Identification of Eimeria bovis merozoite cDNAs using differential mRNA display

Identification of differentially expressed cDNAs in Acanthamoeba culbertsoni after mouse brain passage

Free-living amoebae of the genus Acanthamoeba are causative agents of granulomatous amebic encephalitis and amebic keratitis. Because the virulence of Acanthamoeba culbertsoni cultured in the laboratory is restored by consecutive brain passages, we examined the genes induced in mouse brain-passaged A. culbertsoni by differential display reverse transcriptase polymerase chain reaction (DDRT-PCR). Enhanced A. culbertsoni virulence was observed during the second mouse brain passage, i.e., infected mouse mortality increased from 5% to 70%. Ten cDNAs induced during mouse brain passage were identified by DDRT-PCR and this was confirmed by northern blot analysis. BlastX searches of these cDNAs indicated the upregulations of genes encoding predictive NADH-dehydrogenase, proteasomal ATPase, and GDP-mannose pyrophosphorylase B, which have previously been reported to be associated with A. culbertsoni virulence factors.

Differential display analysis of gene expression in two immunologically distinct strains of Eimeria maxima

Gene expression during sporulation and sporozoite excystation of two strains of Eimeria maxima was analyzed using the mRNA differential display technique. The two strains, the Guelph strain (GS) and a single sporocyst-derived strain (M6) from Florida, have been shown to be immunologically distinct. We isolated and cloned a 453-bp complimentary DNA (cDNA) fragment (GS-453) found only in GS sporozoites. In GS, this mRNA begins to be expressed during the earliest stages of oocyst sporulation and is continuously expressed up to and including in the excysted sporozoite. In all Northern blots, digoxigenin (DIG)-labeled GS-453 probe recognized an mRNA of approximately 1.6 kb from GS but not from RNA of M6. Southern blots using various endonucleases and probed with DIG-labeled GS-453 demonstrated that the genomes of both strains contained sufficiently similar sequences to permit hybridization with the probe, but the pattern of hybridization differed between the two strains. Extensive searches of the GenBank, European Molecular Biology Laboratory, and various apicomplexan expressed sequence tag databases using the DNA or inferred amino acid sequences of GS-453 cDNA clone did not identify similarity to any existing sequences.

Identification of a sporozoite-specific member of the Toxoplasma SAG superfamily via genetic complementation

Toxoplasma gondii sporozoites possess an array of stage-specific antigens that are localized to the membrane and internal cellular space, as well as secreted into the primary parasitophorous vacuole. Specific labelling of viable sporozoites excysted from oocysts reveals a complex admixture of surface proteins partially shared with tachyzoites. SAG1, SRS3 and SAG3 were detected on sporozoites as well as numerous minor antigens. In contrast, tachyzoite SAG2A and B were completely absent whereas a dominant 25 kDa protein was unique to the sporozoite surface. The sporozoite gene encoding this protein was identified in tachyzoites genetically complemented with a sporozoite cDNA library and cloned via site-specific recombination into a bacterial shuttle vector. The sporozoite cDNA identified in these experiments encoded a protein with conserved structural features of the prototypical T. gondii SAG1 (P30) and shared sequence identity with surface proteins from Sarcocystis spp. This new member of the SAG superfamily was designated SporoSAG. Expression of SporoSAG in tachyzoites conferred enhanced invasion on transgenic parasites suggesting a role for this protein in oocyst/sporozoite transmission to susceptible hosts.

Plasmodium falciparum: differential display analysis of gene expression during gametocytogenesis

With the Plasmodium falciparum genome sequencing near completion, functional analysis of individual parasite genes has become the major task of the postgenomic era. Understanding the expression patterns of individual genes is the initial step toward this goal. In this report, we have examined gene expression during gametocytogenesis of the malaria parasite, P. falciparum, using a modified differential display (DD) method. The modifications of this method include adjusting the dNTP mix, using upstream primers with higher AT contents, and reducing the extension temperature of the polymerase chain reaction (PCR). With a combination of 16 arbitrary upstream primers and 3 one-base-anchored oligo(dT) primers, we have successfully cloned 80 unique cDNA tags from stage IV-V gametocytes. Further analysis by dot blots and semiquantitative reverse transcriptase-PCR showed that at least 49 cDNAs had induced or elevated levels of expression in gametocytes. These results indicate that this modified DD procedure is suitable for large-scale identification of developmentally regulated genes in the AT-rich Plasmodium genome.

Theileria annulata: identification, by differential mRNA display, of modulated host and parasite gene expression in cell lines that are competent or attenuated for differentiation to the merozoite

To identify both host and parasite genes that show altered expression during differentiation of Theileria annulata from the macroschizont to the merozoite stage of the life cycle, the RNA profiles of two T. annulata-infected clonal cell lines (D7 and D7B12) with the same genetic background have been compared by RNA display. In the cloned cell line D7, T. annulata differentiates from the macroschizont to the merozoite at 41 degrees C, whereas in the cell line D7B12, which was derived by recloning D7, the parasite does not differentiate. Therefore, genes that show altered expression levels in either clone could be modulated by the differentiation event and are possible candidates for regulators of this process. Differential display was carried out initially on RNA extracted from D7 and D7B12 macroschizont-infected cells cultured at 37 degrees C and secondly on RNA extracted from the two cell lines incubated at 41 degrees C to induce differentiation to the merozoite. The first procedure identified 29 cDNA fragments that displayed altered levels between D7 and D7B12, 9 of which were confirmed to be differentially expressed by Northern blot analysis. Of these 9 gene fragments, 8 were found to be of host origin, while 1 was parasite derived. The second RNA display analysis identified 14 transcripts that showed altered levels during a differentiation time course, of which 6 were confirmed to be differentially expressed between D7B12 cells and differentiating D7 cells by Northern blot analysis. Of these 6 gene fragments, 1 was of host and 5 were of parasite origin. The parasite genes either showed levels of RNA consistent with constitutive gene expression or, in one case, a genuine upregulation of mRNA associated with the differentiation process.

Identification and characterization of three differentially expressed genes, encoding S-adenosylhomocysteine hydrolase, methionine aminopeptidase, and a histone-like protein, in the toxic dinoflagellate Alexandrium fundyense

Genes showing differential expression related to the early G(1) phase of the cell cycle during synchronized circadian growth of the toxic dinoflagellate Alexandrium fundyense were identified and characterized by differential display (DD). The determination in our previous work that toxin production in Alexandrium is relegated to a narrow time frame in early G(1) led to the hypothesis that transcriptionally up- or downregulated genes during this subphase of the cell cycle might be related to toxin biosynthesis. Three genes, encoding S-adenosylhomocysteine hydrolase (Sahh), methionine aminopeptidase (Map), and a histone-like protein (HAf), were isolated. Sahh was downregulated, while Map and HAf were upregulated, during the early G(1) phase of the cell cycle. Sahh and Map encoded amino acid sequences with about 90 and 70% similarity to those encoded by several eukaryotic and prokaryotic Sahh and Map genes, respectively. The partial Map sequence also contained three cobalt binding motifs characteristic of all Map genes. HAf encoded an amino acid sequence with 60% similarity to those of two histone-like proteins from the dinoflagellate Crypthecodinium cohnii Biecheler. This study documents the potential of applying DD to the identification of genes that are related to physiological processes or cell cycle events in phytoplankton under conditions where small sample volumes represent an experimental constraint. The identification of an additional 21 genes with various cell cycle-related DD patterns also provides evidence for the importance of pretranslational or transcriptional regulation in dinoflagellates, contrary to previous reports suggesting the possibility that translational mechanisms are the primary means of circadian regulation in this group of organisms.

Cryptosporidium parvum gene discovery

Cryptosporidium parvum is a well-recognized cause of diarrhea in humans and animals throughout the world, and is associated with a substantial degree of morbidity and mortality in patients with acquired immunodeficiency syndrome (AIDS). At the present time, there is no effective therapy for treating or preventing infection with C. parvum. This is primarily due to a lack of understanding of the basic cellular and molecular biology of this pathogen in terms of virulence factors, genome structure, gene expression, and regulation. Over the past few years, large-scale sequencing of randomly selected cDNAs or fragments of genomic DNA has proven to be an efficient approach for obtaining large amount of genomic information. Recently, large-scale sporozoite expressed sequence tag (EST) and genomic sequence tag (GST) projects have been initiated for C. parvum. These projects have greatly increased the number of C. parvum genes identified and demonstrate the usefulness of large-scale sequencing for expanding our understanding of C. parvum biology. Continued characterization of the C. parvum genome will increase our basic understanding of the cellular and molecular biology of C. parvum in terms of gene and genome structure, and will identify key metabolic and pathophysiologic features of the organism for future development of safe and effective strategies for prevention and treatment of disease.

Upregulated expression of the cDNA fragment possibly related to the virulence of Acanthamoeba culbertsoni

Identification of the genes responsible for the recovery of virulence in brain-passaged Acanthamoeba culbertsoni was attempted via mRNA differential display-polymerase chain reaction (mRNA DD-PCR) analysis. In order to identify the regulatory changes in transcription of the virulence related genes by the brain passages, mRNA DD-PCR was performed which enabled the display of differentially transcribed mRNAs after the brain passages. Through mRNA DD-PCR analysis. 96 brain-passaged amoeba specific amplicons were observed and were screened to identify the amplicons that failed to amplify in the non-brain-passaged amoeba mRNAs. Out of the 96 brain-passaged amoeba specific amplicons, 12 turned out to be amplified only from the brain-passaged amoeba mRNAs by DNA slot blot hybridization. The clone, A289C, amplified with an arbitrary primer of UBC #289 and the oligo dT11-C primer, revealed the highest homology (49.8%) to the amino acid sequences of UPD-galactose lipid transferase of Erwinia amylovora, which is known to act as an important virulence factor. The deduced amino acid sequences of an insert DNA in clone A289C were also revealed to be similar to cpsD, which is the essential gene for the expression of type III capsule in group B streptococcus. Upregulated expression of clone A289C was verified by RNA slot blot hybridization. Similar hydrophobicity values were also observed between A289C (at residues 47-66) and the AmsG gene of E. amylovora (at residues 286-305: transmembrane domains). This result suggested that the insert of clone A289C might play the same function as galactosyl transferase controlled by the AmsG gene in E. amylovora.

Should I stay or should I go now? A stochastic model of stage differentiation in Theileria annulata

The events that initiate and determine stage differentiation of protozoan parasites are not fully understood. In this article, Brian Shiels suggests that for differentiation to the merozoite in Theileria annulata the process is predetermined by the parasite, but can be initiated and modulated by changes to the extracellular environment. Shiels proposes a mechanism operating on the basis of factors that regulate gene expression reaching a commitment threshold. Similarities across protozoan and higher eukaryotic differentiation systems lead Shiels to speculate that the T. annulata model may be of relevance to other parasites.

Directing differentiation in Theileria annulata: old methods and new possibilities for control of apicomplexan parasites

Apicomplexan parasites are major pathogens of humans and domesticated animals. The ability of these organisms to evade the host immune response and the emergence of drug-resistant parasites indicates a need for the identification of novel control strategies. Ideally, selected targets should be shared by a range of apicomplexans and fundamental to parasite biology. One process of apicomplexan biology which may provide this type of target is the molecular regulation of stage differentiation. This paper has reviewed studies carried out on differentiation of Theileria annulata and has highlighted general similarities with other apicomplexan differentiation steps. Similarities include asynchrony of differentiation, the loss (attenuation) of differentiation potential and an association between reduced proliferation and differentiation. In addition, novel data are presented assessing a possible role for a signal transduction mechanism or a direct involvement of classical heat-shock polypeptides in regulating differentiation of T. annulata in vitro. These studies, and previously published data, have led to the postulation that progression to the next stage of the life-cycle can be predetermined and involves the attainment of a quantitative threshold by regulators of gene expression. A modification of this model takes into account that for certain in-vitro systems, or differentiation steps in vivo, the process has to be initiated by alteration of the extracellular environment. Work which has shown that the time taken to achieve differentiation can be increased or decreased is also outlined. The ability to change the timing of differentiation suggests that the associated regulatory mechanism could be manipulated directly to significantly influence the outcome of an apicomplexan infection. The observation that a number of existing drugs and control strategies may exert their protective effect by altering differentiation potential supports this possibility.

Identification and cloning of a developmentally regulated Cryptosporidium parvum gene by differential mRNA display PCR

To identify Cryptosporidium parvum genes expressed during intracellular development, differential mRNA display was used to detect differences in gene expression between mock-infected and C. parvum-infected human epithelial cells. A reproducible band present only in C. parvum-infected cells, ddHC-23, was isolated and cloned. Southern blot analysis demonstrated that ddHC-23 represented a C. parvum gene. RT-PCR revealed that HC-23 mRNA levels decreased from 6 to 12h post-infection (pi), were maximally expressed at 24h pi, and returned to low levels at 48 and 72h pi. Northern blot analysis determined that the approx. 3.6kb transcript is expressed by sporozoites prior to invasion of epithelial cells. Screening of a C. parvum genomic library with ddHC-23 isolated a genomic subclone which contained a 2790bp ORF, uninterrupted by introns. Sequence analysis indicated that the encoded protein, which displayed no similarity to any sequences in the public databases, contained a high proportion of polar amino acids, with the most abundant being Asp (17.3%), Ser (15.8%) and Gly (8.1%). Numerous potential sites for posttranslational modification were present including: casein kinase II and protein kinase C phosphorylation sites, N-myristolation sites and N-glycosylation sites. These findings demonstrate the usefulness of differential mRNA display for identifying developmentally regulated C. parvum genes within the background of genes expressed by the host cell. 1998 Elsevier Science B.V.

Progress on developing a recombinant coccidiosis vaccine

The past 10 years of research aimed at developing subunit vaccines against a number of apicomplexans, including Eimeria, Plasmodium and Toxoplasma, have, if anything, revealed the complex nature of parasite-host interactions. The Knowledge gained from this research has shown why developing a subunit vaccine based on a single recombinant antigen from one developmental stage of the parasite was an overly optimistic approach. Many apicomplexan parasites have acquired unique strategies to evade host immunity. The variable expression of genes encoding erythrocyte membrane protein 1 of Plasmodium falciparum [1] (Berendt et al. Parasitology 1994;108:S19-S28) exemplifies one such strategy. The particular mechanism for evading immune destruction depends on a number of interrelated factors, not least of which is the parasite life-cycle and the availability of susceptible hosts. The goal of any vaccine, be it an attenuated organism or a recombinant antigen, is to break the cycle of infection. The development of a recombinant vaccine against apicomplexan parasites will depend on identifying those antigens and intracellular processes that are vital to the parasite survival and those which exist merely as a way of evading immunity. The information that follows is a review of both molecular biology/biochemistry of eimerian parasites and factors that influence host immune responses to coccidia.

Fasciola hepatica: stage-specific expression of novel gene sequences as identified by differential display

Differences in gene expression between adult and immature Fasciola hepatica (liver fluke) parasites isolated from the mammalian host were investigated using the technique of differential display. For any given primer combination used to produce these displays there were, on average, 22% apparently adult-specific and 14% apparently immature-specific cDNA products able to be identified, consistent with a high degree of differential gene expression between these two parasite developmental stages. Several cDNA fragments specific to immature parasite RNA were isolated and cloned. An abundant 400- to 500-bp RNA species was identified on a Northern blot by hybridization to the cloned DD2 cDNA fragment and was determined to be expressed at levels at least 10-fold higher in immature parasites relative to adult parasites. mRNA transcripts corresponding to the remaining cDNA fragments (DD14, DD16, DISP10, and DISP2) were apparently expressed at levels below the sensitivity limits of Northern analysis, although differential expression of these transcripts was confirmed by reverse transcriptase PCR (RT-PCR). The identities or functional significance of each of the five differentially expressed cDNAs identified in this study is still unclear due to the lack of any significant sequence similarity to the entries currently held within sequence databases.

Toxoplasma gondii sporozoites form a transient parasitophorous vacuole that is impermeable and contains only a subset of dense-granule proteins

Toxoplasma gondii sporozoites form two parasitophorous vacuoles during development within host cells, the first (PV1) during host cell invasion and the second (PV2) 18 to 24 h postinoculation. PV1 is structurally distinctive due to its large size, yet it lacks a tubulovesicular network (C. A. Speer, M. Tilley, M. Temple, J. A. Blixt, J. P. Dubey, and M. W. White, Mol. Biochem. Parasitol. 75:75-86, 1995). Confirming the finding that sporozoites have a different electron-dense-granule composition, we have now found that sporozoites within oocysts lack the mRNAs encoding the 5' nucleoside triphosphate hydrolases (NTPase). NTPase first appears 12 h postinfection. Other tachyzoite dense-granule proteins, GRA1, GRA2, GRA4, GRA5, and GRA6, were detected in oocyst extracts, and antibodies against these proteins stained granules in the sporozoite cytoplasm. In contrast to tachyzoite invasion of host cells, however, sporozoites did not exocytose the dense-granule proteins GRA1, GRA2, or GRA4 during PV1 formation. Even after NTPase induction, these proteins were retained within cytoplasmic granules rather than being secreted into PV1. Only GRA5 was secreted by the sporozoite during host cell invasion, becoming associated with the membrane surrounding PV1. Microinjection of sporozoite-infected cells with fluorescent dyes showed that PV1 is impermeable to fluorescent dyes with molecular masses as small as 330 Da, indicating that PV1 lacks channels through which molecules can pass from the host cytoplasm into the vacuole. By contrast, lucifer yellow rapidly diffused into PV2, demonstrating the presence of molecular channels. These studies indicate that PV1 and PV2 are morphologically, immunologically, and functionally distinct, and that PV2 appears to be identical to the tachyzoite vacuole. The inaccessibility of PV1 to host cell nutrients may explain why parasite replication does not occur in this vacuole.

Methods to prepare RNA and to isolate developmentally regulated genes from Eimeria

Coccidians represent a large class of important intracellular parasites that traverse multiple developmental stages that are distinct and required to complete the life cycle. The biochemical details underlying the regulation of transformation from one developmental form to the next are limited and the study of such details presents unique obstacles. However, the genetic program is critical and may provide a basis for understanding the biology of these organisms in addition to the opportunity to suppress development and infection. We provide a basic overview of several strategies, including previously unpublished results, used by this laboratory to isolate stage-specific genes from Eimeria bovis. Additionally, we have included detailed discussions that summarize the associated advantages and disadvantages of each as applied to coccidia and potentially to other parasites in the phylum Apicomplexa. Given that the purification of sufficient quantities of high-quality RNA is vital, we have included detailed protocols for the isolation of RNA from various parasite stages. Also included is a detailed protocol to apply mRNA differential display to investigate stage-specific developmental regulation.

Stage-specific gene expression in lymphatic filarial nematodes

Lymphatic filarial nematodes remain a significant cause of morbidity throughout much of the tropics. One approach to the development of rational control methods is an improved understanding of the basic biology of these organisms in relation to the mechanisms used to complete their life cycles. In this article, Eileen Devaney, Sam Martin and Fiona Thompson review new approaches to defining stage-specific molecules in filarial nematodes, and discuss their recent work on the isolation and characterization of stage-regulated cDNAs from Brugia pahangi.

Sporozoites of Toxoplasma gondii lack dense-granule protein GRA3 and form a unique parasitophorous vacuole

The invasion of host cells by sporozoites of Toxoplasma gondii leads to the formation of parasitophorous vacuoles that are distinctly different from those surrounding tachyzoites. In sporozoite-infected cells, the fluid-filled space surrounding the sporozoite is many times larger in volume than the sporozoite, essentially lacks granular or tubular structures, and has no detectable continuous parasitophorous vacuolar membrane when prepared by conventional electron microscopic methods. Consistent with the ultrastructural differences, dense-granule protein GRA3, which associates with the parasitophorous vacuolar membrane of tachyzoites, was not detected by indirect immunofluorescence in sporozoite-infected cells 2-12 h post-inoculation or by Western blot analysis of sporozoite extracts. Western blots incubated with the alpha ROP/DG antiserum, which recognizes tachyzoite rhoptry and dense-granule proteins, revealed numerous other antigenic differences between sporozoites and tachyzoites. Cell cultures inoculated with sporozoites were monitored at various intervals for the expression of GRA3 and the developmentally-regulated tachyzoite surface protein SAG1. Expression of SAG1 and GRA3 was first observed in 30% of the sporozoite-infected cells at 12 and 15 h post-inoculation, respectively, and in all intracellular parasites at 24 h. Parasite replication was only observed in sporozoite-infected cells that were positive for GRA3 and SAG1. Thus, these data indicate that sporozoites and their interaction with host cells differ substantially from tachyzoites and the expression of tachyzoite-specific proteins is likely required for parasite replication.