Cuticle collagen genes of Haemonchus contortus and Caenorhabditis elegans are highly conserved

Anthelmintic activity of Leucaena leucocephala protein extracts on Haemonchus contortus

The objective of this study was to evaluate the effects of protein extracts obtained from the plant Leucaena leucocephala on the nematode parasite Haemonchus contortus. The seeds, shell and cotyledon of L. leucocephala were separated and their proteins extracted using a sodium phosphate buffer, and named as TE (total seed extract), SE (shell extract) and CE (cotyledon extract). Soluble protein content, protease, protease inhibitory and chitinase activity assays were performed. Exsheathment inhibition of H. contortus larvae were performed at concentrations of 0.6 mg mL-1, and egg hatch assays were conducted at protein concentrations of 0.8, 0.4, 0.2, 0.1 and 0.05 mg mL-1. The effective concentration for 50% hatching inhibition (EC50) was estimated by probit. Different proportions of soluble proteins, protease and chitinase were found in TE and CE. Protease inhibitory activity was detected in all extracts. The EC50 of the CE and TE extracts were 0.48 and 0.33 mg mL-1, respectively. No ovicidal effects on H. contortus were detected in SE extracts, and none of the protein extracts demonstrated larvicidal effects on H. contortus. We therefore conclude that protein extracts of L. leucocephala had a detrimental effect on nematode eggs, which can be correlated with the high protease and chitinase activity of these extracts.

Collagen processing and cuticle formation is catalysed by the astacin metalloprotease DPY-31 in free-living and parasitic nematodes

The exoskeleton or cuticle performs many key roles in the development and survival of all nematodes. This structure is predominantly collagenous in nature and requires numerous enzymes to properly fold, modify, process and cross-link these essential structural proteins. The cuticle structure and its collagen components are conserved throughout the nematode phylum but differ from the collagenous matrices found in vertebrates. This structure, its formation and the enzymology of nematode cuticle collagen biogenesis have been elucidated in the free-living nematode Caenorhabditis elegans. The dpy-31 gene in C. elegans encodes a procollagen C-terminal processing enzyme of the astacin metalloprotease or bone morphogenetic protein class that, when mutated, results in a temperature-sensitive lethal phenotype associated with cuticle defects. In this study, orthologues of this essential gene have been identified in the phylogenetically diverse parasitic nematodes Haemonchus contortus and Brugia malayi. The DPY-31 protein is expressed in the gut and secretory system of C. elegans, a location also confirmed when a B. malayi transcriptional dpy-31 promoter-reporter gene fusion was expressed in C. elegans. Functional conservation between the nematode enzymes was supported by the fact that heterologous expression of the H. contortus dpy-31 orthologue in a C. elegans dpy-31 mutant resulted in the full rescue of the mutant body form. This interspecies conservation was further established when the recombinant nematode enzymes were found to have a similar range of inhibitable protease activities. In addition, the recombinant DPY-31 enzymes from both H. contortus and B. malayi were shown to efficiently process the C. elegans cuticle collagen SQT-3 at the correct C-terminal procollagen processing site.

Stage-specific gene expression in Teladorsagia circumcincta (Nematoda: Strongylida) infective larvae and early parasitic stages

Suppression subtractive hybridisation was used to enrich genes expressed in a stage-specific manner in infective, exsheathed L3s (xL3) versus early L4s of the ovine nematode, Teladorsagia circumcincta prior to gene expression profiling by microarray. The 769 cDNA sequences obtained from the xL3-enriched library contained 361 unique sequences, with 292 expressed sequence tags (ESTs) being represented once ("singletons") and 69 sequences which were represented more than once (overlapping and non-overlapping "contigs"). The L4-enriched EST dataset contained 472 unique sequences, with 314 singletons and 158 contigs. Of these 833 sequences, 85% of the xL3 sequences and 86% of the L4 sequences exhibited homology to known genes or ESTs derived from other species of nematode. Quantitative differential expression (P<0.05) was demonstrated for 563 (68%) of the ESTs by microarray. Within the L3-specific dataset, more than 30% of the transcripts represented the enzyme, guanosine-5'-triphosphate (GTP)-cyclohydrolase, which is the first and rate-limiting enzyme of the tetrahydrobiopterin synthesis pathway and may be involved in critical elements of larval development. In L4s, proteolytic enzymes were highly up-regulated, as were collagens and a number of previously characterised secretory proteins, reflecting the rapid growth of these larvae in abomasal glands. Nucleotide sequence data reported in this paper are available in the EMBL, GenBank and DDJB databases under accession numbers AM 743198-AM 744942.

Unravelling the moulting degradome: new opportunities for chemotherapy?

Replacement of the nematode cuticle with a newly synthesized cuticle (a process known as moulting) occurs four times during larval development. Therefore, the key components of this essential developmental process represent attractive targets for new chemotherapeutic strategies. Recent advances in understanding the molecular genetics of nematode moulting should stimulate and facilitate development of novel drugs that target the essential molecules of the moulting cycle. In particular, we argue that further understanding of the moulting degradome and its key peptidase members offers an important opportunity for the development of novel antinematode agents.

Molecular cloning of a cDNA encoding a putative cuticle collagen of Trichinella spiralis

A 5-day-old adult stage-specific cDNA fragment from Trichinella spiralis was identified by suppression subtractive hybridization and was used as a probe to screen the cDNA library. The cDNA sequence coding for a putative T. spiralis cuticle collagen was isolated. The cDNA encoded an open reading frame of 343 amino acid residues with molecular weight of 35.1 k Da. The deduced protein contained an N-terminal signal peptide, a nematode cuticle collagen N-terminal domain and a collagen triple helix repeat domain. Searches in GenBank using BLASTP showed up to 47% identity to cuticle collagens from other nematodes. Southern blot analysis of genomic DNA indicated this gene was present as a single copy in T. spiralis genome.

Genes and genomes of parasitic nematodes

Our knowledge of gene and genome organization in nematodes is growing rapidly, partly as a result of the Caenorhabditis elegans genome project. Here Martin Hammond and Ted Bianco review what is known about the organization of genes and genomes in parasitic nematode species, using information gained from molecular and cytological approaches. They suggest that there are implications not only for a wide range of problems in parasitology but also for our understanding of genome evolution in eukaryotes.

Enzymes involved in the biogenesis of the nematode cuticle

Nematodes include species that are significant parasites of man, his domestic animals and crops, and cause chronic debilitating diseases in the developing world; such as lymphatic filariasis and river blindness caused by filarial species. Around one third of the World's population harbour parasitic nematodes; no vaccines exist for prevention of infection, limited effective drugs are available and drug resistance is an ever-increasing problem. A critical structure of the nematode is the protective cuticle, a collagen-rich extracellular matrix (ECM) that forms the exoskeleton, and is critical for viability. This resilient structure is synthesized sequentially five times during nematode development and offers protection from the environment, including the hosts' immune response. The detailed characterization of this complex structure; it's components, and the means by which they are synthesized, modified, processed and assembled will identify targets that may be exploited in the future control of parasitic nematodes. This review will focus on the nematode cuticle. This structure is predominantly composed of collagens, a class of proteins that are modified by a range of co- and post-translational modifications prior to assembly into higher order complexes or ECMs. The collagens and their associated enzymes have been comprehensively characterized in vertebrate systems and some of these studies will be addressed in this review. Conversely, the biosynthesis of this class of essential structural proteins has not been studied in such detail in the nematodes. As with all morphogenetic, functional and developmental studies in the Nematoda phylum, the free-living species Caenorhabditis elegans has proven to be invaluable in the characterization of the cuticle and the cuticle collagen gene family, and is now proving to be an excellent model in the study of cuticle collagen biosynthetic enzymes. This model system will be the main focus of this review.

Immunolocalization of a putative cuticular collagen protein in several developmental stages of Meloidogyne arenaria, Globodera pallida and G. rostochiensis

The monoclonal antibody IACR-CCNj.3d has previously been used to isolate a gene (gp-col-8) with strong similarity to cuticular collagen from a mixed stage Globodera pallida cDNA expression library. The antibody has also been shown to label specifically the amphidial canal of pre-parasitic second stage juveniles (J2) of several plant nematode species without any reactivity on the cuticular surface, indicating that this protein is either not present or is inaccessible on the cuticular surface. This paper investigates the cross-reactivity of Mab IACR-CCNj.3d with Meloidogyne arenaria and the localization of the putative collagen protein on the cuticular surface of parasitic stages in planta and on the cuticular surface of juveniles inside eggs. The antigen was shown to be present in all developmental stages of the two species of potato cyst nematodes and M. arenaria. The antibody bound strongly to the amphidial canal and hypodermis of pre-parasitic J2 and adult females. The antigen was present on the cuticular surface of the sausage-shaped J2 in planta and of first stage juveniles (J1) inside the eggs. The presence of collagen on the surface of the cuticle of moulting stages of plant parasitic nematodes has been observed for the first time. It is clear that this protein has a role in the construction of the cuticle of the first stage juveniles and parasitic second stage juveniles, during moulting inside the eggs and in the root tissue, respectively.

Cuticular collagen synthesis by Ascaris suum during development from the third to fourth larval stage: identification of a potential chemotherapeutic agent with a novel mechanism of action

The dominant proteins released by Ascaris suum during development in vitro from the L3 to L4 stage were identified as collagenous cuticular proteins by sequence analysis and susceptibility to digestion by collagenase. Under reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the collagen proteins separated into 3 groups with molecular weights estimated at 32 kDa, 54-60 kDa, and 71-91 kDa. The 32-kDa protein represents monomeric collagen; the 54-60- and 71-91-kDa components represent dimeric and trimeric forms, respectively, polymerized by nonreducible cross-links. Furthermore, the release of these forms of collagen was developmentally regulated, as exemplified by a sequential temporal progression from monomeric to dimeric to trimeric forms in association with the in vitro transition from L3 to L4. The data suggest that collagen released in vitro during development of A. suum L3 to L4 reflects the increased translation of collagen gene products and their initial assembly into higher molecular weight molecules associated with the synthesis of the L4 cuticle. A biotinylated dipeptidyl fluoromethylketone cysteine protease inhibitor (Bio-phe-ala-FMK) bound specifically to the 32-kDa collagen and, to a lesser extent, to a 30-kDa protein; binding was dependent on the presence of dithiothreitol (DTT) and was prevented by iodoacetamide. Because cysteine residues play an essential role in the initial assembly of the collagen monomers into the higher molecular weight oligomers present in the mature nematode cuticle, inhibition of molting of A. suum L3 to L4 by the cysteine protease inhibitor Z-phe-ala-FMK might be due to its binding to thiol groups of collagen monomers during a critical phase of collagen assembly. Prevention of cystine cross-links during this critical period of cuticle assembly by peptide-FMK inhibitors may represent a potential control mechanism having a novel mechanism of action.

Characterization and expression of enzymatically active recombinant filarial prolyl 4-hydroxylase

The cuticle of parasitic nematodes consists primarily of a network of collagen molecules. The enzyme responsible for collagen maturation is prolyl 4-hydroxylase, making this enzyme a central activity in cuticle biosynthesis and a potentially important chemotherapeutic target. Adult and embryonic Brugia malayi are shown to be susceptible to inhibitors of vertebrate prolyl 4-hydroxylase, with exposed parasites exhibiting pathologies consistent with a disruption in cuticle biosynthesis. A full-length cDNA (Ov-phy-1) encoding a catalytically active alpha-subunit of Onchocerca volvulus prolyl 4-hydroxylase was isolated and characterized. The derived amino acid sequence of Ov-phy-1 encoded a peptide that was most similar to the two Caenorhabditis elegans prolyl 4-hydroxylase homologues and to the isoform II enzymes of vertebrates. Expressed sequence tag (EST) analysis and developmental polymerase chain reaction (PCR) studies demonstrated that Ov-phy-1 was expressed in L3 and adult parasites. The gene encoding the Ov-phy-1 open reading frame contained 11 introns, similar in structure to the gene encoding human prolyl 4-hydroxylase isoform I. Genomic Southern blot, EST and genomic PCR studies demonstrated that the O. volvulus genome contained between three and eight genes closely related to Ov-phy-1. Co-expression of Ov-phy-1 with the O. volvulus homologue of protein disulfide isomerase in a baculovirus system resulted in the production of enzymatically active O. volvulus prolyl 4-hydroxylase. In vitro production of enzymatically active O. volvulus prolyl 4-hydroxylase should facilitate identification of specific inhibitors of the parasite enzyme.

Characterisation of a collagen gene subfamily from the potato cyst nematode Globodera pallida

We have isolated two full-length genomic DNA sequences, which encode the cuticle collagen proteins GP-COL-1 and GP-COL-2, from the potato cyst nematode Globodera pallida. A third, partial collagen gene ORF termed gp-col-t(t=truncated) has also been isolated and appears to represent an unexpressed pseudogene. The gp-col-1 and gp-col-2 genes both contain three short (<97 bp) introns which disrupt coding regions predicted to specify proteins with molecular weights of 33 and 32.7 kDa respectively. All three sequences show high similarity to each other and to the previously isolated G. pallida cDNA clone gp-col-8. The conserved pattern of cysteine residues and non-(Gly-X-Y)(n) region sequence similarity observed in all four G. pallida genes suggests that these molecules form part of the same subfamily of collagens. Southern analysis indicates that this subfamily is likely to contain further members. The G. pallida collagen sequences show striking similarity to twelve genes from Caenorhabditis elegans which collectively represent the recently classified Group 1a collagen subfamily. No data exists on the function of this subfamily in C. elegans. gp-col-1 and gp-col-2 are developmentally regulated with transcripts of both genes detected in adult virgin and gravid females but not in pre-parasitic second stage juveniles. A similar expression pattern is observed for the Group 1a collagen lemmi 5 from Meloidogyne incognita perhaps indicating a generic link between subfamily and function during the various changes in cuticular structure which accompany nematode growth and reproduction. Immunochemical studies indicate that the GP-COL-1 protein is specifically located in the hypodermis of G. pallida adult females.

Serodiagnosis of haemonchosis with a somatic antigen (Hc26) in several breeds of sheep

Sera from 53 sheep belonging to Castellano, Churro, Manchego, and Merino breeds were analyzed to test the diagnostic value of a 26-kD antigen from adult Haemonchus contortus at prepatency and early and late patency of experimental haemonchosis. Animals that received zero, 1, or 2 infections with the parasite were tested. In addition, sera from 20 experimentally infected and 10 noninfected Texel sheep were used to test the antigen. Sera from 37 infected animals at prepatency as well as at patency in primary and secondary infection were found positive with the 26-kD antigen. However, sera from 10 animals with the lowest worm burdens (second infection) did not recognize the antigen during early patency (day 28 postinfection). IgG1 was the only isotype implicated in antigen recognition because IgG2, IgA, and IgM, in the same sera, showed no reactivity with the peptide. Antigen specificity was confirmed because hyperimmune sera against infective larvae and adult stages of the most common gastrointestinal nematodes found in natural infections in sheep (Trichostrongylus colubriformis and Teladorsagia circumcincta) did not recognize this peptide. The antigen was recognized only by anti-adult H. contortus hyperimmune sera and appeared to be absent in the L3 parasite stage. In addition, the partial N-terminal amino acid sequence of the diagnostic peptide is reported.

Defined characteristics of cathepsin B-like proteins from nematodes: inferred functional diversity and phylogenetic relationships

Numerous cathepsin B-like protein sequences (CBLs) have been reported from nematodes. However, the relationships among these proteins remain unclear. Here, expression of several CBL transcripts in the gut of the parasitic nematode Haemonchus contortus was demonstrated. To assess potential functional diversity, multiple nematode CBL sequences were compared with known functional domains of cathepsin B. These domains included the occluding loop, S2' and S2 subsites, and the pro region. Four groups of CBLs were defined based on variable characteristics in the occluding loop region, which incorporates a portion of the S2' subsite. Further diversity was observed in amino acids expected to contribute to the S2 subsite. In addition, short signature sequences near the cysteinyl active site region characterized known CBLs of parasites from the orders Strongylida and Rhabditida. The criteria established were used to identify two predicted CBLs from parasitic (Ascaris suum) and free-living (Caenorhabditis elegans) nematodes as potential orthologues, and provided a basis to evaluate orthologue status of other CBLs. Variability in the domains analyzed suggests substantial functional diversity in enzymatic properties of nematode CBLs. Results suggest that the selective amplification and evolution of distinct CBL lineages has contributed to differences in CBLs among species and groups of nematodes. Nutrient digestion is one potential factor promoting CBL diversification in these organisms.

Polymorphic DNA markers in the genome of parasitic nematodes

Polymorphic molecular markers are being identified to characterize the genomes of parasitic nematodes. The aim is to construct a map with markers evenly spread over the six chromosomes. With such a map, regions can be identified that are under selection pressure when attempts are being made to eradicate worms, be it by drugs, vaccines or genetic resistance in the sheep. Several types of markers have been developed, microsatellites, transposon-associated markers, amplified fragment length polymorphism (AFLP) and expressed sequence tag (EST) markers. Linkage groups can be constructed using several genetic crosses between inbred and drug resistant strains. EST markers will be especially important for comparative mapping with the genome of Caenorhabditis elegans, and therefore localization of the linkage group on a chromosome. It will then be possible to identify functional genes close to markers that have changed allele frequencies under selection pressure and identify the mechanisms of resistance to parasite control.

A tissue specific approach for analysis of membrane and secreted protein antigens from Haemonchus contortus gut and its application to diverse nematode species

General methods to conduct tissue specific analysis are largely lacking for nematodes. An approach is described that focused on isolation of membrane and secreted protein genes from the gut of the parasitic nematode Haemonchus contortus. The approach capitalized on a monoclonal antibody that recognizes multiple membrane and secreted worm proteins. Polyclonal antisera made against these proteins were used to screen expression cDNA libraries made either from adult worm gut or whole worm. The genes identified encode predicted or known membrane and secreted proteins from gut, including a cysteine protease, a zinc metallopeptidase and a previously described GA1 protein. Another gene, Hc40, was isolated from the whole worm cDNA library and is nearly identical to a vaccine patent sequence pBTA879. Tissue analysis demonstrated the intended focus on membrane and secreted proteins from parasite gut was achieved. Proteins related to each of those described were identified from other nematode species through data base analysis. Additionally, this analysis led to (1) identification of homologues of each gene in C. elegans; (2) deduction of a dimorphic structure in the Hc40 protein; (3) recognition of both monomorphic and dimorphic families of Hc40-related proteins; and (4) detection of two apparent classes of transcripts (mep1a and mep1b) that would each encode a divergent version of the putative zinc metallopeptidase MEP1. The tissue specific approach and information base described should generally contribute to investigations on nutrient digestion and related secretory processes in nematode gut.

The first isolated collagen gene of the root-knot nematode Meloidogyne javanica is developmentally regulated

The nematode's surface comprises a multilayered cuticle, which consists mainly of collagen proteins. We identified, cloned and characterized the first cuticular collagen gene, Mjcol-3, of the plant-parasitic nematode Meloidogyne javanica. The gene putatively encodes a 32.4-kDa collagen protein, including a propeptide which possesses a subtilisin-like protease-cleavage site. Six introns were identified in the gene sequence, with three slightly different acceptor-splicing sites. The basic structure of the predicted MJCOL-3 protein sequence is highly similar to that of the Caenorhabditis elegans DPY-7, with 65.9% identity between the two amino acid sequences. Relative to DPY-7, the putative MJCOL-3 protein has a shorter carboxy-terminus. This non-conserved feature may indicate different contributions of DPY-7 and MJCOL-3 collagens to the structure of the cuticle. Mjcol-3 is developmentally regulated: transcripts were found mainly in preparasitic developing eggs, less in parasitic third- and fourth-stage juveniles and young females shortly after the fourth molt, and much less in females before egg-laying.

Conservation of the Caenorhabditis elegans cuticle collagen gene col-12 in Caenorhabditis briggsae

The functional importance of the majority of Caenorhabditis elegans cuticle collagen genes is unknown. We have identified, cloned and sequenced the Caenorhabditis briggsae homologue of the C. elegans gene col-12, a cuticle collagen for which no mutants have yet been identified. Homology in the flanking sequence has allowed us to unambiguously identify this gene as the col-12 homologue, as opposed to some other closely related member of this large multigene family. The whole of the predicted polypeptide is highly conserved (94.9% identical), including those regions not yet shown by mutational analysis to be important for C. elegans cuticle collagen function. These include the whole of the N-terminal non-Gly-X-Y domain and the X and Y positions of the Gly-X-Y domain. This may be a consequence of the requirement of cuticle collagens to participate in intermolecular interactions throughout the full length of the polypeptide. There is increasing evidence to suggest that conservation between C. elegans and C. briggsae is confined to functionally significant sequence. Hence, the conservation of col-12 between these two species provides evidence that this member of the cuticle collagen family has a significant structural function.

Cloning and sequence analysis of the candidate nicotinic acetylcholine receptor alpha subunit gene tar-1 from Trichostrongylus colubriformis

A T. colubriformis genomic library in lambda EMBL3 was screened for sequences homologous to the Caenorhabditis elegans unc-38 nicotinic acetylcholine receptor (nAChR) alpha-subunit gene. The candidate gene tar-1 (for Trichostrongylus acetylcholine receptor subunit gene 1) comprising 13704 base pairs was thus identified. BLAST comparison of the sequenced clone with GenBank, followed by comparison of translated regions in six reading frames with protein databases, identified clearly defined tracts corresponding to 12 putative exons sharing high sequence homology to other nAChR genes and able to code for sequential regions of a putative nAChR alpha-subunit protein (tar-1). Tar-1 shares sequence similarities with over 40 nAChR subunit proteins. The highest similarity (91.6%) is with unc-38, suggesting that nAChR sequences from nematodes are closely related. The sequence includes motifs typical of these molecules including adjacent cysteine residues at the ACh binding site and four transmembrane regions. The DNA sequence presents the longest genomic tract described for this organism and should prove useful as a probe source in the search for nAChR genes from this and other nematodes and for studying the molecular mechanism of resistance to levamisole, a drug which is known to act on nAChRs of worms and which is widely used for parasite control.

Isolation and characterization of a putative collagen gene from the potato cyst nematode Globodera pallida

A cDNA clone encoding a full length putative collagen has been isolated in a screen of a mixed stage Globodera pallida expression library. Comparison of the deduced amino acid sequence of this molecule with other collagens suggests it is a cuticular collagen and a member of the col-8 subfamily of collagen genes. Northern blots show the gene is expressed specifically in gravid, adult females of the parasite as compared to second (invasive) stage juveniles and virgin females. Preliminary immunocytochemical studies indicate this collagen is present in areas other than the cuticle; these findings and the potential functional role of this collagen are discussed.

Cuticular collagen genes from the parasitic nematode Ostertagia circumcincta

The nematode cuticle is a multifunctional structure whose roles include exoskeleton and barrier between the animal and its environment. It is an extracellular matrix which consists predominantly of small collagen-like proteins. For those species studied, these cuticular collagens are encoded by a multigene family. In the free living nematode Caenorhabditis elegans, this family has approximately 100 members. Our data indicate a gene family of similar size in the parasitic nematode Ostertagia circumcincta. We have characterised a pair of tandemly duplicated collagen genes from O. circumcincta, colost-1 and colost-2, which we believe to be the direct homologues of col-12 and col-13, a tandemly duplicated pair previously identified in C. elegans. The interspecies comparison of these homologues indicates regions of extreme conservation. We conclude that the gene duplication event that resulted in the creation of col-12 and col-13 in C. elegans is most likely the same duplication that generated colost-1 and colost-2 in O. circumcincta, and thus this particular gene duplication precedes the divergence of the two species. These two nematode species are deeply diverged, O. circumcincta belonging to the order Strongylata and C. elegans to Rhabditata. The ability to identify direct homologues of individual cuticular collagen genes between deeply diverged species provides a powerful method for determining regions of structural importance in these small collagens. Characteristics that are conserved between homologues in divergent species, but not conserved with other members of the multigene family within one species, must relate to the specific function of that particular cuticular collagen.

Identification and sequence comparison of a cuticular collagen of Brugia pahangi

The cuticle of filarial nematodes is a specialized extracellular matrix that covers the parasite and protects it from adverse conditions of the environment. As a surface structure it is in direct contact with the host defence mechanisms and therefore plays an important role in the molecular host-parasite relationship. Using polyclonal antisera raised against the insoluble components of the cuticle of the adult filarial parasite Brugia pahangi, we have isolated cDNA clones encoding collagen molecules of the cuticle. The protein domain structure of cDNA clone Bpcol-1 was compared with the known structures of cuticular collagens of the nematodes Brugia malayi, Caenorhabditis elegans, Ascaris suum and Haemonchus contortus, confirming interspecies similarities. Using affinity-purified anti-Bpcol-1 antibodies we identified Bpcol-1 antigenic determinants in different nematode extracts, and determined the localization of such epitopes within the cuticle of B. pahangi.

Identification and partial purification of a 26 kilodalton antigen of adult Haemonchus contortus

Adult H. contortus soluble extracts were fractionated by means of gel filtration (S-200) and anion exchange chromatography (DEAE-Sephacel). Fractions from both analyses were checked by ELISA and western blotting (WB) with sera from lambs infected with H. contortus, monospecific heterologous sera (anti-Trichostrongylus colubriformis and anti-Teladorsagia circumcinta) and sera from naturally infected sheep with mixed trichostrongylid infections. High cross reactivity was seen between H. contortus and heterologous sera, particularly with the anti-T. colubriformis serum, when fractions from gel filtration were checked by ELISA. Individual fractions containing the highest positive/negative and positive/heterologous ratios were pooled and analysed by SDS-PAGE. One of the pools (A4) containing 2 regions around 48-55 and 25-27 kDa were strongly recognized by homologous sera in WB. Similar results were obtained with the first peak eluted in the DEAE-Sephacel chromatography with NaCl 0.1 M. The pooled fraction A4 from gel filtration was further fractionated by anion exchange chromatography and the peak obtained with the NaCl gradient contained a ca. 26 kDa antigen apparently specific for the diagnosis of H. contortus infections in lambs.

Identification and analysis of a cuticular collagen-encoding gene from the plant-parasitic nematode Meloidogyne incognita

The vast majority of proteins in the nematode cuticle are collagens. Cuticular collagen-encoding genes (col) have been described for the animal parasites Ascaris suum and Haemonchus contortus and for the free-living Caenorhabditis elegans. The proteins encoded by all these genes seem to have the same basic structure, indicating that there is a conserved subfamily of cuticular col in these nematodes. In this paper, we describe the identification and characterization of a cDNA (Lemmi 5) which corresponds to a cuticular col of the plant-parasitic nematode Meloidogyne incognita. The derived protein structure is very similar to the basic structure of the C. elegans cuticular collagens. Using PCR technology, we have shown the presence of Lemmi 5-related sequences in the genome of Ditylenchus destructor. Our data strongly support the existence of a cuticular col subfamily which is highly conserved in the phylum Nemata.

Cross antigenicity among ovine trichostrongyloidea. Preliminary report

A preliminary trial on the extent of cross-antigenicity among the sheep strongylids Haemonchus contortus, Trichostrongylus colubriformis, Teladorsagia circumcincta and Nematodirus battus in 2.5- to 4-month-old lambs has been carried out using ELISA and Western blotting (WB). Cross antigenicity was tested using soluble extracts from adult and third stage larvae (L3) of H. contortus as antigenic source probed with sera from lambs with monospecific heterologous infections. There was cross-antigenicity between L3 of H. contortus and Trichostrongylus colubriformis in ELISA and WB. Immunodetection results with adult H. contortus antigen showed a closer relationship to Teladorsagia circumcincta. Certain heterologous sera reacted with H. contortus antigens more strongly than the homologous one, but sera from the H. contortus-infected animals had reactivity around the 25 kDa region from adult antigens which could have potential diagnostic use.

The role of dityrosine formation in the crosslinking of CUT-2, the product of a second cuticlin gene of Caenorhabditis elegans

A second cuticlin gene, cut-2, of the nematode Caenorhabditis elegans, has been isolated and its genomic and cDNA sequences determined. The gene codes for a component of cuticlin, the insoluble residue of nematode cuticles. Conceptual translation of cut-2 reveals a 231-amino acid secreted protein which, like CUT-1, begins with a putative signal peptide of 16 residues. The central part of the protein consists of 13 repetitions of a short hydrophobic motif, which is often degenerated with substitutions and deletions. Parts of this motif are present also in CUT-1 (Caenorhabditis elegans) as well as in several protein components of the larval cuticle and of the eggshell layers of various insects (Locusta migratoria, Ceratitis capitata and Drosophila species). These sequence similarities are related to the similar functions of these proteins: they are all components of extracellular insoluble protective layers. Immunolocalisation and transcription analysis suggest that CUT-2 contributes to the cuticles of all larval stages and that it is not stage-specific. Analysis by reverse transcriptase-PCR suggests that it is not stage-specific. Analysis by reverse transcriptase-PCR suggests that transcription is not continuous throughout larval development but occurs in peaks which precede the moults. Dityrosine has been detected in the cuticle of nematodes and of insects; formation of dityrosine bridges may be one of the cross-linking mechanisms contributing to the insolubility of cuticlins. Recombinant, soluble CUT-2 is shown to be an excellent substrate for an in vitro cross-linking reaction, catalysed by horseradish peroxidase in the presence of H2O2, which results in the formation of insoluble, high-molecular weight CUT-2 and of dityrosine.

The cuticle of the nematode Caenorhabditis elegans: a complex collagen structure

The cuticle of the nematode Caenorhabditis elegans forms the barrier between the animal and its environment. In addition to being a protective layer, it is an exoskeleton which is important in maintaining and defining the normal shape of the nematode. The cuticle is an extracellular matrix consisting predominantly of small collagen-like proteins that are extensively crosslinked. Although it also contains other protein and non-protein compounds that undoubtedly play a significant part in its function, the specific role of collagen in cuticle structure and morphology is considered here. The C. elegans genome contains between 50 and 150 collagen genes, most of which are believed to encode cuticular collagens. Mutations that result in cuticular defects and grossly altered body form have been identified in more than 40 genes. Six of these genes are now known to encode cuticular collagens, a finding that confirms the importance of this group of structural proteins to the formation of the cuticle and the role of the cuticle as an exoskeleton in shaping the worm. It is likely that many more of the genes identified by mutations giving altered body form, will be collagen genes. Mutations in the cuticular collagen genes provide a powerful tool for investigating the mechanisms by which this group of proteins interact to form the nematode cuticle.

Lamb serum recognition of infective larvae and adult Haemonchus contortus antigens

Sixteen- to eighteen-week-old lambs were infected with 2500 3rd stage larvae (L-3) of Haemonchus contortus or kept as uninfected controls. Two months later all animals were challenged with 5000 L-3 of this parasite. Soluble antigens of H. contortus L-3 and adult worms were analyzed by SDS-PAGE and Western blotting during experimental infection and challenge. Antigens from both sources, particularly of low molecular weight under reducing conditions, were recognised by the pooled sera of infected lambs. No single L-3 antigen was recognised by all infected lambs, whereas two peptides having around 25 and 26 kDa from adults were recognised by infected animals during the patency and could be of potential use in the diagnosis of lamb haemonchosis.

Characterization of the mRNA encoding a proline-rich 37-kilodalton glycoprotein from the excretory-secretory products of Trichostrongylus colubriformis

A glycoprotein, with apparent molecular weight in SDS-polyacrylamide gels of 37 kDa, has been isolated from the excretory-secretory (ES) products of the adult stage of Trichostrongylus colubriformis, a parasitic nematode. This protein is the major ES product recognized in immunoblots by lymph from a naturally infected sheep. A synthetic oligonucleotide, based on peptide sequence data from a digest of the purified protein was used to successfully screen a cDNA library. A cDNA clone was isolated which encoded a presumptive protein precursor of 220 amino acids that contained a 63 amino acid region of which more than 35% of the residues were proline, three peptide sequences determined from the natural component, and three potential N-glycosylation sites, consistent with the protein being isolated from the lectin-bound fraction of the adult ES products. The presumptive, processed, amino terminus encoded by the cDNA clone was preceded by a signal-like, hydrophobic-rich region of 16 amino acids.

Biochemistry of the nematode cuticle: relevance to parasitic nematodes of livestock

The cuticle of nematodes is a thin, flexible outer covering composed primarily of protein with trace amounts of lipid and carbohydrate. There has been considerable recent interest in the biochemistry, immunology and molecular biology of the cuticle of parasitic nematodes because of its role as an interface between parasite and host. The cuticle consists of: (1) collagen-like proteins that form the medial and basal layers; (2) non-collagen proteins that form the epicuticular and external cortical regions; (3) non-structural proteins associated with the external surface. The collagen-like proteins are solubilized by reducing agents, have molecular weights of 30-120 kDa and exhibit stage and species variations. Nematode collagen genes, however, code only for proteins with molecular weights of 30 kDa. The non-collagenous proteins, referred to as cuticlin, exhibit unusual chemical properties as indicated by their resistance to solubilization even under strongly denaturing conditions. Recent studies of Ascaris suum have demonstrated the presence of tyrosine-derived cross-links, dityrosine and isotrityrosine, that may form the linkage between subunits in assemblage of the collagenous and noncollagenous structural components of the cuticle. A peroxidase enzyme has been implicated in the synthesis of these cross-links. Recent 125I labeling studies of Haemonchus contortus have identified and characterized stage-specific proteins on the cuticular surface.

Isolation of putative cysteine protease genes of Ostertagia ostertagi

Recombinant phage containing putative Ostertagia ostertagi cysteine protease genes have been isolated from a lambda EMBL-3:genomic DNA library using a Haemonchus contortus cathepsin B-like cysteine protease cDNA as hybridization probe. Restriction enzyme maps of the phages suggest that they identify at least 3 genes, 2 of which appear to be linked in tandem. The complete nucleotide sequence of one gene, CP-1, was determined. The CP-1 gene appears to be organized into 12 exons than span 4.5 kb of DNA. The number and sizes of the exons are essentially identical to those in the H. contortus AC-2 cysteine protease gene. Partial nucleotide sequences obtained for a second O. ostertagi gene, CP-3, revealed a similar organization for exons 8-12 in this gene. Like other cathepsin B-like cysteine proteases, CP-1 appears to be synthesized initially as a preproprotein that is proteolytically processed to its mature form. The amino acid identity between the presumptive CP-1 and CP-3 proteins is 66%, which is similar to the level of homology between the presumed mature protein regions of CP-1 and AC-2. Amino acid identity between CP-1 and AC-2 is greatest in the mature protein region and lowest in the signal sequence and propeptide regions. The CP-3 protein appears to be most closely related to the H. contortus AC-5 protein. CP-1 and CP-3 display significantly greater homology to H. contortus cysteine proteases than they do to human cathepsin B or the Sm31 cysteine protease of Schistosoma mansoni (about 40% identity with each).

Cloning and sequence comparisons of four distinct cysteine proteases expressed by Haemonchus contortus adult worms

Three new members of a developmentally regulated cysteine protease gene family of the parasitic nematode Haemonchus contortus have been isolated and characterized. One of the new genes, AC-3, was found to be linked in tandem to the previously characterized AC-2 gene. Nucleotide sequence analyses revealed that the first 90 amino acids of AC-3 are organized into four exons, similar to the situation in AC-2. A cDNA that appears to be a near full-length copy of the AC-3 gene was isolated using the polymerase chain reaction (PCR) technique to amplify cDNAs from adult worm poly(A)+ mRNAs. In addition to AC-3, a distinct cysteine protease cDNA, AC-4, was amplified by the same oligonucleotide primers. cDNAs encoding a fifth cysteine protease, AC-5, were isolated from an adult worm cDNA expression library using specific rabbit antisera and by PCR. Comparison of the predicted amino acid sequences of AC-3, AC-4 and AC-5 reveal that they share 64-77% identity with one another and with the previously reported AC-1 and AC-2 sequences. The amino acids surrounding the active site cysteine are highly conserved, as are the positions of other cysteine residues in the mature protein sequences. The H. contortus proteases are more similar to one another than they are to human cathepsin B (38-44% amino acid identity) or to the Sm31 cysteine protease of Schistosoma mansoni (36-40% identity). Our studies indicate that H. contortus adult worms express mRNAs for several distinct cysteine proteases. The significant primary sequence differences between the proteases suggest that they differ in their substrate specificities and precise physiological functions.

Caenorhabditis elegans as a model for parasitic nematodes: A focus on the cuticle

The phylum Nematoda consists of over half a million species of worms that inhabit astoundingly diverse environments. Nematodes can live as obligatory parasites of plants and animals, or alternate a parasitic with a free-living life style. The fact that the vast majority of species are strictly free living often surprises parasitology students, for obviously the highest research priorities in this field have involved parasites of medical, veterinary and agricultural importance. Here Samuel Politz and Mario Philipp contend that some basic questions concerning the biology of the parasite cuticle can be investigated more easily and in greater depth in the free-living nematode Caenorhabditis elegans than in the parasites themselves.

Protective studies in sheep immunized with cuticular collagen proteins and peptides of Haemonchus contortus

Twenty-eight nonsibling sheep aged approximately 12 months and raised in a helminth-free environment were used in two protection studies. Immunizations were conducted by two intramuscular injections 30 days apart with a synthetic 18AA cuticle collagen peptide and native cuticle collagens derived from the third- and fourth-stage larvae of Haemonchus contortus. Ten days following the last immunization, the sheep were each given 500 infective H. contortus larvae per day for five consecutive days by intraruminal injection. Both collagen materials induced antibodies reactive with cuticle collagens; however, neither induced reproducible protection to H. contortus infections in vaccinated/infected sheep. In the most extensive test, there were no statistical differences in mean faecal worm egg count for 56 days post worm challenge, in mean numbers of H. contortus and female fecundity ratios at necropsy of immunized and unimmunized sheep. Failure to reproducibly immunize sheep with cuticle collagens may be due to the inability of antibodies or host immune cells to reach the collagen epitopes in the nematode cuticle without prior surface coat removal as postulated in human nematode studies.

Serum IgG response of Manchego lambs to infections with Haemonchus contortus and preliminary characterization of adult antigens

Manchego lambs (16-18 weeks old) were infected with 2500 infective larvae (L3) of Haemonchus contortus and challenged 2 months later with 5000 L3. The serum IgG anti-Haemonchus response was estimated by enzyme-linked immunosorbent assay (ELISA) using soluble proteins from adults and L3. Previously infected Manchego lambs failed to mount a protective immune response against challenge, at least as assessed by faecal egg counts and pre-patency periods. Primary infection did not provoke any rise in specific anti-parasite serum antibodies, whereas a weak but significant rise was observed in challenged 6.5-month-old lambs which was very similar in both infected and non-infected lambs. The serum IgG anti-parasite response was higher against larval antigens than adult soluble proteins. Preliminary characterization of adult and larval soluble proteins by electrophoresis under reducing and denaturing conditions and Western blotting showed high cross-reactivity of both extracts. Immunoblots of adult H. contortus probed with infected and challenged lambs' sera did not yield conclusive results, although some low molecular weight peptides were recognized.

Nematode collagen genes

The collagen genes of nematodes encode proteins that have a diverse range of functions. Among their most abundant products are the cuticular collagens, which include about 80% of the proteins present in the nematode cuticle. The structures of these collagens have been found to be strikingly similar in the free-living and parasitic nematode species studied so far, and the genes that encode them appear to constitute a large multigene family whose expression is subject to developmental regulation. Collagen genes that may have a role in cell-cell interactions and collagen genes that correspond to the vertebrate type IV collagen genes have also been identified and studied in nematodes.

A developmentally regulated cysteine protease gene family in Haemonchus contortus

The nucleotide sequence of a gene encoding a 35-kDa thiol protease of the parasitic nematode Haemonchus contortus has been determined. The gene, designated AC-2, shares 97% nucleotide sequence identity and 98% amino acid identity with previously characterized AC-1 cDNAs encoding the thiol protease. The AC-2 gene spans 8 kb and appears to contain 11 introns, ranging in size from 57 bp to over 5.2 kb. One of the introns interrupts the proposed active site region that is conserved between the H. contortus protease and the related thiol proteases cathepsin B and papain. Southern blot hybridization experiments indicate that the protease is encoded by a small gene family in H. contortus. Rabbit antisera prepared against the recombinant protein react on Western blots with 35 and 37-kDa proteins of adult worms. These proteins were not detectable by Western blot analysis in three larval parasitic developmental stages of H. contortus. Northern blot hybridizations indicate that mRNA transcripts for the gene family are present at low levels in a mixed population of third- and fourth-stage larvae but highly abundant in adult worms. Expression of the protease correlates with blood-feeding and suggests a role for the protease in blood digestion.

Molecular cloning and primary sequence of a cysteine protease expressed by Haemonchus contortus adult worms

We have cloned cDNAs encoding a 35-kilodalton cysteine protease that is a major component of protective extracts isolated from blood-feeding Haemonchus contortus adult worms. Near full-length cDNAs for the protease were isolated by immunoscreening an adult worm cDNA expression library with a rabbit antiserum prepared against the protein eluted from preparative SDS gels and by rescreening the library with oligonucleotide probes. The protein predicted from the nucleotide sequence of the cDNAs and of a genomic DNA clone comprises 342 amino acids and contains an N-terminal signal sequence, 16 cysteine residues and four potential N-linked glycosylation sites. The enzyme appears to be glycosylated in vivo. The H. contortus protease, called AC-1, displays an overall 42% sequence identity with the human lysosomal thiol protease cathepsin B. The similarities between cathepsin B and AC-1 are localized primarily to regions of cathepsin B that comprise the mature, active form of the enzyme. A stretch of six amino acids that includes the active site cysteine of cathepsin B is conserved, and is present in the same relative location in AC-1, suggesting that this region comprises the active site of the H. contortus enzyme.

Haemonchus contortus: evidence that the 3A3 collagen gene is a member of an evolutionarily conserved family of nematode cuticle collagens

Rabbit antisera were raised against an 18 amino acid-long peptide that corresponds to the predicted sequence of the carboxy-terminal, nontriple helical region of the Haemonchus contortus 3A3 collagen gene. This sequence is highly conserved and diagnostic for members of the col-l collagen family, which includes the 3A3 gene. We find that these antisera react predominantly with multiple, high molecular weight (greater than 68 kDa) proteins on Western blots of whole worm extracts. The number and molecular weights of the reacting proteins vary depending upon the developmental stage of the worms analyzed. All of the reacting proteins are collagenase sensitive. The reacting collagens copurify with cuticles and are released from cuticles by reducing agents. In indirect immunofluorescence assays the antisera react only with the broken edges of isolated cuticles, suggesting that the antisera are reacting with an internal cuticle layer. This layer appears to be circular and to extend throughout the length of the worm. The antisera react on Western blots with multiple, high molecular weight collagens of eight other nematodes examined, representing two classes and several orders. These data provide additional support for the notion that the 3A3 collagen gene, and other members of the col-l collagen family, encode cuticle collagens. Collagens with this peptide sequence, presumably other members of the col-l collagen family, appear to be widely distributed in the phylum Nematoda.