition. One representative trial is presented. Error bars represent standard error mean. *p<0.05, ns, not significant, compared to wild-type animals exposed to the same bacteria by repeated measures ANOVA using Tukey's post hoc test. Figure 3—source data 1 Related to Figure 3. https://cdn.elifesciences.org/articles/75831/elife-75831-fig3-data1-v2.xlsx Download elife-75831-fig3-data1-v2.xlsx Next, we tested avoidance behavior of dbl-1(-) populations exposed to the test bacteria and compared it with wild-type animals fed on the same test bacteria. Loss of DBL-1 did not result in an avoidance response to the control bacteria (Figure 3A). Loss of DBL-1 resulted in a significantly stronger avoidance response to all three tested Gram-negative bacteria (Figure 3B–D). Interestingly, the avoidance response of dbl-1(-) animals upon exposure to Gram-positive B. megaterium, E. faecalis, and S. epidermidis was similar to wild type (Figure 3E–G). The protective behavioral response displayed by dbl-1(-) populations on bacteria that wild-type animals do not avoid suggests that animals lacking DBL-1 perceive the tested Gram-negative (but not Gram-positive bacteria) to be more harmful than wild-type animals do. This also suggests that DBL-1 signaling normally suppresses avoidance depending on the specific bacterial exposure. Canonical DBL-1 signaling suppresses avoidance to Gram-negative bacteria but is dispensable for avoidance to Gram-positive bacteria Because we observed strong bacteria-specific avoidance responses in animals lacking DBL-1, we next asked if the canonical DBL-1 signaling pathway is required to attenuate this response. Canonical signaling occurs by DBL-1 ligand binding to receptors SMA-6 and DAF-4, which activate downstream Smad transcription factors SMA-2, SMA-3, and SMA-4 (Savage et al., 1996). A non-canonical DBL-1 pathway, which does not signal through SMA-2 and SMA-4, is required for C. elegans to respond to the fungus D. coniospora (Zugasti and Ewbank, 2009). To identify the Smads required for DBL-1 pathway-mediated bacterial avoidance, we measured the avoidance response of sma-2(-), sma-3(-), and sma-4(-) strains fed on the test Gram-negative or Gram-positive bacteria and compared them with the avoidance response on the control bacteria. On the control bacteria, loss of sma-2 and sma-3 did not result in significantly increased avoidance. However, populations with sma-4(e727) showed a moderate but significant avoidance response to the control bacteria (Figure 3A). Because sma-4(e727), a strong loss-of-function point mutation (Q246Stop), initially displayed a stronger avoidance response, we confirmed this effect was reproducible in the sma-4(jj278) null strain, in which most of the open reading frame was deleted using CRISPR (McKillop et al., 2018). sma-2(-), sma-3(-), and both sma-4(-) populations displayed strong, reproducible avoidance responses to all Gram-negative bacterial strains tested that were comparable to the dbl-1(-) populations' response (Figure 3B–D). In comparison, the response of Smad mutant populations to the panel of Gram-positive bacteria was notably different. Loss of sma-2, sma-3, or sma-4 resulted in avoidance responses on the Gram-positive B. megaterium and E. faecalis similar to the wild type and dbl-1(-) responses (Figure 3E and F). This indicates that avoidance elicited in response to these bacterial strains is independent of not only DBL-1, but also of the Smad machinery. However, both sma-4 mutant strains but not dbl-1, sma-2, or sma-3 strains had a stronger, moderate avoidance response on the Gram-positive S. epidermidis in comparison to the wild type (Figure 3G). Together, our findings indicate that while canonical DBL-1 signaling does not play a major role in responding to E. coli, a standard Gram-negative food source, and Gram-positive bacteria, it plays a major role in suppressing animal avoidance responses to the tested Gram-negative bacteria. sma-4 expression is specifically induced in response to Gram-positive bacteria We next asked if animals alter expression of the DBL-1 Smads in response to the panel of opportunistic pathogens. We tested gene expression levels of sma-2, sma-3, and sma-4 in wild-type and dbl-1 mutant backgrounds in response to our panel of bacteria. Gene expression was assessed by real-time PCR experiments that were performed in triplicate in three independent trials. Expression of mRNA from these three Smad genes was not changed in dbl-1(-) animals on control E. coli OP50 compared to the wild type (Figure 4—figure supplement 1A). The relative levels of sma-2 mRNA were consistently decreased in the dbl-1 mutant background upon exposure to all test bacterial strains except S. epidermidis, where sma-2 mRNA levels were increased in both the wild-type and dbl-1(-) backgrounds (Figure 4A and B and Figure 4—figure supplement 1A and B). The relative levels of sma-3 mRNA were not reproducibly different between dbl-1(-) and wild-type backgrounds exposed to the same control or test bacteria (Figure 4—figure supplement 1C and D). Whereas sma-3 expression levels remained largely unchanged in wild-type animals when exposed to Gram-negative and Gram-positive bacteria, exposure to E. faecalis or S. epidermidis resulted in increased expression of sma-3 in the dbl-1(-) background compared to control bacteria (Figure 4C and D). On test Gram-negative bacteria, sma-4 expression was similar in the dbl-1(-) background as in the wild type (Figure 4E, Figure 4—figure supplement 1E). However, sma-4 was significantly induced in response to Gram-positive bacteria in both wild-type and dbl-1 mutant backgrounds, albeit less in the dbl-1(-) populations (Figure 4F and Figure 4—figure supplement 1F). Together, these results suggest that the DBL-1 Smads are differently regulated at the level of gene expression by molecular pathways that are responsive to specific bacterial challenges. sma-2, but not sma-3, requires DBL-1 for full expression on all bacterial food sources except S. epidermidis. Neither sma-2 nor sma-3 expression is affected to a great extent by test bacteria. In contrast, sma-4 expression is not altered by Gram-negative bacteria, but is responsive to Gram-positive bacteria in the panel, possibly by both DBL-1 and DBL-1-independent mechanisms. The Smads may be regulated post-transcriptionally to contribute to the differential avoidance responses to various bacteria. Investigation of downstream genes regulated by Smads will further our understanding of the role of Smads in differential avoidance responses. Figure 4 with 1 supplement see all Download asset Open asset Smad transcription factors gene expression is altered by specific bacteria. Wild-type and dbl-1(-) animals at the L4 stage were exposed to E. coli OP50 (control), E. cloacae, K. oxytoca, S. marcescens, B. megaterium, E. faecalis, or S. epidermidis for 48 hr. Relative mRNA expression levels of (A, B) sma-2, (C, D) sma-3, and (E, F) sma-4 were quantitated by real-time PCR. Experiments were performed in three technical replicates and in three independent biological trials. One representative trial is presented. Error bars represent standard deviation. *p<0.05, mRNA expression level in respective genotype exposed to test bacteria compared to control E. coli OP50, by one-way ANOVA with Dunnett's multiple-comparisons test. Figure 4—source data 1 Related to Figure 4. https://cdn.elifesciences.org/articles/75831/elife-75831-fig4-data1-v2.xlsx Download elife-75831-fig4-data1-v2.xlsx DBL-1 signaling is activated in response to specific Gram-negative bacteria and is repressed in response to Gram-positive bacteria We next asked if DBL-1 signaling activity is altered in response to the bacterial panel. To address this question, we fed the bacterial panel to wild-type or dbl-1(-) animals expressing an integrated fluorescent DBL-1 pathway reporter called RAD-SMAD. This reporter of the gene the control of of a et al., 2010). The expression of this reporter is robust in of stage wild-type animals, and changes in DBL-1 signaling with expression of et al., 2010; et al., et al., 2014; et al., et al., 2019). We measured the of the populations fed control or test Gram-negative bacteria. to the wild-type expression of on E. coli control bacterial (Figure reporter in the wild-type background on Gram-negative bacteria E. cloacae and K. oxytoca was increased (Figure C, and While Gram-negative S. marcescens increased expression of the DBL-1 reporter in the it did not Figure and Figure Download asset Open asset DBL-1 signaling is activated upon exposure to Gram-negative bacteria but is repressed in response to Gram-positive bacteria. of wild-type animals expressing the reporter exposed to (A) E. coli OP50 (control), (B) E. cloacae, (C) K. oxytoca, (D) S. marcescens, (E) B. megaterium, (F) E. faecalis, or (G) S. epidermidis. were consistent in indicate fluorescent of wild-type animals expressing the reporter and fed on control E. coli OP50 or test Gram-negative bacteria are compared in of per animal was and n = animals per in each Experiments were performed in three independent trials. One representative trial is presented. Error bars represent of from wild-type animals expressing the reporter on control E. coli OP50 or test Gram-positive bacteria. of animals or no from three is *p<0.05, in wild-type background on test bacteria compared to control bacteria by test. Figure data 1 Related to Figure Download In contrast, in wild-type animals was lost upon exposure to test Gram-positive bacteria. Because of the absence of we compared the fraction of wild-type population
Source: eLife
Language: English
Subfield: Immunology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: gold
Estimated APC paid: $2,500
OpenAlex ID: W4387547533