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

CUP-1 is a novel protein involved in dietary cholesterol uptake in Caenorhabditis elegans

Sterols transport and distribution are essential processes in all multicellular organisms. Survival of the nematode Caenorhabditis elegans depends on dietary absorption of sterols present in the environment. However the general mechanisms associated to sterol uptake in nematodes are poorly understood. In the present work we provide evidence showing that a previously uncharacterized transmembrane protein, designated Cholesterol Uptake Protein-1 (ChUP-1), [corrected] is involved in dietary cholesterol uptake in C. elegans. Animals lacking ChUP-1 [corrected] showed hypersensitivity to cholesterol limitation and were unable to uptake cholesterol. A ChUP-1-GFP [corrected] fusion protein colocalized with cholesterol-rich vesicles, endosomes and lysosomes as well as the plasma membrane. Additionally, by FRET imaging, a direct interaction was found between the cholesterol analog DHE and the transmembrane "cholesterol recognition/interaction amino acid consensus" (CRAC) motif present in C. elegans ChUP-1. [corrected]. In-silico analysis identified two mammalian homologues of ChUP-1. [corrected]. Most interestingly, CRAC motifs are conserved in mammalian ChUP-1 [corrected] homologous. Our results suggest a role of ChUP-1 [corrected] in cholesterol uptake in C. elegans and open up the possibility for the existence of a new class of proteins involved in sterol absorption in mammals.

Characterization of the protein fraction of the temporary adhesive secreted by the tube feet of the sea star Asterias rubens

Sea stars are able to make firm but temporary attachments to various substrata by secretions released by their tube feet. After tube foot detachment, the adhesive secretions remain on the substratum as a footprint. Proteins presumably play a key role in sea star adhesion, as evidenced by the removal of footprints from surfaces after a treatment with trypsin. However, until now, characterisation was hampered by their high insolubility. In this study, a non-hydrolytic method was used to render most of the proteins constituting the adhesive footprints soluble. After analysis by SDS-PAGE, the proteins separated into about 25 bands, which ranged from 25 to 450 kDa in apparent molecular weight. Using mass spectrometry and a homology-database search, it was shown that several of the proteins are known intracellular proteins, presumably resulting from contamination of footprint material with tube foot epidermal cells. However, 11 protein bands, comprising the most abundant proteins, were not identified and might correspond to novel adhesive proteins. They were named 'Sea star footprint proteins' (Sfps). Tandem mass spectrometry analysis of the protein bands yielded 43 de novo-generated peptide sequences. Most of them were shared by several, if not all, Sfps. Polyclonal antibodies were raised against one of the peptides (HEASGEYYR from Sfp-115) and were used in immunoblotting. They specifically labelled Sfp-115 and other bands with lower apparent molecular weights. The different results suggest that all Sfps might belong to a single family of related proteins sharing similar motifs or, alternatively, they are the products of polymerization and/or degradation processes.

Isolation and culture of larval cells from C. elegans

Cell culture is an essential tool to study cell function. In C. elegans the ability to isolate and culture cells has been limited to embryonically derived cells. However, cells or blastomeres isolated from mixed stage embryos terminally differentiate within 24 hours of culture, thus precluding post-embryonic stage cell culture. We have developed an efficient and technically simple method for large-scale isolation and primary culture of larval-stage cells. We have optimized the treatment to maximize cell number and minimize cell death for each of the four larval stages. We obtained up to 7.8×10(4) cells per microliter of packed larvae, and up to 97% of adherent cells isolated by this method were viable for at least 16 hours. Cultured larval cells showed stage-specific increases in both cell size and multinuclearity and expressed lineage- and cell type-specific reporters. The majority (81%) of larval cells isolated by our method were muscle cells that exhibited stage-specific phenotypes. L1 muscle cells developed 1 to 2 wide cytoplasmic processes, while L4 muscle cells developed 4 to 14 processes of various thicknesses. L4 muscle cells developed bands of myosin heavy chain A thick filaments at the cell center and spontaneously contracted ex vivo. Neurons constituted less than 10% of the isolated cells and the majority of neurons developed one or more long, microtubule-rich protrusions that terminated in actin-rich growth cones. In addition to cells such as muscle and neuron that are high abundance in vivo, we were also able to isolate M-lineage cells that constitute less than 0.2% of cells in vivo. Our novel method of cell isolation extends C. elegans cell culture to larval developmental stages, and allows use of the wealth of cell culture tools, such as cell sorting, electrophysiology, co-culture, and high-resolution imaging of subcellular dynamics, in investigation of post-embryonic development and physiology.

MLT-10 defines a family of DUF644 and proline-rich repeat proteins involved in the molting cycle of Caenorhabditis elegans

Molting of nematodes involves the synthesis and removal of a collagen-rich exoskeleton. We describe Caenorhabditis elegans MLT-10, which defines a large family of DUF644 and proline-rich repeat proteins. We show that MLT-10 is released from the epidermis during molting and that MLT-10 is involved in renewal of the exoskeleton and development of the epidermis.

The molting cycle of nematodes involves the periodic synthesis and removal of a collagen-rich exoskeleton, but the underlying molecular mechanisms are not well understood. Here, we describe the mlt-10 gene of Caenorhabditis elegans, which emerged from a genetic screen for molting-defective mutants sensitized by low cholesterol. MLT-10 defines a large family of nematode-specific proteins comprised of DUF644 and tandem P-X₂-L-(S/T)-P repeats. Conserved nuclear hormone receptors promote expression of the mlt-10 gene in the hypodermis whenever the exoskeleton is remade. Further, a MLT-10::mCherry fusion protein is released from the hypodermis to the surrounding matrices and fluids during molting. The fusion protein is also detected in strands near the surface of animals. Both loss-of-function and gain-of-function mutations of mlt-10 impede the removal of old cuticles. However, the substitution mutation mlt-10(mg364), which disrupts the proline-rich repeats, causes the most severe phenotype. Mutations of mlt-10 are also associated with abnormalities in the exoskeleton and improper development of the epidermis. Thus, mlt-10 encodes a secreted protein involved in three distinct but interconnected aspects of the molting cycle. We propose that the molting cycle of C. elegans involves the dynamic assembly and disassembly of MLT-10 and possibly the paralogs of MLT-10.

Distribution and possible function of the marine alkaloid, norzoanthamine, in the zoanthid Zoanthus sp. using MALDI imaging mass spectrometry

The role of the marine alkaloid, norzoanthamine, in the colonial zoanthid Zoanthus sp. was previously unknown. High concentrations of norzoanthamine are present in the epidermal tissue of Zoanthus sp., as determined using protonated molecular ion peak mapping of norzoanthamine by matrix-assisted laser desorption/ionization mass spectrometry and high-performance liquid chromatography quantification. Sodium dodecylsulfate polyacrylamide gel electrophoresis experiments indicate that norzoanthamine increases the resistance of collagen to damage from UV light, probably not via UV light absorption, but by strengthening collagen itself, thus suggesting that collagen strengthening may be the function of norzoanthamine in Zoanthus sp.

CUTI-1: A novel tetraspan protein involved in C. elegans CUTicle formation and epithelial integrity

The nematode cuticle is a tough extracellular matrix composed primarily of cross-linked collagens and non-collagenous cuticulins. It is required for nematode motility and protection from the external environment. Little is known about how the complex process of cuticle formation has been adapted to the specialized requirements of the nematode cuticle, which is structurally and compositionally unique from other organisms. The C. elegans gene cuti-1 (CUTicle and epithelial Integrity) encodes a nematode-specific protein. We have shown that CUTI-1 is expressed in the epithelia and in seam cells. Within these tissues the expression of cuti-1 mRNA cycles throughout development in line with the molting cycle, a process that involves synthesis of a new cuticle. In addition, knockdown of cuti-1 by RNA interference (RNAi) results in worms that display post-embryonic phenotypes related to cuticle dysfunction and defects in epithelial integrity. This is one of the first reports of a nematode-specific protein involved in extracellular matrix formation. It provides further insight into how novel ways have evolved to regulate the formation of the cuticle, which is the primary protective barrier and skeletal component of nematodes.

Cuticle laccase of the silkworm, Bombyx mori: purification, gene identification and presence of its inactive precursor in the cuticle

Laccase is a multi-copper enzyme found in variety of organisms including plants, fungi and bacteria. In insects, laccase is thought to play an important role in cuticle sclerotization with its ability to catalyze the oxidation of phenolic compounds to their corresponding quinones. From the newly ecdysed pupae of the silkworm, Bombyx mori, we purified a dimer form of cuticular laccase with 70-kDa polypeptides. Mass spectrometric analysis of the tryptic fragments and cDNA sequence analysis revealed that the gene for the purified laccase (BmLaccase2) is an ortholog of laccase2, one of the multiple laccase genes found in insect genomes. BmLaccase2 is highly expressed in the epidermis prior to ecdysis, suggesting that the BmLaccase2 protein accumulates before ecdysis. However, the cuticle of newly ecdysed pupa does not have laccase activity, and the activity only becomes detectable several hours after ecdysis. These data suggest that cuticle laccase is synthesized as an inactive precursor, which is later activated after ecdysis. We also found that urea-solubilized cuticle protein extract contains an inactive form of laccase that can be activated by trypsin treatment.

The use of collagenase to improve the detection of plant viruses in vector nematodes by RT-PCR

Tomato ringspot virus (ToRSV), Tobacco ringspot virus (TRSV) and Tobacco rattle virus (TRV) are transmitted to healthy plants by viruliferous nematodes in the soil. A method was developed for extraction of genomic viral RNA from virus particles carried within nematodes and a sensitive nested RT-PCR detection assay. The procedure has been adapted to microscale for handling multiple samples. This assay is effective for detection of ToRSV or TRSV in Xiphinema americanum or TRV in Paratrichodorus allius. With this method, viruses can be detected in nematodes fed on infected plants or from field-collected nematodes where the percentage of viruliferous nematodes is unknown. Soil samples from four red raspberry fields infected with ToRSV were collected in 2003 and 2004. Nematodes isolated from these samples were assayed for ToRSV by RT-PCR and compared to cucumber baiting bioassay for virus transmission from the same soil samples. ToRSV was detected in nematodes throughout the season with similar frequencies by the RT-PCR assay and the transmission bioassay.

Analysis of nematode mechanics by piezoresistive displacement clamp

Studying animal mechanics is critical for understanding how signals in the neuromuscular system give rise to behavior and how force-sensing organs and sensory neurons work. Few techniques exist to provide forces and displacements appropriate for such studies. To address this technological gap, we developed a metrology using piezoresistive cantilevers as force-displacement sensors coupled to a feedback system to apply and maintain defined load profiles to micrometer-scale animals. We show that this system can deliver forces between 10(-8) and 10(-3) N across distances of up to 100 mum with a resolution of 12 nN between 0.1 Hz and 100 kHz. We use this new metrology to show that force-displacement curves of wild-type nematodes (Caenorhabditis elegans) are linear. Because nematodes have approximately cylindrical bodies, this finding demonstrates that nematode body mechanics can be modeled as a cylindrical shell under pressure. Little is known about the relative importance of hydrostatic pressure and shell mechanics, however. We show that dissipating pressure by cuticle puncture or decreasing it by hyperosmotic shock has only a modest effect on stiffness, whereas defects in the dpy-5 and lon-2 genes, which alter body shape and cuticle proteins, decrease and increase stiffness by 25% and 50%, respectively. This initial analysis of C. elegans body mechanics suggests that shell mechanics dominates stiffness and is a first step in understanding how body mechanics affect locomotion and force sensing.

Neural circuits mediate electrosensory behavior in Caenorhabditis elegans

The nematode Caenorhabditis elegans deliberately crawls toward the negative pole in an electric field. By quantifying the movements of individual worms navigating electric fields, we show that C. elegans prefers to crawl at specific angles to the direction of the electric field in persistent periods of forward movement and that the preferred angle is proportional to field strength. C. elegans reorients itself in response to time-varying electric fields by using sudden turns and reversals, standard reorientation maneuvers that C. elegans uses during other modes of motile behavior. Mutation or laser ablation that disrupts the structure and function of amphid sensory neurons also disrupts electrosensory behavior. By imaging intracellular calcium dynamics among the amphid sensory neurons of immobilized worms, we show that specific amphid sensory neurons are sensitive to the direction and strength of electric fields. We extend our analysis to the motor level by showing that specific interneurons affect the utilization of sudden turns and reversals during electrosensory steering. Thus, electrosensory behavior may be used as a model system for understanding how sensory inputs are transformed into motor outputs by the C. elegans nervous system.

Divergent evolution of arrested development in the dauer stage of Caenorhabditis elegans and the infective stage of Heterodera glycines

BACKGROUND

The soybean cyst nematode Heterodera glycines is the most important parasite in soybean production worldwide. A comprehensive analysis of large-scale gene expression changes throughout the development of plant-parasitic nematodes has been lacking to date.

RESULTS

We report an extensive genomic analysis of H. glycines, beginning with the generation of 20,100 expressed sequence tags (ESTs). In-depth analysis of these ESTs plus approximately 1,900 previously published sequences predicted 6,860 unique H. glycines genes and allowed a classification by function using InterProScan. Expression profiling of all 6,860 genes throughout the H. glycines life cycle was undertaken using the Affymetrix Soybean Genome Array GeneChip. Our data sets and results represent a comprehensive resource for molecular studies of H. glycines. Demonstrating the power of this resource, we were able to address whether arrested development in the Caenorhabditis elegans dauer larva and the H. glycines infective second-stage juvenile (J2) exhibits shared gene expression profiles. We determined that the gene expression profiles associated with the C. elegans dauer pathway are not uniformly conserved in H. glycines and that the expression profiles of genes for metabolic enzymes of C. elegans dauer larvae and H. glycines infective J2 are dissimilar.

CONCLUSION

Our results indicate that hallmark gene expression patterns and metabolism features are not shared in the developmentally arrested life stages of C. elegans and H. glycines, suggesting that developmental arrest in these two nematode species has undergone more divergent evolution than previously thought and pointing to the need for detailed genomic analyses of individual parasite species.

The C terminus of collagen SQT-3 has complex and essential functions in nematode collagen assembly

The nematode exoskeleton is a multilayered structure secreted by the underlying hypodermal cells and mainly composed of small collagens, which are encoded by a large gene family. In previous work, we reported analysis of the C. elegans dpy-31 locus, encoding a hypodermally expressed zinc-metalloprotease of the BMP-1/TOLLOID family essential for viability and cuticle deposition. We have generated a large set of extragenic suppressors of dpy-31 lethality, most of which we show here to be allelic to the cuticle collagen genes sqt-3 and dpy-17. We analyzed the interaction among dpy-31, sqt-3, and dpy-17 using a SQT-3-specific antiserum, which was employed in immunofluorescence experiments. Our results support a role for DPY-31 in SQT-3 extracellular processing and suggest that the SQT-3 C-terminal nontrimeric region serves multiple roles during SQT-3 assembly. Different missense mutations of this region have diverse phenotypic consequences, including cold-sensitive lethality. Furthermore, the biochemical and genetic data indicate that the extracellular assemblies of DPY-17 and SQT-3 are interdependent, most likely because the collagens are incorporated into the same cuticular substructure. We find that absence of DPY-17 causes extensive intracellular retention of SQT-3, indicating that formation of the SQT-3-DPY-17 polymer could begin in the intracellular environment before secretion.

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.

Expression profiling of five different xenobiotics using a Caenorhabditis elegans whole genome microarray

The soil nematode Caenorhabditis elegans is frequently used in ecotoxicological studies due to its wide distribution in terrestrial habitats, its easy handling in the laboratory, and its sensitivity against different kinds of stress. Since its genome has been completely sequenced, more and more studies are investigating the functional relation of gene expression and phenotypic response. For these reasons C. elegans seems to be an attractive animal for the development of a new, genome based, ecotoxicological test system. In recent years, the DNA array technique has been established as a powerful tool to obtain distinct gene expression patterns in response to different experimental conditions. Using a C. elegans whole genome DNA microarray in this study, the effects of five different xenobiotics on the gene expression of the nematode were investigated. The exposure time for the following five applied compounds beta-NF (5 mg/l), Fla (0.5 mg/l), atrazine (25 mg/l), clofibrate (10 mg/l) and DES (0.5 mg/l) was 48+/-5 h. The analysis of the data showed a clear induction of 203 genes belonging to different families like the cytochromes P450, UDP-glucoronosyltransferases (UDPGT), glutathione S-transferases (GST), carboxylesterases, collagenes, C-type lectins and others. Under the applied conditions, fluoranthene was able to induce most of the induceable genes, followed by clofibrate, atrazine, beta-naphthoflavone and diethylstilbestrol. A decreased expression could be shown for 153 genes with atrazine having the strongest effect followed by fluoranthene, diethylstilbestrol, beta-naphthoflavone and clofibrate. For upregulated genes a change ranging from approximately 2.1- till 42.3-fold and for downregulated genes from approximately 2.1 till 6.6-fold of gene expression could be affected through the applied xenobiotics. The results confirm the applicability of the gene expression for the development of an ecotoxicological test system. Compared to classical tests the main advantages of this new approach will be the increased sensitivity and it's potential for a substance class specific effect determination as well as the large numbers of genes that can be screened rapidly at the same time and the selection of well regulated marker genes to study more in detail.

Functional genomic analysis of C. elegans molting

Although the molting cycle is a hallmark of insects and nematodes, neither the endocrine control of molting via size, stage, and nutritional inputs nor the enzymatic mechanism for synthesis and release of the exoskeleton is well understood. Here, we identify endocrine and enzymatic regulators of molting in C. elegans through a genome-wide RNA-interference screen. Products of the 159 genes discovered include annotated transcription factors, secreted peptides, transmembrane proteins, and extracellular matrix enzymes essential for molting. Fusions between several genes and green fluorescent protein show a pulse of expression before each molt in epithelial cells that synthesize the exoskeleton, indicating that the corresponding proteins are made in the correct time and place to regulate molting. We show further that inactivation of particular genes abrogates expression of the green fluorescent protein reporter genes, revealing regulatory networks that might couple the expression of genes essential for molting to endocrine cues. Many molting genes are conserved in parasitic nematodes responsible for human disease, and thus represent attractive targets for pesticide and pharmaceutical development.

The authors use a genome-wide RNA-interference screen to identify and characterize genes involved in C. elegans molting. They investigate regulatory networks involved in molting, lending important new insights into this complex process.

Comparative genomics of gene expression in the parasitic and free-living nematodes Strongyloides stercoralis and Caenorhabditis elegans

Although developmental timing of gene expression is used to infer potential gene function, studies have yet to correlate this information between species. We analyzed 10,921 ESTs in 3311 clusters from first- and infective third-stage larva (L1, L3i) of the parasitic nematode Strongyloides stercoralis and compared the results to Caenorhabditis elegans, a species that has an L3i-like dauer stage. In the comparison of S. stercoralis clusters with stage-specific expression to C. elegans homologs expressed in either dauer or nondauer stages, matches between S. stercoralis L1 and C. elegans nondauer-expressed genes dominated, suggesting conservation in the repertoire of genes expressed during growth in nutrient-rich conditions. For example, S. stercoralis collagen transcripts were abundant in L1 but not L3i, a pattern consistent with C. elegans collagens. Although a greater proportion of S. stercoralis L3i than L1 genes have homologs among the C. elegans dauer-specific transcripts, we did not uncover evidence of a robust conserved L3i/dauer 'expression signature.' Strikingly, in comparisons of S. stercoralis clusters to C. elegans homologs with RNAi knockouts, those with significant L1-specific expression were more than twice as likely as L3i-specific clusters to match genes with phenotypes. We also provide functional classifications of S. stercoralis clusters.

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.

Two sets of interacting collagens form functionally distinct substructures within a Caenorhabditis elegans extracellular matrix

A ubiquitous feature of collagens is protein interaction, the trimerization of monomers to form a triple helix followed by higher order interactions during the formation of the mature extracellular matrix. The Caenorhabditis elegans cuticle is a complex extracellular matrix consisting predominantly of cuticle collagens, which are encoded by a family of approximately 154 genes. We identify two discrete interacting sets of collagens and show that they form functionally distinct matrix substructures. We show that mutation in or RNA-mediated interference of a gene encoding a collagen belonging to one interacting set affects the assembly of other members of that set, but not those belonging to the other set. During cuticle synthesis, the collagen genes are expressed in a distinct temporal series, which we hypothesize exists to facilitate partner finding and the formation of appropriate interactions between encoded collagens. Consistent with this hypothesis, we find for the two identified interacting sets that the individual members of each set are temporally coexpressed, whereas the two sets are expressed approximately 2 h apart during matrix synthesis.

Further studies on the structural analysis of the cuticle of Litomosoides chagasfilhoi (Nematoda: Filarioidea)

In order to obtain further information on the structural organization of the cuticle of nematodes, this structure was isolated from adult forms of the filariid Litomosoides chagasfilhoi. The purity of the fraction was determined by light and transmission electron microscopy, deep-etching, high resolution scanning electron microscopy, atomic force microscopy, immunocytochemistry, gel electrophoresis (SDS-PAGE) and Western blot. The epicuticle presented a rugous surface with parallel rows and several globular particles that could be involved in the absorption of nutrients and secretion of products. Analysis by SDS-PAGE of purified cuticles revealed five major polypeptides corresponding to 151, 41, 28, 13 and 11 kDa. A polyclonal antibody against a synthetic 18 amino-acid peptide that corresponds to the sequence of domain E of the Haemonchus contortus3A3 collagen gene recognized several protein bands on the Western blot of purified cuticle, and labeled all cuticular layers, as shown by immunocytochemistry.

The Brugia malayi genome project: expressed sequence tags and gene discovery

To advance and facilitate molecular studies of Brugia malayi, one of the causative agents of human lymphatic filariasis, an expressed sequence tag (EST)-based gene discovery programme has been carried out. Over 22,000 ESTs have been produced and deposited in the public databases by a consortium of laboratories from endemic and non-endemic countries. The ESTs have been analysed using custom informatic tools to reveal patterns of individual gene expression that may point to potential targets for future research on anti-filarial drugs and vaccines. Many genes first discovered as ESTs are now being analysed by researchers for immunodiagnostic, vaccine and drug target potential. Building on the success of the B. malayi EST programme, significant EST datasets are being generated for a number of other major parasites of humans and domesticated animals, and model parasitic species.

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.

MUP-4 is a novel transmembrane protein with functions in epithelial cell adhesion in Caenorhabditis elegans

Tissue functions and mechanical coupling of cells must be integrated throughout development. A striking example of this coupling is the interactions of body wall muscle and hypodermal cells in Caenorhabditis elegans. These tissues are intimately associated in development and their interactions generate structures that provide a continuous mechanical link to transmit muscle forces across the hypodermis to the cuticle. Previously, we established that mup-4 is essential in embryonic epithelial (hypodermal) morphogenesis and maintenance of muscle position. Here, we report that mup-4 encodes a novel transmembrane protein that is required for attachments between the apical epithelial surface and the cuticular matrix. Its extracellular domain includes epidermal growth factor-like repeats, a von Willebrand factor A domain, and two sea urchin enterokinase modules. Its intracellular domain is homologous to filaggrin, an intermediate filament (IF)-associated protein that regulates IF compaction and that has not previously been reported as part of a junctional complex. MUP-4 colocalizes with epithelial hemidesmosomes overlying body wall muscles, beginning at the time of embryonic cuticle maturation, as well as with other sites of mechanical coupling. These findings support that MUP-4 is a junctional protein that functions in IF tethering, cell-matrix adherence, and mechanical coupling of tissues.

Studies on the immunoglobulin E responses to Teladorsagia circumcincta in sheep: purification of a major high molecular weight allergen

Studies on the immunoglobulin (Ig)E immune responses to the gastric nematode, Teladorsagia circumcincta, have demonstrated a major high molecular weight allergen (HMWTc). Cross reactive allergens of similar MW were demonstrated for Trichostrongylus colubriformis and Cooperia curticei, but not for Haemonchus contortus. Purification of HMWTc was achieved by gel-filtration chromatography, and nonreducing SDS-PAGE and Western blot analysis revealed two closely associated bands with a molecular weight of approximately 140-150 kDa. Reduction showed four IgE reactive bands of 120, 50, 45 and 30 kDa, and deglycosylation abrogated the immunoreactivity of the 120 and 30 kDa bands. Ultrastructural immunolocalization by electron microscopy revealed that the IgE reactivity was confined to the cuticular surface of the infective (L3) larvae. ELISA studies to determine the IgE anti-HMWTc responses in lambs during their first grazing season, demonstrated significantly higher IgE antibody in lambs with low accumulative faecal egg count (FEC) compared to animals with high accumulative FEC. These studies provide evidence for a protective function of IgE antibody in Teladorsagia infections in lambs.

Functional analysis of leucine aminopeptidase in Caenorhabditis elegans

To investigate the function of the enzyme leucine aminopeptidase in nematodes, a Caenorhabditis elegans leucine aminopeptidase gene identified in the genome sequence was functionally analysed by transfection of a leucine aminopeptidase beta-galactosidase reporter construct and characterisation of a null mutant. The leucine aminopeptidase transgene is expressed along the length of the gut, and immunolocalisation shows the enzyme in the buccal cavity, pharynx, anterior gut and rectum. It is constitutively expressed as seen by analysis of cDNAs constructed from mRNAs of nematodes taken at 2 h intervals through the life-cycle; and by western blot analysis of protein from the same set of nematodes. Leucine aminopeptidase null mutants had a slower growth rate and delayed onset of egg-laying. We suggest that in C. elegans, leucine aminopeptidase is a digestive enzyme.

Form of the worm: genetics of epidermal morphogenesis in C. elegans

The development of the epidermis of the nematode worm Caenorhabditis elegans illustrates many common processes of epithelial morphogenesis. In the worm, these morphogenetic movements have been described with single-cell resolution, and the roles of individual cells have been probed in laser killing experiments. Genetic dissection is yielding insights into the molecular mechanisms of these complex morphogenetic processes.

Prolyl 4-hydroxylase is required for viability and morphogenesis in Caenorhabditis elegans

The genome of Caenorhabditis elegans possesses two genes, dpy-18 and phy-2, that encode alpha subunits of the enzyme prolyl 4-hydroxylase. We have generated deletions within each gene to eliminate prolyl 4-hydroxylase activity from the animal. The dpy-18 mutant has an aberrant body morphology, consistent with a role of prolyl 4-hydroxylase in formation of the body cuticle. The phy-2 mutant is phenotypically wild type. However, the dpy-18; phy-2 double mutant is not viable, suggesting an essential role for prolyl 4-hydroxylase that is normally accomplished by either dpy-18 or phy-2. The effects of the double mutation were mimicked by small-molecule inhibitors of prolyl 4-hydroxylase, validating the genetic results and suggesting that C. elegans can serve as a model system for the discovery of new inhibitors.

Conservation and novelty in the evolution of cell adhesion and extracellular matrix genes

New proteins and modules have been invented throughout evolution. Gene "birth dates" in Caenorhabditis elegans range from the origins of cellular life through adaptation to a soil habitat. Possibly half are "metazoan" genes, having arisen sometime between the yeast-metazoan and nematode-chordate separations. These include basement membrane and cell adhesion molecules implicated in tissue organization. By contrast, epithelial surfaces facing the environment have specialized components invented within the nematode lineage. Moreover, interstitial matrices were likely elaborated within the vertebrate lineage. A strategy for concerted evolution of new gene families, as well as conservation of adaptive genes, may underlie the differences between heterochromatin and euchromatin.

Cuticle collagen genes. Expression in Caenorhabditis elegans

Collagen is a structural protein used in the generation of a wide variety of animal extracellular matrices. The exoskeleton of the free-living nematode, Caenorhabditis elegans, is a complex collagen matrix that is tractable to genetic research. Mutations in individual cuticle collagen genes can cause exoskeletal defects that alter the shape of the animal. The complete sequence of the C. elegans genome indicates upwards of 150 distinct collagen genes that probably contribute to this structure. During the synthesis of this matrix, individual collagen genes are expressed in distinct temporal periods, which might facilitate the formation of specific interactions between distinct collagens.

CHR3: a Caenorhabditis elegans orphan nuclear hormone receptor required for proper epidermal development and molting

CHR3 is a Caenorhabditis elegans orphan nuclear hormone receptor highly homologous to Drosophila DHR3, an ecdysone-inducible gene product involved in metamorphosis. Related vertebrate factors include RORalpha/RZRalpha, RZRbeta and RevErb. Gel-shift studies show that CHR3 can bind the DR5-type hormone response sequence. CHR3 is a nuclear protein present in all blastomeres during early embryogenesis. During morphogenesis, both CHR3 protein and zygotically active reporter genes are detectable in epidermal cells and their precursors. Inhibition of the gene encoding CHR3 results in several larval defects associated with abnormal epidermal cell function, including molting and body size regulation, suggesting that CHR3 is an essential epidermal factor required for proper postembryonic development.

Cloning of three Caenorhabditis elegans genes potentially encoding novel matrix metalloproteinases

Three genes potentially encoding novel matrix metalloproteinases (MMPs) were identified by sequence similarity searching of Caenorhabditis elegans genome database, and cDNAs for these MMPs were cloned. The predicted gene products (MMP-C31,-H19 and -Y19) display a similar domain organization to human MMPs. MMP-H19 and -Y19 are unique in that they have an RXKR motif between the propeptide and catalytic domains that is a furin-like cleavage site, and conserved only in stromelysin-3 and membrane-type MMPs. The amino acid sequence homology with MMP-1/human interstitial collagenase at the catalytic domain is 45%, 34% and 23% for MMP-C31, -H19 and -Y19, respectively. Recombinant proteins of C. elegans MMPs cleaved an MMP peptide substrate with efficiency proportional to their amino acid homology with human MMPs. Digestion of gelatin was observed only with MMP-C31. Enzyme activity of MMP-C31 and -H19 was inhibited by human tissue inhibitor of MMPs (TIMP)-1, TIMP-2 and synthetic MMP inhibitors, BB94 and CT543, indicating that the catalytic sites of these C. elegans MMPs are structurally closely related with those of mammalian MMPs.

Caenorhabditis elegans as a model for parasitic nematodes

Caenorhabditis elegans has become a popular model system for genetic and molecular research, since it is easy to maintain and has a very fast life-cycle. Its genome is small and a virtually complete physical map in the form of cosmids and YAC clones exists. Thus it was chosen as a model system by the Genome Project for sequencing, and it is expected that by 1998 the complete sequence (100 million bp) will be available. The accumulated wealth of information about C. elegans should be a boon for nematode parasitologists, as many aspects of gene regulation and function can be studied in this simple model system. A large array of techniques is available to study many aspects of C. elegans biology. In combination with genome projects for parasitic nematodes, conserved genes can be identified rapidly. We expect many new areas of fertile research that will lead to new insights in helminth parasitology, which are based not only on the information gained from C. elegans per se, but also from its use as a heterologous system to study parasitic genes.

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.

Differentially expressed, abundant trans-spliced cDNAs from larval Brugia malayi

Isolation and cloning of abundant reverse transcriptase-polymerase chain reaction (RT-PCR) products from the filarial nematode Brugia malayi using the conserved nematode spliced leader sequence and poly A as amplification targets has allowed us to identify abundant, stage specific transcripts from infective and post-infective larvae. The predicted protein products of the most prominent full-length transcripts from mosquito-derived L3 parasites are: (i) Bm-ALT-1, a homologue of a Dirofilaria immitis abundant larval protein: (ii) Bm-CPI-1, a cystatin-type cysteine protease inhibitor; (iii) Bm-ALT-3, a novel predicted 6 kDa glycine/tyrosine-rich protein; and (iv) Bm-TPH-1, a homologue of a mammalian translationally-controlled tumour protein. Some transcripts were not full-length but had mis-primed at A-rich stretches of coding sequence: the most abundant of these was Bm-col-3, a which encodes a collagen homologous to Bp-COL-1 of Brugia pahangi. Similar analysis of abundant spliced leader (SL)/oligo-dT products from fourth-stage larvae 9 days post-infection yielded two dominant transcripts: (i) Bm-cdd-1, which encodes a protein with homology to cytidine deaminase, differing at only one amino acid position from its homologue described in Brugia pahangi; and (ii) the same truncated form of Bm-col-3 found in L3 preparations. Expression of the major transcripts was assessed by PCR amplification of cDNA libraries derived from each stage of the life cycle. alt1, alt-3 and cpi-1 were all found to be specific to the L3 stage, while cdd-1 was found only in the L4 cDNA library. Expression of these larval-specific transcripts was not detected in either microfilarial or adult libraries.

cis regulatory requirements for hypodermal cell-specific expression of the Caenorhabditis elegans cuticle collagen gene dpy-7

The Caenorhabditis elegans cuticle collagens are encoded by a multigene family of between 50 and 100 members and are the major component of the nematode cuticular exoskeleton. They are synthesized in the hypodermis prior to secretion and incorporation into the cuticle and exhibit complex patterns of spatial and temporal expression. We have investigated the cis regulatory requirements for tissue- and stage-specific expression of the cuticle collagen gene dpy-7 and have identified a compact regulatory element which is sufficient to specify hypodermal cell reporter gene expression. This element appears to be a true tissue-specific promoter element, since it encompasses the dpy-7 transcription initiation sites and functions in an orientation-dependent manner. We have also shown, by interspecies transformation experiments, that the dpy-7 cis regulatory elements are functionally conserved between C. elegans and C. briggsae, and comparative sequence analysis supports the importance of the regulatory sequence that we have identified by reporter gene analysis. All of our data suggest that the spatial expression of the dpy-7 cuticle collagen gene is established essentially by a small tissue-specific promoter element and does not require upstream activator or repressor elements. In addition, we have found the DPY-7 polypeptide is very highly conserved between the two species and that the C. briggsae polypeptide can function appropriately within the C. elegans cuticle. This finding suggests a remarkably high level of conservation of individual cuticle components, and their interactions, between these two nematode species.

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.

Tissue distribution and developmental expression of type XVI collagen in the mouse

The expression of a recently identified collagen, alpha 1 (XVI), in adult mouse tissue and developing mouse embryo was examined by immunohistochemistry and in situ hybridization. A polyclonal antiserum was raised against a recombinant fusion protein, which contained a segment of 161 amino acids in the N-terminal noncollagenous domain of the human alpha 1 (XVI) collagen. Immunoprecipitation of metabolically labelled human or mouse fibroblast cell lysates with this antibody revealed a major, bacterial collagenase sensitive polypeptide of approximately 210 kDa. The size agrees with the prediction from the full-length cDNA. Immunofluorescence examination of adult mouse tissues using the affinity purified antibody revealed a rather broad distribution of the protein. The heart, kidney, intestine, ovary, testis, eye, arterial walls and smooth muscles all exhibited significant levels of expression, while the skeletal muscle, lung and brain showed very restricted and low signals. During development, no significant expression of the mRNA or protein was observed in embryo of day 8 of gestation, but strong signals was detected in placental trophoblasts. Expression in embryos was detectable first after day 11 of gestation with weak positive signals appearing in the heart. In later stages of development, stronger RNA hybridizations were observed in a variety of tissues, particularly in atrial and ventricular walls of the developing heart, spinal root neural fibers and skin. These data demonstrate that type XVI collagen represents another collagenous component widely distributed in the extracellular matrix and may contribute to the structural integrity of various tissues.

Extracellular proteins needed for C. elegans mechanosensation

The mec-5 and mec-9 genes encode putative extracellular proteins that allow a set of six touch receptor neurons in C. elegans to respond to gentle touch. MEC-5 is a collagen made by the epidermal cells that surround the touch cells. Mutations causing touch insensitivity affect the Gly-X-Y repeats of this collagen. mec-9 produces two transcripts, the larger of which is expressed in the touch cells and two PVD neurons. This transcript encodes a protein with 5 Kunitz-type protease inhibitor domains, 6 EGF-like repeats (2 of the Ca(2+)-binding type), and a glutamic acid-rich region. Missense mutations causing touch insensitivity affect both the EGF-like and Kunitz domains. Since mec-9 loss of function mutations dominantly enhance the touch insensitive phenotype of several mec-5 mutations, MEC-5 and MEC-9 may interact. We propose that these proteins provide an extracellular attachment point for the mechanosensory channels of the touch cells.