Analysis of the humoral responses of Toxoplasma gondii-infected cats using immunofluorescent assays with tachyzoite, bradyzoite, and gametogenic stages

We investigated levels of Toxoplasma gondii specific antibodies present in sera, intestinal secretions, and fecal extracts obtained from cats following primary and challenge infections. Antibodies specific to T. gondii tachyzoites, bradyzoites, sporozoites, and enteroepithelial stages were detected by indirect immunofluorescence assay. Enteroepithelial stage-specific antibodies were detected in serum as early as 2 wk after infection, whereas antibodies from intestinal secretions did not appear until 3 wk following infection. The T. gondii-specific IgG and IgA antibodies were present in serum, but only specific IgA antibodies were detected in the intestinal secretions. Serum IgG bound to tachyzoites, bradyzoites, sporozoites, and enteroepithelial stages of T. gondii, whereas serum IgA bound strongly to enteroepithelial stages but only weakly to tachyzoites and bradyzoites. IgA from intestinal secretions bound to antigens on all enteroepithelial stages and the distal tips of sporozoites and bradyzoites but did not bind to tachyzoites. IgA present in fecal extracts also bound to enteroepithelial stages of T. gondii. Toxoplasma gondii infection in cats induces the production of antibodies that bind with all forms of the parasite, including the enteroepithelial stages. Comparison of the staining patterns of T. gondii stages for serum and intestinal secretion IgA indicated differences. Thus, the intestinal antibody immune response may be uniquely focused on the intestinal stages relative to the circulating antibodies, resulting in a compartmentalization of the humoral response.

Localization of Toxoplasma gondii in feline intestinal tissue using PCR

Gametogony of Toxoplasma gondii occurs only in the epithelial cell layers within the intestine of the definitive feline host. Infected feline intestine is required in order to study the physiology, histology, and molecular biology of the gametogenic stages. Therefore, we set out to devise a rapid, conservative, and reproducible technique to determine which portions of the intestine were infected. Several methods of collecting and processing infected material were assessed for their ability to detect T. gondii. Infected and uninfected intestines from domestic cats were used to produce nitrocellulose lift impressions along the entire small intestine. The nitrocellulose was analyzed for the presence of T. gondii DNA using polymerase chain reaction (PCR) primers specific for the T. gondii alpha-tubulin gene. In addition, mucosal tissue scrapings, derived from segments of intestinal tissue, were used to isolate DNA and RNA for subsequent PCR and reverse transcriptase PCR analysis, respectively. The nitrocellulose impression lift method demonstrated distribution of parasite throughout the intestine. Histological staining and indirect immunofluorescence antibody analysis of sections obtained from the same infected tissue confirmed the presence of T. gondii intraepithelial stages. Comparison among the different techniques indicates that the nitrocellulose impression lift technique proved to be effective for easily and quickly assessing presence of T. gondii in infected tissue. This technique does not require a significant amount of the experimental material.

Identification of a small RNA containing the trypanosome spliced leader: a donor of shared 5' sequences of trypanosomatid mRNAs?

The 35 nucleotide spliced leader (SL) sequence is found on the 5' end of numerous trypanosome mRNAs, yet the tandemly organized reiteration units encoding this leader are not detectably linked to any of these structural genes. Here we report the presence of a class of discrete small SL RNA molecules that are derived from the genomic SL reiteration units of Trypanosoma brucei, Trypanosoma cruzi, and Leptomonas collosoma. These small SL RNAs are 135, 105, and 95 nucleotides, respectively, and contain a 5'-terminal SL or SL-like sequence. S1 nuclease analyses demonstrate that these small SL RNAs are transcribed from continuous sequence within the respective SL reiteration units. With the exception of the SL sequence and a concensus donor splice site immediately following it, these small RNAs are not well conserved. We suggest that the small SL RNAs may function as a donor of the SL sequence in an intermolecular process that places the SL at the 5' terminus of many trypanosomatid mRNAs.

The IsTaR 1 serodeme of Trypanosoma brucei: development of a new serodeme

An extensive serodeme of sequentially-isolated antigenic variants of African trypanosomes has been produced from both syringe-passaged and cyclically-transmitted Trypanosoma brucei of the IsTaR 1 clone derived from EATRO 164. The majority of the antigenic variants were isolated from chronically-infected deer mice (Peromyscus leucopus). The pattern of parasitemias during the course of infections initiated with syringe-passaged trypanosomes differed from those initiated with cyclically-transmitted trypanosomes. Trypanosome populations from syringe-passaged (192) and cyclically-transmitted (31) clones were each amplified by growth in lethally-irradiated mice and cryopreserved for retrospective analysis. Five clones derived from a single deer mouse during the first 44 days of infection, and 2 clones derived from an acutely-infected rat were established from these amplified populations. Homogeneous populations were grown in lethally-irradiated rats and mice for antigenic analysis purification of variant-specific glycoprotein. Six of the 7 clones were distinct variants by immunological criteria using antisera derived from whole cells or purified surface glycoproteins. Two clones, one derived from the acutely-infected rat, and the other from the first parasitemia in a chronic infection that was initiated with the former clone, were immunologically identical. Production of these clones established a well-defined serodeme that will allow detailed analysis of antigenic variation.

Molecular characterization of initial variants from the IsTat I serodeme of Trypanosoma brucei

Variant surface glycoproteins (VSGs) were isolated from variant antigen types (VATs) of the IsTat 1 serodeme. Molecular weight and isoelectric focusing analysis demonstrate that seven early VSGs possess properties generally attributed to VSGs isolated from other trypanosome serodemes. Six of the seven VSGs characterized are distinct from one another, while two (D and 1) appear identical. The presence of VSG specific mRNA in corresponding VATs was demonstrated by in vitro translation of RNA from each of the VATs, followed by immunoprecipitation with homologous and heterologous antisera. Hybridization of VSG cDNA clones with RNA from each VAT confirm that VSG mRNA is present only in homologous VATs and verifies the transcriptional control of these VSG genes. The two VATs D and 1 express indistinguishable VSGs by a variety of biochemical criteria, as well as by reactivity with 24 monoclonal antibodies. The VSG mRNAs in VATs D and 1 also appear identical. However, this identity is not reflected at the genomic level. Data is presented which establishes that DNA rearrangements can occur around both expressed and non-expressed VSG genes without qualitatively affecting VSG gene expression.

Genomic organization of Trypanosoma brucei variant antigen gene families in sequential parasitemias

cDNA libraries were made from mRNA purified from each of seven sequentially isolated variant antigen types (VATs) of the IsTat 1 serodeme. Plasmids containing variant surface glycoprotein (VSG) sequences corresponding to each of the isolates were used in Southern analyses to examine the genomic organization of VSG nucleotide sequences. In most cases, cells expressing a given VSG were shown to have an extra copy of the corresponding VSG gene. In one case an expression-linked copy (ELC) was not detectable. VSG gene rearrangements not obviously correlated with the expression of homologous sequences were detected in four of six VSG gene families. Thus, even cDNAs which detected an ELC revealed additional genomic reorganization in regions flanking VSG sequences. The cells used to initiate the chronic infection expressed the same VSG as those isolated from the first parasitemia. The extent of genomic rearrangement observed between these two sequentially derived populations was comparable to that observed between any of the other serially derived VATs. Thus, within a short period of time and in the absence of detectable antigenic variation, the amount of genetic flux in sequences associated with VSG genes can be substantial.

Caulobacter flagellin mRNA segregates asymmetrically at cell division

Molecular processes which promote the spatial localization of subcellular components are fundamental to cell development and differentiation. At various stages in development unequal segregation of molecular information must occur to result in the differentiated characteristics which distinguish cell progeny. Biological attributes of the dimorphic bacterium, Caulobacter crescentus, provide an experimental system permitting examination of the generation of asymmetry at the molecular level. When a Caulobacter cell divides, two different daughter cells are produced--a motile swarmer cell with a polar flagellum and a non-motile cell with a static appendage referred to as a stalk. The two cell types are distinct with respect to surface morphology, developmental potential, protein composition and biosynthetic capabilities. One of the more conspicuous manifestations of asymmetric expression of macromolecules in this system, the flagellum, has been studied extensively. We have cloned the flagellin genes of Caulobacter and report here the use of these sequences as probes to demonstrate that (1) the level of flagellin mRNA is regulated during the cell cycle in a pattern coincident with flagellum polypeptide synthesis and (2) flagellin mRNA synthesized before cell division is segregated with progeny swarmer cells. This provides molecular evidence of specific partitioning of an mRNA at the time of cell division.

Tubulin genes are tandemly linked and clustered in the genome of trypanosoma brucei

We have isolated cDNA and genomic clones containing alpha- and beta-tubulin genes from Trypanosoma brucei. Each clone has been mapped, and the identity of the tubulin genes has been established by cross-hybridization with cloned chicken tubulin genes and by hybridization-selection and translation of trypanosome tubulin mRNA. In contrast with the dispersed organization of tubulin genes in other organisms, trypanosome alpha- and beta-tubulin genes are physically linked and clustered in tandem repeats of approximately 13-17 copies per haploid genome of alternating alpha- and beta-tubulin sequences.

Cloning of developmentally regulated flagellin genes from Caulobacter crescentus via immunoprecipitation of polyribosomes

Immunoprecipitation of Caulobacter crescentus polyribosomes with antiflagellin antibody provided RNA for the synthesis of cDNA probes that were used to identify three specific EcoRI restriction fragments (6.8, 10, and 22 kilobases) in genomic digests of Caulobacter DNA. The RNA was present only in polyribosomes isolated from a time interval in the Caulobacter cell cycle that was coincident with flagellin polypeptide synthesis. The structural gene for Mr 27,500 flagellin polypeptide was assigned to a region of the 10-kilobase EcoRI restriction fragment by DNA sequence analysis. Analysis of mutants defective in motility further established a correlation between the Mr 27,500 flagellin gene and the flaE gene locus [Johnson, R. C. & Ely, B. (1979) J. Bacteriol. 137, 627-634]. The other EcoRI fragments that hybridize with the immunoprecipitated polyribosome-derived cDNA probe are also temporally regulated and have features that suggest they encode other polypeptides associated with the flagellum. Modifications were required to adapt the procedure of immunoprecipitation of polyribosomes for use with Caulobacter and should be applicable to the production of specific structural gene probes from other prokaryotic systems.

Regulation of polypeptide synthesis during Caulobacter development: two-dimensional gel analysis

The gram-negative bacterium Caulobacter crescentus progresses through three distinct morphological transitions, including both motile and nonmotile cell types, during its cell cycle. Assessment of the extent of regulation of polypeptide synthesis during these transitions was carried out with two-dimensional gel electrophoresis of whole-cell extracts. Synchronous cells were pulse-labeled with 14C-amino acids for 10-min intervals throughout the entire 2-h cell cycle. The radioactively labeled polypeptides were analyzed by two-dimensional polyacrylamide gel electrophoresis. Autoradiograms resulting from fluorography of the second dimension provided the detection of approximately 1,000 unique spots. The 600 predominant polypeptide spots, representing approximately 40% of the coding capacity of Caulobacter deoxyribonucleic acid, were analyzed for major changes in their synthetic rates. Quantitation by densitometric scanning of individual polypeptide spots represented on the sequential fluorograms demonstrated significant changes in the temporal synthesis of 6% of the polypeptides. Extracts from asynchronous cells were fractionated to obtain total-membrane and deoxyribonucleic acid-binding polypeptide fractions. Subsequent electrophoresis of these cellular fractions revealed approximately 100 membrane polypeptides and 25 deoxyribonucleic acid-binding polypeptides. Eight of the regulated polypeptides were identified as membrane or deoxyribonucleic acid-binding proteins. The regulated polypeptides can be grouped into three main categories based on their interval of synthesis. The three categories are in direct correlation with the three distinct cell cycle stages. This analysis has also revealed a unique transition period in the cell cycle in which a significant proportion of gene expression is regulated.

Structural analysis of variant and invariant genes in trypanosomes

Variant surface antigens have been purified from variants of a newly developed serodeme of Trypanosoma brucei 164, and found to be distinct by immunological and molecular criteria. cDNA clones containing variant and invariant gene sequences were isolated by using RNA from different variants and cloned DNAs from other systems as probes. These trypanosome and heterologous cloned DNAs were used as probes of trypanosome gene structure and activity. Regulation of variant antigen gene expression is at the level of transcription, and the variant antigen genomic sequences differ in their arrangement between the variants. Chick alpha- and beta-tubulin sequences hybridize to trypanosome-tubulin gene sequences, while chick beta-actin sequences do not. A 1650 bp alpha-tubulin trypanosome cDNA has been isolated. The trypanosome alpha- and beta-tubulin sequences appear to be clustered in the genome. Sequence rearrangement of tubulin genes does not occur during antigenic variation.

Evidence for an essential lysine in glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides

1. Pyridoxal 5'-phosphate inhibits glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides reversibly which Ki equals 0.04-0.06 mM. 2. This inhibition is competitive with respect to glucose 6-phosphate and non-competitive with respect to NADP+ or NAD+. Interaction between enzyme and excess pyridoxal 5'-phosphate follows pseudo-first-order kinetics and indicates that one molecule of inhibitor reacts with each active unit of enzyme. 3. Substrate and coenzyme protect the enzyme from inhibition by pyridoxal 5'-phosphate. Dissociation constants for NADP+ and glucose 6-phosphate were determined from their effects on the kinetics of enzyme--inhibitor interaction. 4. Reaction of the enzyme with pyridoxal 5'-phosphate produces a typical Schiff-base absorbance peak at 430 nm. Subsequent reduction with sodium borohydride leads to spectral changes characteristic for the formation of a secondary amine. 5. The irreversibly inactivated enzyme thus produced contains two moles of inhibitor per mole of enzyme (two subunits per mole). After protein hydrolysis, N-6-pyridoxyllysine can be identified by paper chromatography. 6. The enzyme is inhibited irreversibly by 1-fluoro-2,4-dinitrobenzene, even in the presence of excess 2-mercaptoethanol. At least one dinitrophenyl group is bound per active unit of enzyme; 4 to 5 moles of dinitrophenyl group are bound per mole of enzyme. NADP+ AND GLUCOSE 6-PHOSPHATE PROTECT AGAINST INHIBITION BY 1-FLUORO-2,4-DINITROBENZENE. The absorption spectrum of dinitrophenyl-enzyme corresponds to that for dinitrophenylated amino groups. 7. These studies indicate that there is an essential lysine at the active site of the enzyme. It is suggested that the function of this lysine is to bind glucose 6-phosphate. 8. It is proposed that a group of "active lysine" proteins may exist (in analogy with the "active serine" enzymes), which share a common structural feature at their substrate-binding site and to which pyridoxal 5'-phosphate binds specifically.