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Xue-Jie Yu

Publications and source records attributed to Xue-Jie Yu.

14 recordsLinked to original sources
PubMed2006

Restriction and expansion of Ehrlichia strain diversity.

Ehrlichia are tick-borne gram negative, obligately intracellular bacteria. The 16S rRNA gene DNA sequences are highly conserved among strains of each Ehrlichia species. The 28-kDa/Map-1 outer membrane protein genes are highly diversified among strains of Ehrlichia chaffeensis and E. ruminantium, but are highly conserved among E. canis isolates. The diversity of the immunodominant proteins of E. chaffeensis and E. ruminantium in contrast with the conservation of the immunodominant proteins of E. canis suggests that E. chaffeensis and E. ruminantium face more host immune pressure than E. canis or that E. chaffeensis and E. ruminantium evolved earlier than E. canis and have diverged.

Bacterial Outer Membrane Proteins↗
PubMed2005

A mutation inactivating the methyltransferase gene in avirulent Madrid E strain of Rickettsia prowazekii reverted to wild type in the virulent revertant strain Evir.

Rickettsia prowazekii Madrid E (E) strain is an effective vaccine, but can revert to virulent status when passaged in animals. The aim of this study is to identify the reverse mutation that may determine the virulence of R. prowazekii by comparing the genetic structures of E strain and its virulent revertant Evir strain. We determined that the gene (Rp028/Rp027) encoding the methyltransferase was mutated by frameshift in avirulent E strain but not in virulent revertant Evir strain and wild type virulent Breinl strain. We conclude that the mutation in the E strain gene reverts to wild type in the virulent revertant Evir strain. Whether the mutation plays an essential role in the attenuation of E strain needs to be further investigated.

Base Sequence↗
PubMed2005

Expression of the Rickettsia prowazekii pld or tlyC gene in Salmonella enterica serovar Typhimurium mediates phagosomal escape.

Members of the genus Rickettsia possess the ability to invade host cells and promptly escape from phagosomal vacuoles into the host cell cytosol, thereby avoiding destruction within the endosomal pathway. The mechanism underlying rickettsial phagosomal escape remains unknown, although the genomic sequences of several rickettsial species have allowed for the identification of four genes with potential membranolytic activities (tlyA, tlyC, pat1, and pld). This study was undertaken to determine which of the selected genes of Rickettsia prowazekii mediate the escape process. Quantitative ultrastructural analyses indicated that the period of active phagosomal escape was between 30 and 50 min postinfection. Reverse transcriptase PCR analyses determined that tlyC and pld were transcribed during the period of active phagosomal escape but that tlyA and pat1 were not. The functionality of both tlyC and pld was determined by complementation studies of Salmonella, which replicates within endosomes. Complementation of Salmonella organisms with either tlyC or pld resulted in the escape of transformants from endosomal vacuoles into the host cell cytosol demonstrated by quantitative ultrastructural analyses. These data suggest a role for tlyC and pld in the process of phagosomal escape by R. prowazekii.

Animals↗
PubMed2005

Progress in rickettsial genome analysis from pioneering of Rickettsia prowazekii to the recent Rickettsia typhi.

Three rickettsial genomes have been sequenced and annotated. Rickettsia prowazekii and R. typhi have similar gene order and content. The few differences between R. prowazekii and R. typhi include a 12-kb insertion in R. prowazekii, a large inversion close to the origin of replication in R. typhi, and loss of the complete cytochrome c oxidase system by R. typhi. R. prowazekii, R. typhi, and R. conorii have 13, 24, and 560 unique genes, respectively, and share 775 genes, most likely their essential genes. The small genomes contain many pseudogenes and much noncoding DNA, reflecting the process of genome decay. R. typhi contains the largest number of pseudogenes (41), and R. conorii the fewest, in accordance with its larger number of genes and smaller proportion of noncoding DNA. Conversely, typhus rickettsiae contain fewer repetitive sequences. These genomes portray the key themes of rickettsial intracellular survival: lack of enzymes for sugar metabolism, lipid biosynthesis, nucleotide synthesis, and amino acid metabolism, suggesting that rickettsiae depend on the host for nutrition and building blocks; enzymes for the complete TCA cycle and several copies of ATP/ADP translocase genes, suggesting independent synthesis of ATP and acquisition of host ATP; and type IV secretion system. All rickettsiae share two outer membrane proteins (OmpB and Sca 4) and LPS biosynthesis machinery. RickA, unique to spotted fever rickettsiae, plays a role in induction of actin polymerization in R. conorii, but not in R. prowazekii or R. typhi. The genome of R. typhi contains four potentially membranolytic genes (tlyA, tlyC, pldA, and pat-1) and five autotransporter genes, sca 1, sca 2, sca 3, ompA, and ompB. The presence of six 50-amino acid repeat units in Sca 2 suggests function as an adhesin. The high laboratory passage of the sequenced strains raises the issue of the occurrence of laboratory mutations in genes not required for growth in cell culture or eggs. Resequencing revealed that eight annotated pseudogenes of E strain are actually intact genes. Comparative genomics of virulent and avirulent strains of rickettsial species may reveal their virulence factors.

Genome, Bacterial↗
PubMed2005

Overcoming barriers to the transformation of the genus Ehrlichia.

While bacterial transformation has evolved since the early 20th century to allow for the genetic manipulation of a variety of microbial agents, rickettsial organisms have proved resistant to such advances until only recently. The Ehrlichia are small, gram-negative, obligately intracellular bacterial parasites, which belong to the family Anaplasmataceae and cause a variety of infections in human and animal hosts. E. chaffeensis is the causative agent of human monocytotropic ehrlichiosis and is transmitted by Amblyomma americanum, the Lone Star tick. In this work, we describe the first report of successful transformation of a closely related ehrlichial species, the murine monocytotropic species E. muris. Application of these techniques should allow for a wide variety of molecular studies to be performed that were previously impossible. This heralds the beginning of a new era in ehrlichial research.

Animals↗
PubMed2005

Analysis of ehrlichial p28 gene expression in a murine model of persistent infection.

Historically, ehrlichioses were tick-borne diseases of veterinary medical importance and are now important emerging infectious diseases in humans. p28s are encoded by multigene families with ORFs tandemly arranged with intergenic spaces of variable lengths. We reported initial sequencing of the Ehrlichia muris p28 locus. A model of persistent infection was described and provided tools for study of persistent ehrlichial infection. We completed the sequence of the E. muris p28 locus and examined mRNA expression.

Animals↗
PubMed2004

Complete genome sequence of Rickettsia typhi and comparison with sequences of other rickettsiae.

Rickettsia typhi, the causative agent of murine typhus, is an obligate intracellular bacterium with a life cycle involving both vertebrate and invertebrate hosts. Here we present the complete genome sequence of R. typhi (1,111,496 bp) and compare it to the two published rickettsial genome sequences: R. prowazekii and R. conorii. We identified 877 genes in R. typhi encoding 3 rRNAs, 33 tRNAs, 3 noncoding RNAs, and 838 proteins, 3 of which are frameshifts. In addition, we discovered more than 40 pseudogenes, including the entire cytochrome c oxidase system. The three rickettsial genomes share 775 genes: 23 are found only in R. prowazekii and R. typhi, 15 are found only in R. conorii and R. typhi, and 24 are unique to R. typhi. Although most of the genes are colinear, there is a 35-kb inversion in gene order, which is close to the replication terminus, in R. typhi, compared to R. prowazekii and R. conorii. In addition, we found a 124-kb R. typhi-specific inversion, starting 19 kb from the origin of replication, compared to R. prowazekii and R. conorii. Inversions in this region are also seen in the unpublished genome sequences of R. sibirica and R. rickettsii, indicating that this region is a hot spot for rearrangements. Genome comparisons also revealed a 12-kb insertion in the R. prowazekii genome, relative to R. typhi and R. conorii, which appears to have occurred after the typhus (R. prowazekii and R. typhi) and spotted fever (R. conorii) groups diverged. The three-way comparison allowed further in silico analysis of the SpoT split genes, leading us to propose that the stringent response system is still functional in these rickettsiae.

Chromosome Inversion↗
PubMed2004

Ehrlichia chaffeensis: a prevalent, life-threatening, emerging pathogen.

Ehrlichia chaffeensis are small, obligately intracellular, endosomal bacteria with tropism for macrophages. Persistent infection in reservoir white-tailed deer is transmitted by lone star ticks. Flu-like illness can progress to severe multisystem disease with toxic shock-like syndrome, meningitis, or ARDS. The case-fatality rate is 2.7%. Leukopenia and thrombocytopenia are diagnostically useful. Granulomas are associated with control of the infection. Ehrlichial proteins and glycoproteins have been sequenced and expressed for diagnostic serology and vaccine development. Mouse models (mild disease and persistent infection with E. muris and fatal monocytotropic ehrlichiosis with a Japanese tick isolate) revealed that CD4 and CD8 T type 1 lymphocyte responses, IFN-gamma, TNF-alpha, and antibodies play roles in protective immunity, while a weak CD4 T-helper response, overproduction of TNF-alpha, and very high IL-10 are associated with toxic shock-like mortality. Protection against fatal ehrlichiosis was achieved by prior infection with low virulence E. muris. Acute clinical diagnosis is difficult except by PCR. Response to doxycycline is dramatic.

Animals↗
PubMed2003

Experimental Ehrlichia chaffeensis infection in beagles.

A canine model for human monocytic ehrlichiosis was used to assess persistent infection and antigenic variation of Ehrlichia chaffeensis. Two beagle dogs were infected subcutaneously with E. chaffeensis Arkansas strain. The dogs were observed for 6 months after inoculation for clinical signs, blood chemistry changes, antibodies to E. chaffeensis and presence of E. chaffeensis in the blood. Both dogs developed thrombocytopenia, but exhibited normal body temperatures during the entire course of infection. In one dog, E. chaffeensis was cultivated for up to 74 days post-inoculation and E. chaffeensis DNA was detected in the dog's blood for up to 81 days. In the other dog, E. chaffeensis was cultured for up to 102 days and E. chaffeensis DNA was detected in the blood for up to 117 days. PCR amplification and DNA sequence analysis indicated that there was no genetic variation in the 120 kDa outer-membrane glycoprotein gene of E. chaffeensis during infection of the dogs. The dogs developed antibodies to the immunodominant proteins of E. chaffeensis, including the 175, 140, 120, 80, 50 and 28 kDa proteins, starting in the fifth week post-inoculation. The dogs maintained high antibody titres throughout the 6-month study period. These results indicate that dogs become carriers of E. chaffeensis for 2-4 months after infection without exhibiting signs of clinical disease, suggesting that dogs may serve as a natural host for E. chaffeensis.

Animals↗
PubMed2003

Identification of CD8 T-lymphocyte epitopes in OmpB of Rickettsia conorii.

The 1.2-kb DNA fragment of the Rickettsia conorii outer membrane protein B gene (OmpB(451-846)) was subcloned using site-specific PCR primers and expressed as six smaller fragments: OmpB(458-652), OmpB(595-744), OmpB(595-654), OmpB(645-692), OmpB(689-744), and OmpB(739-848). NCTC cells transfected with a mammalian expression vector expressing the fragments OmpB(689-744) and OmpB(739-848) stimulated immune anti-R. conorii CD8 T lymphocytes, suggesting the presence of CD8 T-lymphocyte-stimulating epitopes on these fragments. In order to further characterize the CD8 T-lymphocyte-stimulatory elements, CD8 T-lymphocyte epitopes on OmpB(689-744) and OmpB(739-848) were mapped by overlapping synthetic peptides. The ability of these synthetic peptides to stimulate immune CD8 T lymphocytes was determined by gamma interferon (IFN-gamma) production and cell proliferation after incubation with simian virus 40-transformed murine vascular endothelial cells in the presence of a 20 micro M solution of each synthetic peptide. Five synthetic peptides, SKGVNVDTV (OmpB(708-716)), ANVGSFVFN (OmpB(735-743)), IVSGTVGGQ (OmpB(749-757)), ANSTLQIGG (OmpB(789-797)), and IVEFVNTGP (OmpB(812-820)), induced secretion of IFN-gamma at significantly higher levels than the controls. Three of these five peptides, SKGVNVDTV (OmpB(708-716)), ANSTLQIGG (OmpB(789-797)), and IVEFVNTGP (OmpB(812-820)), also stimulated the proliferation of immune CD8 T lymphocytes. Significantly higher levels of specific cytotoxic T-lymphocyte killing were observed with the same three synthetic peptides, SKGVNVDTV (OmpB(708-716)), ANSTLQIGG (OmpB(789-797)), and IVEFVNTGP (OmpB(812-820)).

Animals↗
PubMed2003

Evaluation of transovarial transmission and transmissibility of Ehrlichia chaffeensis (Rickettsiales: Anaplasmataceae) in Amblyomma americanum (Acari: Ixodidae).

It has long been assumed that Ehrlichia chaffeensis (Anderson, Dawson & Wilson), is not transmitted transovarially in the lone star tick vector Amblyomma americanum (L.). To test this hypothesis, three beagle dogs, Canis familiaris (L.) (Carnivora: Canidae), were subcutaneously infected with E. chaffeensis (Arkansas strain). Uninfected nymphal lone star ticks were placed on the infected dogs and allowed to feed to repletion. These nymphal ticks were allowed to molt, and five of five adult female ticks sampled were confirmed to be infected by polymerase chain reaction (PCR). Forty infected adult ticks, the majority of which were female with several males included to stimulate feeding, were then placed on two uninfected dogs. Fourteen females were removed early and the rest were allowed to feed to repletion. After feeding to repletion, the six remaining females detached and two of these females were tested preoviposition, whereas the remaining four were allowed to lay eggs. All six of these fully engorged females tested negative by PCR. The egg clutches laid by four engorged adult females, and the larvae that hatched from these eggs along with larvae from a previously untested egg clutch, were shown to be uninfected by PCR. This seems to support the long-held assumption of lack of transovarial transmission. Also of interest, we found that these PCR-confirmed infected adult ticks reared in the laboratory did not transmit E. chaffeensis to uninfected dogs.

Animals↗
PubMed2002

Antigenic variation of Ehrlichia chaffeensis resulting from differential expression of the 28-kilodalton protein gene family.

The transcriptional activity and allele variation of the 28-kDa outer membrane protein gene (p28) of Ehrlichia chaffeensis were analyzed to determine the mechanism of the antigenic variation of the 28-kDa outer membrane proteins. Reverse transcriptase PCR amplification of mRNA indicated that 16 of the 22 members of the p28 multigene family were transcribed. Amino acid sequence analysis indicated that the p28-19 protein was produced in vitro in the Arkansas strain. The p28-19 gene and its promoter region were sequenced and compared in 12 clinical isolates of E. chaffeensis to determine allele variation. The variation of the p28-19 gene among the isolates is limited to three types represented by strains Arkansas, 91HE17, and Sapulpa, respectively. These results indicate that the majority of the p28 genes are active genes and that antigenic variation of the E. chaffeensis 28-kDa proteins may result from differential expression of the p28 gene family members rather than gene conversion.

Alleles↗