Project description:Malaria is caused by Plasmodium parasites, which are transmitted via the bites of infected Anopheline mosquitoes. Midgut invasion is a major bottleneck for Plasmodium development inside the mosquito vectors as a rapidly responding immune system recognizes ookinetes and recruits killing factors from the midgut and surrounding tissues, dramatically reducing the population of invading ookinetes before they can successfully traverse the midgut epithelium. Understanding molecular details of the parasite-vector interactions requires precise measurement of nascent protein synthesis in the mosquito during Plasmodium infection. Current expression profiling primarily monitors alterations in steady-state levels of mRNA, but does not address the equally critical issue of whether the proteins encoded by the mRNAs are actually synthesized. In this study, we used sucrose density gradient centrifugation to isolate actively translating Anopheles gambiae mRNAs based upon their association with polyribosomes (polysomes). The proportion of individual gene transcripts associated with polysomes, which is determined by RNA deep sequencing, reflects mRNA translational status. This approach led to identification of 1017 mosquito transcripts that were primarily regulated at the translational level after ingestion of Plasmodium falciparum-infected blood. Caspar, a negative regulator of the NF-kappaB transcription factor Rel2, appears to be substantially activated at the translational levels during Plasmodium infection. In addition, transcripts of Dcr1, Dcr2 and Drosha, which are involved in small RNA biosynthesis, exhibited enhanced associations with polysomes after P. falciparum challenge. This observation suggests that mosquito microRNAs may play an important role in reactions against Plasmodium invasion. We analyzed both total cellular mRNAs and mRNAs that are associated with polysomes to simultaneously monitor transcriptomes and nascent protein synthesis in the mosquito. This approach provides more accurate information regarding the rate of protein synthesis, and identifies some mosquito factors that might have gone unrecognized because expression of these proteins is regulated mainly at the translational level rather than at the transcriptional level after mosquitoes ingest a Plasmodium-infected blood meal.

Project description:Malaria is caused by Plasmodium parasites, which are transmitted via the bites of infected Anopheline mosquitoes. Midgut invasion is a major bottleneck for Plasmodium development inside the mosquito vectors as a rapidly responding immune system recognizes ookinetes and recruits killing factors from the midgut and surrounding tissues, dramatically reducing the population of invading ookinetes before they can successfully traverse the midgut epithelium. Understanding molecular details of the parasite-vector interactions requires precise measurement of nascent protein synthesis in the mosquito during Plasmodium infection. Current expression profiling primarily monitors alterations in steady-state levels of mRNA, but does not address the equally critical issue of whether the proteins encoded by the mRNAs are actually synthesized. In this study, we used sucrose density gradient centrifugation to isolate actively translating Anopheles gambiae mRNAs based upon their association with polyribosomes (polysomes). The proportion of individual gene transcripts associated with polysomes, which is determined by RNA deep sequencing, reflects mRNA translational status. This approach led to identification of 1017 mosquito transcripts that were primarily regulated at the translational level after ingestion of Plasmodium falciparum-infected blood. Caspar, a negative regulator of the NF-kappaB transcription factor Rel2, appears to be substantially activated at the translational levels during Plasmodium infection. In addition, transcripts of Dcr1, Dcr2 and Drosha, which are involved in small RNA biosynthesis, exhibited enhanced associations with polysomes after P. falciparum challenge. This observation suggests that mosquito microRNAs may play an important role in reactions against Plasmodium invasion. We analyzed both total cellular mRNAs and mRNAs that are associated with polysomes to simultaneously monitor transcriptomes and nascent protein synthesis in the mosquito. This approach provides more accurate information regarding the rate of protein synthesis, and identifies some mosquito factors that might have gone unrecognized because expression of these proteins is regulated mainly at the translational level rather than at the transcriptional level after mosquitoes ingest a Plasmodium-infected blood meal. Midguts from female Anopheles gambiae mosquitoes were dissected at around 24 h after ingestion of P. falciparum-infected blood. Mosquitoes fed on uninfected blood were used as control. A portion of the midguts were used for isolation of total cellular RNA. Extracts of the remaining midguts were fractionated over sucrose density gradients, and fifteen fractions were collected from the top of each gradient. Non-polysomal fractions, as well as polysomal fractions were combined, respectively, to obtain two RNA pools per gradient for three independent experiments. The first, last and the sample between non-polysomal and polysomal, were all discarded to ensure pure pools from each set. A fourth experiment was conducted where the polysomal and non-polysomal samples were not pooled, to be used later for qRT-PCR. The mRNA levels of individual mosquito genes in polysome (PS) fractions, nonpolysome (NP) fractions and unfractionated steady-state (total) RNA were determined using high throughput RNA deep sequencing. Each RNA pool generated 2.1-9.8 million raw read . Signal intensities of transcripts from each PS pool were compared to those of transcripts from a matching NP pool. To quantify the translational status of individual mRNA species, we define the relative PS loading [PL=P/(P+NP)] as the extent of mRNA association with polysomes. PL values were compared between the mosquitoes fed on P. falciparum-infected or -uninfected blood.

Project description:Background: The mosquito Anopheles gambiae is a major vector of human malaria. Increasing evidence indicates that blood cells (hemocytes) comprise an essential arm of the mosquito innate immune response against both bacteria and malaria parasites. To further characterize the role of hemocytes in mosquito immunity, we undertook the first genome-wide transcriptomic analyses of adult female An. gambiae hemocytes following infection by two species of bacteria and a malaria parasite. Results: We identified 4047 genes expressed in hemocytes, using An. gambiae genome-wide microarrays. While 279 transcripts were significantly enriched in hemocytes relative to whole adult female mosquitoes, 959 transcripts exhibited immune challenge-related regulation. The global transcriptomic responses of hemocytes to challenge with different species of bacteria and/or different stages of malaria parasite infection revealed discrete, minimally overlapping, pathogen-specific signatures of infection-responsive gene expression; 105 of these represented putative immunity-related genes including anti-Plasmodium factors. Of particular interest was the specific co-regulation of various members of the Imd and JNK immune signaling pathways during malaria parasite invasion of the mosquito midgut epithelium. Conclusion: Our genome-wide transcriptomic analysis of adult mosquito hemocytes reveals pathogen-specific signatures of gene regulation and identifies several novel candidate genes for future functional studies. In order to identify hemocyte-specific and immune-responsive transcripts, we first compared transcripts expressed in hemocytes from one day old sugar-fed mosquitoes to transcripts detected in whole mosquitoes of the same age and feeding status. This resulted in identification of the hemocyte-enriched transcriptome. We then compared hemocytes from 1 day old mosquitoes, 1 hour after immune challenge with heat-killed Escherichia coli or Micrococcus luteus, to control female mosquitoes injected with sterile PBS to determine the bacteria challenge responsive transcriptomes. We used heat-killed bacteria in these assays, because our primary interest was in identifying the bacterial responsive transcriptome and to avoid the potentially confounding effects of altered gene expression due to the lethal effects of a systemic infection associated with injection of living bacteria. Lastly, we compared hemocytes from mosquitoes at 24 hours and 19 days after ingestion of a blood meal infected with Plasmodium berghei to mosquitoes of the same age fed a non-infected blood meal to determine the ookinete and sporozoite infection responsive transcriptomes, respectively. This design resulted in a total of five experimental treatments. The following samples are not included in this submission: Hemo E coli vs. hemo unchallenged A Hemo E coli vs. hemo unchallenged B Hemo m luteus vs. hemo unchallenged A Hemo m luteus vs. hemo unchallenged B

Project description:The mosquito Anopheles gambiae uses its innate immune system to control bacterial and Plasmodium infection of its midgut tissue. The activation of potent IMD pathway-mediated anti-Plasmodium falciparum defenses is dependent on the presence of the midgut microbiota, which activate this defense system upon parasite infection through a peptidoglycan recognition protein, PGRPLC. We employed transcriptomic and reverse genetic analyses to compare the P. falciparum infection-responsive transcriptomes of septic and aseptic mosquitoes and to determine whether bacteria-independent anti-Plasmodium defenses exist. To examine the impact of P. falciparum infection on the mosquito midgut and carcass transcriptomes in the presence or absence of midgut bacteria, we used A. gambiae whole genome microarrays to compare the mRNA abundance of P. falciparum-infected and -naÃ¯ve mosquitoes of antibiotic- and non-antibiotic treated cohorts. P. falciparum infection induced changes in the abundance of as many as 2,183 and 2,429 transcripts in whole mosquitoes belonging to a variety of functional groups in aseptic and septic mosquitoes. Ultimately, we were interested in identifying the genes involved in bacteria-independent anti-Plasmodium responses, and therefore we focused on transcripts displaying increased abundance in the parasite-infected aseptic midguts, placing a particular emphasis on those with predicted immune functions. Because of the central role of serine protease cascades in regulating insect immune defenses, we focused the remainder of our analysis on a clip-domain serine protease C2 (CLIPC2, AGAP004317) and a serine protease inhibitor 7 (SRPN7, AGAP007693) that were specifically upregulated in the parasite-infected, aseptic mosquito midgut. We showed that SRPN7 negatively and CLIPC2 positively regulate the anti-Plasmodium defense, independently of the midgut-associated bacteria. Co-silencing assays suggested that these two genes may function together in a signaling cascade. Neither gene was regulated, nor modulated, by infection with the rodent malaria parasite Plasmodium berghei, suggesting that SRPN7 and CLIPC2 are components of a defense system with preferential activity towards P. falciparum. Further analysis using RNA interference determined that these genes do not regulate the anti-Plasmodium defense mediated by the IMD pathway, and both factors act as agonists of the endogenous midgut microbiota, further demonstrating the lack of functional relatedness between these genes and the bacteria-dependent activation of the IMD pathway. This is the first study confirming the existence of a bacteria-independent, anti-P. falciparum defense. Aseptic and septic midguts and carcasses from P. falciparum-infected A. gambiae vs aseptic and septic midguts and carcasses from uninfected, blood-fed A. gambiae. 3 biological replicates and 1 pseudo-replicate per each array.

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Searching for new molecules involved in Anopheles mosquitoes’ response to Plasmodium infection

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