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PubMed1992

Molecular cloning and expression of the gene encoding the kinetoplast-associated type II DNA topoisomerase of Crithidia fasciculata.

A type II DNA topoisomerase, topoIImt, was shown previously to be associated with the kinetoplast DNA of the trypanosomatid Crithidia fasciculata. The gene encoding this kinetoplast-associated topoisomerase has been cloned by immunological screening of a Crithidia genomic expression library with monoclonal antibodies raised against the purified enzyme. The gene CfaTOP2 is a single copy gene and is expressed as a 4.8-kb polyadenylated transcript. The nucleotide sequence of CfaTOP2 has been determined and encodes a predicted polypeptide of 1239 amino acids with a molecular mass of 138,445. The identification of the cloned gene is supported by immunoblot analysis of the beta-galactosidase-CfaTOP2 fusion protein expressed in Escherichia coli and by analysis of tryptic peptide sequences derived from purified topoIImt. CfaTOP2 shares significant homology with nuclear type II DNA topoisomerases of other eukaryotes suggesting that in Crithidia both nuclear and mitochondrial forms of topoisomerase II are encoded by the same gene.

Amino Acid Sequence↗
PubMed2002

A new expression vector for Crithidia fasciculata and Leishmania.

Crithidia fasciculata is a monogenetic parasite of insects. It grows in fully defined media without requiring serum, which facilitates biochemical analysis. We have constructed a series of expression systems that allows expression of transfected genes in the kinetoplastid protozoa Crithidia and Leishmania. These cells can be readily transfected with plasmid DNA by electroporation and transformants selected with various antibiotic resistance markers. 5'-Trans-splicing signals and poorly defined regions within the 3'-untranslated regions of genes are required for optimal expression of genes in trypanosomatids. We, therefore, inserted the intergenic region of the C. fasciculata phosphoglycerate kinase (PGK) genes A and B, which allows polyadenylation of the target gene and spliced leader addition to the selectable marker gene. Part of the intergenic region of the PGK locus was added upstream of the target gene to permit its trans-splicing. A 3'-untranslated sequence from the Crithidia glutathionylspermidine synthetase (GSPS) was also added to allow the polyadenylation of the selectable marker gene. Genes can be readily inserted using a multiple cloning site and can be expressed as a fusion protein with a poly-histidine sequence at either the N or C-terminus or fused with green fluorescent protein. Biologically active proteins can be expressed in C. fasciculata or L. amazonensis promastigotes and purified by affinity chromatography using a metal chelating column.

Animals↗
PubMed2001

Immune response of Drosophila melanogaster to infection with the flagellate parasite Crithidia spp.

Insects are able to recognize invading microorganisms and to mount an immune response to bacterial and fungal infections. Recently, the fruitfly Drosophila melanogaster has emerged as a promising invertebrate model to investigate innate immunity because of its well-characterized genetics. Insects are also vectors of numerous parasites which can trigger an immune response. We have investigated the interaction of Drosophila melanogaster with the flagellate protozoan Crithidia spp. We show that a per os parasitic infection triggers the synthesis of several antimicrobial peptides. By reverse phase HPLC and mass spectrometry, peptides were shown to be present in the hemolymph and not in the gut tissue, suggesting the presence of immune messengers between the site of the infection, namely the gut, and the fat body, the main site of synthesis for antimicrobial peptides. Interestingly, we have identified one molecule which is specifically induced in the hemolymph after infection with Crithidia, but not with bacteria, suggesting that Drosophila can discriminate between pathogens. When flagellates were injected into the hemolymph, a low synthesis of antimicrobial peptides was observed together with phagocytosis of parasites by circulating hemocytes. The data presented here suggest that Drosophila-Crithidia spp. represents an interesting model to study host defense against protozoan parasites.

Animals↗
PubMed1983

Purification and properties of dihydroorotate oxidase from Crithidia fasciculata and Trypanosoma brucei.

Dihydroorotate oxidases have been highly purified from the parasitic protozoa Crithidia fasciculata and Trypanosoma brucei. The Crithidia enzyme was purified 4200-fold from a crude soluble protein extract in four steps. The protein is a dimer as judged from the native (Mr 60 000) and subunit (Mr 32 700) molecular weights. The purified enzyme exhibits a characteristic flavin electronic spectrum, and each mole of native dimer contains 1.0 mol of tightly bound flavin mononucleotide. Under anaerobic conditions, the flavin chromophore is reduced upon addition of L-dihydroorotate. In air-saturated buffer, the enzyme catalyzes the conversion of L-dihydroorotate to orotate with concomitant reduction of equimolar amounts of molecular oxygen to hydrogen peroxide. A variety of low molecular weight oxidants (e.g., quinones or ferricyanide) may replace oxygen as the electron acceptor during catalysis. The dihydroorotate oxidase of T. brucei was purified 1400-fold to apparent homogeneity by a highly similar isolation procedure. The estimated native (Mr 62 000) and subunit (Mr 30 500) molecular weights indicated a dimeric protein comparable in size to the enzyme from Crithidia. These results suggest that dihydroorotate oxidation is mediated by flavoprotein oxidases in these parasitic protozoa rather than by pterin-linked hydroxylases as recently proposed [Kidder, G. W., & Nolan, L.L. (1973) Biochem. Biophys. Res. Commun. 53, 929-936; Gutteridge, W. E., Dave, D., & Richards, W. H. G. (1979) Biochim. Biophys. Acta 582, 390-401].

Animals↗
PubMed1982

A cytochrome c methyltransferase from Crithidia oncopelti.

The mitochondrial cytochrome c-557 of Crithidia oncopelti contains two lysine residues and an N-terminal proline residue that are methylated in vivo by the methyl group of methionine. The purified cytochrome can act as a methyl acceptor for a methyltransferase activity in the cell extract that uses S-adenosylmethionine as methyl donor. Crithidia cytochrome c-557 is by far the best substrate for this methyltransferase of those tested, in spite of the fact that methylation sites are already almost fully occupied. The radioactive uptake of [14C]methyl groups from S-adenosylmethionine occurred only at a lysine residue (-8) and the N-terminal proline residue. This methyltransferase appears to differ from that of Neurospora and yeast [Durban, Nochumson, Kim, Paik & Chan (1978) J. Biol. Chem. 253, 1427-1435; DiMaria, Polastro, DeLange, Kim & Paik (1979) J. Biol. Chem. 254, 4645-4652] in that lysine-72 of horse cytochrome c is a poor acceptor. Also, the Crithidia methyltransferase appears to be stable to carry lysine methylation much further to completion than do the enzymes from yeast and Neurospora, which produce very low degrees of methylation in native cytochromes c.

Amino Acids↗
PubMed1985

The majority of minicircle DNA in Crithidia fasciculata strain CF-C1 is of a single class with nearly homogeneous DNA sequence.

DNA minicircles found within the kinetoplast of the trypanosomatid Crithidia fasciculata, like those of most other kinetoplastid species, are heterogeneous in sequence. The pattern of minicircle DNA fragments generated by cleavage of kinetoplast DNA with various restriction enzymes has been used to demonstrate this heterogeneity. Here we describe a strain of Crithidia fasciculata in which more than 90% of the DNA minicircles exhibit a common pattern of restriction enzyme cleavage sites. A map of cleavage sites within this major minicircle DNA class is presented for seven restriction enzymes with hexanucleotide recognition sequences. Sequence homogeneity at an even finer level is reflected in minicircle DNA digestion patterns generated by restriction enzymes with tetranucleotide recognition sites. Partial DNA sequence analysis of multiple clones from the major minicircle class shows nearly complete homogeneity at the nucleotide level. The existence of a near homogeneous complement of DNA minicircles in Crithidia should facilitate the study of their replication in this organism.

Animals↗
PubMed1995

A new non-LTR retrotransposon provides evidence for multiple distinct site-specific elements in Crithidia fasciculata miniexon arrays.

We have identified a new member of the family of trypanosome site-specific retrotransposons, using a degenerate oligonucleotide PCR strategy. The 9595 bp element, termed Crithidia retrotransposable element 2 (CRE2), was cloned and found to be inserted in the tandemly arrayed miniexon genes of Crithidia fasciculata. The element is flanked by 29 bp target site duplications but lacks the 3' poly dA tract characteristic of most other non-long terminal repeat retrotransposons. The amino terminal region of the single 2518-codon open reading frame contains a putative metal-binding motif and a proline-rich region similar to gag-like domains of other retrotransposons. The carboxy terminal region of this open reading frame shares sequence homology with the reverse transcriptase and putative endonuclease regions of three previously described trypanosomatid site-specific retrotransposons. All four of these retrotransposons are specifically inserted between nucleotides 11 and 12 of the highly conserved 39mer sequence of the miniexon gene. Most copies of CRE2 and the previously characterized CRE1 are located on different sized chromosomes. Additional CRE-related sequences were identified by screening Crithidia libraries. These results suggest that a particular sequence in the C. fasciculata miniexon repeat is the target for multiple distinct site-specific retrotransposon insertions.

Amino Acid Sequence↗
PubMed1988

Detection of anti-DNA antibodies: a comparison between two Farr assays, Crithidia luciliae and a human chromosomal substrate assay.

Four commercially available assays were compared with a 14C DNA Farr assay for their ability to detect anti-DNA antibodies in 119 sera from 109 patients with systemic lupus erythematosus (SLE) and 25 control sera. The 14C DNA Farr assay was the most sensitive and specific assay (SLE, 57% positive, controls, 0%). A commercial 125I DNA Farr assay was significantly less sensitive (SLE, 39% positive). The fluorescence human chromosomal preparation assay was as sensitive as the 14C DNA Farr assay (SLE, 58% positive) but less specific (controls, 8% positive). The immunofluorescence Crithidia luciliae assay was specific, but less sensitive (SLE, 37% positive) than the 14C DNA Farr assay. Adaptation of Crithidia to immunoperoxidase did not alter its sensitivity or performance. These results confirm that the 14C DNA Farr assay, locally refined and performed by experienced hands, is the most sensitive and specific assay for anti-DNA antibodies. The 125I DNA Farr was no more sensitive than the Crithidia assay but considerably more laborious. The human chromosomal preparation may be suitable as a rapid screening test for anti-DNA antibodies.

Animals↗
PubMed1980

Morphologic and biochemical characterization of Crithidia brasiliensis sp. n.

A trypanosomatid with a choanomastigote stage and, therefore, belonging to the genus Crithidia, was isolated in culture from the alimentary tract of the hemipteran genus Zelus. The trypanosomatid was able to grow at 37 C, a characteristic reported to date from only 2 other members of Crithidia, C hutneri and C. luciliae thermophila. Subsequently, the flagellate was cloned for biochemical studies which involved cleaving of kDNA by restriction endonucleases and analyses of the isoenzyme and histone patterns. In all the attributes revealed by the foregoing methods, the organism from Zelus differed from the latter 2 congeneric species. On these and morphologic grounds, this organism appears to belong in a new species for which the name Crithidia brasiliensis sp. n. is proposed.

Animals↗
PubMed1985

Isolation and partial characterization of mutants of the trypanosomatid Crithidia fasciculata and their use in detecting genetic recombination.

Crithidia fasciculata was used as a model trypanosomatid to study the possible existence of genetic recombination in this group of protozoa. The approach was based on the ability to select a variety of mutants on agar plates. Following mutagenesis of wild type cells by nitrosoguanidine or ethylmethanesulfonate, stable mutant phenotypes were obtained. These included mutants resistant to the drugs actinomycin D, 6-azauracil, 6-azauridine, and 5-fluorouracil, auxotrophs and colony morphology mutants. Following mixed growth of pairs of drug-resistant mutants on selective media, isolates exhibiting stable recombinant phenotypes were obtained. The data presented suggest that 1) Crithidia undergoes some type of genetic recombination and 2) Crithidia must be diploid at some time during this process.

Amino Acids↗
PubMedDate not supplied

A giant phosphoprotein localized at the spongiome region of Crithidia luciliae thermophila.

A giant protein with an apparent molecular mass of 2,300-kDa was identified in the Triton X-100 soluble fraction of Crithidia luciliae thermophila. Polyclonal antibody raised against this protein reacted by immunoblot analysis with proteins of similar molecular mass in Crithidia fasciculata and Crithidia oncopelti. In addition, the antibody immunoprecipitates the protein either after in vivo phosphorylation with [32P]orthophosphoric acid or after metabolically labeling with [35S]methionine. Indirect immunofluorescence microscopy analysis performed either with fixed or with live parasites showed a single fluorescent spot at the level of the flagellar pocket region. Immunogold electron microscopy of thin sections of the parasite revealed that the antigen is localized at a restricted area of the spongiome, between the contractile vacuole and the flagellar pocket. Furthermore, Triton X-114 phase separation of whole cell membrane proteins, metabolically labeled with [35S]methionine, demonstrated that the giant protein remains in the aqueous phase. These results indicate that this phosphoprotein behaves as a peripheral membrane protein localized at the spongiome region, suggesting that it might be involved in the osmoregulatory process.

Animals↗
PubMed2001

Differential expression of proteolytic enzymes in endosymbiont-harboring Crithidia species.

Crithidia oncopelti, Crithidia deanei and Crithidia desouzai are flagellates of the Trypanosomatidae family that present bacterium-like endosymbionts in their cytoplasm. Gelatin-SDS-PAGE analysis was used to characterize cell-associated and extracellular proteinases in these organisms. Our survey indicates that the proteolytic profiles of C. deanei and C. desouzai are identical; that C. oncopelti displays a distinct zymogram; and that species naturally lacking endosymbionts have a more complex extracellular proteolytic activity, which illustrates the heterogeneity of this genus. This is the first report on the presence of cysteine proteinases in the culture supernatant of monoxenic trypanosomatids, and by the use of wild and aposymbiotic strains from C. deanei we also demonstrated that the prokaryote endosymbiont somehow alters quantitatively the expression of extracellular proteinases in this trypanosomatid.

Animals↗
PubMed1979

The ribosomal RNA of the trypanosomatid protozoan Crithidia fasciculata: physical characteristics and methylated sequences.

When extracted and analyzed under conditions which maintain noncovalently associated RNA-RNA complexes, the bulk cellular RNA of Crithidia fasciculata contains species of apparent molecular weights 1.3, 0.825, 0.08, 0.065, and 0.045 x 10(6) in addition to 5S rRNA and tRNA. Heat denaturation results in the disappearance of the 1.3 x 10(6) dalton RNA and the appearance of three new species having molecular weights of 0.67, 0.575, and 0.059 x 10(6). In addition, the apparent molecular weight of the 0.825 x 10(6) dalton component is reproducibly lowered to 0.81 x 10(6) after heat treatment. With the exception of tRNA, all of the RNA species are present in close to equimolar amounts in either undenatured or heat-denatured C. fasciculata bulk cellular RNA. On the basis of previous observations on the ribosomal RNA of the closely related organism, Crithidia oncopelti (Spencer, R. & Cross, G.A.M. (1976) J. Gen. Microbiol. 93, 82-88), the 1.3 and 0.825 x 10(6) dalton RNA's are considered to be components of the large and small subunits, respectively, of C. fasciculata ribosomes, but the subunit localization of the other RNA's described here has not yet been determined. O2'-Methylnucleosides account for about 1.4 mol% of the total nucleoside constituents of unfractionated C. fasciculata rRNA. Quantitative analysis suggests that the rRNA molecules in a C. fasciculata ribosome contain a total of 95-100 O2'-methyl groups, distributed in 80-85 Nm-Np sequences (including four 'hypermodified' Nm-Np, each containing a modification of a base or base-sugar linkage in addition to sugar methylation), six different Nm-Nm-Np sequences, and one Nm-Nm-Nm-Np sequence. While the specific pattern of O2'-methylation in the rRNA of C. fasciculata is distinct, both qualitatively and quantitatively, from the pattern observed in other organisms, Crithidia rRNA does contain certain 'universal' O2'-methylated sequences which appear to have been extensively conserved in evolution. The base-methylated nucleoside, N6,N6-dimethyladenosine (m26A), has been isolated from both C. fasciculata and wheat embryo rRNA in the form of the alkali-resistant dinucleotide, m26A-m26Ap. This dinucleotide and its enzymatic degradation products have been characterized by examination of their ultraviolet absorption spectra and electrophoretic and chromatographic properties.

Animals↗
PubMed1983

Primary structures of four novel small ribosomal RNAs from Crithidia fasciculata.

We report here the complete primary structures of four novel small RNA species (designated e, f, g, and j) found in the large ribosomal subunit of Crithidia fasciculata, a trypanosomatid protozoan. These RNAs, which are distinct from Crithidia 5S (species h) and 5.8S (species i) rRNAs, do not have counterparts in the more conventional eukaryotic ribosomes characterized to date. The small RNAs are 212 (e), 183 (f), 135-136 (g), and 72-73 (j) nucleotides long, with g and j displaying 5'-terminal heterogeneity. All have unique sequences and all contain 5'-monophosphorylated and 3'-unphosphorylated termini. In their basic structural features, therefore, species e, f, g, and j are indistinguishable from other RNAs (including 5S and 5.8S) that are recognized components of eukaryotic ribosomes, although they are unrelated to 5S or 5.8S rRNA in sequence. Since previous work from this laboratory has ruled out the possibility that these small RNAs are generated by quantitative and highly specific (albeit artifactual) RNase cleavage of large rRNAs during isolation, we conclude that species e, f, g, and j are native components of the Crithidia ribosome. With the exception of e, which appears to contain a single pseudouridine residue, all of these novel RNA species are devoid of modified nucleosides. In connection with primary sequence analysis, we present a simple modification of the standard G-specific chemical sequencing reaction which in our hands yields reproducible and unambiguous results using commercially available dimethyl sulfate.

Animals↗
PubMed2002

Identification of CfNek, a novel member of the NIMA family of cell cycle regulators, as a polypeptide copurifying with tubulin polyglutamylation activity in Crithidia.

Post-translational glutamylation of tubulin plays an important role in regulating the interaction between microtubules and associated proteins, but so far the enzymes involved in this process have not been cloned from any cellular source. Using a modified purification scheme that employs a hydroxyapaptite chromatography as the final step we identified a 54 kDa band as the major polypeptide copurifying with tubulin polyglutamylation activity from the trypanosomatid Crithidia fasciculata. Based on peptide sequence information we have cloned the corresponding cDNA and identify Crithidia p54 as a novel member (termed CfNek) of the NIMA family of putative cell cycle regulators. CfNek is a protein of 479 amino acids that contains an unusual protein kinase domain that lacks the glycine-rich loop in subdomain I. The protein also harbours a PEST sequence and a pleckstrin homology domain. The tubulin polyglutamylase preparation displays the beta-casein phosphorylation activity typical for NIMA related kinases. Recombinant His-tagged CfNek expressed in Crithidia localises to the flagellar attachment zone/basal body of the parasite. After purification on a Ni(2+)-column the recombinant enzyme preparation displays ATP-dependent tubulin polyglutamylation activity as well as casein-phosphorylation activity.

Amino Acid Sequence↗
PubMed1999

Isolation of tubulin polyglutamylase from Crithidia; binding to microtubules and tubulin, and glutamylation of mammalian brain alpha- and beta-tubulins.

Trypanosomatids have a striking cage-like arrangement of submembraneous microtubules. We previously showed that alpha- and beta- tubulins of these stable microtubules are extensively modified by polyglutamylation. Cytoskeletal microtubular preparations obtained by Triton extraction of Leishmania tarentolae and Crithidia fasciculata retain an enzymatic activity that incorporates radioactive glutamic acid in a Mg2+-ATP-dependent manner into alpha- and beta-tubulins. The tubulin polyglutamylase is extracted by 0.25 M salt. The Crithidia enzyme can be purified by ATP-affinity chromatography, glycerol-gradient centrifugation and ion-exchange chromatography. After extraction from the microtubular cytoskeleton the glutamylase forms a complex with alphabeta tubulin, but behaves after removal of tubulin as a globular protein with a molecular mass of 38x10(3). In highly enriched fractions a corresponding band is the major polypeptide visible in SDS-PAGE. The enzyme from Crithidia recognises mammalian brain tubulin, where it incorporates glutamic acid preferentially into the more acidic variants of both alpha- and beta-tubulins. Synthetic peptides with an oligoglutamyl side chain, corresponding to the carboxy-terminal end of brain alpha- and beta-tubulins, are accepted by the enzyme, albeit at low efficiency. The polyglutamylase elongates the side chain by up to 3 and 5 residues, respectively. Other properties of the tubulin polyglutamylase are also discussed.

Amino Acid Sequence↗
PubMed2002

[Study of DNA-containing structures in the nucleus and cytoplasm of the Crithidia flagellates using the Miller method].

Weakly condensed interphase chromosomes made of chromatin, and the tightly packed kinetoplast DNA (kpDNA) of a single mitochondrion of Crithidia (Kinetoplastidea, Trypanosomatida) flagellates were studied on the Miller-type spread preparations by electron microscopy. Chromatin of organisms lysed at low ionic strength conditions for 5-10 min unfolds up to 10-nm nucleosomal filaments and 20-nm chromatin fibers. The initial indications of kpDNA decompaction become visible after a 10-13 min dispersion of lysed flagellates. However, at least a 15 min long procedure is required for well-defined identification of intrakinetoplast structures. In this case, the kinetoplast looks like a heterogeneous network disposed close to the kinetosome of a single flagellum. Cells with diameters of 162.5 nm and contour wall length of 510 nm dominated within the network. With the prolongation of the dispersion time up to 20 min both these parameters increased up to 218 and 686 nm, respectively. Further prolongation of the treatment up to 60 min results in wall disruption in many cells. Within these cells, some isolated circular kpDNA molecules appear with the contour length of 588-792 nm. The circles of this size correspond to individual minicircles of the Crithidia kpDNA. Partly unfolded maxicircles of the kpDNA can be found only at early stages of dispersion (10 min). Special features of compaction of DNA-containing structures in both the nucleus and cytoplasm of Crithidia are discussed.

Animals↗
PubMed1984

[Determination of anti dsDNA antibodies by immunofluorescence using Crithidia luciliae. I--Diagnostic and prognostic value in systemic lupus erythematosus. Comparison with the Farr radioimmunoassay].

Antibodies to double stranded (ds) DNA were sought by the indirect immunofluorescence method using Crithidia luciliae in 196 sera from patients suffering from hepatic, thyroid or inflammatory rheumatic disorders. Anti ds DNA antibodies were demonstrated in 29 out of 45 systemic lupus erythematosus (SLE) sera. Lower titers were found in 3 out of 7 sera from drug-induced SLE, 2 out of 6 from mixed connective tissue diseases, 1 out of 60 from scleroderma, 2 from unclassified arthritis, 8 out of 40 from rheumatoid arthritis with antinuclear factors, and in 4 out of 15 sera from chronic hepatitis. For SLE diagnosis the sensitivity of the method was 73 percent, its specificity was 87 percent. 84 percent of these results were in agreement with those obtained with the Farr method, but titers did not correlate well. The sensitivity of the Farr method was 64.5 percent, its specificity was 85 percent. In this study, high titers of anti ds DNA antibodies demonstrated on Crithidia Luciliae did not correlate with disease severity. Low titers of anti14C labelled DNA antibodies demonstrated by the Farr assay correlated with inactive SLE without nephritis. The immunofluorescence assay using Crithidia luciliae is a valid method to detect anti ds DNA antibodies but does not allow prognostic conclusions in SLE.

Animals↗