Identification of critical host mitochondrion-associated genes during Ehrlichia chaffeensis infections

CCDC58 is a potential biomarker for diagnosis, prognosis, immunity, and genomic heterogeneity in pan-cancer

Coiled-coil domain-containing 58 (CCDC58) is a member of the CCDC protein family. Similar to other members, CCDC58 exhibits potential tumorigenic roles in a variety of malignancies. However, there is no systematic and comprehensive pan-cancer analysis to investigate the diagnosis, prognosis, immune infiltration, and other related functions of CCDC58. We used several online websites and databases, such as TCGA, GTEx, UALCAN, HPA, CancerSEA, BioGRID, GEPIA 2.0, TIMER 2.0, and TISIDB, to extract CCDC58 expression data and clinical data of patients in pan-cancer. Then, the relationship between CCDC58 expression and diagnosis, prognosis, genetic alterations, DNA methylation, genomic heterogeneity, and immune infiltration level were determined. In addition, the biological function of CCDC58 in liver hepatocellular carcinoma (LIHC) was investigated. Pan-cancer analysis results showed that CCDC58 was differentially expressed in most tumors and showed excellent performance in diagnosis and prediction of prognosis. The expression of CCDC58 was highly correlated with genetic alterations, DNA methylation, and genomic heterogeneity in some tumors. In addition, the correlation analysis of CCDC58 with the level of immune infiltration and immune checkpoint marker genes indicated that CCDC58 might affect the composition of the tumor immune microenvironment. Enrichment analysis showed that CCDC58-related genes were mainly linked to mitosis, chromosome, and cell cycle. Finally, biological function experiments demonstrated that CCDC58 plays an important role in tumor cell proliferation and migration. CCDC58 was first identified as a pan-cancer biomarker. It may be used as a potential therapeutic target to improve the prognosis of patients in the future.

The biology of insect chitinases and their roles at chitinous cuticles

Chitin is one of the most prevalent biomaterials in the natural world. The chitin matrix formation and turnover involve several enzymes for chitin synthesis, maturation, and degradation. Sequencing of the Drosophila genome more than twenty years ago revealed that insect genomes contain a number of chitinases, but why insects need so many different chitinases was unclear. Here, we focus on insect GH18 family chitinases and discuss their participation in chitin matrix formation and degradation. We describe their variations in terms of temporal and spatial expression patterns, molecular function, and physiological consequences at chitinous cuticles. We further provide insight into the catalytic mechanisms by discussing chitinase protein domain structures, substrate binding, and enzymatic activities with respect to structural analysis of the enzymatic GH18 domain, substrate-binding cleft, and characteristic TIM-barrel structure.

Signaling through the dystrophin glycoprotein complex affects the stress-dependent transcriptome in Drosophila

Deficiencies in the human dystrophin glycoprotein complex (DGC), which links the extracellular matrix with the intracellular cytoskeleton, cause muscular dystrophies, a group of incurable disorders associated with heterogeneous muscle, brain and eye abnormalities. Stresses such as nutrient deprivation and aging cause muscle wasting, which can be exacerbated by reduced levels of the DGC in membranes, the integrity of which is vital for muscle health and function. Moreover, the DGC operates in multiple signaling pathways, demonstrating an important function in gene expression regulation. To advance disease diagnostics and treatment strategies, we strive to understand the genetic pathways that are perturbed by DGC mutations. Here, we utilized a Drosophila model to investigate the transcriptomic changes in mutants of four DGC components under temperature and metabolic stress. We identified DGC-dependent genes, stress-dependent genes and genes dependent on the DGC for a proper stress response, confirming a novel function of the DGC in stress-response signaling. This perspective yields new insights into the etiology of muscular dystrophy symptoms, possible treatment directions and a better understanding of DGC signaling and regulation under normal and stress conditions.

Circ-TRIO promotes TNBC progression by regulating the miR-432-5p/CCDC58 axis

Numerous studies have shown that circRNAs are aberrantly expressed in various cancers and play a significant role in tumor progression. However, the molecular mechanisms of circRNAs in triple-negative breast cancer (TNBC) remain ambiguous. By intersecting throughput data and qRT-PCR results from tissues and cell lines, circ-TRIO was identified as a potential oncogenic regulator of TNBC. Moreover, circ-TRIO expression was detected in TNBC tissues and was correlated with the recurrence and prognosis of TNBC patients. The circular characteristics of circ-TRIO were verified by RNase R and CHX assays. Functionally, the knockdown of circ-TRIO inhibited the proliferation, migration and invasion of TNBC cells, while the overexpression of circ-TRIO resulted in the opposite impacts. Mechanistically, a dual luciferase reporter assay and RNA immunoprecipitation were performed and indicated that circ-TRIO could combine with miR-432-5p to regulate the expression of coiled-coil domain containing 58 (CCDC58). In summary, our study illustrates that circ-TRIO plays an important role in the progression of TNBC by regulating the miR-432-5p/CCDC58 axis, which could broaden our insight into the underlying mechanisms and provide a novel prognostic marker of TNBC in the clinic.

Mitochondria as environments for the nuclear genome in Drosophila: mitonuclear G×G×E

Mitochondria evolved from a union of microbial cells belonging to distinct lineages that were likely anaerobic. The evolution of eukaryotes required a massive reorganization of the 2 genomes and eventual adaptation to aerobic environments. The nutrients and oxygen that sustain eukaryotic metabolism today are processed in mitochondria through coordinated expression of 37 mitochondrial genes and over 1000 nuclear genes. This puts mitochondria at the nexus of gene-by-gene (G×G) and gene-by-environment (G×E) interactions that sustain life. Here we use a Drosophila model of mitonuclear genetic interactions to explore the notion that mitochondria are environments for the nuclear genome, and vice versa. We construct factorial combinations of mtDNA and nuclear chromosomes to test for epistatic interactions (G×G), and expose these mitonuclear genotypes to altered dietary environments to examine G×E interactions. We use development time and genome-wide RNAseq analyses to assess the relative contributions of mtDNA, nuclear chromosomes, and environmental effects on these traits (mitonuclear G×G×E). We show that the nuclear transcriptional response to alternative mitochondrial "environments" (G×G) has significant overlap with the transcriptional response of mitonuclear genotypes to altered dietary environments. These analyses point to specific transcription factors (e.g., giant) that mediated these interactions, and identified coexpressed modules of genes that may account for the overlap in differentially expressed genes. Roughly 20% of the transcriptome includes G×G genes that are concordant with G×E genes, suggesting that mitonuclear interactions are part of an organism's environment.

Development of a macrophages-related 4-gene signature and nomogram for the overall survival prediction of hepatocellular carcinoma based on WGCNA and LASSO algorithm

BACKGROUND

Immune system instability and poor prognosis are the two major clinical performance of hepatocellular carcinoma (HCC). Abnormal expression of MiR-424-5p has been reported to accelerate the progression of liver cancer, but it mediated immune cell infiltration imbalance is still unknown. We aim to mine the immune-related genes (IRGs) targeted by miR-424-5p and construct a multi-gene signature to improve the prognostic prediction of HCC.

METHODS

The HCC-related data of the cancer genome atlas (TCGA) database and the GSE14520 dataset of the gene expression omnibus (GEO) database were downloaded as the discovery dataset and the validation dataset, respectively. Weighted gene co-expression network analysis (WGCNA), the deconvolution algorithm of CIBERSORT and LASSO algorithm participated in the identification of IRGs and the development of prognostic signature and nomogram.

RESULTS

Our study found that the abundance of macrophages M0, M1 and M2 are all drastically changed during the cancerous process. A total of 920 macrophages infiltration-related LRGs were identified and a novel 4-gene signature (CDCA8, CBX2, UCK2 and SOCS2) with superior prognostic independence was established. The prognostic signature based risk score has superior capability to identify high-risk patients and predict overall survival (p < 0.001; AUC = 0.798 for 1 year; AUC = 0.748 for 3 years; AUC = 0.721 for 5 years). And it (C-index = 0.726) has a better prognostic potential than the TNM stage (C-index = 0.619), which is widely adopted in clinical practice. Additionally, the nomogram formed by combining the risk score and TNM stage further improved the accuracy of survival prediction (C-index = 0.733).

CONCLUSION

In summary, the immune landscape with abnormal infiltration of macrophages may be one of the prelude to the cancerous process. The novel macrophages-related 4-gene signature is expected to become a potential prognostic marker in liver cancer.

The intermembrane space protein Mix23 is a novel stress-induced mitochondrial import factor

The biogenesis of mitochondria requires the import of hundreds of precursor proteins. These proteins are transported post-translationally with the help of chaperones, meaning that the overproduction of mitochondrial proteins or the limited availability of chaperones can lead to the accumulation of cytosolic precursor proteins. This imposes a severe challenge to cytosolic proteostasis and triggers a specific transcription program called the mitoprotein-induced stress response, which activates the proteasome system. This coincides with the repression of mitochondrial proteins, including many proteins of the intermembrane space. In contrast, herein we report that the so-far-uncharacterized intermembrane space protein Mix23 is considerably up-regulated when mitochondrial import is perturbed. Mix23 is evolutionarily conserved and a homolog of the human protein CCDC58. We found that, like the subunits of the proteasome, Mix23 is under control of the transcription factor Rpn4. It is imported into mitochondria by the mitochondrial disulfide relay. Mix23 is critical for the efficient import of proteins into the mitochondrial matrix, particularly if the function of the translocase of the inner membrane 23 is compromised such as in temperature-sensitive mutants of Tim17. Our observations identify Mix23 as a novel regulator or stabilizer of the mitochondrial protein import machinery that is specifically up-regulated upon mitoprotein-induced stress conditions.

Comparative proteomic analysis of different stages of breast cancer tissues using ultra high performance liquid chromatography tandem mass spectrometer

BACKGROUND

Breast cancer is the fifth most prevalent cause of death among women worldwide. It is also one of the most common types of cancer among Malaysian women. This study aimed to characterize and differentiate the proteomics profiles of different stages of breast cancer and its matched adjacent normal tissues in Malaysian breast cancer patients. Also, this study aimed to construct a pertinent protein pathway involved in each stage of cancer.

METHODS

In total, 80 samples of tumor and matched adjacent normal tissues were collected from breast cancer patients at Seberang Jaya Hospital (SJH) and Kepala Batas Hospital (KBH), both in Penang, Malaysia. The protein expression profiles of breast cancer and normal tissues were mapped by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The Gel-Eluted Liquid Fractionation Entrapment Electrophoresis (GELFREE) Technology System was used for the separation and fractionation of extracted proteins, which also were analyzed to maximize protein detection. The protein fractions were then analyzed by tandem mass spectrometry (LC-MS/MS) analysis using LC/MS LTQ-Orbitrap Fusion and Elite. This study identified the proteins contained within the tissue samples using de novo sequencing and database matching via PEAKS software. We performed two different pathway analyses, DAVID and STRING, in the sets of proteins from stage 2 and stage 3 breast cancer samples. The lists of molecules were generated by the REACTOME-FI plugin, part of the CYTOSCAPE tool, and linker nodes were added in order to generate a connected network. Then, pathway enrichment was obtained, and a graphical model was created to depict the participation of the input proteins as well as the linker nodes.

RESULTS

This study identified 12 proteins that were detected in stage 2 tumor tissues, and 17 proteins that were detected in stage 3 tumor tissues, related to their normal counterparts. It also identified some proteins that were present in stage 2 but not stage 3 and vice versa. Based on these results, this study clarified unique proteins pathways involved in carcinogenesis within stage 2 and stage 3 breast cancers.

CONCLUSIONS

This study provided some useful insights about the proteins associated with breast cancer carcinogenesis and could establish an important foundation for future cancer-related discoveries using differential proteomics profiling. Beyond protein identification, this study considered the interaction, function, network, signaling pathway, and protein pathway involved in each profile. These results suggest that knowledge of protein expression, especially in stage 2 and stage 3 breast cancer, can provide important clues that may enable the discovery of novel biomarkers in carcinogenesis.

Interaction between Intracellular Bacterial Pathogens and Host Cell Mitochondria

Mitochondria are essential and highly dynamic organelles whose morphology is determined by a steady-state balance between fusion and fission. Mitochondrial morphology and function are tightly connected. Because they are involved in many important cellular processes, including energy production, cell-autonomous immunity, and apoptosis, mitochondria present an attractive target for pathogens. Here, we explore the relationship between host cell mitochondria and intracellular bacteria, with a focus on mitochondrial morphology and function, as well as apoptosis. Modulation of apoptosis can allow bacteria to establish their replicative niche or support bacterial dissemination. Furthermore, bacteria can manipulate mitochondrial morphology and function through secreted effector proteins and can also contribute to the establishment of a successful infection, e.g., by favoring access to nutrients and/or evasion of the immune system.

Spatially Restricting Bioorthogonal Nucleoside Biosynthesis Enables Selective Metabolic Labeling of the Mitochondrial Transcriptome

The cellular RNA pool in animals arises from two separate genomes stored in the nucleus and multiple mitochondria. Chemical methods to track nascent RNA synthesis are unable to distinguish between these two with stringency. Herein, we report that spatially restricting bioorthogonal nucleoside biosynthesis enables, for the first time, selective metabolic labeling of the RNA transcribed in the mitochondria. We envision that this approach could open the door for heretofore-impossible analyses of mitochondrial RNA. Beyond our results revealed herein, our approach provides a roadmap for researchers to begin to design strategies to examine biomolecules within subcellular compartments.

MyD88-dependent inflammasome activation and autophagy inhibition contributes to Ehrlichia-induced liver injury and toxic shock

Severe hepatic inflammation is a common cause of acute liver injury following systemic infection with Ehrlichia, obligate Gram-negative intracellular bacteria that lack lipopolysaccharide (LPS). We have previously shown that type I IFN (IFN-I) and inflammasome activation are key host-pathogenic mediators that promote excessive inflammation and liver damage following fatal Ehrlichia infection. However, the underlying signals and mechanisms that regulate protective immunity and immunopathology during Ehrlichia infection are not well understood. To address this issue, we compared susceptibility to lethal Ixodes ovatus Ehrlichia (IOE) infection between wild type (WT) and MyD88-deficient (MyD88^-/-) mice. We show here that MyD88^-/- mice exhibited decreased inflammasome activation, attenuated liver injury, and were more resistant to lethal infection than WT mice, despite suppressed protective immunity and increased bacterial burden in the liver. MyD88-dependent inflammasome activation was also dependent on activation of the metabolic checkpoint kinase mammalian target of rapamycin complex 1 (mTORC1), inhibition of autophagic flux, and defective mitophagy in macrophages. Blocking mTORC1 signaling in infected WT mice and primary macrophages enhanced bacterial replication and attenuated inflammasome activation, suggesting autophagy promotes bacterial replication while inhibiting inflammasome activation. Finally, our data suggest TLR9 and IFN-I are upstream signaling mechanisms triggering MyD88-mediated mTORC1 and inflammasome activation in macrophages following Ehrlichia infection. This study reveals that Ehrlichia-induced liver injury and toxic shock are mediated by MyD88-dependent inflammasome activation and autophagy inhibition.

Human monocytic ehrlichiosis (HME) is the most prevalent emerging infectious disease in the United States. Ehrlichia chaffeensis, etiologic agent of HME, is a Gram negative obligate intracellular bacterium transmitted by infected tick bites and can infect different cell type. Although Ehrlichia lack lipopolysaccharide (LPS), they induce potentially life threatening HME that mimic sepsis or toxic shock associated with multi-organ failure. The clinical diagnosis of HME is difficult, and definitive diagnosis is most often retrospective. Late antibiotic treatment is frequently ineffective in preventing disease progression to fatal multi-organ failure. Liver failure is one of the most serious complications and the most frequent cause of death in patients with HME, however we only have a limited understanding of how this liver failure is caused during fatal Ehrlichia infection. The objective of this study is to determine how LPS-negative Ehrlichia activates inflammatory responses in macrophages during Ehrlichia infection to promote liver damage. We show here that MyD88-signaling causes detrimental derangement of the immune system and subsequent liver damage by regulating two key innate immune events in macrophages: autophagy and inflammasome activation. Targeting host-pathogenic pathways in ehrlichiosis can be incorporated into future design of novel therapeutic approaches for HME.

Analysis of the genome of the New Zealand giant collembolan (Holacanthella duospinosa) sheds light on hexapod evolution

BACKGROUND

The New Zealand collembolan genus Holacanthella contains the largest species of springtails (Collembola) in the world. Using Illumina technology we have sequenced and assembled a draft genome and transcriptome from Holacanthella duospinosa (Salmon). We have used this annotated assembly to investigate the genetic basis of a range of traits critical to the evolution of the Hexapoda, the phylogenetic position of H. duospinosa and potential horizontal gene transfer events.

RESULTS

Our genome assembly was ~375 Mbp in size with a scaffold N50 of ~230 Kbp and sequencing coverage of ~180×. DNA elements, LTRs and simple repeats and LINEs formed the largest components and SINEs were very rare. Phylogenomics (370,877 amino acids) placed H. duospinosa within the Neanuridae. We recovered orthologs of the conserved sex determination genes thought to play a role in sex determination. Analysis of CpG content suggested the absence of DNA methylation, and consistent with this we were unable to detect orthologs of the DNA methyltransferase enzymes. The small subunit rRNA gene contained a possible retrotransposon. The Hox gene complex was broken over two scaffolds. For chemosensory ability, at least 15 and 18 ionotropic glutamate and gustatory receptors were identified, respectively. However, we were unable to identify any odorant receptors or their obligate co-receptor Orco. Twenty-three chitinase-like genes were identified from the assembly. Members of this multigene family may play roles in the digestion of fungal cell walls, a common food source for these saproxylic organisms. We also detected 59 and 96 genes that blasted to bacteria and fungi, respectively, but were located on scaffolds that otherwise contained arthropod genes.

CONCLUSIONS

The genome of H. duospinosa contains some unusual features including a Hox complex broken over two scaffolds, in a different manner to other arthropod species, a lack of odorant receptor genes and an apparent lack of environmentally responsive DNA methylation, unlike many other arthropods. Our detection of candidate horizontal gene transfer candidates confirms that this phenomenon is occurring across Collembola. These findings allow us to narrow down the regions of the arthropod phylogeny where key innovations have occurred that have facilitated the evolutionary success of Hexapoda.

The mitochondrial permeability transition pore in AD 2016: An update

Over the past 30years the mitochondrial permeability transition - the permeabilization of the inner mitochondrial membrane due to the opening of a wide pore - has progressed from being considered a curious artifact induced in isolated mitochondria by Ca(2+) and phosphate to a key cell-death-inducing process in several major pathologies. Its relevance is by now universally acknowledged and a pharmacology targeting the phenomenon is being developed. The molecular nature of the pore remains to this day uncertain, but progress has recently been made with the identification of the FOF1 ATP synthase as the probable proteic substrate. Researchers sharing this conviction are however divided into two camps: these believing that only the ATP synthase dimers or oligomers can form the pore, presumably in the contact region between monomers, and those who consider that the ring-forming c subunits in the FO sector actually constitute the walls of the pore. The latest development is the emergence of a new candidate: Spastic Paraplegia 7 (SPG7), a mitochondrial AAA-type membrane protease which forms a 6-stave barrel. This review summarizes recent developments of research on the pathophysiological relevance and on the molecular nature of the mitochondrial permeability transition pore. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

Chitinases and Imaginal disc growth factors organize the extracellular matrix formation at barrier tissues in insects

The cuticle forms an apical extracellular-matrix (ECM) that covers exposed organs, such as epidermis, trachea and gut, for organizing morphogenesis and protection of insects. Recently, we reported that cuticle proteins and chitin are involved in ECM formation. However, molecular mechanisms that control assembly, maturation and replacement of the ECM and its components are not well known. Here we investigated the poorly described glyco-18-domain hydrolase family in Drosophila and identified the Chitinases (Chts) and imaginal-disc-growth-factors (Idgfs) that are essential for larval and adult molting. We demonstrate that Cht and idgf depletion results in deformed cuticles, larval and adult molting defects, and insufficient protection against wounding and bacterial infection, which altogether leads to early lethality. We show that Cht2/Cht5/Cht7/Cht9/Cht12 and idgf1/idgf3/idgf4/idgf5/idgf6 are needed for organizing proteins and chitin-matrix at the apical cell surface. Our data indicate that normal ECM formation requires Chts, which potentially hydrolyze chitin-polymers. We further suggest that the non-enzymatic idgfs act as structural proteins to maintain the ECM scaffold against chitinolytic degradation. Conservation of Chts and Idgfs proposes analogous roles in ECM dynamics across the insect taxa, indicating that Chts/Idgfs are new targets for species specific pest control.

Attenuation of enoyl coenzyme A hydratase 1 expression in colorectal cancer cells using small interfering RNA inhibits cell proliferation and migration

Colorectal cancer is one of the most commonly diagnosed types of cancer and is a leading cause of cancer-associated mortality worldwide. Short chain enoyl coenzyme A hydratase 1 (ECHS1) is an important gene involved in the mitochondrial fatty acid β-oxidation pathway. In addition, ECHS1 has been implicated in a variety of cancers, including breast, prostate, colon and liver cancer. The aim of the present study was to examine the expression of ECHS1 in the human HCT-8 colorectal cancer cell line. The results showed that ECHS1 expression was significantly increased in poorly-differentiated cells compared with that in well-differentiated cells. In order to further investigate the functions of ECHS1 in colorectal cancer cells, a stably transfected HCT-8 cell line expressing small interfering (si)RNA targeting the ECHS1 gene was established. The expression of the ECHS1 siRNA was found to reduce ECHS1 protein levels in ECHS1-silenced cells by >40%. Cell proliferation and cell migration of the siECHS1 cells were characterized using Cell Counting Kit-8 and Transwell assays, respectively, the results of which showed that the constitutive knockdown of the ECSH1 gene in HCT-8 cells significantly inhibited cell proliferation and migration. Furthermore, decreased levels of Akt and glycogen synthase kinase (GSK)3β phosphorylation were observed in ECHS1-silenced HCT-8 cells compared with that of parental or pU6 empty vector-transfected cells. In conclusion, the results of the present study suggested that ECHS1 may have an important role in colorectal cancer cell proliferation and migration via activation of Akt- and GSK3β-associated signaling pathways.

Quantitative profiling of Drosophila melanogaster Dscam1 isoforms reveals no changes in splicing after bacterial exposure

The hypervariable Dscam1 (Down syndrome cell adhesion molecule 1) gene can produce thousands of different ectodomain isoforms via mutually exclusive alternative splicing. Dscam1 appears to be involved in the immune response of some insects and crustaceans. It has been proposed that the diverse isoforms may be involved in the recognition of, or the defence against, diverse parasite epitopes, although evidence to support this is sparse. A prediction that can be generated from this hypothesis is that the gene expression of specific exons and/or isoforms is influenced by exposure to an immune elicitor. To test this hypothesis, we for the first time, use a long read RNA sequencing method to directly investigate the Dscam1 splicing pattern after exposing adult Drosophila melanogaster and a S2 cell line to live Escherichia coli. After bacterial exposure both models showed increased expression of immune-related genes, indicating that the immune system had been activated. However there were no changes in total Dscam1 mRNA expression. RNA sequencing further showed that there were no significant changes in individual exon expression and no changes in isoform splicing patterns in response to bacterial exposure. Therefore our studies do not support a change of D. melanogaster Dscam1 isoform diversity in response to live E. coli. Nevertheless, in future this approach could be used to identify potentially immune-related Dscam1 splicing regulation in other host species or in response to other pathogens.

Coinfection of tick cell lines has variable effects on replication of intracellular bacterial and viral pathogens

Ticks transmit various human and animal microbial pathogens and may harbour more than one pathogen simultaneously. Both viruses and bacteria can trigger, and may subsequently suppress, vertebrate host and arthropod vector anti-microbial responses. Microbial coinfection of ticks could lead to an advantage or disadvantage for one or more of the microorganisms. In this preliminary study, cell lines derived from the ticks Ixodes scapularis and Ixodes ricinus were infected sequentially with 2 arthropod-borne pathogens, Borrelia burgdorferi s.s., Ehrlichia ruminantium, or Semliki Forest virus (SFV), and the effect of coinfection on the replication of these pathogens was measured. Prior infection of tick cell cultures with the spirochaete B. burgdorferi enhanced subsequent replication of the rickettsial pathogen E. ruminantium whereas addition of spirochaetes to cells infected with E. ruminantium had no effect on growth of the latter. Both prior and subsequent presence of B. burgdorferi also had a positive effect on SFV replication. Presence of E. ruminantium or SFV had no measurable effect on B. burgdorferi growth. In tick cells infected first with E. ruminantium and then with SFV, virus replication was significantly higher across all time points measured (24, 48, 72h post infection), while presence of the virus had no detectable effect on bacterial growth. When cells were infected first with SFV and then with E. ruminantium, there was no effect on replication of either pathogen. The results of this preliminary study indicate that interplay does occur between different pathogens during infection of tick cells. Further study is needed to determine if this results from direct pathogen-pathogen interaction or from effects on host cell defences, and to determine if these observations also apply in vivo in ticks. If presence of one pathogen in the tick vector results in increased replication of another, this could have implications for disease transmission and incidence.

Ehrlichia chaffeensis replication sites in adult Drosophila melanogaster

Ehrlichia chaffeensis is a Gram-negative, obligate intracellular bacterium which causes the tick-borne disease human monocytic ehrlichiosis. In vertebrates, E. chaffeensis replicates in monocytes and macrophages. However, no clear cell or tissue tropism has been defined in arthropods. Our group identified two host genes that control E. chaffeensis replication and infection in vivo in Drosophila, Uridine cytidine kinase and separation anxiety. Using the UAS-GAL4 RNAi system, we generated F1 flies (UAS-gene of interestRNAi x tissue-GAL4 flies) that have Uck2 or san silenced in ubiquitous or tissue-specific fashion. When Uck2 or san were suppressed in the hemocytes or in the fat body, E. chaffeensis replicated poorly and caused significantly less severe infections. Silencing of these genes in the eyes, wings, or the salivary glands did not impact fly susceptibility or bacterial replication. Our data suggest that in Drosophila, E. chaffeensis replicates within the hemocytes, the insect homolog of mammalian macrophages, and in the fat body, the liver homolog of mammals.