Formation by the uterus of a peripheral layer of the sheath in microfilariae of Litomosoides carinii and Brugia malayi

Localization of gender-regulated gene expression in the filarial nematode Brugia malayi

We used in situ hybridization (ISH) to localize expression of gender-biased genes in the filarial parasite Brugia malayi that were previously identified by microarray analysis and quantitative reverse transcriptase PCR (qRT-PCR). We studied seven genes with male-biased expression, 11 genes with female-biased expression, and one control gene with equal expression in males and females. RNA probes were hybridized to frozen sections of adult worms. ISH confirmed gender-biased expression for all 18 of the differentially expressed genes and non-biased expression for the control. We identified six patterns of expression for these genes. As expected, most of the gender-biased genes were expressed in reproductive organs, developing gametes and embryos. Hybridization signal intensities correlated with relative mRNA levels as assessed by qRT-PCR. Some of the differentially expressed genes had tightly regulated expression patterns. For example, a high mobility group protein gene (Bm-hmg) was exclusively expressed in developing larvae in females. Expression was first detected in late stage oocytes, peaked in morula stage embryos and no signal was detected in late pretzel stage or in stretched microfilariae. Another female up-regulated gene (microfilarial sheath protein Bm-shp-1) was exclusively expressed in the epithelium of uterine sections that contained morulae or early pretzel embryos. No signal was detected in other female structures, in late embryos or in male worms. This result suggests that microfilarial sheath proteins are produced by the uterus epithelium and not by embryos. Transcripts of the male-upregulated major sperm protein-1 (Bm-msp-1) were detected in spermatocytes in the early spermatogenesis zone and in spermatids but not in spermatozoa in the vas deferens. Thus, ISH provides a means to independently confirm differential expression of genes identified by other methods. In addition, localization patterns provide insight regarding the function of known or novel genes in the parasite.

Fine structure and cytochemical analysis of the intestinal wall along the body of adult female of Litomosoides chagasfilhoi (Nematoda: Filarioidea)

Litomosoides chagasfilhoi is a filariid nematode parasite of the abdominal cavity of the wild rodent Akodon cursor (Winge, 1887), that has been described and used in Brazil as a new model for human filariasis. The fine structure of the intestine of this nematode was analyzed based on observations made by light and transmission electron microscopies of serial sections along the body. Cytochemical analysis was carried out to investigate the composition of the intestinal wall. This structure consisted of a basal lamina and an epithelium of variable thickness, composed of cells that have an irregular shape. The cytoplasm of intestinal cells contains few organelles: vacuoles, lysosomal bodies, spheroid bodies, endoplasmic reticulum, and many large lipid droplets. In the anterior portion of the intestine, the lysosomal bodies, spheroid bodies, and vacuoles presented positive reaction for acid phosphatase, and carbohydrates were detected in lysosomal bodies. The midbody and posterior regions presented less organelles and lipid droplets, and nuclei were more abundant. Residues of L-fucose were detected by Ulex europaeus lectin binding in the midbody sections. Basic proteins were associated to lipid droplets, in the posterior region. In the whole extension of the intestine, carbohydrates were detected on tight junctions. These results indicate that the metabolized material in the epithelium can contribute to the microfilariae development and also probably can be involved with the excretory/secretory mechanism of these nematodes.

Cloning and expression analysis of two mucin-like genes encoding microfilarial sheath surface proteins of the parasitic nematodes Brugia and Litomosoides

In several filarial genera the first stage larvae (microfilariae) are enclosed by an eggshell-derived sheath that provides a major interface between the parasite and the host immune system. Analysis of the polypeptide constituents of the microfilarial sheath from the cotton rat filaria Litomosoides sigmodontis identified two abundant surface glycoproteins: Shp3a and Shp3. The corresponding genes and the orthologues of the human parasite Brugia malayi and the rodent filaria Brugia pahangi were cloned and sequenced. They encode secreted, mucin-like proteins with N-terminal Ser/Thr-rich repeats and a C-terminal anchor domain rich in aromatic amino acids. About 75% of the protein molecular masses result from post-translational modifications. The Ser/Thr-rich motifs are supposed to serve as targets for dimethylaminoethanol-phosphate substitutions. These modifications were detected only on the sheaths of the late developmental stage of stretched microfilariae, corresponding with the expression of the proteins in the epithelium of the distal part of the uterus and the specific transcription of shp3 and shp3a in the anterior female worm segment. Genomic analysis of all three species demonstrated a conserved linkage of the two genes. Their transcripts undergo cis- and trans-splicing. The transcription start sites of the primary transcripts were determined for the L. sigmodontis genes. The core promoter regions are remarkably conserved between the paralogue genes Ls-shp3a and Ls-shp3 and their orthologues in Brugia, implicating conserved regulatory elements.

Molecular characterization of a Litomosoides sigmodontis protein involved in the development of the microfilarial sheath during embryogenesis

A cDNA clone Ls110 was isolated from a female Litomosoides sigmodontis expression library using an antiserum raised against the microfilarial sheath. The complete cDNA encodes a protein (Ls110) of 382 amino acids. Southern and PCR analyses revealed the presence of Ls110 in L. sigmodontis as a single copy gene. The transcription of the Ls110 gene was limited to female worms. In these worms the transcription was confined to the epithelial cells of the uterus. The protein Ls110 was detected not only in the epithelial layer of the uterus but also secreted in the lumen of the uterus. All the intra-uterine embryonic stages showed the protein bound to their egg shell/sheath, except the early multicellular embryonic stages and fully developed microfilariae. The transient occurrence of Ls110 on these structures of intra-uterine stages besides the presence of a cysteine-rich N-terminal region (SXC-like domain) suggest that the protein may play a role in the formation of the microfilarial sheath during embryogenesis.

Brugia spp. and Litomosoides carinii: identification of a covalently cross-linked microfilarial sheath matrix protein (shp2)

A microfilarial sheath protein gene (shp2) coding for the major constituent of the insoluble, cross-linked sheath remnant (SR) from Brugia malayi, Brugia pahangi and Litomosoides carinii has been cloned and sequenced, based on peptide partial amino-acid sequences. All three closely related single-copy shp2 genes in the two genera carry a single intron in identical position; shp2 mRNAs are post-transcriptionally modified by both cis-splicing and trans-splicing. In accordance with their extracellular destinations the encoded proteins include signal peptide sequences; molecular masses of approx. 23 kDa are hence predicted for the mature secreted polypeptides. In their structures sheath matrix proteins shp2 may be regarded as extreme cases of a modular constitution, since these proteins largely consist of two different segments of multiple sequence repetitions, PAA and QYPQAP (or QYPQ), separated by elements of unique sequence. Extreme insolubility and cross-linking are likely to originate from these repetitive sequences within shp2, and to constitute the basic properties of a microfilarial matrix largely consisting of an shp2 network.

Surface antigens of Litomosoides carinii microfilariae: agglutinating antibodies react with sheath components of 40 and 120 kilo Dalton molecular mass

This study was conducted to identify surface antigens of the microfilarial sheath of Litomosoides carinii which are accessible to antibodies. Rabbit antisera were raised against the soluble and insoluble fractions of purified sheaths by extracting them with a buffer containing 2-mercaptoethanol and sodium dodecylsulphate. These sera and rabbit hyperimmune sera directed against homogenates of total microfilariae, mature (i.e. microfilariae liberating) female parasites and excretory-secretory products of adult females were able to agglutinate live and formaldehyde-fixed microfilariae. When the antisera directed against sheath constituents were administered to patently infected Mastomys coucha, the microfilaraemia of these animals was rapidly reduced and remained low for a period of 2-3 weeks. Antibodies specifically binding to the microfilarial surface were immunoaffinity-purified on formaldehyde-fixed microfilariae. The antibodies react with sheath antigens of 40 and 120 kDa molecular mass which are produced by the epithelium of the distal uterus of the mature female, secreted and attached to the surface of the sheaths. A 120 kDa antigen recognized by anti-sheath surface antibodies was also detected in the excretory-secretory products of in vitro-cultured immature female L. carinii from day 30 post-infection onwards. In the excretory-secretory products of mature adult female parasites recovered on day 130 post-infection, this 120 kDa molecule was absent. However, material reacting with the antibody was detected in the stacking gel of SDS-polyacrylamide gels. This finding may indicate that the basic units forming the 120 kDa antigen of immature adults or microfilarial sheath surface antigens occur in a highly polymerized form in the excretory-secretory products of mature female parasites.

The gene coding for the major sheath protein of Litomosoides carinii microfilariae, gp22, is transcribed in oocytes and embryonic cells

The transcription and translation of the gene encoding gp22, a major constituent of the microfilarial sheath of the filarial parasite Litomosoides carinii were studied by in situ hybridisation and immunohistology. Transcription of the gp22 gene is confined to oocytes and embryos in the reproductive organs of adult female worms. It starts in oocytes in the rhachis zone, is maximal in multicellular embryos and decreases slowly as the microfilariae develop. Blood microfilariae lack the gp22 transcript. The gp22 gene product is first detectable in parasites recovered on day 32 post infection. Expression of gp22 begins in multicellular embryos in the uteri of mature female worms and can be detected in all further developed intrauterine stages. The gp22 gene product appears to be exported by the embryonic cells and becomes integrated into the sheath where it may contribute to the flexibility of the latter structure.

Trans-splicing of an early embryo mRNA in Litomosoides carinii, coding for the major microfilarial sheath protein gp22

Both genomic and cDNA clones have been isolated encoding the major sheath glycoprotein, gp22, of Litomosoides carinii microfilariae. The mature gp22 mRNA is shown to result from both trans-splicing of a 22-nucleotide 5'-leader sequence to an acceptor site at position 313 of the pre-mRNA, immediately upstream from the start codon, and from cis-splicing of a 117-nt intron located within the coding sequence. Cis-splicing precedes the trans-splicing reaction. The gp22 reading frame of 148 codons has the inferred structure of a prepro-protein and includes a leader peptide and a pro-segment ahead of the known N terminus of the mature, extracellular protein of 105 amino acids. The N-terminal part of that protein contains five repeats of an elastin-related pentapeptide sequence, which, together with a proline-threonine segment between two Cys clusters in the center and at its C terminus, may cause an elongated conformation with an apparent molecular size of 22 kDa in contrast to the calculated M(r) of 11,200.

Chemical composition of Litomosoides carinii microfilarial sheaths

Litomosoides carinii microfilariae were exsheathed by freezing and thawing, and the sheaths were separated by filtration. Samples of pure sheaths thus obtained were hydrolyzed, methanolyzed or oxidized with nitric acid under pressure at 300 degrees C, respectively, and were analyzed for amino acids, sugars, fatty acids or for metal ions and phosphorus. Almost 75% of the sheath dry weight could thus be accounted for. Amino acids (55 weight %) were the major constituents, and amongst these glutamine and proline (approximately 11% each). The detection of 2% cysteine/cystine indicated the possible presence of disulfide crosslinks. Besides amino acids, approximately 8% of sugars--roughly equimolar amounts of (N-acetyl)galactosamine and uronic acids--1.5% of monovalent cations (Na+ and K+) and 9.5% of phosphate were detected. No appreciable amounts of fatty acids, neutral sugars, neuraminic acid, or (N-acetyl)glucosamine (i.e. no chitin) were found.

Litomosoides carinii: extraction of the microfilarial sheath components and antigenicity of the sheath fractions

Microfilarial sheaths of Litomosoides carinii were isolated and extracted with 2% sodium dodecyl sulfate (SDS) and 5% 2-mercaptoethanol (2ME). Extraction with SDS alone did not alter the ultrastructure of the sheaths and yielded five polypeptides (27-67 kDa) that were not recognized by antibodies of infected hosts but reacted with antibodies to host-serum proteins. 2ME treatment caused partial solubilization of the sheaths (45% as determined by amino acid analysis), which could be further improved by combining 2ME with SDS. The remainder showed filamentous/threadlike structures on electron microscopic examination. As compared with whole sheaths, the insoluble proportion was markedly enriched in alanine and cysteine but contained less galactosamine, serine, and threonine. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of 2ME/SDS-extractable components showed 12-16 bands of 14- greater than 120 kDa. A predominant component had an apparent molecular mass of 22 kDa. Two bands (42 and 120 kDa) could be stained with Coomassie blue but showed "negative" staining when gels were stained with silver. Several components (but not the 22-kDa polypeptide) bore phosphocholine epitopes. Apart from the negatively staining bands, most of the 2ME-soluble sheath components were recognized by antibodies of L. carinii-infected Mastomys coucha. Except for several polypeptides that had been unspecifically recognized by IgM, the antibody response to sheath components started at the end of the prepatent period.

A major Litomosoides carinii microfilarial sheath glycoprotein (gp22): amino terminal sequence and immunological studies with corresponding synthetic peptides

The major glycoprotein of the sheath of Litomosoides carinii microfilariae (gp22) was analysed for its amino acid and amino sugar composition. It is rich in proline, glutamine/glutamic acid and glycine and contains (N-acetyl)galactosamine. The N-terminal amino acid sequence was determined up to position 37. It consists of a group of 6 repeats of the pentapeptide sequence methionine-glycine-proline-glutamine-proline with two minor modifications in repeats 3-6, while the first two repeats follow the general pattern more loosely. Identical N-terminal amino acid sequences were found in at least two other sheath polypeptides (33 kDa, 39 kDa). Antisera prepared against 3 overlapping synthetic peptides corresponding to the amino terminus of gp22 recognized different epitopes. They all reacted with identical patterns of sheath polypeptides. The antisera failed to recognize antigens of 4th-stage larvae of L. carinii. In contrast, cross-reacting epitopes were detected in other parasite stages. Antisera reacted with material surrounding embryos and microfilariae in the uterus of females, and caused patchy fluorescence on the sheath of blood-derived and in vitro-released microfilariae.

The sheaths of Brugia microfilariae: isolation and composition

Burgia malayi and B. pahangi microfilariae were isolated from the blood of infected Mastomys natalensis, and were exsheathed by freezing, thawing and agitation. Pure sheaths were obtained by a filtration procedure. The sheaths were found to contain about 95 mol% of amino acids, with proline, glutamic acid/glutamine, alanine, cysteine/cystine and glycine being the major components, and 5 mol% of carbohydrates, notably (N-acetyl)galactosamine, but no (N-acetyl)glucosamine.

Lectin binding studies on adult filariae, intrauterine developing stages and microfilariae of Brugia malayi and Litomosoides carinii

Sections of macrofilariae of Brugia malayi and Litomosoides carinii revealed binding of the gold-labelled lectins WGA, DBA and PNA. Specificity of binding was controlled by competitive inhibition with the respective sugars. N-acetyl-glucosamine, N-acetylgalactosamine and galactose residues seem to be present in the respective tissues. The lectins were bound preferentially to parts of the reproductive organs and to the fluid contents of their lumina. The results of the chitosan test and binding experiments with WGA-gold conjugate suggest the presence of chitin in the sheath of oocytes or zygotes. Binding of WGA could not be inhibited with 0.5 M N-acetylglucosamine, but only with 10 mM triacetyl chitotriose. In older stages, binding of WGA to the sheath could be inhibited by 0.5 M N-acetylglucosamine. In mature microfilariae, the outer surface of the sheath did not show affinity for WGA, but small amounts were bound to the inner surface. Therefore, the sheath of later developmental stages and microfilariae does not contain chitin but only N-acetylglucosamine residues. The degradation of the chitin content might enable the elongation and flexibility of the sheath of microfilariae.

Isolation of pure sheaths of Litomosoides carinii microfilariae

A method is described for the isolation of pure, chemically intact sheaths of blood microfilariae of Litomosoides carinii. Microfilariae were isolated according to standard techniques. Exsheathment was performed by freezing-thawing-shaking procedures, repeated 5-10 times, i.e., larvae were frozen in liquid nitrogen, thawed at room temperature, and shaken vigorously for 5 s. Exsheathment rates were about 50%. Sheaths were separated from ensheathed and exsheathed microfilariae and microfilariae fragments by filtration through a polycarbonate filter (2 micron pore size). The achievable yield (about 15% of the sheaths of a batch of microfilariae) was approximately 1 microgram of sheaths per 10(6) microfilariae.